GB705209A - Improvements in or relating to ultra short wave radio communication and radar systems - Google Patents

Abstract

705,209. Directive radio systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 13, 1952 [Sept. 7, 1951], No. 21194/51. Class 40 (7) In a radio transmission system comprising two plane-polarized channels associated simultaneously or selectively with a common channel in space, a plane polarized mirror is arranged between said two channels and said common channel so as to provide a reflecting path between one of said two channels and the common channel and a transmitting path between the other of said two channels and said common channel. The invention is described as applied to (1) representing the transmission and reception channels in a circularly polarized radar system; (2) feeding energy to or from a circularly polarized channel and (3) selectively coupling a plane polarized wave channel to either or both of two separate channels. (1) Radar system. As shown the horizontally and vertically polarized transmitting and receiving horns HT, HR are at right angles to one another and at 45 degrees to a vertically polarized mirror M which is transparent to horizontally polarized waves and acts as a reflector for vertically polarized waves, the axis of the horn intersecting at the mirror at x and the horn being equi-distant from x. The energy from HT is therefore transmitted through the mirror to the common channel CP and through a waveguide lens L and circular polarizer P and the energy reflected by the target which is circularly polarized in the opposite sense is converted by the polarizer P into a horizontally polarized wave which is reflected by the mirror M to the receiving horn HR. In the second embodiment, Fig. 2 (not shown), the polarizer P is omitted and a transmitter or receiver is coupled by a forked waveguide to two horns disposed as above, the two electrical path lengths from the transducer to the point x via the two horns differing by an odd number of quarter wavelengths so that for transmission the horizontally and vertically polarized waves combine to give a circularly polarized wave and for reception a circularly polarized wave is resolved into two orthogonally polarized waves which are then combined. By moving the mirror the polarization in the common channel may be changed from circular, via elliptical to plane. This embodiment may be employed as a TR system for a circularly polarized radar by coupling the transmitter and receiver to the forked waveguide by a hybrid junction, Fig. 3 (not shown). In the third embodiment, Fig. 4 (not shown), the circular polarizer is again omitted and two separate transmitting or receiving horns of like polarity are arranged as above the mirror being rotatable in its own plane so that plane polarized waves incident on the mirror from the common channel CP are either totally reflected, totally transmitted or partially reflected and transmitted depending on the orientation of the mirror. Such an arrangement is suitable for converting a direction-finder from pencil beam to split beam separation. The mirror may comprise a number of parallel thin conductive wires, or strips suspended in air or mounted in or on a dielectric the spacing between the conductors being well below cut off and " self-matching " may be effected by making the length of the conductors equal to a multiple of a half wavelength or by providing two sets of conductors, one spaced behind the other by an odd number of quarter wavelengths, or by incorporating in the mirror an auxiliary matching grating.