Compact Substrate Integrated Waveguide Diplexer with Large Frequency Ratio

Abstract

In this paper, a novel compact diplexer based on substrate integrated waveguide (SIW) cavities is proposed. To achieve high isolation between different channels, a coupling-line isolation network is embedded in the slot between a semi-circular SIW cavity and a triangular SIW cavity. The proposed diplexer consists of a coupling-line feeding line at the port 1 and a semicircular SIW cavity and a triangular SIW cavity. The slotline in the circular and the triangular SIW cavity can lower the frequency of TE <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">201</inf> mode of the cavities, which yields second order filtering response and large frequency ratio. For the sake of out-of-band isolation, port 2 and 3 are placed in the specific zone to suppress the higher-order modes according to the electric-field distribution. A prototype diplexer with center frequency f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</inf> =5.4 GHz and f <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> =8.5 GHz is designed. The isolation of the diplexer is better than 30 dB and 27 dB over interested channels.