Lead-Strontium-Titanate varactor-tuned CPW bandstop filter on liquid crystal polymer substrates

This paper presents an investigation of a tunable coplanar waveguide (CPW) bandstop filter with slotted ground structure. Spurious responses resulting from the shapes of resonator and the tuning position have been investigated by EM simulations. As a tuning element, Lead- Strontium- Titanate (PST) varactor chip is deployed. Also, in order to reduce required elements and unwanted spurious, LCP substrates are used as multi-layered laminates. A 2-pole tunable bandstop filter of this type is measured at the center frequency from 905 to 1040 MHz and its maximum rejection is more than 25 dB at the stopband with a wide passband response.