Tunable Cavity-Based Diplexer With Spectrum-Aware Automatic Tuning

This paper presents, for the first time, an automatically tunable diplexer using evanescent-mode cavity filters, with spectrum-aware and interference mitigation capabilities. The diplexer consists of two second-order bandpass filters and a bandstop filter (BSF) at the receiving path. The BSF is utilized in a spectrum sensing methodology to detect potential jammers. The automatic tuning system monitors each resonator in the diplexer and biases them to accurately reach the targeted frequency accordingly. The presented diplexer presents a measured tuning range 0.75–1 GHz, with an insertion loss (IL) of less than 3.7 dB in the receive path and 2.2 dB in the transmit path and a tuning resolution of ~0.05%. The closed-feedback loop tuning time, which accounts for all mechanical and electrical time constants, is around 250 ms. The spectrum sensing capability has been experimentally demonstrated to detect a jammer. Automatic diplexer tuning results in a total jammer suppression of 30 dB with 33-MHz transmit–receive separation. Further rejection of up to ~50 dB can be achieved for higher separations. The automatic tuning control system is also analyzed for stability.