Compact 1.4-2.2-GHz Reconfigurable Bandpass-to-Bandstop Filter with Wide Stopband Using Tunable SIDGS Resonators

In this paper, a miniaturized reconfigurable bandpass-to-bandstop filter is proposed based on the hybrid microstrip and substrate-integrated defected ground structure (SIDGS). Firstly, the compact stepped-impedance E-shape SIDGS resonator with cascaded varactors is developed for allocating resonances with a wide tuning range. Secondly, the 0° coupled scheme with feeding varactors using two identical tunable SIDGS resonators is used for filtering bandpass operation. Thirdly, the bandpass-to-bandstop transformation is achieved by RF MEMS switches, where the bandstop mode is achieved by the inverter of a notch filter. To verify the aforementioned mechanism, a prototype of miniaturized reconfigurable bandpass-to-bandstop filter is proposed and fabricated with a wide frequency tuning range for bandpass and bandstop responses. In the bandpass mode, a center frequency tuning of 1.4–2.5 GHz is achieved with a tunable 3-dB FBW of 17.3% to 18.7%. In the bandstop mode, the stopband is tuned from 1.2 to 2.2 GHz with the rejection level higher than 20 dB. Good agreement among the model-calculation, EM-simulation, and measurement is achieved.