US2131108A - Short wave communication system - Google Patents

Description

P 1938- N. E. LINDENBLAVD 2,131,108

SHORT WAVE COMMUNICATION SYSTEM Filed April 28, 1936 7 Sheets-Sheet 1 l/N/NG AN TRANS m zzm cs M/7'7'ER MAfCH/NG many/7 TRANS- MITTER 2 0 TEAMS/\e INVENTOR.

ATTORNEY.

QNILS. E. LINDENBLAD P 1938- N. E; LINDENBLAD 2,131,103

SHORT WAVE COMMUNICATION SYSTEM Filed April 28,1936 7 Sheets-Sheet 2 3 ATTORNEY.

Sept. 27, 1938. N. E. LINDENBLAD SHORT WAVE COMMUNICATION SYSTEM 7 Sheets-Sheet 3 Filed April 28, 1936 INVENTOR. NILS E. LINDENBLAD A g/k/x. A 1w 9 IRA/VS- MINER ATTORNEY.

Sept. 27, 1938 N. E. LINDENBLAD SHORT WAVE COMMUNICATION SYSTEM 7 Sheets-Sheet 4 Filed April 28, 1936 D R Y OM E m m E O V W W NL .42 QZ 'VA A A 1 A s L MM 4 0 g. 2 3, 3 M L Q 4 4 f 7- 42 F. +4.. Y p w B 3 Wm 42 a] 4 T o 7C L 7. 2 U 7 Q1 Q a v e L m W "M 42 J52 a \mms LI MAME k mmmm -42 MM A L 7'0 TRANS 0R RECEIVER Sept. 27, 1938. N. E. LINDENBLAD 2,131,108

SHORT WAVE COMMUNICATION "S1ISTEM Filed April 28, 1936 7Sheets-Sheet 5 INVENTOR. NILS E. LINDENBLAD BY H? firm ATTORNEY.

Sept. 27, 1938. N. E. LINDENBLAD SHORT WAVE COMMUNICATION SYSTEM Filed April 28, 1936 7 Sheets-Sheet 6 INVENTOR. gNILS E. LINDENBLAD ROOF PM TE ATTORNEY.

Sept. 27, 1938. N. E. LINDENBLAD 2,131,108

SHORT WAVE COMMUNICATION SYSTEM Filed April 28, 1936 7 Sheets-Sheet 7 70 ANTfA/A/A (H610) "j FILTER {53 EA 4 1 l i I 70 W050 l 4 1 TRANS. I

VOICE }m4/vs. 54 2 INVENTOR.

' NILS E. LINDENBLAD BY m ATTORNEY.

Patented Sept. 27, 1938 PATENT OFFICE SHORT WAVE COMlIUNICAT-ION SYSTEM Nils E. Lindenblad, Port Jefferson, N. Y., assignor. to Radio Corporation of America, a. corporation of Delaware Application April 28, 193 6, Serial No. 76,745

Claims.

This invention relates to improvements in antenna systems and to the associated equipment for use therein.

Some of the objects of the invention are; to

5 obtain substantially uniform radiation in the plane of the radiating elements; to enable the transmission of waves substantially uniformly in the horizontal plane; to provide an antenna which has a substantially uniform response charl acteristic over a wide band of frequencies,- such as might be used for television: to provide a rigid and practical antenna'structure for use on the tops of high buildings wherein the feeders themselves form supports for the radiating elements; to match the surge impedances of the radiating elements to the impedances of the supporting feeders; to obtain an impedance match between a plurality of branch feeders and a main feeder without introducing excessive circulatingenergy in the system; to. provide an impedance matching device in'the form of a concentric transmission line; to enable the connection and impedance matching of a single concentric conductor system to a plurality of concentric conductor systems.

The invention includes among its features:

(1) An antenna system having a plurality of aerial or radiating conductors angularly disposed at substantially 60 with respect to each other, located in the same plane, and so arranged and energized as to produce substantially uniform radiation in the plane of the elements.

(2) An antenna unit having three aerial or radiating elements which form sides of an equilateral triangle, each of whose sides is equal to onehalf the length of the communication wave, for effecting uniform radiation in the'plane of the unit.

(3) An antenna system formed of a plurality of units in different parallel planes, each unit of which comprises an equilateral triangular affair having a plurality of half wavelength conductors which are angularly disposed at substantially 60 with respect to one another, the conductors in one unit being fed at points intermediate the ends while the conductors in a parallel plane are fed from the ends.

(4) A feeder in the form of a concentric line having inner and outer conductors whose relative diametrical dimensions vary to produce desired changes in impedance of the feeder.

(5) An arrangement for feeding an antenna system directly from the same elements which support the aerial or radiating conductors.

(6) A metallic bracing structure for the supporting feeders, which merely acts as an inductance shunted across the aerial elements.

Among the advantages obtained by the present invention is the provision of a novel type of impedance matching circuit which is compact, me- 5 chanically rigid, and electrically self-shielding.

Other objects, features and advantages will appear from a reading of the following description, which is accompanied by drawings wherein like reference numerals indicate like parts throughout the figures. 2

Figs. 1, 1a and 2 illustrate simplified antenna systems in accordance with the invention, for obtaining substantially uniform radiation in the plane of the aerial elements;

Fig. lb is an approximate radiation field pattern in the plane of the aerial elements for a sys-' tem such as is illustrated in Figs. 1 and la;

Figs. 3, 4, 5, 6, 6a and 7 illustrate various antenna embodiments of'the invention employing aerial elements which form sides of one or more equilateral triangles;

Figs. 4a, 4b, 7a and 7b are given for the purpose of exposition and show the current distribution pattern in the aerial elements of adjacent triangular units; I

Fig. 7c is a view showing the system of Fig. 'l unfolded in a single plane in order to more completely illustrate the structure of Fig. 7 and the manner in which the various elements thereof are energized;

Figs. 8, 9 and 9a show different metallic brace arrangements across the feeders for providing greater mechanical rigidity of the antenna structure;

Fig. 10 illustrates a preferred embodiment of antenna, impedance matching system, and feeder system in accordance with the invention;

Fig. 11 is a detail of the system of Fig. 10 showing one pair of supporting feeders and associated apparatus in order to more clearly illustrate the principles of the invention;

Fig. 110. discloses an alternative arrangement to that of Fig. 11 for feeding the doublets of the diiferent triangular units;

Fig. 12 illustrates a circuit arrangement of filter and impedance circuit which may be employed infeeding energy from a plurality of transmitters to. an antenna system of the type shown in Fig. 10.

Fig. 1 shows a simplified antenna system for practicing the present invention comprising a pair of V-shaped aerial wires 1, 2 angularly disposed at substantially 60 with respect to each other and located in a single plane, such as the 55 mediate their ends, instead of at one of their ends, and one way of "accomplishing this is shown in Fig. 1a, wherein each doublet is fed from a 'separate transmission line 5' which connects with the antennatuning and. impedance matching circuit 4. In all other respects the systems of Figs. 1 and 1a are similar.

