US2447879A - Antenna - Google Patents

Description

Aug. 24, 1948.

M. w. SCHELDORF ANTENNA Filed Nov. 19, 1945 I HIGH FREQUENCY APPARA TUS Inventor: Marvel W. Soheldorw,

by% x? 72mm,

His Atstorney a full wavelength.

Patented Aug. 24, 194.8

I ANTENNA MarvelW. Sche ldorf, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York l Application November 19, 1945, serial No. 629,665

, /My invention relates to a high frequency antenna system and inv particular to a high frequency directive antenna suitable for transmit- ,ting frequency modulated waves. Itis the primary object of my invention to provide a new and improved antenna suitable. for transmitting large amounts of .high frequency power.

In United States Patent 2,324,462, granted July 13, 1943, there is disclosed a high frequency antenna system inwhich a radiating dipole is formed as a-pair of closely spaced, peripherally incomplete, metallic loopsencircling a metallicmast memben. Corresponding ends of the twoloops areconnectedtogether and capacitive means are inserted between the. ends of the individual loops. In this way, there. is formed a radiating element which has an effective electrical length substantially equal to a half wavelength at the desired 8 Claims. (01. 250 33.53)

operating frequency of the system. For transmitting largeramounts of power, themast is encircled by two or more bays or sets of loops, (the bays being spaced apart vertically along the rnast 'at an electrical length equal to, afull 'wavelength. a r Q It is an object of my presentinveritionfto provide an improved antenna of this type suitable for transmitting larger amounts of power at higher frequencies and in whicha radiating element has an electrical length of substantially Briefly stated, in accordance-with the illustrated embodiment of' my invention, 1 provide a high frequency antenna system which consists of a vertical mast which is surrounded by. aplurality of bays. The radiating dipoles'of the upper bays are formed as pairs of closely'spaced, peripherally incomplete, metallic loops having-an electrical length substantially equal to a, half wavelength at the operating frequency oi'the 7 system. The lower bays are formed as a pair of closely spaced, semi-circular conductors which are conductively connected at one end and capacitively connected to a third semi-circular conductor, likewise having an electrical length substantially equal to a half wavelength. The capacitive coupling between the pair" of conduc tors and the third conductor is adjustable so that the resultant antenna structure; may be tuned over a relatively wide band of frequencies. For 'a' better understanding of my invention,

reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims. Fig. 1 is.a schematic perspective viewof. an antenna array having four bays constructed in accordance with. the invention.

Fig. 2 is a perspective view, partly'schematic, of a portion of a practical antenna system embodying the invention, and Fig. 3 is a schematic diagram of a modification of the invention.

In the'antenna array schematically illustrated in Fig. 1, I haveshown' a single central. mast I,

indicated in dotted outline; which is encircledby fourvertically spaced bays or units 2-5; The bays 2, .3 are similar in construction and comprise afpair of closely spaced, separated conductorsB, 1, each ofwhich' is formed into the arc of a circle. The circles are peripherally incomplete and the conductors 6, I are joined at their ends by a pair of conductive members 8, 9 which form .a capacitive coupling between the ends of the respective circles. The conductors 6, 1 function as a folded, dipole and the resonant frequency of .th edipole is adjusted by variation of the total capacitance between the conductive members 8, 9. The lower dipole 'l is opened at its center at a pointopposite the conductive members 8, 9 to provide suitable terminal connections I'll, II and 'a suitable form of transmission line such as the two concentric lines l2 may be used to transfer energy between the connections H], H and high ifi quen'cy radio apparatus represented schematically by the box [3. I

v The folded dipole 6, I, performs the dualfunc tion of a radiator and .an impedance matching transformer. In order that impedancematching between the lines 12 and the dipole 6, I may be effected, I provide a variable shunt capacity [4 acrossthe input terminals III, II. By variationof, the capacitor M, the feeding point imjpedance in the terminals In, H may be varied within limits to match the impedance on the transmission line, connected with the antenna, The-manner in which this is achieved is explained in Patent 2,324,462.

