GB796660A - H.f. electrical wave guide coupling arrangement - Google Patents

Abstract

796,660. Waveguide couplings and band-pass filters. STANDARD TELEPHONES & CABLES, Ltd. May 28, 1956, No. 16428/56. Class 40 (8). A metal circular waveguide 1 is connected to at least one circumferentially disposed waveguide 2, forming a substantially complete turn therearound, through cophasally acting coupling apertures in the common wall spaced circumferentially with at least one aperture per free space wavelength at the mean operating frequency of the waveguide 2. The coupling may function as a band-pass filter. The common wall forms the shorter side of the rectangular waveguide 2, Figs. 1 and 2, and the slots 3 are alternately inclined in opposite directions and are preferably spaced at intervals of one half of the mean operating free space wavelength of the guide 2. One end of the guide 2 is connected to an input or output circuit and the other end is terminated by a short-circuiting element 5 preferably spaced from the nearest slot by substantially one quarter of said wavelength of the guide 2. A conductor 6 extends axially through the guide 1 and is spaced radially therefrom by between a half and a whole of said wavelength of the guide 2, except at the ends and away from the region of coupling with the guide 2 and any similar feeder guides. Fig. 3 illustrates a directional coupling in which two rectangular guides 2, 2<SP>1</SP>, disposed around a circular guide 1 are spaced axially thereof by three (or other odd number of) quarter wavelengths at the mean operating frequency in the guide 1. The guides 2, 2<SP>1</SP> are connected to a common circuit through a hybrid T-junction displaced from the centre line between the guides 2, 2<SP>1</SP> by one-eighth of the wavelength in the latter at the mean operating frequency. If energy is fed into the arm 13 of the T, it will flow along the guide 1 only in the direction 15, and if supplied through the arm 14 it will flow only in the direction 16. The efficiency of the coupling arrangement as a band-pass filter is discussed mathematically, and it is shown that an effective filter is obtained by providing at least one resonant cavity between the rectangular guide and the circuit connected thereto, e.g. the resonators 19, 20, Fig. 3.