Impact of test area in antenna gain measurement using image theory

This paper presents the measured gain values of a passive horn antenna, acquired by employing metallic reflector alone coupled with a vector network analyzer, in compliance with the image theory. Such novel methodology provides an alternative to the conventional three-antenna or two-antenna gain measurement method. The gain values were computed by a simple formula based on the distance between antenna and reflector, operating frequency, S-parameter and the speed of light. The antenna was directed first at an absorber, and then at a reflector to obtain the S11 parameter with the aid of a complex network analyzer. The studies were conducted in three settings - shielding room, anechoic chamber and open space - at antenna-reflector distances of 0.5 m, 1 m, 2 m, 3 m and 4 m. The computed results were compared with and analyzed in accordance to the manufacturing data. Encouragingly, the computed data corresponded closely to the manufacturer's data at the distance of 0.5 m for anechoic chamber, with a correlation coefficient of 0.93; and at the distance of 1 m for shielding room and open space, with a correlation coefficient of 0.77 and 0.79, respectively. These findings suggest that while the image theory-based single-antenna method demands less space, time and cost, this economical approach can be further improved by taking into consideration such governing factors as signal losses, reflective sources, optimization of far-field distances as well as the reflector size required for calculating the gain.