A Novel Feeding Structure to Generate Multiple Transmission Zeros for Miniature Waveguide Bandpass Filters Composed of Frequency-Selective Surfaces

Masataka OHIRA
Zhewang MA
Hiroyuki DEGUCHI

IEICE TRANSACTIONS on Electronics   Vol.E94-C    No.10    pp.1586-1593
Publication Date: 2011/10/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E94.C.1586
Print ISSN: 0916-8516
Type of Manuscript: Special Section PAPER (Special Section on Microwave and Millimeter-Wave Technology)
Category: Passive Devices and Circuits
waveguide filters,  frequency-selective surfaces,  bandpass filters,  transmission zeros,  coaxial probe,  

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In this paper, we propose a novel feeding structure for a coaxial-excited compact waveguide filter, which is composed of planar resonators called frequency-selective surfaces (FSSs). In our proposed feeding structure, new FSSs located at the input and output ports are directly excited by the coaxial line. By using the FSSs, the transition from the TEM mode to the TE10 mode is realized by the resonance of the FSSs. Therefore, the backshort length from the coaxial probe to the shorted waveguide end can be made much shorter than one-quarter of the guided wavelength. Additionally, the coaxial-excited FSS provides one transmission zero at each stopband. As a design example, a three-stage bandpass filter with 4% bandwidth at the X band is demonstrated. The designed filter has a very compact size of one cavity and has high skirt selectivity with six transmission zeros. The effectiveness of the design is confirmed by the comparison of frequency characteristics obtained by the simulation and measurement.