Tunable Coplanar Wave Guide Band Stop Filters

A tunable band stop filter is designed in the frequency range of 0.5GHz to 1GHz and its performance is simulated with Agilent ADS. The filter is fabricated on FR-4 substrates. The BST parallel plate ferroelectric varactors are fabricated on sapphire substrates by MOD technique with Platinum Electrodes and ion-milling. The ferroelectric capacitors show a tunability over 50% within an applied DC bias of 5 V. The filter response was measured using Agilent Vector network analyzer. For the third order BST varactor tuned band stop filters, the notch frequency can be tuned from 480MHz to 620MHz by the application of 5 V tuning voltage with a maximum band attenuation of 20 dB.