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).