A Low-Insertion Loss Cryogenic Edge-Mode Isolator With 18 GHz Bandwidth

Cryogenic isolators play an important role in low-noise receiver systems widely employed in millimeter and submillimeter telescopes. To enable a significantly wider Intermediate Frequency (IF) bandwidth, there is strong demand for a wideband, low-loss isolator in modern facilities like the Submillimeter Array (SMA) and Atacama Large Millimeter/submillimeter Array (ALMA). In this article, we present a novel cryogenic edge-mode isolator that incorporates an innovative circuit design. Operating at a cryogenic temperature of 4 K, this isolator delivers unprecedented performance, covering a frequency range from 4 GHz to 22 GHz. It exhibits insertion loss of less than 1 dB, together with return loss below -15 dB. In particular, it provides an isolation better than 17 dB across most of the band, a significant improvement over the previous generation of edge-mode isolators. This new isolator design is suitable for a wide array of low-noise receiver applications, from radio-astronomy to quantum computing.