US2689303A - Antenna array - Google Patents

Description

Sept. 14, 1954 J. R. RlssER ANTENNA ARRAY Filed nay 24, 194s AT TORNEY Patented Sept. 14, 1954 ANTENNA ARRAY Jacob R. Risser, West Lafayette, Ind., assignor, by mesne assignmentato the United States of America as represented by the Secretary of War Application May 24, 1946, Serial No. 672,012

3 Claims. (Cl.

This invention relates to electrical apparatus and more particularly to means for radiating electromagnetic energy.

It is frequently desirable in electrical apparatus to employ an antenna which will provide a directed beam of electromagnetic energy. One method often found suitable to accomplish this result is to utilize what is known as a wave guide array, which usually consists of a wave guide fed from a source of electromagnetic energy and having multiple radiating elements fed from the wave guide.

Among the difficulties encountered with wave guide arrays are the obtaining of a simulated line source of radiation, the impedance matching of the elements to the wave guide from which they draw energy, and the reduction of the frequency sensitivity of the array.

Therefore, it is among the objects of this invention to provide a wave guide fed array which closely simulates a line source of electromagnetic radiation.

It is another object of this invention to provide a wave guide fed array with radiating elements or means which aid in the simulation of a line source of electromagnetic radiation.

It is a further object of this invention to provide a wave guide fed array which is comparatively insensitive to frequency variations.

Other and further objects, advantages and novel features of my invention will become apparent from the following description and the accompanying drawing wherein:

Fig. 1 is a top view of one preferred embodiment of the invention;

Fig. 2 is a top view of another preferred embodiment of the present invention; and

Fig. 3 is a cross-sectional view of an alternative to assist in the reduction of frequency sensitivity, and employing apertures as radiatingl elements.

Referring now to Fig. 1, there is illustrated in top view `a center fed wave guide array. Feed wave guides I0 and II of the array are supplied with energy by a Wave guide I2 from a source (not shown). The energy is caused to divide in substantially equal amounts in wave guides I0 and II from whence small amounts pass through each of apertures I3 and I4 from where it is directed between a pair of parallel metallic surfaced plates I5 into outer space. The array is symmetrical along a median plane I6, and consequently, it will be sufficient to describe the structure on one side of the plane. l Wave guides II and I2 are viewed in the E-plane, that is, electric vectors, when the guides are excited, are in the plane of the drawing. Wave guide il' is formed so that the wall I I thereof from which energy escapes through apertures It makes an angle 0 with median plane IS which is less than 90. Elements or apertures I4 are substantially equally spaced and of the same size and shape. Walls I and I8 of wave guide il are tapered in the direction away from the source so that each element It will receive approximately the same amount of power. Apertures I4 are slots which 'constitute small wave guides communicat1 ing with wave guide Il. They may be cut in the broad wave guide wall I1 and are so calculated in cross-sectional dimension that they can be excited only in the fundamental mode having an electric vector oriented parallel to the plane of the View of Fig. 1. Where parallel plates it* join walls Il they enclose slots i4, which may not extend entirely from top to bottom of wall I 1. By decreasing the space between the parallel plates I5, which may be considered as forming a parallel plate wave guide, and decreasing the angle 0, the spacingbetween wave guide apertures I 4 may be increased substantially beyond a wavelength as measured in wave guide II.. Consequently, the slots I4 are preferably spaced greater than a wave guide wavelength so that energy from each one lags slightly in phase the energy from the preceding aperture (moving outwardly from median line It), and energy arriving at aperture I9 of the plates I5 will be substantially in phase. Thus aperture IE! simulates a line source of electromagnetic radiation. The'aper-` yof power between wave guides Iii and II, a

tapered septum 25 is introduced centrally in wave guide I2 extending from the top and bottom walls thereof and the resulting divided wave guide leads into twobranch guides 2t and 21 which respectively communicate directly with wave guides I and II. Wave guides 2e and 2T are gradually widened to the proper width. Wave guides I0 and I I are tapered, as mentioned above, so that substantially equal amounts of energy are withdrawn therefrom by each of slots i3 and I4.

Wave guide II is suitably terminated with a matched absorptive load 23 (diagrammatically illustrated) to reduce the reflection of any power not radiated by elements I!! to a negligible amount.

The reduction of the angle 0 to a value less than 90, which is not customary to the art, together with corresponding increase of spacing between slots Id, provides a reduction in frequency sensitivity, and further, the close spacing of parallel plates I5 contribute to reduce diiraction effects. The frequency may be altered over a substantial band without causing the direction of the electromagnetic energy radiated from aperture I9 to depart from the direction of line I.