An essential condition in the practice of the invention is that the centers of the angularly disposed doublets should not physically coincide in the plane of the wires, or, putting it another way, the branches should not make the symmetrical configuration of an X, although the more closely adjacent ends of the doublets may cross one another to some extent. In the last case, where the doublets do cross each other to from the doublets of the V are in phase in certain directions, such as in the plane of the bisector which is perpendicular to the plane of the V wires, in which directions the centers of the doublets are on the same wave front and have no space difference, whereas in other directions such as along a line passing through the centers of the branches of the V, the radiations from the doublets of the V are in opposing phase but displaced in space to prevent cancellation of the radiations from the two doublets of the V. In the last particular instance the ideal arrangement would be to have a space displacement between the centers of the branches of the V equal to half the length of the communication wave or an odd multiple thereof. Such spacing, however, is detrimental to uniform radiation in the plane of the V because there are two factors to be considered; namely, maximum radiation efiiciency and minimum variation in the radiation pattern in the plane of the wires. These two factors depend to an extent upon the linear spacing between the doublets of the V while maintaining the angle between the doublets approximately constant. If the linear spacing between centers of the doublets of the v is greater than, let us say, one-half wavelength-then for certain of these spacings beyond one-half wavelength there is obtained maximum radiation in directions other than the plane of the wires. Consequently there are certain spacings between the centers of the branches wherein there is a compromise between maximum radiation emciency of the system and minimum variation in the a spacing of approximately one-quarter wave, from which it will be seen that radiation is substantially uniform in the plane.

The radiation pattern of a single V in accordance with the invention is considerably improved by adding a third half wavelength doublet between the morewidely spaced ends of the V to provide an antenna system in the form of an equilateral triangle, each angle of which is 60. One such arrangement is shown in Fig. 3, wherein each doublet or radiating element 5", 6 or 1 forms with each adjacent doublet a V, thus each doublet is a side of two .V's. In the system of Fig. 3, the spacings between the centers of all doublets are such as again to provide minimum variation of the radiation pattern in the plane of the wires. The optimum value of spacing for maximum uniform radiation in the plane of the triangle can be determined by trial, since the mathematical computations involved are exceedingly complicated. By experiment, spacings have been found where the variation is substantially not more than 5% in amplitude. Such order of uniformity of radiation has been obtained with spacings between centers of the wires of an equilateral triangle, such as herein described, of approximately a quarter of the length of the communication wave, or half the length of each side of the triangle, although it is to be distinctly understood that the invention is not limited to this particular spacing.

Doublets 5", 6 and 1 are coupled together by half wavelength radiationless loops A, B and C and energized from high frequency transmitter 3 connected to one of these loops, here shown as C through transmission line TL. This line connects with loop C at points where the impedance of the line is matched to the impedance of the loop and antenna. The lengths of the loops A, B and C are so chosen as to give desired opposite instantaneous polarities on adjacent ends of adjacent doublets as indicated. If desired, the system of Fig. 3 can be fed in other ways; for example, each doublet 5", 6, I can be energized at points intermediate their ends in the manner shown in Fig. 1a, in which case loops A, B and C will be dispensed with.

Fig. 3 is merely one unit which gives uniform radiation in the plane of the triangle, and to obtain greater directivity in a plane perpendicular to the plane of the triangle, several such units may be stacked one above the other. Fig. 4 shows, by way of example, one embodiment by means of which this stacking can be achieved.

In Fig. 4 there are shown four horizontal equilateral triangular units D, E, F and G stacked one above the other and spaced one-half wavelength apart. These equilateral triangular units each comprise half wavelength doublets which are energized through vertical supporting feeder lines 8, 9 and ill, in turn, connected to line TL and transmitting apparatus 3. The triangular units are so arranged that correspondingly located wires in the different units connect with the lines 8, 9 and ill to produce similar voltage curves therein. These voltage curves are indicated by broken lines on all the doublets of the units, as well as the instantaneous -polarities at the ends of the doublets. The optimum value of the spacing between doublets of an individual triangular unit, 1. e., the spacing which gives a minimum of variation in radiation at good radiation efliciency, where several triangular units are made to form an antenna array will now vary from the simple case of Fig. 3, and should again be determined by trial, because of the mu-f tual reaction between the triangular units. The vertical broken line of sine wave form indicates the standing wave on each vertical. feeder of a pair. Since adjacent feeders of'the; same pairs each have standing waves of opposite instantaneous polarity at correspondingly'located points along the feeders, there will be radiation cancellation. The feeders of each pairarejsepa- S. The transmission line TL from the transmitter 3 is matched at the bottom of one corner ofone pair of feeders, here shown as 8, although it.

The equilateral triangular units D,'-"E, F' and t G, are spaced one-half wavelength apart, for

which reason, to obtain like polarities in similar- 19 located doublets of the units, the individual" doublets of adjacent triangular units must be connected to opposite sides of the vertical feede x ers. This mode of connection of the triangularv 1 units to the feeders appears more understandable from Figs. 4a, 4b which show 'the'individual triangles as they appear from a plan view. .Aiternate triangles would appear inithe same way.

The feeder pairs 8, 9 and iii are respectively terminated at their'lowerends by loopsA', B and C each of which has an overall length of a half 1 wave, each leg of the loops being aquarter wave-'* length. Consequently, if the loops are made-to be extensions of the feeder pairs 8, 9 and i0, as

shown in the drawings, and their midpoints rest, on a support, the tuning of the antenna system will not be afiected by such supports since the midpoints of the loops A. B and C" are voltage to the terminal impedance of the radiating doubletsof the triangular units.

of both the radiating doublets and the feeders.

The feeders of the system, of course, need not be matched to the triangular units to provide a practical systemfor radiating one particular frequency or a narrow band of frequencies such as in telephony. Where, however, a wide band, such as in television, is required tobe uniformly radi ated, it is essential that all feeders be matched to the radiating doublets to insure a minimum ratio of circulated energy in the system versus radiated energy from the system. The desired matching may be obtained by employing a plurality of stacked triangle units of the type shown in Fig. 3. Such an arrangement is illustrated in Fig. 5, which shows, as an example, only two triangular units H and I, and wherein the correspondingly located loops of the triangular units A", A', B", B' and C", C are connected to the vertical feeders ll, i2 and i3 at points on the loops where the impedance value equals the characteristic impedance of the feeder. As the load of each stacked unit is added to the preceding unit as we move away from the transmitter 3, it will be observed that the points of capacitors l connection on. the at. A", a" and c" to the .vertical feeders ll, i2 and it will approachthe radiating doublets of the associated triangular units I less closely than the points of connection on the correspondingly located loops A', B'. and-C"! of the lower or preceding unit H.

