Patent GB-1003286-A (GB)
Title: Improvements in or relating to electromagnetic wave hybrid junctions
IPC: H01P1/163
Filed: 1961-12-14
Abstract: 1,003,286. Waveguide junctions. WESTERN ELECTRIC CO. Inc. Dec. 14, 1961 [Dec. so 1960], No. 44753/61. Heading H1W. An electromagnetic hybrid junction for use, e.g. as a channel-dropping filter comprises a bifurcated waveguide whose branches enclose and are coupled to a common rectangular waveguide. As shown, a circular waveguide 10, Fig. 1, supporting circular electric H 01  mode energy in a number of discrete frequency bands f a  ... f n  is divided by a diametral septum 11 and connected to a pair of spaced, parallel guides 12, 13 of semi-circular section. The planar sides of these guides are contiguous to the narrow sides of a common rectangular waveguide 14 and apertures 18, 19 in the contiguous sides provide directional coupling between the guides. The configuration of the H 01  mode in the semi-circular guides is such that the field components are out of phase at the opposite sets of coupling apertures and no energy is transferred to the rectangular guide. However, energy in the channel f a  to be separated is reflected by the series-resonant structures 21, 22 which are so positioned that the two portions of reflected energy undergo a differential phase shift of 180 degrees and reappear at the coupling apertures 18, 19 in the proper phase for coupling to the branch 14. Thus channel f a  propagates in waveguide 14 and channels f b  ... f n  in the recombining waveguide 17. As shown, the resonant obstacles are in the form of a number of C-shaped conductive members spaced around the semi-circular wall of the guide. Iterative instead of simple structures may be used. Other channels may be dropped by arranging other coupled branch guides together with appropriate filters in a cascade arrangement. If all the channels are dropped, the guides 12, 13 may be terminated by a resistive element, e.g. a dissipative internal lining. The branching junction is preferably made less abrupt than is shown, the branching angle and the lengths of the curved intermediate guide employed being dimensioned to prevent mode conversion. In a modification (Fig. 7, the coupling means takes the form of a pair of cavities 70, 71 resonant at the frequency of the dropped channel. These are spaced by a distance equal to an odd number of quarter wavelengths at the same frequency and are coupled to the semi-circular branch guides by single apertures. The rectangular output guide 76 is coupled to the cavity 70 by a single aperture 77. In order to suppress the H 21  and H 81  modes which may propagate in the semicircular guides 12, 13, these are provided with mode filters in the form of sets 80-85 of radial conductive vanes. These are spaced by distances equal to an odd number of quarter wavelengths at the cavity frequency whereby an impedance mismatch for the spurious modes is produced. In a further modification (Fig. 10, not shown), the circular and semi-circular guides are replaced by rectangular guides and opposite broad faces of the branch guides are arranged contiguous with the broad faces of the coupled guide. In this case, it is necessary to introduce a differential phase-change of 180 degrees between the two portions of forward-going energy to obtain the required phase relation at the coupler. This may be done by twisting one of the guides or by loading it with a solid dielectric.