Design and performance of a compact superconducting duplexer at VHF-band

This paper presents the design, fabrication, and performance of a compact high temperature superconducting duplexer at VHF-band. The duplexer consists of a T -junction and two four-pole filters with an ultra-narrow bandwidth of 400 kHz at 216 MHz and 220 MHz, respectively. By using gap-coupled feedlines in the filter design procedure, the duplexer is constructed by connecting the two filters using a T -junction with short-length branches. The two filters are fabricated on separate substrates and are carefully packaged to achieve a high isolation between the duplexer channels. The duplexer has a compact size of 41.6 mm × 28 mm. The measured results at 73 K show a high performance. The return loss is −17 dB, the insertion losses of both channels are less than 0.16 dB, and the out-of-band rejections are higher than 60 dB. The isolation between the two channels is better than 76 dB.