' The folded dipole 6, 1 preferably has, an effective electrical length equal to a half wavelength at the desired operating frequency of the antenna system and the adjacent ones of the bays -{2-5 are spaced apart vertically by a distance substantially equal to a full wavelength at the desired operating frequency. Furthermore, each of the bays 2-45 is connected to the transmission lines l2 by quarter Wave matching sections IS, IS, l7, l8. By virtue of the operation of these quarter wave matching sections and the adjustment effected by the capacitor 4, the effective impedance presented to the transmission lines l2 by each bay or unit may be matched to equal the impedance of the transmission line l2.

When the system of Fig. 1 is to be used for frequency modulation transmission or reception and is operatedat a relatively high frequency, of the order of, for example, 100 megacycles, I have found that for high power installations with many bays the mast required for supporting the bays, which is commonly tapered, is of such a size that its circumference approaches an electrical half wavelength of this frequency as its base is approached and prevents mounting them at the proper position. Accordingly, the units or bays 4, are modified in form. Thus, the bay 4 comprises two closely spaced, separated, semicircular conductors I9, 2|] which are similarly oriented with respect to the mast l and connected at their open ends by means of vertical conductive members 2|, 22. The conductive members 2|, 22 are in spaced relation with two additional conductive members 23, 24 connected at the ends of a third semi-circular conductor 25. The dimensions of the semi-circular conductors I3, 25 are such that their total electrical length is effectively equal to a full wavelength at the operating frequency of the system. This length may be adjusted by variation of the capacity formed between the conductive members 2|, 23 and '22, 24, respectively, to equal exactly a full wavelength, so as to present a purely resistive terminal impedance.

In Fig. 2 there is shown a perspective view of a portion of an actual antenna including a bay constructed as the bay 4 of the system of Fig. 1. In this figure, the mast I is shown as a metallic pole from which the semi-circular conductors I9, 20, 25 are supported by means of metallic members 26. The conductive members 21-24 are illustrated as metallic plates which are welded, or otherwise afiixed, to the ends of the respective semi-circular conductors. The capacities formed by the plates 21, 23 and 22, 24, respectively, are shown as adjustable, suitable variation capacity being obtained by means of flat disks 2?, 28 carried respectively by sh-afts 29, 30 threaded into the plates 2|, 23, respectively. Similar disks 21a,

28a are also mounted on plates 22, 24 as shown.

The spacing between the disks may readily be adjusted by rotation of either or both of the capacitor plates 21, 28 or 27a, 28a. The pair of transmission line conductors, illustrated conventionallyas the conductors 3|, 32, supply high frequency energy to or from the high frequency apparatus l3. The conductors 3|, 32 may be connected to the adjacent ends of conductor 20 by means of studs 33, 34 attached to those ends and the nuts 35.

In the operation of the portion of the antenna structure shown in Fig. 2, the conductors i9, 20 perform the dual function of a radiator and an impedance matching transformer the transformation ratio being determined by the relative cross-sections of theconductors. The conductor '25 functions likewise as a radiator and a continnation of the conductors I9, 20 about'the mast l. The resonant frequency of the antenna structure may be adjusted by the variation of the capacitance between the plates 21, 28 or 21a, 28a and matching of the terminal impedance or input impedance is effected by quarter wavelength matching sections such as the section l5 shown in Fig. 1. In the system, the mast preferably is grounded and the :metallic supports 26 are connected to the conductors I9, 25 at points of zero voltage and effectively lie in a neutral plane so far as the currents in the radiators are concerned. The members 26 thus do not disturb the electri cal performance of the system.

