A Circular-Electric Hybrid Junction and Some Channel-Dropping Filters

The importance of hybrid junctions for many purposes -- measuring, filtering, balancing, equalizing, etc. -- need hardly be emphasized. The long distance waveguide communication system 1 operating with the low-loss circular-electric TE 0 i° mode has only two hybrids available: the directional coupler, which has a fixed power division, and the optical hybrid, 2 which requires multimode waveguides. This paper describes a third hybrid, which operates like Riblet's coupler 3 and which adds to the well-known advantages of that coupler the unique property of adjustable power division. Adjusted for 3-db power division, the hybrid, together with modeconversion band-rejection filters, 4 band transmission filters or cutoff waveguides, 2 can be used as low-loss components of constant-resistance channel-dropping filters. 5 The scheme that- uses high-pass filters (cutoff waveguides) deserves special attention because the amplitude transfer characteristic of the dropped channel can be made to approach a 185