US2787788A - Short wave radio aerials and aerial systems - Google Patents

Description

April 2 1957 N. H. CLOUGH 2,787,788

SHORT WAVE RADIO AERIALS AND AERIAL SYSTEMS Filed April 16 1951 2 Sheets-Sheet l April 2 1957 N. H. CLOUGH 2,787,788

' SHORT WAVE RADIO AERIALS AND AERIAL SYSTEMS Filed April 16, 1951 8 z Sheets-SheetZ SHORT WAVE RADIO AERIALS AND AERIAL SYSTEMS Newsomc Henry Qiough, Brent'wood, England, assignor to Marconis Wireless Telegraph (Company Limited, London, England, a company of Great Eritain Application April 16, 1951, Serial No. 221,141 Claims priority, application Great Britain April 27, 1950 '7 Claims. (Cl. 343-867) This invention relates to short-wave radio aerials and aerial systems and has for its object to provide improved aerials which shall be mechanically simple, such as may be rotated, if required, at relatively high speed with 21v minimum of mechanical difliculties, and which can be conveniently and satisfactorily built up into aerial systems to give directional polar diagrams or omni-directional diagrams for radio beacon, radio direction finding and similar purposes.

The primary intended application of the invention is to serials or aerial systems for horizontally polarized waves and the various embodiments to be described herein are intended for such use. It is to be understood, however, that the terms horizontal and vertical as herein employed, are used in a relative sense only and that any of the aerials or systems herein described as for use with horizontally polarized waves may be turned through a right angle-i. e. place on their sidesin which case they will be for use with vertically polarized waves. As will be apparent hereinafter the invention provides aerial and aerial systems which can be used either for transmission or reception.

According to the main feature ofthis invention a shor wave radio aerial consists of a pair of bent dipoles each having a central portion which. is horizontal or approximately horizontal and a pair of similar end portions which are vertical or approximately vertical, the end portions of one extending upwards and those of the other extending downwards, and the dipoles being placed over one another and being substantially mirror images of one another.

The invention is illustrated in the accompanying drawings which show schematically a number of embodiments thereof.

The central portion of each dipole may be straight and horizontal and the end portions straight and vertical and extending towards one another so that each dipole becomes of rectangular U form, one being inverted and combining with the other to constitute a rectangle. Alternatively the dipoles may have a-common central portion and the end portions may be straight and vertical and extending away from one another so that each dipole is again of rectangular U form, one being inverted, but the two combine to form a structure of H shape. In the former case the far ends of the dipole end portions may be united mechanically and electrically, the end portions of one dipole continuing into and being structurally one with the end portions of the mirror image dipole. in this type of construction an aerial in accordance with this invention becomes a loop or frame of curved shape so energized that the points of maximum current flow occur substantially at the mid-points of the horizontal dimension and the points of maximum voltage occur substantially at the mid-points of the vertical dimension. Thus one form of aerial in accordance with the invention consists as shown in Fig. l of arectangular frame A with its vertical dimension longer than its horizontal dimension, with points of maximum current flow at the mid-points of the shorter sides of the rectangle, the directions of current flow at these mid-points being as indicated by the arrows mutually parallel and in the same direction in space. In Fig. 1 one horizontal side is ceritrally interrupted for connection to a feeder F. Insteadof a rectangular frame a curved frame might be used,

t. e points of maximum current flow being at the mid- Fig. 2 shows this points of the horizontal dimension. modification.

A preferred form of aerial in accordance with the main feature of this invention is, therefore, in electrical essence, two dipoles which are mirror images of one another and which are united electrically and mechani-- cally with one another at points of'zero relative potential:

difference. 1

surface e. g. part of the curved surface of a cylinder. Thus the rectangular frame structure of Fig. 1 might be modified as shown in Fig. 3 by making the horizontal sides arcuate so that what may be termed an arcuately bent rectangle is formed with straight vertical sides lying on the curved surface of an imaginary cylinder and arcuately curved horizontal sides each lying along the periphery of one or other of the circular ends of said cylinder. In the description which follows an aerial with all its conductors in a plane (e. g. as in Figs. 1 and 2) ill be described as a flat aerial while one which is bent so that its conductors lie ina curved surface e. g. the curved surfaceof a cylinder (as in Fig. 3) will be described as a bent aerial e. g. an arcuately bent. aerial. In practice such a bent aerial would not be used alone but in electrical association. with at least one other similar aerial, the bent serials being symmetrically disposed round a common imaginary cylinder; Such an aerial system would, of course, be virtually omni-directional.