Referring no-w to Fig. 2, there is illustrated a top view of another embodiment of the invention which includes a wave guide 3B which carries energy from a source (not shown) to feed wave guides 3| and 32 in substantially equal amounts. Energy is fed through slots or radiating elements 33 and 34 of wave guide 3| and 35 and 35 ofwave guide 32. These slots feed energy betweenparallel plates 31 which have a suitably flared aperture 3B.Slots 33 and 35 are rectangular slots in the side walls of 3I and 32 respectively, whereas adjacent slots 34 and 3S respectively may be formed by inserting a tongue member 3i! in agrooved space 39. There is thereby provided a wave guide of small dimensions having a longer path for the energy to traverse than the sim ple straight slots. As a result, the additional path length is calculated, for example, to be a half wavelength longer than the path length through the straight slots so that energy leaking into the slots from the feed wave guides is radiatedin phase as it leaves the slots spaced a half guide wavelength apart. Unwanted diffraction lobes are thereby eliminated.

A further improvement is provided by causing the energy to divide betweenwave guides 3l and 32 but increasing the total distance traveled by energy to corresponding slots in wave guide 3i and inwave guide 32 by a quarter wave length. The distance between adjacent slots 33-33 and of wave guide 3I is equal to the distance between adjacent slots 35-35 and Sii- 35 ofwave guide 32, but the initial distance traversed by the energy in reaching from wave guide 363 to the tongued slot 34 closest to median plane il@ in wave guide 3I is a quarter wavelength longer than the initial distance traversed by the energy in reaching fromwave guide 30 to thetongued slot 36 inwave guide 32 closest to median plane et. However, the entire slot structure ofwave guide 32 is displaced a quarter wavelength farther fromaperture 38 in a direction parallel to median line di), so that compensation is made for the extra travel to cause the energy to be in phase as it leavesaperture 38. The advantage in this type of structure lies in the cancellation of reflections caused by corresponding slots, as energy reflected from the slots travels a half wavelength longer in its total journey froml the source into the wave guide 3l and return than does similar reflected energy traveling from the source intoWave guide 32 and return. Thus, the half wavelength dilerential secures an improved impedance characteristic insofar as the source of energy is concerned.

Referring now to Fig. 3, there is illustrated in top view an alternative structure for the slots. It will be understood that for purposes of clarity the proportions of the structure are somewhat different than may be encountered in actual practice. There is shown in Fig. 3 a section of afeed wave guide 50 of a wave guide feed array which may be similar to those hereinbefore discussed. The E vector within the guide is oriented as illustrated by the arrow 5I and a small percentage of the energy inguide 50 is radiated through each small aperture or opening 52. The apertures permit the passage of energy having its E vector oriented as illustrated by arrows E53, and metallic surfaces forming the slot side walls are then triangulated to gradually reach a point. The effect of such construction is to reduce the difficulties of small discrete radiating elements, the latter tending to result in a diffraction pattern having lobes. With this invention the tapering causes the energy to be gradually distributed over the entire area between the points 5ft of the material through which the slots are cut or formed so that rather than a series of discreet radiating elements, there is presented a substantially uniform radiating line.

Referring now to Fig. 4, there is again illustrated an alternative construction for radiating slots in a wave guide feed array wherein the slots are provided in side wall 6E of feed wave guide 6I. In this instance the arrows again illustrate orientation of the electric vector` within the guides and again there is provided a short space of substantially rectangular slot t?. followed by a widening so that the structure between each ofslots 62 approaches a peint either Figs. 3 or 4 the side walls may e solid and the desired space cut therein, orV constructed of adjacent solid members, or hollow tubing or metallic coated substance may be used. The alternative construction employing a hollow member is illustrated in each instance by one member as shown in the figures.

Having thus described my invention, I wish it understood that I do not desire to be bound only to the specific embodiments herein disclosed, but I intend by the accompanying claims, to claim all such modifications, variations and equivalents as fairly fall within the scope and spirit of my invention.

What is claimed is:

1. An antenna array with a radiation pattern broad in one plane and highly directional in a plane perpendicular thereto for radiation of a broad frequency band of electromagnetic energy polarized in said one plane comprising a source wave guide, two feed wave guides branching therefrom, each of said feed wave guides Vhaving a rst broad wall facing in the general direction of energy radiation, said rst walls of saidffeed wave guides being at an angle less than 13e and greater than with respect to one another, said rst walls being provided with energy radiation slots, and a rpair of parallel plates formplates providing therebetween a plane aperture for energy radiation, the spacing between said slots being greater than a wavelength at the midfrequency of said frequency band for providing in-phase radiation in the plane of said aperture.

2. An antenna array according to claim 1 wherein means are mounted adjacent each of said slots outside said wave guides providing energy propagation paths of increasing width to minimize side lobes in the radiation pattern of the array.

3. An array according to claim 1, in which the space between said parallel plates is less than thel width of said broad walls for minimizing the necessary number of slots.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,453,414 Devore Nov. 9, 1948 2,402,622 Hansen June 25, 1946 2,405,242 Southworth Aug. 6, 1946 2,408,435 Mason Oct. 1, 1946 2,461,005 Southworth Feb. 8, 1949 2,469,419 Tawney May 10, 1949 2,482,162 Feldman Sept. 20, 1949

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