RADIO-FREQUENCY BAND-PASS FILTER WHEREIN MAGIC-TEE ARMS ARE COUPLED TO CAVITIES AND RESONATORS

摘要

1,268,189. Band-pass filters. GENERAL ELECTRIC CO. Ltd. 20 June, 1969 [20 June, 1968], No. 29577/68. Heading HlW. A self-equalizing band-pass filter comprises a hybrid-T waveguide junction having a pair of conjugate arms terminated by resonant cavities of different loaded Q-factors, the other pair of arms forming input and output and containing waveguide resonant cavities. As shown, a magic-T junction 3 is provided with an E arm 5 matched to the junction by an iris 12, and an H arm 4 matched to the junction by a post 11. The arms are reflectively terminated by resonant cavities coupled to respective arms by posts 14, 13, these posts being of different diameters so that the cavities have different loaded Q-factors. The input and output arms 1, 2 comprise identical post-coupled cavities providing a band-pass filter. It is shown in the Specification that the construction shown is equivalent to a lattice network comprising resonant arms coupled to input and output band-pass networks. The Specification discusses in detail how the group delay and attenuation characteristics of such a network can be independently determined whereby a band-pass network having constant group delay may be realized. The lumped equivalent circuits (Figs. 5, 6, not shown) take no account of the finite lengths of waveguide between the junction and the coupling posts 15 of the band-pass filters or those between the junction and the coupling posts 13, 14 of the cavities in the H and E arms. It is shown that these lengths are critical. They are determined by experiment.