DESIGN OF H-PLANE INDUCTANCE DIAPHRAGM WAVEGUIDE BAND-PASS FILTER FOR MILLIMETER IMAGING FRONTEND

Abstract

This study presents an equivalent circuit and a design of an H-plane waveguide bandpass fllter (BPF) with chamfer. Traditionally, only thin inductive diaphragm with no chamfers considered in the direct-coupled cavity theory, but this will lead to di-culties in the BPF manufacturing. During manufacturing process the chamfer cannot be avoided, and its equivalent circuit and efiects on frequency shifting are investigated in this paper. A new design method is proposed in order to compensate the efiect of chamfer in the half-wavelength resonator connection between the inductance diaphragm and the waveguide. A modifled empirical formula and corresponding procedure are provided for designing such fllters. The working center frequency and 3dB bandwidths (BW) are simulated considering difierent chamfer radius. The simulated center frequencies are 18GHz, 26GHz, 34GHz and 42GHz, and BWs are 2.265%, 2.5%, 10%, 15% and 20%. Results show that the modifled formula, which conforms better with the simulated results, is superior to the traditional formula. Two H-plane waveguide BPFs are manufactured with center frequency 26GHz with 2.5% BW and 34GHz with 2.265% BW. The results of the modifled formula are in good agreement with measured ones.