As is exemplified in Figs. 1 to 3 (and in other figures to be described later) bent dipoles employed in an aerial system in accordance with this invention, or some of them, may be centrally interrupted electrically for the insertion of feeder connections. Also, as will be seen later, they may be interrupted for the insertion of quarter wave lines or of capacities.

A vertically mounted single fiat aerial in accordance with this invention e. g. an aerial as in Fig. 1 willgive a polar diagram of the figure-of-eight type in the plane bisecting its vertical dimension at right angles and, if mounted for rotation about its vertical axis, may be used with advantage where horizontally polarized transmission With a rotating directional diagram is required or for direction finding reception. Owing to the relatively small horizontal dimension of the frame and its me.- chanical symmetry with respect to its vertical axis, mechanical rotation, even at relatively high speeds, involves far less mechanical difficulties than in the case of an otherwise comparable plain horizontal dipole. It is, in general however, preferred to obtain rotation of the diagram (where required) without mechanical movement and arrangements enabling this to be done will be described later herein.

.Where a rectangular frame is used it may be made tunable in various different waysfor example by making one of its horizontal portions (usually the upper one) in the form of a slider which can he slid along the vertical conductors it spans, so that the frame may be tuned and adjusted on site. Such an arrangement is illustrated in Fig. 4 in which S is the slider. A convenient associated feeder arrangement is, one in which the two wires of a feeder are connected to points symmetrically Patented Apr. 2,19 57- 3 disposed on either side of the mid-point of one of the horizontal conductors. These points of connection may with advantage be adjustable or slidable along the horizontal conductor to facilitate tuning and matching. This arrangement is also illustrated in Fig. 4 in which F5 are the slidable feeder points.

A preferred directional aerial system in accordance with the invention is illustrated in Fig. 5. This consists of two similar fiat aerials A1, A2. mounted at right angles to one another and having a common vertical axis. The horizontal conductors at top or bottom may e coincident where they cross as is indicated at P in Fig. 5 so that in this case these conductors may be constituted by a four-armed spider. There may be two such spiders one vertically over the other, and one at the top and the other at the bottom conveniently situated for mounting and supporting purposes. Only one spider is however indicated in Fig. 5. The feeders F1, F2 associated with the frames may be connected thereto in any of a number of different ways, for example as already described. The method shown in Fig. 5 is the same as in Fig. 1. For beacon or radio direction finding purposes the aerials may be connected through their feeders to one or other of the mutually perpendicular stator coils STE, 8T2 of a radio-goniometer the rotor R of which is connected to a transmitter or receiver TR, as the case may be. By rotating the search coil R of the radio-goniometer the orientation of the diagram may be rotated in azimuth. Such an arrangement, with the search coil driven at constant predetermined speed, is eminently suitable for use as the directional portion of a so-called very high frequency omni-directional range (V. O. R.). Instead of a goniometer of the induction type as illustrated a capacitative goniometer can be used an is indeed preferred.

As the proportion of the central portion to end portions of a dipole in accordance with this invention increases, the radiation increases, the curve of increase flattening as the end portions approach the theoretical limit of zero length. With a crossed aerial system as typified by Fig. 5 octantal error increases at the same time but the curve steepens as the said theoretical limit is approached. Accordingly, by judicious choice of the proportion of central to end portions, the combination of strong radiation with little error is obtainable.

