A pi-type Isolation Network for Improvement of Matching and Isolation in Reconfigurable Multifunctional Bandpass Filter

Abstract

In this paper, a method for improving the output impedance match and isolation between output ports of the reconfigurable single-to-balanced (SE-BAL), power-dividing (PD) and single-ended (SE) multifunctional filter is presented. By adding the varactor-tuned pi-type isolation network to the outputs of the tunable multifunctional filter, both the matching and isolation at the output ports are improved to a large degree over the full tuning range. Compared to the original standalone multifunctional filter, the measured output return loss and isolation of the filter with pi-type isolation network are improved by more than 10 dB at center frequency of each tuning state under the SE-BAL and PD filtering mode, while the measured output return loss and isolation for the SE filtering mode still keeps better than -20 dB in the whole tuning range.