Synthesis of Extremely Wide Stopband E-plane Bandpass Filters

Abstract

The article presents the results of the development of a novel procedure for the direct synthesis of bandpass E-plane evanescent mode filters. Unlike previously developed synthesis procedures the proposed new and quick synthesis technique makes it possible to obtain the dimensions of all elements of the filter topology, which either do not require further time-consuming optimization, or optimization is reduced to re-application of the proposed technique with specially changed performance requirements. The developed technique was adequate in the development of the proposed E-plane filters, built on segments of the antipodal finline with the significant overlap of its ridges in the evanescent mode rectangular waveguide. Under this conditions the reduction of resonators relative to half the wavelength reaches 80 %. Proposed E-plane implementation of the evanescent mode rectangular waveguide filter allows significantly expanding the bandwidth, increase the attenuation introduced in it and at the same time ensure the repeatability of the characteristics of the filters without any action to adjust them. The effectiveness of the proposed approach to the implementation of the filter and its calculation was demonstrated in the development and experimental study of a 21 GHz filter, which in terms of parameters (loss of about 1 dB, stopband up to the fourth harmonic of the central frequency of passband) meets high requirements for electrical characteristics and cost. It is shown that the developed method of synthesis of such filters remains relevant in the synthesis of filters with a relative bandpass width of up to 40 %.