CPW Tunable Band-Stop Filter Using Hybrid Resonator and Employing RF MEMS Capacitors

This paper presents a coplanar waveguide (CPW) tunable band-stop filter using hybrid resonator and employing RF microelectromechanical systems (MEMS) capacitors. The MEMS switches are used as varactors to tune the filter resonance frequency. Defected ground structures (DGSs) with MEMS switch is employed for filter unit to achieve miniaturization of filter structure. To accurately analyze the filter unit structure parameters, a hybrid resonance circuit is used as equivalent circuit and the relationship of MEMS switch and the transverse slot capacitance is analyzed. Hereby, a CPW tunable band-stop filter, cascaded periodically by DGS and MEMS switches, is fabricated on a glass substrate (ε_r=3.78,tan δ = 0.0012). The filter has a midband retune loss of 2.3-2.8 dB and a tuning range of 35% from 8.5 to 12.3 GHz with a maximum dc voltage of 44 V. Finally, we propose a solution to achieve constant bandwidth when center frequency changes.