High-quality coplanar waveguide tunable band-stop filter using defected ground structure and comb-line resonator with radio frequency microelectromechanical system varactors

A new analog tunable Ka-band band-stop filter is proposed on high resistivity silicon (HRS) substrate using radio frequency microelectromechanical systems (RF MEMS) varactors for satellite and radar applications. The designed filter uses a λ/4 comb-line resonator on the center line of a coplanar waveguide (CPW) with a new uncommon defected ground structure (DGS). Using the DGS in the proposed structure not only decreases the lateral size of the filter but also increases the quality factor. The tuning range of the proposed filter is 29.8–35.6 GHz with a maximum actuation voltage of 44.5 V and a band rejection between 37 and 45 dB. The quality factors of the designed filter in the up and down states of the MEMS varactors are 162 and 292, respectively. The equivalent circuit model of the filter is exactly extracted, and DGS dimensions are optimized. Based on the frequency simulation using ANSOFT HFSS 14, the insertion loss of the designed filter is about 0.51 dB in the 0–20 GHz range and 2 dB in the 0–15 GHz range in, respectively, up and down state of the bridge. The return losses are 0.51 and 0.33 dB at the center frequency for the up- and down-state configuration of the bridge. A step-by-step fabrication process is also proposed for designing the band-stop filter. High quality factor, small size, and improved structure are the advantages of the proposed design.