Using the Three-Antenna Gain Method to Improve Measurement Accuracy for VHF Satellite and Space Applications

Antenna measurements in the VHF band are challenging because of the sensitivity to surroundings in both outdoor and indoor ranges. The large size of the antennas involved makes them difficult to manipulate and therefore more susceptible to damage. In addition, the gain tables for standard gain antennas at these low frequencies is often sparse, especially for older models. This paper proposes to use the three-antenna gain method to mitigate some of these problems by calculating the gains more accurately than other gain calculation methods or the original manufacturer's datasheets. To this end, a new custom NSI2000 script was written and trialed with a trio of antennas commonly used to test new devices for satellite and space related applications. Using our newly refurbished large anechoic chamber with a near-field system, gain data calculated in the 200 - 325 MHz frequency range shows notable differences relative to the datasheets. As compared to other methods of gain calculation, the results for the three-antenna method displayed smaller mean values and standard deviations - indicating a reduction in the influence of any single error on the overall outcome. The lessons learned from this experiment can help improve measurement accuracy at these frequencies.