Investigation of Frequency-Domain and Time-Domain Free-Space Material Measurements

Electromagnetic material characterization is the process of determining the complex permittivity and permeability of a test sample. The primary goal of this thesis is to develop a new two transmission material measurement method to decrease the error associated with using a reflection measurement. The transmission method uses a sample transmission measurement and a acrylic backed sample transmission mea- surement. This technique is first demonstrated in a rectangular waveguide system then extended to frequency-domain and time-domain focus arch free-space systems. Most free-space systems consist of transmit and receive spot-focusing horn lens antennas and a network analyzer (NWA). A six step procedure is used to extract the material characteristics using the NWA. The data is measured (1) using the NWA then it is frequency windowed (2) to knock down the sidelobes that appear in the time-domain after the data is transformed. Once transformed (3) to the time-domain the data is time gated (4) to eliminate multiple reflections between the antennas and sample. The data is transformed (5) back into the frequency-domain for extraction (6) of permittivity and permeability using a Nicolson-Ross-Weir (NRW) method and two transmission method. Windowing and transforming the data, steps two and three, decreases accuracy at the band edges. The use of a digital oscilloscope with a time-domain reflectometer (TDR) module should increase accuracy by removing the windowing and transforming operations.

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