Fig-6 shows a; modification of the antenna of theinventior'i, somewhat similar to the arranger ment of .4, except for the positioning and rated at voltage nodal points by suitable spacers Figufithere are shown three equilateral triangular units K, L and M which ai'espaced onehalf wavelength apart, and. midway between adjacent triangular units on the vertical feeders i4, i5 and [6, there are metallic transverse spacers Sf conductively connecting together each pair of feeders; The points where these spacers ooh- I tact thefeedersare voltage nodal points for the standing waves produced on the'feeders. 1 Cross connections I'I are provided on .both sides 'of the spacers Sfor' connecting each feeder'of each .pair' on one side of the spacer to the other feeder of the same pair on the other side of the spacer :to provide the-equivalent of a transposition of v the feederjwires at the voltage nodal point between triangular ,units.

videlmech'anical"advantages for the system: -It

25 The spacers merely prowilifbe observed that similarly located doublets of 'all triangular-units K,-L and MQare connected to the same feeder wires. This. arrangement employing.metallicispacers is, in practice, not

due mainly. to'th'e introduction of inductancein suitable for useqwhere it is desired to match, the I. characteristic impedanceof. thefeeders to the terminal impedance of the radiating'doublets, 35 g ductance can be tuned out" by further' con'iplieating. heantenna system with? compensating along the feeder pairs. In this figure, just as Fig. 6a is a modification of'Fig. 6, which eliminates the need for transposition. ofthe feeders between radiating units, sincein this case the" triangular units are spaced one'wavelength apart as high definition television, it is of utxnostflirn portance that the antenna systemuhaveainini mumratio "of circulating energy-in thejsystem to radiated energ'yfrom the system,=i. e., 'ahigh. power factor. The systems of Figs; 7,10,.11 and 12, to be described hereinafter, have-been found;

to be especially suitable and superior .for. this purpose to any of the'systems beforedescribed. To achieve this desirable result, the individuailkdoublets of. the triangularunits of. Figs. 7,10, '11 and 12 are connected to the feeders at such points on the radiators where the impedance of; the rai diators match the: characteristic. impedance ;of'-I the feeders.

antenna tuning and impedance matching device Fig.7 shows one satisfactory. antenna embodic 1 ment for achieving wide1-frequency"band,come,

munication. Here there are provided'six transf, mission lines comprisingthree pairsof vertical feeders i8,,l9;*;20,;2l and 22, 23, each of'which connectswith a' two-wire transmission. line extending to high frequency apparatus through.

ation even when the spacing is an appreciable fraction of a wavelength, for example an eighth of a wavelength. The fact that these feeders can be separated without producing radiation is utilized in making the cage serve as a support for the triangular radiating units N, O and P. Each unit comprises three half-wavelength doublets forming sides of an open equilateral triangle.

'Unit P contains doublets 24, 25 and 26; unit 0 contains doublets 21, 28 and 29; and unit N contains doublets 30, 3| and 32.. The feeders l8, I9, 20 etc. are in the form of rigid pipes on which the individual doublets of the equilateral triangular units may be mounted directly or, as shown in the drawings for mechanical and electrical reasons, supported through metallic brackets 25. All brackets 25' are of the same length and the impedance of these including the vertical feeders are matched to the impedance of the doublets at spaced points on the doublets intermediate the ends thereof in well known manner. In other words, each doublet is arranged to introduce a load which matches the vertical feeders at the points of connection so that a minimum or no standing wave is set up on the vertical feeders. Since the phase lag introduced by the additional length of brackets 25 is the same in all triangular unitsN, O and P, they do not affect the phase relations between the triangular units. The units are here shown spaced one-half wavelength apart, correspondingly located doublets of which are located one wavelength apart. Since adjacent equilateral triangular units are one-half wavelength apart, the same feeder will have opposite polarities at the points of connection so spaced, for which reason it is necessary to reverse the order of polarity connection of the individual doublets of the adjacent triangular units so that the currents in adjacent triangles may have the same direction. This current direction is illustrated in Figs. 7a and 7b as being counterclockwise, although it will be appreciated that the direction of the currents in all the equilateral triangular units N, O and P may be reversed. Figs. 7a and 7b are plan views of the triangular units P and 0, respectively, and indi- 'cate how the individual doublets of each unit on each level are fed from different feeder wires. It will be observed, among other things, that the doublets of adjacent triangular units, such as P and O, are differently positioned, while those of alternately located units, such as P and N, are similarly positioned. Referring to Fig. 7a as an example, it will be seen that feeders i8 and 23 feed doublet 24 of unit P, whereas in the adjacent lower unit 0, (note Fig. 7b) these two feeders help feed two different doublets. The manner of feeding all doublets of the triangular units N, O and P will be more clearly understood from an inspection of Fig. 70, which is an unfolded view of the antenna structure as it would look if the feeders and doublets were all placed in a single plane.

When feeding the system of Fig. 7, as shown in 7c, it may be desirable to change the dimensions of the feeders I8, i9, 20 etc. abruptly at successive levels at which they connect with the different triangular units. because of the abrupt change in load impedance on the feeders as the feeders extend past a level of a triangular unit and approach the top of the antenna. In Fig. 7

- the diameters of the feeders decrease toward the top of the antenna system, as shown, with a consequent increase in impedance, of the feeders. In practice, it is difficult to obtain a complete a,1s1,1'oe

impedance matching of the feeders throughout their lengths since this would call for large changes in diameter of the feeders. A slight mismatch of the feeders, especially if the voltage nodal points of the thus created standing wave portion of the total energy on the feeder (since some standing waves are created with a mismatch) are located mid-way between adjacent triangular units, is not, however, detrimental to the system, since in this condition the polarities at the terminals of each half wave section between adjacent triangular units is reversed and of equal amplitude regardless of whether there is a standing or traveling wave in the section.

If now we consider a case where the maximum point of a standing voltage wave on the feeders instead of a minimum falls midway between adjacent triangular radiating units, we may have a very different mode of tuning, if at the same time the impedance offered by the individual doublets across the feeders is inductive. The case then is similar to the situation described in my United States Patent No. 1,821,386, granted September 1, 1931, wherein there is obtained an infinite phase velocity along the feeders so that all points along each feeder is at the same phase. In this particular case the adjacent triangular units do not need to have the order of connection of the individual radiating doublets changed as shown in Figs. 7 to 70, and instead all triangular units may have their correspondingly located doublets similarly located along the feeder line. Because of this phase phenomenon, there is no need to employ any particular spacing between adjacent units. It is evident that a system built to operate according to the principles above set forth in connection with Fig. 7 will have this second degree of freedom (or tuning) just described at a lower frequency. The entire feeders and those portions of the individual radiating doublets in the triangular units falling outside the tapping points on the doublets are then effective capacities which are tuned by the portion of the radiating'doublets between the tapping which are effective inductances. of oscillation, however, is not preferred since it calls for a greater ratio of circulating energy in the system to radiated energy from the system which tends to give the system a lower power factor and consequently sharper tuning, a feature not desirable in connection with communication on wide frequency band high definition television signals.

