Electronically tunable diplexer for frequency-agile transceiver front-end

A varactor-based tunable diplexer is proposed and experimentally validated for IEEE802.16 standard-based system applications. The proposed transmit/receive (Tx/Rx) diplexer consists of two tunable dual-mode bandpass filters. Size reduction and band tunability are achieved by using the capacitance of varactors diodes. With two-tone nonlinear characterization test, the diplexer (with higher biased voltage) is found to introduce, in Tx frequency band, a high level of intermodulation product (IIP3). A better insertion loss in passbands is observed for a lower room temperature. Measured insertion loss of our fabricated diplexer is obtained between 5.3 to 2.89 dB and 5.2 to 3.7 dB over the tuning frequency range for the Tx and Rx channels filters bands, respectively. Both filters exhibit better than 40 dB rejection in the passband of its counterpart. The varactors diodes attached to both filters allow 24.5% and 23.3% center-frequency tunability in Tx and Rx filters bands, respectively.