A Fast Way to Accurately Calibrate Tunable Dipole Antennas at VHF

A fast method is proposed and verified experimentally to calibrate tunable dipole antennas. An adapter is introduced to convert a commercially available balun for dipoles into a three-port network; this allows its S-parameter to be accurately measured. Using this process, the antenna factor, site attenuation (SA), as well as balance, can be calculated with the method of moments (MoM). The calculated SA is verified by precise measurements on a high-performance open-area test site, and the differences are less than 0.3 dB from 30 to 282 MHz. As an application, the mutual impedance correction factors are calculated with the MoM for tunable dipole antennas. Furthermore, the three balun method is proposed to measure the loss of a balun with two simple adapters, which provides a faster method to calculate the free-space antenna factor (Fa). The new method will reduce the time from several days to several hours to calibrate a pair of tunable dipole antennas. A clearer traceability chain for measuring Fa is illustrated, too.