Instead of mounting the aerials to have a common axis they may be mounted so that they are equally spaced from a common axis and lie on the vertical surface of an imaginary solid body e. g. a vertical cylinder or a vertical prism. This is illustrated in Fig. 6 in which the imaginary body is a vertical prism, four aerials A1, A2, A3, A4 being shown. In the case where the imaginary body is a cylinder the aerials will, of course, be arcuately bent aerials. There may be any number of aerials ,(not, of course, less than two) mounted in this way. If the aerials are mounted vertically adjacent one another in this way and are so energized that the currents in the horizontal conductors of the aerials disposed round the imaginary figure are all in the same direction round that figure (as indicated by the arrows in Fig. 6) the result will be a horizontally polarised omni-directional field. So as not to complicate Fig. 6 current directions for the vertical conductors are represented for aerial A1 only. Such an arrangement is eminently suitable for broadcast (e. g. television) transmission and is highly satisfactory both electrically and mechanically. In such an arrangement, radiation from the vertical conductors of the frames tends to cancel out and these conductors may, if desired, be enclosed in pairs by vertical tubular screens such as SC (Fig. 6) each of which encloses two vertical frame conductors one in each of two adjacent frames. Only one screen SC is shown in Fig. 6 so as not to complicate the figure and for the same reason feeder connections are not shown. They may, however, be as in any of Figs. 1 to 5. The additional capacity due to the addition of such screen tubes involves the shortening of the lengths of the screened conductors by about half.

Such an omni-directional aerial system may be mounted co-axially with and surrounding another aerial system (for example a directional aerial system such as the crossed aerial system already described) and the two systems may be operated on the same wave length or on different wave lengths. Thus, for example, a vision and accompanying sound broadcast installation could comprise an omni-directional system as shown in Fig. 6 for the video signals, carried on one wave length, said system co-axially surrounding a pair of crossed frames as shown in Fig. 5 energized in quadrature with the sound modw lated carrier. Or again, for airfield flying control pur poses, an omni-directional system such as that of Fig. 6 could be employed for listening on one wave length, to signals from any aircraft in the service area of an airfield while a co-axiaily surrounded cross frame system such as that of Fig. 5 with the frames associated with a radiogoniometer as already described with reference to Fig. 5 could be independently employed for radio direction finding or individual control of selected individual aircraft in the area. This combination of aerial systems can also be used as a very sensitive detector of reflecting objects in the field for a transmitter operating on one aerial system i. e. on one mode, in conjunction with a receiver tuned to the same frequency and operating via the other system on the other mode forms a combination which is exceedingly sensitive to the presence of such objects. Ideally there should be no pick-up from the receiver but the slightest re-radiation upsets the balance so that moving objects in the field are easily detectable.

A double aerial system comprising an omni-dircctional aerial system co-axially surrounding a crossed-frame system with an associated radio-goniometer, can be employed as a radio direction finger or a V. O. R. if the same wave length tuning is employed for both systems, since the polar diagrams of the inner and outer systems may be caused to combine to give a cardioid or a limacon. Since such a double system forms one of the most useful and advantageous embodiments of the invention one such arrangement will now be described in more detail with reference to Fig. 7(a) and (b). The inner system shown in Fig. 7(a) consists of two crossed flat rectangular aerials A1, A2 as already described each having its upper horizontal conductor vertically slidable along the associated vertical conductors for tuning adjustment purposes. If desired and as shown these upper conductors may be constituted by a four-armed spider. SP1 which slides up and down (for adjustment) as a unit. The lower conductors are constituted by a four-armed spider SP2 centrally bored to receive a central support CSP for the whole structure and, where there is an upper spider, this too may be centrally bored for the support as indicated. These mutually perpendicular flat aerials are connected to two feeders Fl, F2 as already dcscribed each feeder having its wires adjustably tapped on either side of the mid-point of one or other or the lower conductors. The feeders are taken to the mutually perpendicular stators of a radio-goniometer (not shown) the, search coil of which is connected to the transmitter (not shown) in the case of a V. O. R. or to a receiver (not shown) in the case of a direction finder.

The outer structure, Fig. 7(b) concentrically surrounds the inner but is shown separately for ease of drawing. It consists of four similar arcuately bent aerials O1, O2, O3, 04 which lie on an imaginary cylinder concentrically surrounding the inner structure. The lower horizontal conductor of each bent aerial is interrupted centrally at N1, N2, N3 or N4 and the conductors of a quarter wave line QLll, QLZ, QL3, QL4 are attached, in each case, on either side of the interruption. These lines, of which there are four, extend vertically downwards. The lower ends of each line are connected in I each case through a pair of flexible conductors HLl or HLZ which are crossed over centrally at K1 or K2 and are a half-wave length long (or a multiple thereof) to the lower ends of the diametrically opposite quarter wave line. The center points K1 and K2 are brought together and made physically the same point (though for clarity in drawing they are not so shown) and similarly the points K3 and K4 are made physically the same point. The main feeder (not shown) from the transmitter or receiver (as the case may be) has one wire connected to the common point K1, K2 and the other wire connected to the common point K3, K4 through an interposed further quarter wave line (not shown) or other feeding matching network.

