Tunable Impedance-Matching Filters

In this letter, we present a general design method for tunable matching networks that have a prescribed filter characteristic over a range of complex port impedances. The approach enables prediction of the achievable tunable impedance range, given a filter topology and tuning element values. As experimental validation, a 2.5-GHz second-order Chebyshev filter is designed using Skyworks SMV2205-040LF varactor diodes to tune the filter resonator and inverter. It is shown that the filter can match port impedances in a region that spans a range of real and imaginary parts of the impedance between 10 and $150~\Omega $ with an insertion loss of 1.5 dB.