High temperature dielectric stability of liquid crystal polymer at mm-wave frequencies

The temperature dependent dielectric stability and transmission line losses of liquid crystal polymer (LCP) are determined from 11-105 GHz. Across this frequency range, LCP´s temperature coefficient of dielectric constant, τ_εr, has an average value of -42 ppm/°C. At 11GHz the τ_εr is the best (-3 ppm/°C), but this value degrades slightly with increasing frequency. This τ_εr average value compares well with the better commercially available microwave substrates. In addition, it includes information for mm-wave frequencies whereas standard values for τ_εr are usually only given at 10 GHz or below. Transmission line losses on 3- and 5-mil LCP substrates increase by approximately 20% at 75°C and 50% or more at 125°C. These insertion loss increases can be used as a design guide for LCP circuits expected to be exposed to elevated operating temperatures.