Design of Polarization-preserving Circular Waveguide Filters with Attenuation Poles

Bandpass filters in circular wa eguide technology are designed to ha e enhanced stopband responses. Highly dispersi e coupling sections are introduced to replace regular circular irises. The resulting direct-coupled resonator bandpass filters ha e the ad antage of preser ing the polarization of the incident excitation while pro iding sharp cutoff skirts. Attenuation poles at finite frequencies are generated on either side of the passband by using radial stubs, which also perform the role of in erters. In contrast to the pole-extraction technique, or the classical technique of using stubs for the sole purpose of pole generation, the zero-generating elements act as in erters, and are not necessarily the first elements at the input and or output. A simple approximate design technique which pro ides adequate starting alues for optimization-based design is also introduced. Design examples are presented to show the alidity of the approach and the performance of these filters. 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 334 336, 2001.