Earth-Effect Emulation Using Periodic Structures in Scaled-Model Characterization of HF Antennas

We present a technique for emulating the impact of the presence of earth on the responses of high-frequency (HF) antennas characterized using scaled-model measurements. Scaled-model measurements are routinely used to characterize the responses of HF antennas, particularly those mounted on physically large platforms. The presence of the ground in the vicinity of such antennas and its electrical parameters can significantly impact the antenna response. However, this impact is not usually taken into account in scaled-model measurements. In this letter, we demonstrate that the earth impact in such scaled-model measurements can be emulated by using a lossy periodic structure, with subwavelength unit-cell dimensions, designed to emulate the electrical properties of the ground at the scaled frequency of operation. The efficacy of this approach is demonstrated using a design example for a platform-based HF antenna operating in the vicinity of wet earth. A scaled-model prototype of the antenna and the ground-emulating periodic structure are fabricated and experimentally characterized. Measurement and simulation results demonstrate a good agreement and verify the capability of using this approach to perform more accurate, scaled-model measurement of HF antennas.