Fig. 8 is a modification of Fig. 7 and for purposes of simplicity merely shows the uppermost triangular unit, since the remainder of the system is indentical with that of Fig. 7. In this new figure there are provided, for the sake of mechanical rigidity, U-shaped metallic braces 26 which fit into or are attached in suitable manner to the upper ends of the vertical feeders. Braces 26 act merely as inductances shunted across the portion between the tapping points on the doublets. Thus the total inductance of each doublet is decreased, from which it follows that the natural period of the doublet increases. It should be observed at this time that since adjacent feeders are of opposite phase throughout the cage of feeders, it does not matter electrically whether the braces are connected across the pairs of feed- This last mode iii) team, it will be noted, takes the form of a six which feed a single doublet. From a mechanical standpoint, however, it is more advantageous to connect the braces across feeders of different pairs than across feeders of the same pairs.

between pairs of feeders. This new bracing syspoint star. Fig. 9 illustrates a plan view of such system, as illustrated in connection with Fig. 10, is used for each triangular unit of doublets. The braces of Fig. 9 comprise straight metallic straps or bars 2! which are fastened to each other at their points of intersection in suitable manner, such as by welding, soldering, riveting, bolting, threading, etc. Where size permits, the whole brace may be a single casting, or sectionalized into small castings; in the latter case the castings will be fastened together.

Electrically the only portions of the six star brace of Fig. 9 which carry current and act as inductances are those which form, the contour or outline of the star. This is more clearly illustrated in Fig. 9a which shows in unbroken lines the electrically active portions of the star, while the broken lines indicate the electrically inactive portions. The points of intersection of the portions of the brace arrangement are intermediate the points of opposite polarity on the vertical feeders and consequently are of zero potential, as indicated. The members of the bracing system represented by the broken lines are thus connected betweeen points of zero potential and therefore carry no current except secondary currents by induction. Such a bracing arrangement as shown in Figs. 9 and 9a, in combination with the vertical feeder columns, forms an excellent mechanical structure resembling a self supporting tower. If desired, one or more feeder lines can be run through the zero regions of the braces along the length of the structure and supported thereat for other systems, such as antennas, weather observation instruments, or other arrangements which it may be desired to mount at the top of the antenna system of the invention.

It should be noted that the systems of the figures hereinabove discussed, which show a plurality of triangular units stacked in parallel planes, in accordance with the invention, such as Figs. 5, 6, 6a. and 7, have been energized from the base of the antenna structure. From what has been said before in connection with. these figures, it will be apparent that due to the half along the length of the feeders which occurs in the presence of sidebands due to the deviation of the sideband wavelengths from the particular wavelength for which the triangular units are I correctly spaced. Thus while the tuning characteristic of each triangular unit of the system of Figs. 5, 6, 6a and 7 may be sufficiently broad to just referred to.

accommodate the sidebands without appreciable change in amplitude in the radiating elements, the cumulative effect mentioned will disturb, to some extent, the radiation pattern and, therefore, at the distant point of reception cause an apparent greater change in received amplitude than that which is actually caused by the tuning characteristic of the triangular units.

The system of Fig. 10, now to be discussed in connection with Fig. 11, shows one preferred embodiment in accordance with the invention and overcomes, to a large extent, the foregoing disadvantage by minimizing the cumulative error This is achieved, in brief, by connecting only the center triangular unit R. directly to the source of energy by means of feeder lines and coupling the other triangular units W and Q, respectively above and below the center unit, to this center unit R. For this purpose there are employed sections of concentric transmission lines 30 to 35 respectively, whose inner conductors are directly connected to the doublets of the center triangular unit and whose outer conductors serve as coupling feeders for the doublets of the lower triangular unit Q, there being provided an extension 35 of the outer conductor for serving as a coupling feeder for the uppermost triangular unit W. These self-contained concentric transmission line feeders provide, among otherthings, a clean mechanical design of structure.

Fig. 10 shows three equilateral triangular units 'Q, R and W in parallel planes at different levels, spaced one-half wavelength apart, and fed by three pairs of vertical feeders. In order to more clearly explain the manner in which the doublets of Fig. 10 are fed by and matched to the vertical feeder lines, Fig. 11 shows, in simplified manner, a single pair 3| 32 of the feeders if Fig. 10 with the associated doublets of the different triangular units connected to this pair. Since the other pairs of feeders, namely 33 to 35, are connected in similar manner to the other doublets of the likewise applies to these other feeders and their associated doublets.

The middle doublets 31, 31' which are the ones primarily receiving energy from the inner conductors 38 of the transmission lines 3|, 32*are at their ends 56 connected to feeders 58 running more or less parallel withthe doublets 31, 31'. These feeders 58 connect the ends 56 of the doublets to the ends 59 of the inner conductors 38 of the concentric lines 3|, 32. These ends 59, as described later, have an impedance which is rather high, for which reason it is advantageous to make the last quarter wavelength of the inner conductor 38 of the concentric line have a higher ratio between diameters of inner and outer conductors than the rest of the system. As is known,

triangular units, what is set forth hereinafter it is the diametrical ratio and not the actual tained at the feed points 59 will now be given.' In considering a single doublet 31, we know that its series resistance at its center, is '72 ohms. If

we now consider two doublets directly connected in parallel, close together and connected to each other at the ends, we know that they are sur- 'of them must then be four times that of a single doublet alone, for the same power. If the division of the current between the two doublets effectively in parallel is not equal, the series resistance at the middle of one is equal to 72 ohms multiplied by the square of the ratio of the total current in the system and that in the branch under consideration. Now, as a matter of fact 4 the inner conductors 88 of the two transmission lines ii, 32 are connected to the feeders 58 not at the middle of the system but at points farther out (although symmetrical). Due to the falling oil! of the current towards the ends of a doublet, it can-be seen that, on an energy basis, the series resistance of the system is still further increased.

