Cost-effective testing techniques to characterise UHF antennas

Abstract

Engineers require the ability to measure and characterise the reflection coefficient, gain and gain patterns of unknown antennas. Due to the cost of antenna measurement facilities and the associated equipment, many tertiary educational institutes do not have these facilities available. The purpose of this research was to investigate the use of a sports field as a testing range with cost-effective equipment. Measurements were conducted at two commercial ranges and a sports field. The first range was an open area test sight (OATS) where a cost-effective vector network analyser (VNA) (≈R3000) was compared to a commercial VNA (≈R1.5 million). The antennas under test were two identical log-periodic dipole arrays with a frequency range from 180 MHz - 3 GHz. Altair FEKO was used to model the antenna and compare results from different ground plane responses. An anechoic chamber was used to make baseline measurements which were then compared to the FEKO simulation, OATS and sports field measurements. The sports field results had close correlation with the anechoic chamber and OATS measurements. The study finds that by using the two antenna method an antenna can be cost-effectively and reasonably accurately characterised for boresight gain to within 1.7 dB on a sports field. The gain pattern was also achieved on the sports field to within 3 dB of an anechoic chamber measurement. The results enable students and engineers to take antenna measurements at tertiary institutions for under R10,000.