HF/VHF Antenna Characterization from Very-Near-Field Measurements over Arbitrary Closed Surfaces

A novel, efficient characterization technique for HF/VHF antennas from very-near-field measurements is presented. A measurement system with a non-intrusive broadband electro-optical (EO) probe is utilized to measure the tangential electric fields of an antenna under test (AUT) at a very-near surface enclosing the antenna. The non-metallic and small-size fiber-coupled EO probe does not perturb the current distribution over the antenna and is free from the complicated probe compensation. Far-field quantities of the AUT are derived from a newly developed near-field to far-field transformation method. In this way, a full spherical radiation pattern and gain of the AUT are attained without expensive computation and truncation errors. A miniaturized antenna operating low-VHF band (40 MHz) with dimensions 10 cm x 10 cm x 15 cm (0.013 lambda(0)x0.013 lambda(0)x0.02 lambda(0)) is employed as the AUT. The performance of the proposed approach is evaluated through comparison with the results obtained from full-wave simulation and direct far field measurement performed in an outdoor range.