Electronic tunable diplexer with wide tuning range

A varactor-based tunable diplexer with wide tuning range is proposed in this paper. The proposed diplexer consists of two varactor-loaded open-loop resonator filters. Size reduction and wide tuning range are achieved by using the varactor-loaded open-loop resonator. A simple microstrip T junction at the input and two filters responsible for the respective passbands is applied. Simulated insertion loss of our designed diplexer is obtained between 1.3 to 2.1 and 1.2 to 2.7 dB over the tuning range for Tx and Rx channels filter bands, respectively. Both filters exhibit better than 30 dB rejection in the passband of its counterpart. The varactor diode attached to both filters allow 48% and 50% center frequency tunbility in Tx and Rx filters bands, respectively.

1. Introduction

Reconfigurable radio system represents a potential solution for interference, cost, size, and power consumption problems encountered by wireless communication industry [1]. The three-port diplexer as a key component of front-end is widely used in RF/microwave transceivers to direct signals of two different frequencies to appropriate outputs and to prevent mutual interference between channels. Thus, a duplexer can be essentially developed by connecting two filters (different center frequencies) in parallel and each is designed with high selectivity to ensure channel isolation.