X Band RF Interface Technology with Both Low Loss Characteristic and Low Thermal Insulating

We have proposed a new RF interface technology between cold stage and room temperature stage at X band. The RF interface has both low loss characteristic and low thermal insulating. In general, loss characteristic and thermal insulating is relationship of trade off. Conventional cryogenic receiver uses low loss RF coaxial cable and high power cryogenic cooler. High power cryogenic cooler is large volume. Therefore, small cryogenic receiver had been difficult. The dominant cause for thermal insulating is ground metal of RF transmission line. The proposed transmission line for RF interface consists of separated ground metal and floating metal lines for rejection of RF radiation on polyimide substrate. The separated ground metal realizes thermal insulating less than 1/10 that of 3.2 mm semirigid coaxial copper cable. On the other hand, the floating metal lines on both side of signal line realize low loss characteristic. Proposed RF interface was insertion loss of less than 0.2dB at X band and thermal input of about 30 mW. This RF interface technology is impossible to expect of small high-sensitivity cryogenic receiver.