Extensions of Time Domain Metrology above 10 GHz to Materials Measurements

A new time domain measurement technique to obtain the relative complex permeability , μ* and permittivity ϵ* of materials at frequencies above 10 GHz is described. The main feature is the use of a 400-ps-wide RF pulse-excitation waveform that furnishes the necessary spectral amplitude in the 9-to 16-GHz frequency range. The delay line configuration and instrumentation are similar to a previously reported lower frequency system where a sample of solid material less than 5 mm thick is cut to fit into a coaxial sample holder. Experimental values of μ*and ϵ* are given for Teflon and a ferrite material for measurements made in two segments spanning 0.4-10 GHz and 9-16 GHz. These show good agreement with data obtained from direct frequency domain measurements. A discussion is included on the amplitude spectra of a step-recovery diode and tunnel diode pulse generator and their application as time domain sources. Considerations for the optimum choice of sample thickness are also given.