The effect of ground reflections on electric field measurements using a HIRF LLCW test system

A low-level continuous wave (LLCW) radiated field was used to illuminate a Boeing structural test article, providing data on the level of airframe shielding protection from the external high-intensity radiated field (HIRF) environment. LLCW measurements were made using the HP 8753 network analyzer from 200 MHz to 1 GHz and the HP 8510 network analyzer from 1 GHz to 18 GHz. The signal output from the network analyzer was amplified and used to drive horn radiating antennas. The receive antennas were a standard log-periodic below 1 GHz and Boeing-built monopoles above 1 GHz. Electric fields measured in the absence of the test article during calibrations exhibited sharp ground reflection interference in horizontal polarization but not in vertical polarization. These interference frequencies are predicted for three calibration positions, and the polarization difference is examined