Independent control over center frequency and bandwidth of bandpass filter based on SIW loaded with rectangular mushroom resonators

This paper presents a technique to control the center frequency and bandwidth of the passband of a bandpass filter (BPF) based on substrate integrated waveguide (SIW) loaded with two cascaded rectangular mushroom resonators (RMRs). The surface current distributions of both mushroom resonators at the fundamental mode (TE
₁₀₁
) are disturbed by introducing perturbation slots to modulate the current path and change the resonance frequency. The slot gap between the RMRs are varied to affect the internal coupling between them in order to change the split resonances of the fundamental mode and reconfigure the bandwidth of the passband. A partial selectivity of the passband is achieved by generating a transmission zero (TZ) at the lower stopband. The simulated passband shows a shift in center frequency (CF) by 14.5% with nearly constant bandwidth and a change in 3dB fractional bandwidth (FBW) of nearly 3% with a constant center frequency. The proposed filter having a CF of nearly 2.35 GHz undergoes a minimum insertion loss of 0.8 dB and occupies a compact area of 0.26λ
₀
× 0.43λ
₀
where λ
₀
is the guided wavelength of the TE
₁₀₁
mode.