1. INTRODUCTION

Waveguide filters are an inherent part of modern communication systems such as radar and satellite communications. The rapid growth in modern communications systems entails accurate design of waveguide filters. The advancements in computational technology in recent years and the ever increasing demand for accurate design of waveguide filters led to many new computer aided synthesis techniques and several numerical methods for solving the waveguide discontinuity problems. R. Levy w1x proposed many new synthesis techniques based on modern network theory but used empirical formulae w2x for characterizing the waveguide discontinuities present in the filter structure. The inaccurate characterization of waveguide discontinuities necessitated the laborious and cumbersome process of experimentally tuning each and every filter to obtain the desired performance. Presence of tuning screws in the filter structure increases the losses and the vibrations of tuning screws at very high frequencies and distorts the performance of the filter. In this

Correspondence to: Dr. P. Pramanick

paper, a complete computer-aided approach for designing and analyzing waveguide bandpass filters are developed based on modern network theory and field theory based approach for accurate characterization of waveguide discontinuities. The mode matching method w3x, a popular numerical technique is used for solving waveguide discontinuities present in the filter structure. The mode matching method includes higher order mode interactions in the solution of waveguide discontinuities facilitating the accurate design and prediction of the filter passband and stopband characteristics. No experimental adjustments are required and the addition of tuning screws in the structure is eliminated providing a compact and superior performing waveguide filter.

Common rectangular waveguide bandpass filters coupled by inductive irises are composed of halfwave resonator sections. The resonator lengths of H-plane bandpass filters are shorter than 1808 electrical length. Waveguide bandpass filter structures have the problem of harmonic passband in the stopband. Over the last few years, much effort has been devoted to the study of waveguide bandpass filters and to improve the stopband performance of such filters w4]7x. Im-