The actual length of the feeders 58 between the ends of the doublets and the ends of the inner conductors 38 of the transmission lines is less than a quarter wave. In the concentric transmission lines, however, the center conductor current must have an equal and opposite counterpart in the outer conductor, which is called the shell current. This shell current in the outer conductor continues through the aperture in the outer conductor made for the end of the center conductor and continues across the mid portion of the system (star connection and center portion of main doublet) to enter in through the aperture of the other transmission line to again become the shell current. The star members and the portion of the main doublet intermediate two adjacent transmission lines feeding the same doublet serve to complete the path for the split doublet branch formed by the feeder. The current from the feeder branch, however, causes a certain voltage drop across the star members and the middle doublets which is not obtained in thetop and bottom systems. This is equivalent to making the inductance of the mid portion of the mid system higher. The length of the doublets in the mid system therefore has to be somewhat less than in the top and bottom systems. The total voltage drop obtained across the mid section (stars and mid portions of the doublets) is, of course, what energizes the top and bottom systems.

In actual practice, due to the shunting effect of the bracing .star connections, the doublets of all the units W, R and Q are very slightly longer physically than one-half wave, the doublets of the middle unit. B being slightly shorter physically than the doublets of units W and Q. In one em-' bodiment, the upper and lower -doublets were about 4% longer than the physical length of onehalf wave, whereas the middle doublets were only about 2% longer than one-half wave, although it will be understood that the electrical length of all the doublets of Q, R and W is a perfect half wave. This difference between the middle doublets and the upper and lower doublets is due to the connections of the feeders 58 to the ends J of the middle doublets.

From the foregoing it will be appreciated that it is not essential that feeders ll be connected only to the ends 55 of the middle doublets, since they may be tapped to the middle doublets at intermediate points depending upon the' impedance matching requirements of the system.

Such impedance matching requirements, under certain conditions, may even call for the introduction of lumped feeders 58. e

For obtaininga 180 phase reversal between the adjacent concentric transmission lines ii and 32, there is provided a U-shaped concentric line section 39 so connected to an energy supply line 40 that there is a path difference between lines fl and 32 equal to half a wave as measured from the point of connection 4|. In other words, the path to one transmission line 42 is half a wave longer from junction point 4| than to the other transmission line II, and both paths are in parallel relation with respect to energy line 40. Other U-shaped concentric line sections 42 and 43 similarly couple the other concentric transmission lines 30, 35 and, 34 together, and are, in turn,

connected to energy supply feeders 44 and 45. This mode of coupling is adequately described in copending application Serial No. 634,000, filed September 20, 1932, by Albert Gothe et al.- to which reference is made for a more detailed description. It will thus be seen that the six vertical concentric transmission lines to 35, inclusive, of alternate phase, have been reduced to three energy supply feeders 40, 44 and 45 of the same phase. To obtain the desired impedance matching between the U-shaped line sections 39, 42 and 43 and their respective energy supply feeders 40, 44 and 45, the impedance of each feeder 40, 44 and 45 is respectively made to be equal to one-half the impedance of the U-shaped line reactances in some form in section which it will be observed comprises two I transmission lines in parallel. For example, if the impedance of each transmission line of the U-shaped section 38 is 48 ohms, then the impedance of energy feeder should be 24 ohms for a connection which is free from reflection. The

surge impedance of the U branches therefore must be twice that of the T branch feeding into the U. Since the surge impedance of a line is equal to center conductor diameters, is under a logarithm.

That then means that if L is to be doubled or C out in half, the ratio of diameters must be squared. If L was to be made three times and C to be divided by three the ratio would have to be cubed. It can be seen from this that line dimensions must be carefully chosen in order that impossible mechanical dimensions be avoided.

It is now proposed to connect all three feeders.

40,44 and of 24 ohms each to a single feeder.

At first blush, one might consider simply par-,

alleling the three feeders. However, if this is done, then for a connection free from reflection with a single feeder for energizing the three, there would be required a single feeder whose impedance is equal to that of the three feeders 40, 44 and 45 in parallel, that is, a single feeder whose surge impedance is only 8 ohms. Such a practical in this case inasmuch as a desirable ratio of four to one between inner and outer conductors of a concentric line gives a surge im pedance of about 80 ohms, and in order to obtain an impedance of only eight ohms to match the three parallel lines 40, 44 and 45 there would be required a ratio between inner and outer conductors of the single feeder of the tenth root of four, an obviously impractical mechanical arrangement because the inner and outer conductors would then have an extremely small difference in diameter.

The foregoing difllculties are overcome in accordance with the invention by arranging a circuit whereby the three T feeders 40, 44 and 45 are connected in series and joined to-the single feeder 46. By means of this feature of the present invention, the impedance required for the single feeder 46 is three times that of one of the feeders '48, 44 or 45, in other words 72 ohms. This ohmage is a practical amount which the main line or single feeder 46 can be designed to provide. As can be seen, two of three T branches 40 and 44 are surrounded by a shell 41 which makes the outer conductor of the T branch an intermediate shell 48 for the length of a quarter wave. On account of its length, this intermediate shell 48 has a very high impedance on its outside. Now, then, the current in the center conductor 49 of the branch 45, which has no outer shell,'becomes the shell current for the middle branch 44 and the current of the center conductor 50 of the middle branch 44 becomes the shell current for the branch 40. The current in 49 cannot go on the outside of the intermediate sleeve 48 of the middle branch 44 due to the high impedance of a quarter wave conductor; but must go on the inside and become the shell current for the middle T branch 44 as already stated. The shell current of the branch 45, i. e., the current in the outer conductors, follows the cover 5| and becomes the shell current for the main line 46. The center conductor current of the right hand branch becomes the center conductor current of the main line. The three T branches arethus connected in series and in phase with the main line 46. Due to the necessary introduction of cross connectors 52 in this system, it is rather important to make the three T branches 40, 44 and 45 successively longer by an equal amount. Since the voltage of the main line 46 is divided by three, a third for each T branch, or since there are three T branches in series, the surge impedance of each branch must be-a third of the surge impedance of the main line 46. The

ratio of the shell and center conductor diameters of the T branches 40, 44 and 45 must therefore be the cubic root of the ratio in the main line 46 as already stated.

Fig. 11a shows an alternative method to that of Figs. 10 and 11 of connecting a pair of concentric transmission lines, such as 3|, 32, to the doublets of three triangular units, and difi'ers from Fig. 11 only in showing that the concentric lines 3|, 32 may both feed the same doublet in the middle level, instead of different doublets. while feeding different doublets in the upper and lower levels. I

Where it is desired to employ two transmitters on the same antenna system at slightly different frequencies, (M and M) as for instance the video and audio transmitters for transmitting television programs, a filter'system shown in Fig. 12 may be inserted betweenthe main line 46 of Fig. 10 and the transmitters proper. This filter system, shown in box form and designated 58, is described in great detail in the copending application of Philip S. Carter, Serial No. 88,073, flied June 30, 1936, to which reference is herein made.

Obviously the purpose of this filter system is to prevent the energy from one transmitter from enterins the circuits of the other transmitters while P rmitting both transmitters to freely feed energy into the antenna system.

