Impact of group delay on tunable impedance matching networks based on Barium-Strontium-Titanate varactors

In this paper the bit error rate (BER) performance of a tunable impedance matching network (TMN) is shown using a QAM digital modulation scheme over an AWGN channel. The characterized TMN is based on Barium-Strontium-Titanate (BST) ferroelectric thick-film varactors with a maximum DC tuning voltage of 90V. Inherent dispersive behavior is subsumed in the forward transmission of the passive components. Due to this nonlinear phase response, in general to maximize the overall system performance, an agile selection of the varactor values is demonstrated, taking into account the phase and group delay. Detailed simulation results of a testbed are presented and the influence of different matched impedances on the tuning behavior is discussed at a center frequency of 1.9 GHz.