A Tunable Dual-mode SIW Cavity Based Bandpass Filter with Wide Upper Stopband Characteristics

Abstract

A new approach to design a bandpass filter using substrate integrated waveguide (SIW) topology is presented here for 5G applications. The aim of the design is to produce a dual mode passband characteristic with wide upper stopband behaviour, centred at 4.7 GHz. Four identical Stepped Impedance Resonator (SIR) slots are etched into the top surface of the SIW cavity for the proposed filter structure. The SIR slots aid in reducing the cavity's resonant frequency and to generate the dual mode passband characteristics. The SIR slots also mitigate the higher modes in the SIW cavity which helps to accomplish a wide upper stopband response. In order to improve selectivity, the structure is further modified by introducing two E shaped resonator slots on the ground plane to produce two transmission zeros at 3.9 GHz and 6.2 GHz. Tunable characteristic is achieved by loading two surface mount varactor diodes diagonally on the top of the proposed structure. By suitably applying the bias voltage, the center frequency of the passband is tuned over a range of 600 MHz. The developed filter is fabricated in order to verify the simulated and measured results.