New compact MEMS-switch controlled tunable DGS coplanar bandpass filter

A new compact microwave defected-ground-structure (DGS) coplanar bandpass filter (BPF), which operates from 18 to 26 GHz (k-band), has been designed and simulated. The proposed structure can be redesigned for an other frequency range by changing the geometrical parameters of the CPW lines. The bandpass filter occupies an area of 2.8times1.3 mm² and consists of two cascaded parallel-resonance circuits coupled with a series capacitor, forming a series resonator. The use of MEMS series-resistive contact switches between the additional external stub and metallic ground planes permits systematic control of the bandwidth and thus the control of two transmission zeroes in the frequency domain. Therefore, the designed bandpass filter has a wide upper bandstop and an improved symmetry of the bandpass response. The equivalent circuit extraction method has also been derived. Simulations based on the proposed circuit model are in good agreement with the electromagnetic (EM) simulation. The BPF has been designed in CPW environment on high-resistivity silicon substrate and therefore is suitable for standard MIS and MMIS.