Cryogenic microstripline-on-Kapton microwave interconnects

TL;DR

This paper evaluates cryogenic microstripline-on-Kapton microwave interconnects, demonstrating low loss and crosstalk at 77 K and 297 K, suitable for large focal plane radiometer arrays.

Contribution

It provides empirical measurements of loss, crosstalk, and thermal conductivity of microstrip lines on Kapton at cryogenic temperatures, highlighting their suitability for microwave interconnects.

Findings

Good performance up to 20 GHz at cryogenic temperatures

Dielectric constant of Kapton remains stable from 297 K to 77 K

Thermal conductivity comparable to stainless steel coaxial cables

Abstract

Simple broadband microwave interconnects are needed for increasing the size of focal plane heterodyne radiometer arrays. We have measured loss and cross-talk for arrays of microstrip transmission lines in flex circuit technology at 297 and 77 K, finding good performance to at least 20 GHz. The dielectric constant of Kapton substrates changes very little from 297 to 77 K, and the electrical loss drops. The small cross-sectional area of metal in a printed circuit structure yields overall thermal conductivities similar to stainless steel coaxial cable. Operationally, the main performance tradeoffs are between crosstalk and thermal conductivity. We tested a patterned ground plane to reduce heat flux.