Design of polarization‐preserving circular waveguide filters with attenuation poles

Abstract

AbstractBandpass filters in circular waveguide technology are designed to have enhanced stopband responses. Highly dispersive coupling sections are introduced to replace regular circular irises. The resulting direct‐coupled resonator bandpass filters have the advantage of preserving the polarization of the incident excitation while providing 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 inverters. 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 inverters, and are not necessarily the first elements at the input and/or output. A simple approximate design technique which provides adequate starting values for optimization‐based design is also introduced. Design examples are presented to show the validity of the approach and the performance of these filters. © 2001 John Wiley & Sons, Inc. Microwave Opt Technol Lett 31: 334–336, 2001.