A New Microstrip Reconfigurable Transversal Coupling Bandpass Filter with Highly Controllable Number and Positions of Transmission Zeros

This paper proposes a new microstrip reconfigurable transversal coupling bandpass filter that can change both the number and the positions of transmission zeros (TZs) in addition to center frequency and frequency bandwidth of passband. In conventional reconfigurable planar filters, TZs are not significantly moved from both sides to one side of passband, since the number of TZs and their positions are self-adaptive. The proposed filter simply has the parallel arrangement of even/odd-mode half-wavelength resonators, and a frequency-dependent source/load coupling. External Q factor and resonant frequency for each resonator are directly tuned by varactor diodes loaded for each. Thus, TZs can vanish, and up to three TZs can be generated at both sides/one side of passband. It is demonstrated through EM simulations and measurements that a center-frequency tuning of 1.13-1.69 GHz, 1-dB fractional-bandwidth control of 3.4-12.8%, highly controllable TZ positions, and switch-off state can be achieved by the proposed filter.