Large electrical volume coaxial transmission line for microwave chemical sensing

In this paper we demonstrate a method of practically designing a large electrical volume coaxial structure for room-temperature chirped pulse Fourier transform microwave (RT-CP-FTMW) chemical sensing. Both the center and outer conductor are tapered to optimize the volume of molecular analysis while minimizing coupling to higher-order modes in the electrically large coax because they limit the turn on time of the molecular detection receiver, which in turn results in lower measured signal strength. Furthermore, successful spectrum measurement, improvement in spectrum signal-to-noise ratio, and especially the capability of resolving a spectrum with less averages, and therefore significantly less measurement time, demonstrate the utility of the large electrical volume test device in microwave chemical sensing.