Phase-stable v Temperature
Coaxial RF Cable Assemblies

While PTFE is the de facto workhorse dielectric in the RF / Microwave world it has an "Achilles Heel", the dreaded "Teflon Knee". At typical room temperatures, the phase change vs temperature is most dramatic. The result is a very significant phase-change in RF cables overall and most dramatically as the cable temperature passes through room temperatures. RF Cables that exhibit desirable, overall phase-change vs temperature performance come in 3 varieties:
Foamed PFA dielectric is the "new kid on the block". Foamed PFA reduces the dielectric constant, resulting in RF cable assembly construction with lower weight, lower capacitance, higher velocity of propagation, lower attenuation, improved VSWR, and "yes" phase-stability vs temperature. The cool part is that the "Teflon Knee" is nearly eliminated and the overall phase-change vs temperature is reduced significantly. Available from a very, very short list of suppliers, Koaxis has a limited (for now) supply of .047" (KF047P) and .086" (KF086P) diameter cables. For high-frequency and miniaturized applications, Koaxis provides solutions for phase-stability vs temperature challenges. We (will soon) have this solution available Ready 48™.
Tape-wrapped Expanded (microporous) PTFE dielectric has become the go-to choice for more cost-effective phase-stable vs temperature applications with more modest operating temperatures. Typically available in semi-rigid or flexible cable, tape-wrapped Expanded PTFE is available from several well-respected suppliers. Koaxis does NOT offer tape-wrapped Expanded PTFE  solutions. We would. But, for the most part, those well-respected suppliers like to reserve that cable for their own RF cable assembly customers and we don't blame them. We would, too. Suppliers of Tape-wrapped Expanded PTFE RF cable assemblies include Gore Phaseflex®, Micro-coax UTiFLEX®, and Storm Products PhaseMaster®.
Silicon Dioxide (SiO2) dielectric offers the best phase-stability vs temperature performance. If your application operates in very extreme temperatures, this is the only choice. It is also very, very, expensive, difficult to fabricate, is available from a very short list of suppliers, and is only available in rigid form. Koaxis does NOT offer SiO2 solutions. Suppliers of SiO2 RF cable assemblies include Measure TechMeggitt Safety Systems and Times Microwave.