Printed microwave couplers with thermal isolation

This paper discusses design principles and measurements for three printed microwave couplers designed for thermal isolation. These couplers are intended to minimize heat leakage when used as connectors to a cryostat, thereby maintaining the low temperature for a longer period of time. The first coupler is designed for L-band operation and exhibits a 10 dB return loss and 2 dB insertion loss. The second design operates in the cellular band with a maximum return loss of 28 dB and insertion loss less than 0.5 dB. Simple thermal modeling suggests significant improvements over standard coaxial connections. The third coupler is designed for X-band with a 15.6 dB return loss and a measured insertion loss of a few tenths of a dB at 10 GHz.