In Fig. 3, I have shown schematically a modification of the antenna structure illustrated in Fig. 2 and which is particularly useful in systems wherein a large number of bays are desirable and the operating frequency is such that the size of the mast required to support the radiators is such that its circumference at some point t rou ut its heightis greater than a full wavelength at the operating frequency. In this modification, the grounded mast is surrounded by two diametrically spaced pairs of closely spaced, separated conductors 36, 31, the conductors of each pair being similarly oriented with respect to the mast I and having a length equal to approximately a quarter of a circle. The conductors 36, 31 are joined at their ends by vertical conductive membars 38. Each of the vertical members 38 is in spaced relation with respect to a vertical conductive member 39 connected with the respective ends of one of a pair of arcuate conductors 40. Each of the conductors 40 likewise has a length approximately equal to a quarter of a circle.

Thus, the overall effective electrical length 'of the antenna structure may be made equal to two full wavelengths at the desired operating frequency. Furthermore, each of the conductors 36, 40 may be supported from the mast I at its point of minimum voltage by means of a conductive support 4|. The conductors 31 can be provided with input terminals 42, 43 which may be connected through any suitable transmission line to the high frequency apparatus l3.

It is to be understood of course that, preferably, the antenna structure of Fig. 3 is to be used as one bay or unit of an array of the type shown in Fig. 1. In the antenna system, preferably the higher arrays will be constructed as the arr ys 2, 3 of Fig. l; the intermediate ones, as the arrays 4. 5 of Fig. 1; and those near the base of the supporting mast where the circumference of the mast is greater than a full wavelength may be constructed as shown in Fig. 3.

One of the advantages of myv invention is that it permits the use of a circular antenna for supplying large amounts of power at relatively high frequencies. The advantages of the circular antenna are its simplicity and ease of adjustment over an operating frequency range. By my invention, these benefits are extended for use in systems requiring higher values of frequency and power.

While I have shown and described my invention as applied to an antenna array of particular configuration and as employing various elements diagrammatically illustrated, it will be obvious to those skilled in the art that changes and modifications may be made without departing from my invention and I therefore aim in the appended claims to cover all such changesand modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. Ahigh' frequency antenna element comprising a pair of closely spaced, open, arcuate conductors similarly oriented in substantially parallel planes and connected together at their corresponding ends, a third arcuate conductor also ly ing in a substantially parallel plane and having one of ,its ends in spaced relation with and capacitiveliy coupled to one of the connected ends .of said pair of conductors, and Imeanscoupled toone offsaid pair of conductors for supplying high frequency energy to said antenna, said pair of conductors and said third conductor conjointly forming an arcuate antenna element having an effective electrical length substantially equal to a full wavelength at said high frequency.

2. A high frequency antenna comprising a pair of closely spaced, separated, semi-circular conductors similarly oriented and connected together at their corresponding ends, a third semi-circular conductor opposite said pair of conductors and having its ends in spaced relation with and capacitively coupled to the corresponding ends of said pair of conductors, and means coupled to one of said pair of conductors for supplyin high frequency energy to said antenna, said pair of conductors and said third conductor lying in substantially parallel planes and conjointly forming a peripherally incomplete, circular loop having an effective electrical length substantially equal to a full wavelength at said high frequency.

3. A high frequency antenna system comprising a supporting mast, a pair of closely spaced separated semi-circular conductors similarly oriented on one side of a plane through the axis of said mast and connected together at their corresponding ends, a third semi-circular conductor arranged on the opposite side of said plane from said pair of conductors and having its ends in spaced relation with and capacitively coupled to the corresponding ends of said conductors, means coupled to one of said pair of conductors for supplying high frequency energy to said antenna, and conductive means connected to one of said pair of conductors and to said third conductor at points of minimum potential thereon for supporting said conductors from said mast, said pair of conductors and said third conductor lying in parallel planes and conjointly forming a peripherally incomplete, circular loop having an adjustable electrical length substantially equal to a full wave length at said high frequency.

