Compact UHF Diplexer on Multi-Conductor Coaxial Cavity Resonators

In this paper, we developed the compact cavity diplexer for UHF range. We used the model of multi-conductor coaxial resonators with three posts with decreased resonant frequencies. We applied a coupling matrix theory to synthesize the diplexer with passbands 690–862 MHz and 880–960 MHz, 20 dB return loss and 30 dB isolation. The dimensions of diplexer were 40mm
^x
40mm
^x
140 mm. Comparison with known cavity diplexers demonstrated more than 30% volume reduction with similar technical characteristics. We manufactured the diplexer by assembling pre-machined tubular resonators in an empty cavity to obtain high positioning precision and used fine-tuning dielectric screws for each resonator to reduce the PIM.