Design of microwave band stop and band pass filters based on BST thin film varactor technology

This thesis presents a design of band stop and band pass filters for microwave applications. These filters are based on coplanar waveguide (CPW) transmission lines on a 500 æm thick sapphire substrate. 0.25 æm thin film barium strontium titanate (BST) thin film is used as the tunable dielectric layer. The design of the band stop filter is based on the traditional varactor shunt switch (designed by Dr. Subramanyam and his team) coupled to the ground using an inductive path. Thus, the design symbolizes a single pole standard band stop filter with the potential for frequency tunability. The capacitive overlap makes the device tunable. Several designs of the band stop filter based on the same concept, but different capacitive overlaps, inductive configurations and overall device dimensions were designed and studied. The center frequency for these designs varied from 1 to 5GHz. The band pass filter is mostly single layered and represents a microstrip based structure although it is CPW fed. It is shunted to the ground with varactors on either side of the device. The idea of having varactors were to achieve tunability. It has 4 resonant iv traps representing a 4-pole filter. The design, simulation results, experimental results and analyses are presented