Investigation on the effect of impedance changes in broadband antennas with varying antenna height on radiated emission measurement below 1 GHz

According to the standard method for calibration of receive antennas to be used in radiated emission measurement below 1 GHz, the sensitivity of receive antenna is defined as a free-space antenna factor obtained by applying a given correction factor to a near free-space factor that is determined by horizontally polarized antenna calibration at a 2 m antenna height. In actual radiated emission measurement performed while varying the receive antenna height, however, the sensitivity of receive antenna varies with antenna impedance changes at different antenna heights. In this situation, the authors measured how the antenna impedance changes with the antenna height and examined how such impedance changes affect radiated emission measurement results, using biconical, log-periodic dipole, and hybrid antennas under test that are typical below 1 GHz. The authors also studied on a method to estimate an antenna height free from antenna impedance changes and suitable for obtaining free-space factors.