A Low-Loss Edge-Mode Isolator With Improved Bandwidth for Cryogenic Operation

Isolators are important components of low-noise detector and signal processing systems. Conventional wideband edge-mode isolators offer wide bandwidth, but rarely exceeding two octaves. Using modern computer electromagnetic simulation software, one can optimize the isolator circuit and expand the bandwidth performance. We report on the design, fabrication, and measurement of an edge-mode isolator operating over a multioctave frequency range, from 4 to 22 GHz at 4-K cryogenic temperature. This isolator has good input and output reflection coefficients that are below -15 dB from 4 to 22 GHz. The measured insertion loss is about 0.6 dB from 4 to 17 GHz, rising to 1 dB from 17 to 22 GHz, and the isolation is better than 15 dB from 4 to 13 GHz, degrading to about 10 dB above 13 GHz. This edge-mode isolator with improved bandwidth is suitable for a wide range of low-noise receiver applications.