Tunable Low-Loss UHF Circulator for Cryogenic Applications

A 600-MHz above-resonance circulator operating at 4.2 K has been constructed and successfully tested. Its high isolation (>30 dB), extremely low insertion loss (<0.1 dB), low VSWR (< 1.1), and acceptable instantaneous bandwidth (~6 percent) make it a promising device for utilization in narrow-band very low-noise systems.