US2847672A - Antenna arrays - Google Patents

Description

Aug. 12, 1958 G. s. GlFFlN ET AL ,5

ANTENNA ARRAYS Filed July 15, 1956 INVENTORS. GEORGE S. GIFFIN DERLING G. KILLION MARK N. HALLER ATTORNEY United States Patent ANTENNA ARRAYS George S. Giilin and Derling G. Killion, Fort Wayne, Ind.,

and Mar]: N. Haller, Galion, Ohio, assignors to International Telephone and Telegraph Corporation Application July '13, 1956, Serial No. 597,685

3 Claims. Cl. 343-895) This invention relates to antenna arrays and is particularly directed to arrays for producing a substantially uniform circularly polarized hemispherical field-strength pattern. Still more particularly, this invention is directed to arrays of helical antennas, having a circularly polarized hemispherical pattern, for radiating energy of microwave frequencies.

In the co-pending application entitled Antenna Arrays, Serial No. 597,686, filed July 13, 1956, in the name of George S. Griffin and Mark Hallcr, and assigned to the assignee of this application, an antenna array was described comprising a plurality of circularly arranged helical antennas around the side of a cone (or pyramid or sphere). The several helices were energized in phase from acommon source of microwaves, and the several helices were appropriately rotated on their axes to produce at overhead points in space additive energy at those points from the several helices.

The object of this invention is to provide an improved antenna array which will radiate microwave energy substantially uniformly in all directions above a plane at the center of which the array is placed.

The objects of this invention are attained by a circular arrangement of separate radiators of the helix type, the arrangement being characterized by each of the radiators having a probe lead extending into circularly spaced points in a round cavity, said cavity communicating with a round waveguide and with a source of circularly polarized microwave energy so that the wave front passing the plane of the probes energizes the several probes successively and in time phase corresponding to the angular displacement of the probes about the circular wall of the cavity.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a sectional view of an antenna array fed by the waveguide of this invention;

Fig. 2 is a section of the waveguide taken on line 2--2 of Fig. 1;

Fig. 3 is a sectional view of another embodiment of this invention; and

Fig. 4 is a perspective view of the waveguide junction shown in Fig. 1.

As explained in greater detail in the co-pending application, supra, to obtain uniform irradiation of a hemispherical space, the several radiators of a circular array must propagate energy out of phase with respect to each other, and the phase displacement should correspond to the angular displacement of the radiators about the center of the array. In that system, the phase displace ments are obtained by rotating one helix radiator about its axis, with respect to rotational position of the next adjacent helix.

According to this invention, similar results are obr" ice tained by energizing helices successively by phase displaced energy. The ground plane of the array of helical antennas 15 in Fig. 1 is defined by a metal cone 10 of good electrical conductivity, such as copper. The central cavity or bore 11 on the axis of the cone communicates, through the waveguides 12 and 13, with the microwave sources 14. Importantly, the waveguide 12 is so constructed and the excitation of the input endof the waveguide 12 is such that the energy entering the cavity 11 is circularly polarized. The direction or sense of the circular polarization is taken with regard to the winding direction of the helices 15 so that energies at an overhead point in space from the several helices are additive. Circular polarization in waveguide 12 may be effected in a number of ways. For example, the turnstile junction 14, a device known to those skilled in the art, may be used to transform the wave from the guide 13 to a circularly polarized wave in guide 12.

Referring more specifically to the embodiment of Fig. 1, equally spaced around the sides of the ground cone 10 are the helical radiators 15, each constructed of wire wound into spaced turns of the proper diameter and pitch to efliciently radiate the particular microwave energy of source 14a, such as a magnetron. Each coil is supported by the lead probe 16 centered in an insulating bushing or sleeve 17 in holes through the side of the cone. The sleeve is conveniently cast or machined with the thimble 18 for enclosing the coil. The inner ends of the lead probes extend into the cavity 11 a distance to most efliciently transfer energy from the cavity to the helix. Any reflecting from the top end of the cavity may be absorbed in the tapered plug 20, of lossy material, in the stub 21.

As stated above, the waveguide 12 is excited at its input end, as by turnstile junction 14, so that circularly polarized energy will enter the cavity 11. The particular junction shown comprises two short circuited stubs 13a and 13b at right angles to the feed arm 13 and the round guide 12. By adjusting the eifective electrical length of the stubs so that one is one-half wavelength longer than the other at the operating frequency, then two TE -type waves in time and space quadrature may be propagated along guide 12. If the electric and magnetic lines of one such wave are shown in solid and dotted lines as in Fig. 2, a second set of similar lines could be drawn in the same cross plane in space quadrature to the first set, but the fields of the first and second waves would be 90 apart in time phase. Herein lies the classical analysis of true circularly polarized microwave in a round waveguide. The direction or sense of this wave rotation must, of course, be chosen with regard to the winding direction of the helices 15, else cancellation, rather than addition, of energy at an overhead point in space will result as explained in the co-peuding application, supra.

As the flux lines of two TE modes in time and space of quadrature pass the plane of the circle of probes 16, the probes are energized sinusoidally and out of phase with respect to each other and at a frequency corresponding to the phase velocity of the lines passing the probe circle. It follows that the phase displacement of the energy between the probes will correspond exactly with the angular displacement of the probes about the cone axis.

, It is apparent that any figure of revolution may be employed, as well as pyramids.

Experimentation has shown that the field-strength pattern is substantiallyuniform for such an array throughout the entire hemispherical canopy.

While the principles of the invention have been de: scribed in connection with specific apparatus, it is to be clearly understood that this description-is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. An antenna array comprising a circular arrangement of separate radiators of the helix type, the arrangement being characterized by each of the radiators having a probe lead extending into circularly; spaced points in a round cavity, said cavity communicating with a round waveguide and with a source of circularly polarized microwave energy so that the'wave frontpassing the plane of the probes energizes the several probes successively and in time phase corresponding to the angular displacement of the probes about thecircular wall of the cavity.

2. An array of helical radiators, a probe connected with each radiator, the probes being spaced in a circle, a source of microwave energy, and means for transmitting microwave energy of said source transversely through the plane of said probes, the polarization of. the energy in said plane being circular and of proper rotational sense with respect to the winding sense of the helices for energizing the probes successively and in displaced time phase corresponding to the angular placement of the probes in the circle to indicate, an overhead point with in-phase circularly polarized energy from the several radiators.

3. In combination, a plurality of helical antennas, the antennas being arranged in a circle with the axis of the helices defining a right cone, a ground plane device supporting the helices with surfaces of thedevice adjacent the helicessubstantially normal to the axis of the helices, said ground plane device having a cavity, circularly arranged probes in the cavity connected, respectively, with said helices, and means for generating a microwave in the cavity, said wave being circularly polarized with sense dependent upon helix winding in the plane of the probes.

ReferencesCited in the file of this patent UNITED STATES PATENTS 2,630,530 Adcock a a1. Mar; 3, 1953 2,723,377 Cohn Nov. 8, 1955 2,771,605 Kirkman Nov. 20, 1956

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