US2478242A - Antenna - Google Patents

Description

R. E. CLAPP Aug. 9, 1949.

ANTENNA Filed Nov. 4, 1944 FIG-/ INVENTOR.

ROGER E. CLAPP FIG-J.

BY M 1%. LAM firm y Patented Au 9, 194@ R er B. Glenn. .Cam e; Ma s assi' mn. by

'esn a i rim ts, to thefiinitedf'states' of Ameri rep esen a th 'seee rer' War Application. ilove nberze, 194e, Se ia dotfifihttg:

4' C aims This. nv n n re ates. to an nnas. f r. Pr miering nonsymrnetrical radiation patterns andfparticularly to antennas. for producing patterns, wherein'the intensity of radiated energyvaries as,

a power function of cscti' (0. "being, the angle of radiation with respect to the,hoi;iz'on In certainfecho detection systems, for. example, GCA (ground controlof approachin aircraft), apparatus, it is desirable that the energy distribution in one plane throughout. a relatively wide angle follow a csc fl variation. Theoretically. this provides a radiation pattern. of such character. that the echo signals reflected, for instance, from. an aircraft coming inat constantaltitude will be as strong when the-targetis distantQsay, 30 miles, as. whenit is close in, It. also enables the. simultaneous viewing of 116%.?- and, distant aircraft. in. search scanning. Conventional paraholiclrefleca tors do not satisfy these requirements, and more over it. is necessary totilt the parabolic freflector. inorder to follow incoming aircraft. 2

In view of the foregoing, it is a salient object, of this invention to afford complete radiation coverage throughout a relatively wide angle in elevation and inconformity with; the desired mathematical relation between the intensity of radiatedenergy andan-gle of elevation. 2

A further object is to provide'a-novel and simple antenna FWQQHW: Q EH 'i iQQi fiing ii para" bolic reflector and dipole elements so spaced as, toproduce a radiationpatternof csc e configura tion.

In this connection it should be noted;that, re cent investigation has established the possibility that the exact type ofpattern desired may, be closer to a .csc configuration. The present invention has the advantage that; it may be readily adapted to cover either case. 2

These and other novel features and advantages will be apparent from the following disclosure.

In the drawings:

Fig. 1 is a partially diagrammatic View showing the manner in which the antenna may be mounted on a vehicle and the radiation pattern which it produces;

Fig. 2 is a plan view of the antenna; and

Fig. 3 is an elevational view of the antenna; and Fig. 4 shows a preferred embodiment of my invention.

Referring to Figs. 2 and 3, the antenna consists of a dipole array which is fed from a wave guide 1 and which directs its radiated energy against a cylindrical parabolic reflector 5. The spacing and number of the dipole elements 6 along the Wave guide I, in addition to the phasing and energization of eacheiementand co unction withthe, shape, of; the reflector fi; determine the: shape of the intensity pattern in avertical plane: The. dipoles are mounted" on one face of the glljdel andare energizedfin a known manner by probe extendin in tne id rte-primar es:

parabol c. refl tor. 5? .c n en rates' th d ated" energy into, a rather narrow beam in the. horizontal plane. The effective linesourceof radiaon of thedigole ra s le ei near-t f a line of the parabolic lcylinder jthat is, approximately to the nearest halfiwaveleng th'in air;

Fig. 1 illustrates the device. as" mounted in a mobiletypeofsearch station. The antennamay I, be used; in this instance to produce aPEI (plan pes uo inaiceton: typ offswh b th 'sw' rounding vicinity is swept periodically with the; beam from the antenna; The primary function of such a device; is to search. for and'detect the existence of aircraft the vicinity, and" as such, the pattern desired should vary approxirnately as. 050%. That is, an. airplane, flying infrom a d s c a a on n t tude i wa ih tion shouldbesubjected to: an drefiect a varyi g; m n en rg to du estent' r ga n d signalsa th sta n r a dle s e ih ma ma tion of the aircraft." 2

T nt rin ir eie in' a imu by mean which will be described; presently: It-is' apparent that the resolution in azimuth: of the system:de=

pendsupon the beam-width-oftlie ra-diationpat tern. Preferably the horizontal beamwidthshould be approximately constant for a-ll values of 'B-to provide l uniform resolution over the field? I The cylindrical parabolafiiprovidesa satisfactory solution to this problem.

