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

Abstract

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, /spl tau//sub /spl epsi/r/, has an average value of -42 ppm//spl deg/C. At 11GHz the /spl tau//sub /spl epsi/r/ is the best (-3 ppm//spl deg/C), but this value degrades slightly with increasing frequency. This /spl tau//sub /spl epsi/r/ average value compares well with the better commercially available microwave substrates. In addition, it includes information for mm-wave frequencies whereas standard values for /spl tau//sub /spl epsi/r/ 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/spl deg/C and 50% or more at 125/spl deg/C. These insertion loss increases can be used as a design guide for LCP circuits expected to be exposed to elevated operating temperatures.