Since main feeder 46 is a single concentric line and since the transmitters in the above mentioned case of Fig. 12 are preferably of the push-pull type it now becomes necessary to adapt the single concentric transmission line system to a push-pull transmission line system for connecting to the balanced circuit of the transmitter. In this instance, the U-shaped phase transformmg arrangement described above in connection with elements 39, 42 and 43 of Fig. 10 was not found suitable for providing the proper load impedance required by the push-pull transmitter. This will be evident from the fact that the main line 46 has an impedance of 72 ohms and the total impedance across both legs of a U-phase transforming arrangement would have to be 288 ohms, i. e., each leg of the U would have an impedance of 144 ohms. Such an impedance of 288 ohms is for most transmitters too high to draw full power. This difficulty is overcome in accordance with another aspect of the invention which provides a push-pull impedance equal to the impedance of the single concentric conductor line which again effects phase transformation. This circuit comprises a quarter wave concentric line 6| whose inner and outer conductors are each connected at one end 62 to the center conductors- 63 and 64 of a pair of push-pull concentric line branches. An outer metallic sleeve 66 surrounds the line 6| for its entire quarter wavelength, and is joined to the outer conductors of the push-pull branches, as shown. To understand the operation of the circuit. let us visualize the circuit from the transmitter and from which there are fed currents'of opposite direction in the two pushpull branches, as indicated by the arrow marks. Since in a single concentric conductor line the center conductor current and the shell current on the inner surface of the outer conductor are opposite to each other in direction, but of the same magnitude, it follows that the inner conductor of one branch of the push-pull circuit should continue asthe inner conductor of the single concentric line 6| while the inner conductor of the other push-pull branch should con tinue as the shell current of the line 6|. To prevent short circuiting of the push-pull branch connected to the outer conductor of line 6|, it is necessary for the shell of line 6| at point 62 to present a high impedanceon its outer surface, in which case all current arriving over conductor 64 will travel over the inner surface of the shell of line 6|. This is achieved by making sleeve 66 a quarter wavelength and connecting its upper end to the outer conductorof line 6|. Since lines 63 and 64 are effectively in series, each must have a surge impedance equal to half thesurge impedance of the line 6|; consequently, there will be a surge impedance across 63 and 64 of a value equal to the surge impedance of single concentricline6l.

In order not to alter the physical configuration of not to change the surge impedance along the tapered section, the diametrical ratio of the conductors in this section should be constant. To

preserve neatness of appearance, the metallic,-

sleeve 66 is extended beyond quarter wave line 6| to form a continuation of the transmission line leading from filter 53.

It will be understood, of course, from what has gone before, that the invention is not limited to the precise arrangements illustrated and described, since various modiilcations may be made without departing from the spirit and scope of the invention. a.

What is claimed is:

1. An'antenna system comprising two conductors in the same plane and disposedsubstantially at an angle of 60 with respect to each other, each of said conductors being one-half the length of the communication wave, and means for excitin said conductors to have opposite instantaneous polarities at correspondingly located points.

2. An antenna system comprising two conductors in the same plane and. disposed substantially at an angle of 60 with respect'to each other, each of said conductors being one-half the length of the communication wave, and a source of high frequency energy for energizing said conductors to have opposite instantaneous polarities at correspondingly located points, whereby substantially uniform radiation is obtained in the plane of said conductors.

3. An antenna system comprising two conductors in the same plane and disposed substantially at an angle of 60 with respect to each other, each of said conductors being one-half the length of the communication wave, and a source of high frequency energy for energizing said conductors to have opposite instantaneous polarities at correspondingly located points, whereby substantially uniform radiation is obtained in the plane of said conductors, said conductors being fed by said.

source at their more closely adjacent ends.

4. An antenna system comprising two conductors in the same plane and disposed substantially at an angle of 60 with respect to each other, each of said conductors being one-half the length of the communication wave, and a source of high frequency energy for energizing said conductors to have opposite instantaneous polarities at correspondingly located points, whereby substantially uniform radiation is obtained in the plane of said conductors, said conductors being fed by said source through feeders at points on said conductors which are symmetrically located with respect to the centers thereof and so spaced that the im pedance of said conductors matches the impedance of said feeders.

5. An antenna system comprising two conductors in the same plane and disposed substantially at an angle of 60 with respect to each other, each of said conductors being one-half the length of the communication wave, and a source of high frequency energy for energizing said conductors to have opposite instantaneous polarities at correspondingly located points, whereby substantial ly uniform radiation is obtained in the plane of said conductors, said conductors being fed by said source at their more closely adjacent ends,

to the correspondingly located ends of the eleopen-ended equilateral triangle, each of said eleing a length equal to one-half the length of the communication wave, and means for exciting said elements such that adjacent ends of the elements have opposite instantaneous polarities.

'7. An antenna system comprising three spaced aerial elements in the same plane forming an equilateral triangle, each of said elements having a length equal to one-half the length of the communication wave, connections equal to an odd multiple including unity of half the operating wavelength connecting together adjacent ends of said elements, and a source of high frequency energy connected to spaced points on one of said connections for energizing said elements whereby adjacent ends have opposite instantaneous polarities.

8. An antenna system comprising three spaced aerial elements in the same planeforming an open-ended equilateral triangle, each of said elements having a length equal to one-half the length of the communication wave, another similar equilateral triangle similarly located in a parallel plane, three pairs of feeders connecting the adjacent ends of the elements in one plane elements in the same plane forming an equilateral triangle, each of 'said elements having a length equal to one-half the length of the communication wave, a loop having an overall length of one-half wavelength connecting together the end of one element with the adjacent end of another element, similar loops coupling together the other adjacent ends of said elements, a similar equilateral triangle of elements in a parallel plane and similarly placed, a pair of feeders connecting each loop of one triangle with the correspondingly locatedloop of the other triangle, and high frequency apparatus coupled directly to only one of said loops of one of said triangles for energizing all aerial elements of both" triangles whereby adjacent ends of said aerial elements .in each plane have opposite instantaneous polarities, similarly located ends of said elements in different planeshaving polarities of the same sign.

10. An antenna system comprising three spaced aerial elements in the same plane forming an ments having a length equal to one-half the length of the communication wave, another similar equilateral triangle similarly located in a parallel plane, three pairs of feeders connecting the adjacent ends oi the elements in one plane to the correspondingly located ends of the elements in the other plane, said feeders compris-' ing tubular conductors for supporting said aerial elements, said pairs of tubular conductors extending beyond said aerial elements in said last plane impedance of said connections;

said conductors crossing each other for a portion of their lengths less than one-quarter of the length of the communication. wave.

,6. An antenna system comprising three spaced aerial elements in the same plane forming an equilateral triangle, each of said elements hav 11. An antenna system in accordance with claim 10, characterized inthis that said triangles are spaced apart a distance equal to one wavelength, and the ends of correspondingly located to the same feeders. V

2. An antenna system in accordance with aerial elements in. both triangles are connected claim 10, characterized in this that said triangles are spaced apart a distance equal to one-half wavelength, and the ends of correspondingly located aerial elements in both triangles are connected to the same feeders, said feeders between triangles in different planes being transposed.

