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 × 10 cm × 15 cm (0.013λ₀ × 0.013λ₀ × 0.02λ₀).[)) 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.