Effect of ground plane and chamber walls on antenna input impedance

Results of an experimental study undertaken to measure the effect of ground plane and absorber walls on the input impedance of antennas used in electromagnetic compatibility measurements are presented. Measured data for real impedance of biconical, log-periodic and dipole antennas as a function of height (1-2 m) and frequency (50 MHz-1 GHz) show significant variation of ground plane interaction. Horizontally polarized antennas showed more variation than vertically polarized antennas. Biconical antennas with pulse-transformer type baluns show more variation than those with matched hybrid baluns. Resonant antennas show more significant changes near their resonant frequency. All of these effects are more pronounced at lower frequencies.<>