GB811010A - Improvements in resonant directional couplers - Google Patents

Abstract

811,010. Waveguide directional couplers; filters. MARIE, G. R. P. July 17, 1956 [July 27, 1955], No. 22028/56. Class 40 (8). A coupler for directionally coupling a rectangular-section waveguide to a circular-section waveguide utilizing the H 01 mode comprises a pair of annular resonant waveguide sections each directionally coupled to the rectangular and to the circular waveguides. The coupler is constructed from metal blocks 1, 2, 3, 4, 5 machined to provide parallel circular and rectangular guides 6, 7 and annular resonators 8, 9. The walls of rectangular guide 7 are formed from a metallic member 17 which is welded to the block 3. The blocks are held together by screws. Pairs of slots 13, 14 and 23, 24 directionally couple the circular and rectangular guides 6, 7 respectively to the lower and upper parallel limbs of the pair of annular resonators 8, 9. The slots may be replaced by lines of coupling holes. The resonators 8, 9 each have a length equal to an exact multiple of the wavelength of the guided energy and are displaced in relation to one another by a quarter wave. length in the axial direction of the waveguides 6, 7. This may be seen from Fig. 4 where the resonators 8 and 9 are indicated respectively by broken and full lines. By this means the phase conditions for the propagation of a H 01 wave in the circular guide 6 are fulfilled. It is stated in the Specification that the whole of the input energy having an intensity t 0 is found in an output wave of intensity t 1 if the frequency is near the resonant frequency of the cavities 8, 9. A continuous length of circular waveguide may be coupled at different points to a rectangular guide by pairs of annular cavities resonant at different frequencies. If these frequencies are closely spaced the whole arrangement forms a filter of wide band pass. Alternatively, the circular guide may be coupled to a number of different rectangular guides each of which is connected to a transmitter or a receiver utilizing the particular frequency at which the corresponding coupler is resonant. Fig. 7 shows a method whereby an annular resonant cavity 60 is tuned by means of a thin metal or dielectric plate 61 which penetrates the cavity to an adjustable depth. Specification 810,057 is referred to.