Characterization of Propagation on Wires Over Lossy Earth

by Buff, Peter Marcus

The propagation of electromagnetic energy on a wire located above lossy earth is experimentally characterized for the first time. New microwave de-embedding techniques are developed specifically for measurement environments with unknown lossy substrate properties. The novel Through?Match (TM) de-embedding technique developed here is used to de-embed the S-parameters of a line over earth and the results compared to the results produced from the well-known Through?Reflect?Match (TRM) technique. Although TRM is an established method for making microwave measurements, the technique is rederived here to facilitate the development of the new TM technique. Techniques and methodologies for the error analysis of de-embedding calibration methods are introduced. These techniques are valid for methods that use fixtures in the measurements with the assumption that the fixtures can be faithfully reproduced. The well-known Through?Reflect?Line (TRL) technique has errors known as ë/2 errors associated with the differential length of the line standard and through standard and are seemingly unpredictable in nature and extent. The origin of the errors is identified as small errors in the repeatability of the fixtures. To address the issue of outdoor measurements and the mesocopic nature of soil as an unstable and unpredictable medium, a soil surrogate was developed and modeled using a dielectric composite made from gelatin, High Fructose Corn Syrup (HFCS), water and NaCl. The composite is developed with relative permittivity ranging from 8 to 75 with selectable conductive and dielectric losses. The composite comprises gelatin, High Fructose Corn Syrup (HFCS), NaCl and water, and can be used to model soils, loams and sands in the 200 MHz to 20 GHz range. Frequency-dependent electrical characteristics resulting from the mesoscopic nature of soils is captured by the surrogate. The soil surrogate is suited to a laboratory environment providing a medium for repeatable measurements. The TM, TRM and TRL measurement methods are used and compared from 100 to 300 MHz for a single conductor lying on the air/composite interface.