To obtain the proper energy distribution inthe vertical plane, the spacing 'of 'the dipoles' 6 may be approximatelyas-fol-lows% Qver the lengtl'i A' (Fig. 3) representing approximately two-thirds the length of the array, the dipoles 6 are spaced apart slightly less than a half wavelength. Starting from point P and along the length B, the dipoles B are spaced gradually closer together so that at the upper end of the array the spacing is approximately two fifths of a wavelength. This particular spacing has given satisfactory results, although the pattern may be modified if desired by varying the spacing. If, for example, it is determined that the desired radiation pattern is closer to csc 0 rather than csc e, such variation can be achieved by spacing the dipoles 6 accordingly. It should also be noted that in practice the beam pattern is so adjusted that the peak is elevated slightly above the horizon, as indicated by the line Z in Fig. 1, and the beam-cuts off sharply below this line so as to minimize ground interference.

In general, when the dipole spacing is varied, three factors are affected: (1) the sharpness of the beam pattern below the line Z, Fig. 1 is changed; (2) the side lobes are changed; and (3) the vertical coverage of the beam is modified. When the vertical coverage is improved, that is, the curvature of the beam pattern over region X (see Fig. 1) is increased, the sharpness of the beam pattern below the line Z is diminished. Depending upon the relative importance of these factors, the beam may be adjusted to the desired shape. The shape is also governed by the amount of energy radiated from each element 6, which may be adjusted by the depth to which their respective pick-up probes extend into the wave guide 1, Figs. 2 and 3. r

The reflector 5 and the waveguide I feedin the dipoles 6 are supported Vertically in fixed relation to each other on a rotating table 8 provided with gear teeth [2, Figs. 2 and 3. The waveguide 1 is, in this instance, at the center of the table 8, and is coupled through a rotatable joint 9 to the transmitting and receiving means (not shown). A portion of the table 8 is broken away as indicated at Y to more clearly show the waveguide joint. A pinion Ill meshing with the gear 8 is mounted on the shaft of a motor II which drives the antenna structure when search scan ning is being performed.

The nature of the antenna structure may be such as to require that energy be fed to the top of the dipole array in order that the desired energy distribution will be developed in space. Fig. 4 illustrates this structure. Radio frequency energy is coupled through rotatable joint 9 to waveguide I3 which conducts the energy upwardly to bended section l4. Section [4 routes the energy to the top of waveguide 1 which directs the energy downwardly to the radiating dipoles 6. Moreover, it will be appreciated that the dipole array need not be at the center of rotation so long as the desired spacing between the dipoles and the reflector is maintained.

While I have illustrated and described a selected" embodiment of my invention, it is apparent that variations and modifications may be made by those skilled in the art, and therefore I do not desire to limit the scope of the invention to the precise details disclosed herein but wish to avail myself of all improvements and modifications within the purview of the following claims.

-I claim:

1. A combined transmitting and receiving antenna for use in radio object-locating apparatus,

4 comprising a cylindrical parabolic reflector and an array of radiating elements positioned on the focal line of said reflector, said elements being spaced closer together at one end of said array than at the other end thereof and means for controlling the amount of energy radiated from each of said elements to produce a radiation'pattern resulting in substantially uniform received signals at said antenna irrespective of the radiation angle of reflecting objects disposed along a substantially horizontal path in the plane of said reflector and radiating elements.

2. Anantenna for use in radio object-location I comprising a vertically-extending cylindrical parabolic reflector and an array of dipole elements arranged along the focal line of said reflector, said dipole elements being spaced apart.

by substantially a half Wavelength for approximately the lower two-thirds of the length of.

the array, and being spaced gradually closer together for the upper one-third of the length of the array so as to attain a spacing of substantially two-fifths of a wavelength at the upperend thereof.

3. An antenna as claimed in claim 1, wherein. said elements are spaced progressively closer together at one end of said array than at the other end thereof.

4. An antenna for use in radio object-location. comprising a vertically-extending cylindrical parabolic reflector and an array of dipole elements arranged along the focal line of said refiector, said dipole elements being spaced apart by substantially a half wavelength for approximately the lower two-thirds of the length of the array, and being spaced gradually closer together for the upper one-third of the length of the array so as to attain a spacing of substantially two-fifths of a wavelength at the upper end thereof, and means for rotating said reflector and said array in fixed relation to each other.

ROGER E. CLAPP.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,908,595 Franklin et a1 May 9, 1933 2,156,653 Ilberg May 2, 1939 2,275,646 Peterson Mar. 10, 1942 2,276,497 Kroger Mar. 17, 1942 2,408,435 Mason Oct. 1, 1946 2,427,688 Norgaard Sept. 23, 1947 2,436,380 Cutler Feb. 24, 1948 2,438,735 Alexanderson Mar. 30, 1948

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