If desired the upper horizontal conductor of each bent aerial may also be interrupted centrally and the conductors of quarter wave lines attached, in each case, on either side of the interruption in the same way as for the lower horizontal conductors of the bent aerials. These quarter wave lines, which extend upwards, are interconnected in the same way as the quarter wave lines associated with the lower horizontal conductors but there need not be any connected feeder, i. e. the interconnecting system at the top may be left blind.

In yet another form of outer, omni-directional structure, illustrated in Fig. 8 there are again four (or some other number of) rectangular aerials A1, A2, A3, A4 which concentrically surround the inner structure. The middle points of the adjacent vertical conductors of adjacent aerials are coupled by coupling condensers KK and accordingly the physical height of each aerial may be reduced.

In Fig. 8, for reasons of simplicity of drawing only two condensers KK are shown, the other two condensers being not shown but their places of connection being indicated by the other two references KK. The lower conductor of each aerial is interrupted centrally for the in sertion of a quarter wave line QL or other feeder matching network.

In the case of a V. O. R. a common transmitter would be employed for both aerial systems. If desired and as known per se for reference purposes in V. O. R. practice, the Omani-directional (outer) system may be fed with a main carrier which is amplitude-modulated by a frequency modulated sub-carrier whose frequency is varied with and is thus an indication of, the variation of the orientation of the polar diagram from the directional (inner) system.

Further, in the case of a V. O. R. substantial advantage may be obtained by mounting the double aerial system in a vertical cylindrical cavity resonator or wave guide having a ring of vertical radiating slots around it. Such a cavity resonator or wave guide tower which does not per se form part of this invention, not only provides mechanical and weather protection but is of substantial advantage in clearing up accidental secondary emissions of unwanted polarization from the aerial system. Such a Wave guide tower (which may enclose a co-axial double aerial system such as that shown in Fig. 7(a) and (12)), is shown in Fig. 9. Here T is the tower, and SL are the slots. The enclosed aerial system does not, of course, appear in Fig. 9, but it may be any one of the aerials heretofore described with feeders as hereinbefore illustrated. The center of the directional systerm may be substantially at the same height as the centers of the slots SL in the tower and the omni-directional system may be below it though other arrangements are possible. For example since the directional system will propagate satisfactorily along the height of the tower if the latter is suitably proportioned it may be mounted below the level of the slots at a vertical spacing of a half wave length in the tower (i. e. half a guided wave length) or a multiple thereof between the middle of the omni-directional system and the middle of the directional system. In other words, where a tower is employed, the two systems may be co-axial but vertically spaced. Where ing by nearby objects. In such cases, in order to avoid multiple path earth reflections a counterpoise e. g. in

the form of a concentric disc at right angles to the tower axis and approximately half a wave length below the plane of the mid points of the slots, is preferably provided. Such a counterpoise is shown at CP in Fig. 9. v

The invention is not limited to the particular embodiments and applications so far described. Thus, for example, with an l i-shaped aerial in accordance with this invention with the wires of a feeder connected on either side of and symmetrically With respect to the mid-point of the cross-piece of the H the said cross-piece may be uninterrupted or it may be interrupted centrally i. e. between the wires of the feeder, and if desired, a capacity may bridge the interruption. Such arrangements are illustrated in Figs. 10, 11 and 12 in all of which there is an H shaped aerial H with an associated feeder F. In Fig. 10 the cross-piece of the H is interrupted; and in Fig. 11 it is not; and in Fig. 12 it is interrupted and a condenser HK connected across the interruption. A pair of such aerials H1, H2 mounted as shown in Fig. 13 at right angles to one another so that the cross-pieces combine to make a cross with its arms at right angles may be used where a figure of eight diagram is required. Four such H aerials H1, H2, H3, H4 mounted as shown in Fig. 14 with their cross pieces coplanar and each H on the side of an imaginary right prism of square cross section will give an omni-directional diagram. Feeders are indicated at F in Fig. 14. Such an omnidirectional aerial, with a cross H figure of eight aerial (such as that of Fig. 13) within it could be used, for example for a V. O. R. The feed shown in Fig. 14 may be used in the arrangement shown in Fig. 13.