13. In combination, a plurality of pairs of feeder lines in the form of supporting elements arranged symmetrically with respect to a center point, a load connected to each of said pairs and supported thereby, high frequency apparatus coupled to said pairs whereby adjacent feeders have opposite instantaneous polarities thereon, and metallic braces connecting the feeders of each pair with the adjacent feeders of the adjacent pairs, said braces being in effect inductances which electrically are shunted across said loads.

14. In combination, a plurality of pairs of feeders arranged to form a cage, an antenna element coupled to each of said pairs and supported thereby, high frequency apparatus coupled to said pairs in such manner that adjacent feeders have opposite instantaneous polarities, and a metallic brace between adjacent feeders.

15. In combination, three pairs of feeders arranged to form a cage, an antenna element coupled to the feeders of each pair, and a metallic brace in the form of a six point star mechanically connecting said pairs of feeders together, the points of said star being the location of said feeders, the portions of said brace between feeders acting effectively as inductances across said feeders.

16. An antenna system comprising a concentric feeder line having inner and outer conductors, an aerial element conductively coupled to said inner conductor, another aerial element in a plane parallel to the plane of said first element conductively coupled to said outer conductor, said planes being spaced a predetermined distance apart, means for supplying energy to said inner conductor for directly exciting said first aerial element.

1'7. A system in accordance with claim 16, characterized in this that the planes in which said aerial elements lie are spaced one-half wavelength apart.

18. An antenna system comprising a pair of concentric feeder lines, each having an inner and an outer conductor, a first doublet having a length equal to half the length of the communication wave conductively coupled to said inner conductors, a second doublet of similar length in a plane parallel to the plane of said first doublet conductively coupled to the outer conductor of one of said feeder lines, a third doublet in the plane of said second doublet and conductively coupled to the outer conductor of said other feeder line, and means for energizing said inner conductors of said pair of feeder lines out of phase with respect to each other, whereby said first doublet is directly excited from said means.

19. A system in accordance with claim 18, characterized in this that said planes are spaced apart an odd multiple of a half wavelength, and said first doublet is connected to the ends of said inner conductors.

20. An antenna system comprising a pair of concentric feeder lines each line having an inner and an outer conductor, a first doublet having a length equal to half the length of the communication wave conductively coupled to the ends of said inner conductors, second and third doublets of similar lengths in a plane parallel to the plane in which said first doublet lies conductively coupled one to one of said outer conductors and the other to the other of said outer conductors, said parallel planes being spaced one-half wavelength apart, said outer conductors extending beyond said ends of said inner conductors for at least half the length of the communication wave, and fourth and fifth half wavelength doublets lying in another parallel plane oppositely disposed to the plane of said second and third doublets with respect to the plane of said first doublet, said fourth doublet being conductively coupled to the extension of one of said outer conductors and said fifth doublet being coupled to the extension of said other outer conductor, and

means for energizing said inner conductors out of phase with respect to each other.

21. A system in accordance with claim 20, characterized in this that said first doublet is energized from its ends, while said other doublets are connected to said outer conductors at points intermediate their ends.

22. An antenna system comprising a pair of concentric feeder lines each line having an inner and an outer conductor, a first doublet having a length equal to half the length of the com munication wave conductively coupled to the ends of said inner conductors, second and third dou-' blets of similar lengths in a plane parallel to the plane in which said first doublet lies conductively coupled one to one of said outer conductors and the other to the other of said outer conductors, said parallel planes being spaced one-half wavelength apart, said outer conductors extending beyond said ends of said inner conductors for at least half the length of the communication wave, and fourth and fifth half wavelength doublets lying in another parallel plane oppositely disposed to the plane of said second and third doublets with respect to the plane of said first doublet, said fourth doublet being conductively coupled to the extension of one of said outer conductors and said fifth doublet being coupled to the extension of said outer conductor, and means for energizing said inner conductors out of phase with respect to each other, said fourth doublet being coupled to the same outer conductor as said second doublet, and said fifth doublet being coupled to the same outer conductor as said third doublet, said fourth and second doublets being parallel, and said fifth and third doublets being parallel.

;23. An antenna system in accordance with claim 16, characterized in this that said aerial elements are each a half wavelength long and said planes are spaced a half wavelength apart,- said second and third doublets being coupled to said outer conductors intermediate the ends of said, doublets.

24. In combination, a plurality of pairs of vertical parallel feeder lines in the form of a cage, aerial elements coupled to said lines, and means for energizing each of said pairs such'that corre spondingly located points on the feeders of each pair have opposite instantaneous polarities, said means comprising a U-shaped conductor a half wavelength long connecting together the bottom ends of each pair of feeder lines, and a single feeder line connecting one bottom end of one feeder of each pair to high frequency apparatus.

25. A system in accordance with claim '24, characterized in this that the impedance of the single feeder line associated with the U-shaped conductor is equal to half the surge impedance of each vertical feeder line of its pair.

an angle of 60 with respect to each other, said conductors being Physically separated from each other and in the form of a V, whereby one end of one conductor is more closely located to one end of the other conductor than the other ends of said conductors are to each other, each of said conductors being substantially one-half the length of the communication wave, and means for exciting said conductors such that their adjacent ends have opposite instantaneous polarities.

27. An antenna system comprising two conductors in the same plane and disposed substantially at an angle of 60 with respect to each other, each of said conductors being one-half the length of the communication wave, the centers of said conductors being spaced apart by a distance approximately equal to one-quarter of the length of the communication wave, and means for exciting said conductors to have opposite instantaneous polarities at correspondingly located points.

28. An antenna system comprising three spaced aerial elements in' the same plane forming an equilateral triangle, each of said elements having a length equal toone-half the length of the communication wave, a loop having an overall length of one-half wavelength connecting together the end of one element with the adjacent end of another element, similar loops coupling together the other adjacent ends of said elements, a similar equilateral triangle of elements in a parallel plane and similarly positioned, a pair of feeders connecting each loop of one triangle with the correspondingly located loop of the other triangle, said equilateral triangles of radiating elements being spaced apart substantially by the length of the communication wave, and high frequency apparatus coupled directly to only one of said loops of one of said triangles for energizing all aerial elements of both triangles whereby adjacent ends of said aerial elements have opposite instantaneous polarities, similarly located ends of said elements in diiferent planes having polarities of the same sign.

