A 1.16–3.89-GHz Tunable Six-Channel Diplexer with Compact Size and High Isolation

A compact microstrip varactor-based diplexer with six tunable channels is proposed. Each output path contains only two varactor-loaded multi-mode resonators, by which three two-pole passbands/channels can be independently and continuously tuned over a wide bandwidth. Given the input return loss greater than 10 dB and output isolation greater than 26.1 dB, the six channels of the fabricated diplexer can be experimentally tuned in the range of 1.16~1.36, 1.65~1.81, 2.05~2.36, 2.57~2.86, 3~3.52, and 3.3~3.89 GHz, respectively. Measured results agree well with simulated results.