A High-Quality Waveguide Directional Filter

The purpose of this paper is to describe at high-quality, narrow-band bandpass-bandstop directional filter for use in the microwave frequency range. Filters of this type are commonly used for channel separation and channel combination in microwave radio systems.* In rather general terms, a bandpass-bandstop directional filter can be described as a passive 3-port (Fig. 1), whose | | = 0 for all frequencies, whereas | S 2 i | exhibits a bandpass characteristic and | | exhibits a bandstop characteristic around a midband frequency f 0 . The 3-port may be reciprocal or nonreciprocal, lossless or lossy, f For quite a number of applications in the microwave frequency range, the bandwidth of low attenuation ( ^ 3 dB) between port 1 and port 2 and of high attenuation (^ 3 dB) between port 1 and port 3 * For a rather complete account on microwave directional filters see Ref. 1 (diplexers and directional filters). Additional references may be found there. f From an even more general viewpoint the strict condition | S n | = 0 might be replaced by |