GB594416A - Improvements in or relating to the transmission and reception of electromagnetic waves - Google Patents

Abstract

594,416. Directive radio systems ; phase shifting. WESTERN ELECTRIC CO., Inc. Jan. 18, 1945, No. 1646. Convention date, Jan. 19, 1944. [Classes 40 (iii) and 40 (v)] The invention relates to dielectric phase shifters for electromagnetic waves having minimum reflection loss, and the use of such phase shifters in zone plate and antenna systems. One form of phase shifter for waves of a given wavelength comprises a single dielectric plate mounted with its faces normal to the direction of propagation of the waves, the thickness of the plate being equivalent to an electrical length of 180 degrees or an odd multiple thereof, and the phase shift of the waves passing through the plate being greater than the phase shift which would be produced by the waves travelling the same distance in air bv an amount equal to the desired phase shift. In an alternative form the phase shifter may comprises a pair of parallel dielectric plates arranged so that the paths perpendicular to-the-faces connecting the wave front and one face of one plate and the wave front and the corresponding face of the other plate differ in length by a quarter of the operating wavelength or an odd multiple thereof, the total thickness of the plates being such that the phase shift of the waves passing through is greater than the phase shift in an air path of equivalent length by an amount equal to the desired phase shift. In a directive antenna having a zone plate system such as is described in Specification 483,797, the conductive zone plate shown therein in zone B (see Fig. 3) may be replaced by a dielectric plate 40, being a low reflection loss phase shifter as described, producing' a phast shift of 180 degrees in the waves passing through it. By this means the radiation passing through the zone adds to that of the other zones and the efficiency of the antenna is increased. To further increase the efficiency, half zone plates 42 are introduced into each of the zones, the difference in the paths extending from the focus 39 of the system at the end of feeding waveguide 35 to the inner and outer edges of these plates being a quarter of the operating wavelength. The phase shift introduced by these plates is 90 degrees and by their use the vectors representing energy received at or radiated from the source through the two halves of any of the zones are rendered colinear.