Patent GB-681780-A (GB)
Title: Improvements in or relating to directional microwave antennas
IPC: H01Q13/02
Filed: 1950-11-22
Abstract: 681,780. Aerials. WESTERN ELECTRIC CO., Inc. Nov. 22, 1950 [Nov. 26, 1946], No. 28541/50. Class 40 (vii). Relates to means for increasing the directivity and reducing side lobes in directional microwave aerial systems in which the waves transmitted or received by the aerial system are passed through a cellular wave-guide structure comprising a central cell and outer cells arranged to impart a non-uniform amplitude distribution to the wave components passing through the individual cells. According to the present invention, the cells are arranged so that more energy is transmitted or received through the outer cells than through the central cell and means are provided to produce a relative phase-shift of 180 degrees between the components passing through adjacent cells, the transverse dimensions of the cells in the plane of directivity being less than #/2 and the dimensions in the direction of propagation being less than a wavelength for waves polarized perpendicularly to a transverse dimension less than #/2. In the embodiments described, the cellular structure is located in an electromagnetic horn, but alternatively the structure may be located in front of the horn aperture or it may be associated with other types of " aperture " aerials, e.g. lenses, reflectors or diffractors. Fig. 2 shows a cross-section through a sectoral horn, Fig. 1 (not shown), having diverging walls 7 and 8 and a pair of diverging conductive rigid partitions 16 perpendicular to the parallel sides of the horn which define three wave-guide channels 13, 14 and 15, the front widths h of the channels being less than #/2, e.g. #/4, the back widths b, a, b being such that the amplitude distribution in channels 13, 14 and 15 is 4:3:4 and channel 14 contains dielectric 23 such that the waves passing through that channel are delayed 180 degrees relative to waves passing through the outer channels 14 and 15. For waves polarized perpendicular to partitions 16, the amplitude distribution across the throat of the horn is uniform and the amplitude in the channel is directly proportional to its inner width, i.e. a or b, but such proportionality does not hold for waves polarized parallel to the partitions since the distribution across the throat is then sinusoidal. In a modification, Fig. 4 (not shown), the conductive partitions are parallel and comprise copper foil attached to the surfaces of the dielectric phase changer. Fig. 5 shows a pyramidal horn 30 producing a pencil beam and containing two perpendicular pairs of partitions defining nine channels with dielectric phase shifters in the middle outer channels, the horizontal and vertical dimensions h and v of each channel at the front being less than #/2. The partitions converge towards the rear, the channel rear dimensions being such that the horizontal amplitude and phase distribution in the upper and lower rows of channels is +16/3 :-4:+16/3 and in the middle row is - 4: + 3 : - 4 so that the phase and amplitude ratio of the algebraic sums of the components of the horizontal rows and of the vertical columns is + 4: - 3: +4, Fig. 6 (not shown), thus producing optimum directivity in both the horizontal and vertical planes. In any of the embodiments, the dielectric phase shifter may be replaced by a metallic delay phase shifter and in the embodiments of Figs. 1 and 2 and Fig. 4 metallic advance phase shifters may be employed for waves polarized perpendicularly to the partitions. Specifications 579,746, 594,416 and 661,081 are referred to.