A compact ferroelectric tunable bandpass filter with flexible frequency responses

An asymmetric inductively-coupled lumped tunable bandpass filter using epitaxial BST thin film varactors and SMT inductors is designed, fabricated and tested. To the best of the authors' knowledge, the proposed filter is the smallest reported filter among tunable ferroelectric filters for VHF/UHF applications. The biasing conditions (simultaneously or not) of the frequency responsible varactors (C
p
) and the magnitude responsible varactor (C
g
) give the ability to choose between different frequency responses, including stable fractional bandwidths and stable insertion loss levels. The largest frequency tuning is about 37% from 1.06 GHz to 1.45 GHz at bias voltages of 30 V, and the best insertion loss is 3.55 dB (V
Cp
= 30 V, V
Cg
= 0 V).