Dual-Mode Wide Band Microstrip Bandpass Filter with Tunable Bandwidth and Controlled Center Frequency for C-Band Applications

This paper presents a unique approach for designing dual-mode wide band BPF with tunable bandwidth and controlled center frequency for C-band (4–8 GHz) applications. The proposed filter is designed using radial stub-loaded dual-mode λ_g/2 resonator to get wide passband. The dual-mode behavior of the resonator, i.e., odd- and even-mode resonance frequencies are realized by inserting a radial stub at the center of the resonator and further the size of filter is reduced by folding the resonator. A modified feed structure which embraces the two arms of the resonator is used to obtain two transmission zeros in upper stop band. By keeping all calculated dimensions of filter fixed and by varying only radial angle θ (in degrees) of radial line stub, FBW is tuned while controlling center frequency. From simulation results, it is observed that the designed filter has very good passband characteristics, a wide 3-dB passband from 4.4 to 7.8 GHz with center frequency at 6 GHz, fractional bandwidth of 56.6%, return loss S11 more than 13 dB, and transmission loss S21 better than 0.3 dB, respectively.