29. An antenna system comprising three spaced aerial elements in the same plane forming an open-ended equilateral triangle, each of said elements having a length equal to one-half the length of the communication wave, another similar equilateral triangle similarly located in a parallel plane and spaced from said first plane by a distance equal to half the length of the communcation wave,- means for energizing the aerial elements in one plane in such manner that the adjacent ends of said elements in said one plane have opposite instantaneous polarities, a pair of feeders connecting the adjacent ends of the elements in said one plane'to the similarly positioned adjacent ends of the elements in the other plane such that said elements in the last plane also have their adjacent ends at opposite instantaneous polarities.

30. An antenna system comprising three spaced aerial elements in the same plane forming an equilateral triangle, each of said elements hav ing a length equal to one-half the length of the communication wave, the centers of adjacent aerial elements being spaced apart by a distance approximately equal to one-quarter of the length of the communication wave, and means for exciting said elements such that adjacent ends of the elements have opposite instantaneous polarities.

tric feeder line having inner and outer conductors,

31. An antenna system comprising a concenan aerial element conductively coupled to said inner conductor, another aerial element in a plane parallel to the plane of said first element conductively coupled to said outer conductor, said planes being spaced a predetermined distance apart, means for supplying energy to said inner conductor for directly exciting said first aerial element, whereby said other aerial element is excited from said outer conductor.

32. An antenna system comprising a pair of concentric feeder lines each line having an inner and an outer conductor, a first doublet having a length equal to half the length of the communication wave conductively coupled at its ends to the ends of said inner conductors, second and third doublets each of similar length in a plane parallel to the plane in which said first doublet lies conductively coupled one to one of said outer conductors and the other to the otherof said outer conductors, said parallel planes being spaced onehalf wavelength apart, said outer conductors extending beyond said ends of said inner conductors for at least half the length of the communication wave, and fourth and fifth half wavelength doublets lying in another parallel plane oppositely disposed to the plane of said second and third doublets with respect to the plane of said first doublet, said fourth doublet being conductively coupled to the extension of one of said outer conductors and said fifth doublet being coupled to the extension of said, other outer conductor, and

. means for energizing said inner conductors out of phase withrespect to each other.

33.v An antenna system in accordance with claim 16, characterized in this that said aerial elements are each a half wavelength long and said planes are spaced a half wavelength apart, said second, third, fourth and fifth doublets being coupled to said outer conductors intermediate the ends of said doublets.

34. An antenna system comprising three spaced aerial elements in the same horizontal plane forming a central equilateral triangle, a pair of vertical feeders for each of said aerial elements, said aerial elements being connected to said feeders from the ends of the elements, upper and lower equilateral triangles of aerial elements located on opposite sides of said central triangle of aerial elements, all of said triangles of aerial elements being in horizontal planes, said planes being separated from one another by a distance substantially equal to half the length of the communication wave, each of the aerial elements in said triangles being electrically equal to onehalf. the length of the communication wave, said points intermediate the ends of the elements,

whereby adjacent ends of aerial elements in the same triangle have opposite instantaneous polarities.

35. An antennasystem comprising three spaced aerial elements in the same horizontal plane forming a central equilateral triangle, a pair of vertical feeders for each of said aerial elements, said aerial elements being connected to said feeders from the ends of the elements, upper and lower equilateral triangles of aerial elements located on opposite sides of said central "triangle of aerial elements, all of said triangles of aerial elements being in horizontal planes, said planes being separated from one another by a distance substantially equal to half the length of the communication wave, each of the aerial elements in said triangles being electrically equal to one-half the length of the communication wave, said aerial elements in the upper and lower triangles being energized by said vertical feeders at spaced points intermediate the ends of the elements, whereby adjacent ends of aerial elements in the same triangle have opposite instantaneous polarities, said aerial elements in the upper triangle each having a parallel aerial element in the lower triangle, located in a corresponding position and fed by the same feeders, said aerial elements in said central triangle each being positionedat an angle with respect to the aerial elements in the upper and lower triangles which are connected to the same feeders.

36. An antenna system comprising a plurality of equilateral triangles of aerial elements located in parallel planes at different levels, and means for exciting the aerial elements of each triangle such that adjacent ends of the elements have opposite instantaneous polarities and the currents in the aerial elements'of adjacent triangles are in the same direction.

3'7. An antenna system in accordance with claim 35, characterized in this that said feeders comprise concentric lines upon which the aerial elements of said triangles are mounted, said lower triangle of aerial elements being positioned onequarter of a wavelength above a surface of relatively fixed radio frequency potential.

38. An antenna system comprising three equilateral triangular units of aerial elements located in parallel planes at different levels, substantially one-half wavelength apart, each of said aerial elements being equal electrically to half the length of the communication wave, and means for exciting the aerial elements of each triangle such that adjacent ends of the elements have opposite instantaneous polarities and the currents in the aerial elements of adjacent triangles are in the same direction.

39. An antenna system comprising three equilateral triangular units of aerial elements located in parallel planes at different levels substantially one-half wavelength apart, each of said aerial elements being equal electrically to half the length of the communication wave, three pairs of vertical feeders for said aerial elements, said elements being mounted on said feeders and electrically coupled thereto at spaced points intermediate the ends of the elements, such that the adjacent ends of the aerial elements of each triangle are excited to have opposite instantaneous polarities and the currents in the aerial elements of adjacent triangles are in the same direction.

40. An antenna system comprising three equilateral triangular units of aerial elements located,

length of the communication wave, three pairs of vertical feeders for said aerial elements, said elements being mounted on said feeders and electrically coupled thereto at spaced points intermediate the ends of the elements, such that the adjacent ends of the aerial elements of each triangle are excited to have opposite instantaneous polarities and the currents in the aerial elements .of adjacent triangles are in the same direction,

, thickness for changing the impedance of the feeders to more closely match the impedance of the aerial elements.-

42. An antenna system comprising a plurality of equilateral triangles of aerial elements located in parallel planes at different levels, three pairs of vertical feeders for said aerial elements, said feeders being in the form of a cage, said elements being mounted on said feeders and electrically coupled thereto at spaced points intermediate the ends of the, elements, metallic braces connecting the feeders together, said braces being in effect inductances which electrically are shunted across said aerial elements, said aerial elements being each physically longer than, but electrically equal to one-half the length of the communication wave.

43. In combination, a transmission line feeder, a plurality of aerial elements coupled to said feeder at points spaced along the length of said feeder, the dimensions of said feeder decreasing between successive aerial elements for increasing the impedance of said feeder.

44. In an antenna system, a concentric transmission line having an inner and an outer conductor, a first aerial element coupled to said outer conductor,-a second aerial element'coupled to said inner conductor, said aerial elements being in parallel planes spaced substantially onehalf wavelength apart, said inner conductor having an abrupt change in dimensions between said aerial elements at a point substantially onequarter of a wavelength from the point of connection to said second aerial element, whereby the NILS E. LINDENBLAD.

-ductors is increased.

Images