Independent Control Over the Passband of Bandpass Filter Based on Semi-Circular Mushroom Loaded Substrate Integrated Waveguide

This paper presents a method to control the passband of a bandpass filter by independently varying the bandwidth (BW) and center frequency (CF) of the bandpass filter which is based on a circular substrate integrated waveguide (SIW) loaded with two cascaded semi-circular mushroom resonators (ScMRs). The dimensions of two mushroom vias are varied within a range of 0.6 mm to affect the resonance frequency of the cascaded mushroom resonators and consequently shift the center frequency of the passband by more than 6.5% keeping the passband bandwidth undisturbed. The internal capacitive coupling between the two cascaded ScMRs across the slot gap is varied by changing the slot width by 0.3 mm, which consequently establishes a control over the passband bandwidth and changes the 3dB fractional bandwidth independently by more than 6.6%. A simulative study shows that the proposed filter occupying a compact area of 0.3 λ
0
× 0.3 λ
0
has the passband centered at 2.3 GHz with a minimum insertion loss of 0.7 dB.