Investigation of an impedance based GTEM calibration factor

Presents an investigation into a GTEM calibration factor based on the impedance measured at the cell port. The work begins with the comparison of radiated emissions measurements taken from GTEMs of two different sizes. A radiating source, which radiated on a 5 MHz line spacing, was used for this comparison. The resulting comparison led to the measurement of the impedance, both real and imaginary, at the port of each cell. What was discovered was that there is an impedance variation in each cell. From the viewpoint of the port this variation of impedance traces a curve which is roughly a damped sinusoidal wave. The period of the wave relates roughly to the length of each cell. The study presents and analyzes the differences in radiated emissions measurements made in two different sizes of GTEMs and OATS measurements. It then presents and analyzes the cell port impedance measurements. A beginning is made on relating these two sets of measurements. The relative similarity in the difference plots suggest that the same physical mechanism is involved and that a calibration factor can be developed for the GTEM using impedance measurements in the band from 30-200 MHz, and possibly higher.