Wherever in the claims I have used the expression dipole I intend by this term to convey the same meaning as that set forth in vol. 3 of the Summary Technical Report of the Committee on Propagation N. D. R. C. on The propagation of radio Waves through the standard atmosphere, with particular reference to page 25 and the repeated use of the term dipole as a self-explanatory technical term between pages 22 and 39, of Chapter 3, of said report. For example in Fig. 1, at the lower side of the aerial configuration shown, there is a center fed dipole. The upper part of the aerial configuration is a second dipole, but in the latter case it is end fed from the lower dipole. The total aerial therefore consists of an end fed plus a middle fed dipole, the middle fed dipole being of course current fed, and the upper end fed dipole being voltage fed. In this manner there is obtained current loops in both dipoles in the same direction as indicated by the arrows in Fig. 1 so that the currents in the two dipoles are additive.

The aerial operates precisely in accordance with the foregoing description and it is practical to sever completely the aerial of the type shown in Fig. 1 if this aerial has been dimensioned to operate as two dipoles as explained hereinbefere. The configuration will still operate with its severed sides as an aerial.

When a straight dipole is used octantal error is mainly caused by the wide spacing of the tips of an aerial in terms of wavelength. When an aerial constructed according to this invention is used a substantial reduction in octantal error is effected by a configuration wherein the tips of the aerial are close together. With this arrangement of aerial a large proportion of the halfwave dipole is bent at right angles to the radiating portion and thereby rendered non-radiating. It is found that with this configuration the radiation etfected from the normally central part of a straight dipole is unimpaired.

I claim:

1. A short wave system for the operation of radio frequency apparatus at a predetermined wavelength comprising a slotted substantially vertical screening cavity,

and at least two mutually substantially perpendicular aerials mounted within said cavity, each aerial comprising a loop antenna of one wavelength in perimeter, and each having a vertical portion and a horizontal portion, the vertical portions being substantially longer than the horizontal portions.

2. A short wave system as set forth in claim 1, in which the aerials are adjustable as respects their vertical dimension.

3. A short wave system as set forth in claim 1, wherein the said two aerials are coaxial.

4. A short wave system as set forth in claim 1, in which there are a plurality of aerials synnnetrically dis posed around a common central axis within said cavity.

5. A short Wave system as set forth in claim 1, in which the, said two aerials are coaxial and wherein the screening cavity consists of a plurality of aerials symmetrically disposed around a common central axis, the two mutall'y perpendicular aerials having the same axis as said plurality of aerials.

6. A short wave system for the operation of radio frequency apparatus at a predetermined wavelength comprising two sets of antenna systems, one set comprising two mutually substantially perpendicular aerials consisting of loop antennae each having a perimeter of one wave length with a vertical portion and a horizontal portion, the vertical portions each exceeding in length the length of said horizontal portions, and the other set comprising two pairs of loop antennae arranged around said first mentioned set of loop antennae and forming elements of a cylinder surrounding said first mentioned set of loop antennae.

7. A shortwave system for the operation of radio fre-- quency apparatus at a predetermined wavelength comprising inner and outer loop antenna systems concentri cally mounted, said inner loop antenna system consisting- References Cited in the file of this patent UNITED STATES PATENTS 2,014,732 Hansell Sept. 17, 1935 2,169,377 Walter Aug. 15, 1939 2,210,491 Lewis Aug. 6, 1940 2,247,743 Beverage July 1, 1941 2,289,856 Alford July 14, 1942 2,373,206 Thomas Apr. 10, 1945 2,403,500 Carlson July 9, 1946 2,414,266 Lindenblad Jan. 14, 1947 2,474,242 Gieringer June 28, 1949 2,509,750 Vaudoux et al. May 30, 1950 2,533,900 Shanklin Dec. 12, 1950 FOREIGN PATENTS 519,350 Great Britain Mar. 21, 1940 654,498 Great Britain June 20, 1951 OTHER REFERENCES Concentrated Directional Antennas for Transmission and Reception, QST, October 1937, pages 27 to 30.

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