4. A high frequency antenna system comprising a supporting mast, a pair of closely spaced, separated, semi-circular conductors similarly oriented in planes perpendicular to the axis of said mast and on one side of a vertical plane through said axis, said conductors being connected together at their corresponding ends, a third semicircular conductor lying in a plane perpendicular to said axis on the opposite side of said vertical plane from said pair of conductors and having its ends in spaced relation with and capacitively coupled to the corresponding ends of said conductors, means coupled to one of said pair of conductors for supplying high frequency energy to said antenna, conductive means connected to one of said pair of conductors and to said third conductor at points of minimum potential thereon for supporting said conductors from said mast, said pair of conductors and said third conductor conjointly forming a peripherally incomplete, radiating loop having an adjustable electrical length substantially equal to a full wavelength at said high frequency, and means adjusting the capacity between the ends of said third conductor 6 and said pair of conductors-for tuning said antenna to resonate at said frequency. i

5. A high frequency antenna array comprising to a full wavelength at the desired operating frequencyof said antenna, the highest of'saidradiators having an effective electrical length substantially equal to a half wavelength at said frequency and a lower of said radiators having an effective electrical length equal to a full wavelength at said frequency.

6. A high frequency antenna array comprising a vertical supporting conductive mast, the circumference of said mast increasing in magnitude from the highest point thereof to the base thereof, a plurality of horizontal radiating loops surrounding said mast at points spaced apart vertically along the height thereof by a distance substantially equal to a full wavelength at the desired operating frequency of said antenna, the highest of said loops having an effective electrical length substantially equal to a half wavelength at said frequency and comprising a pair of closely spaced, separated, horizontal, circular conductors, said conductors being circumferentially incomplete, similarly oriented and capacitively connected together at their corresponding ends to form an electrically closed radiator, and a lower of said loops having an effective electrical length equal to a full wavelength at said frequency, said lower loop comprising a second pair of closely spaced, separated, horizontal, semi-circular conductors similarly oriented and connected together at their corresponding ends together with a third, horizontal, semi-circular conductor arranged opposite said second pair of conductors and having its ends in spaced relation with and capacitvely coupled to the corresponding ends of said second pair of conductors to form a second, electrically closed radiator, and means coupled to one of each of said first and second pairs of conductors supplying high frequency energy to said radiators.

'7. An antenna for operation at a high frequency comprising a conductive supporting mast, a pair of closely spaced, semi-circular radiators similarly oriented in planes perpendicular to the axis of said mast with their centers substantially on said axis, said radiators having their corresponding ends connected together, a conductive support extending radially from said mast and attached to one of said radiators at its midpoint, center feed connections from a transmission line to the other of said radiators, a third semi-circular radiator lying also in a plane perpendicular to said axis with its center substantially on said axis, said third radiator having its ends spaced from and capacitively coupled to the ends of said pair, a second conductive support extending radially from said mast diametrically opposite said first support and attached to said third radiator at its midpoint, said radiators conjointly forming a loop antenna having an effective electrical length substantially equal to one wave-length at said frequency.

8. An antenna for operation at a high frequency comprising a substantially circular, incomplete loop, said loop having four separated, quadrantal radiating elements with their ends in closely spaced relationship, each of a first pair of diametrically opposite elements comprising I 8 two substantially parallel, arcuzuze conductors REFERENCES CITED connected together at their ends, means for transferring high frequency energy between one The following references are of record in the of the conductors of each pair and a transmission file of this patent: line, each of the other pair Of diametrically op- UNITED STATES PATENTS Dosite elements comprising a single arcuate conductor with its ends capacitively coupled to ad- Number Name Date jacent ends of the otherv pair of elements, the 1,647,283 Esau Nov. 1, 1927 over-all electrical length of said loop being sub- ,190,816 Wheeler Feb. 20 1940 stantially equal to two wavelengths at said high 10 2,324,462 Lee s et a1 v -r July 13, 1943 frequency.

MARVEL W. SCHELDORF.

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