Free-Space Factor Calibration of Hybrid Antenna

Use of the free-space antenna factor (AFFS) to measure the emission noise from equipment under test (EUT) is stipulated in the international standard. The application of the AFFS was also stipulated with a transition to VCCI-CISPR32 in Japan. The calibration method of biconical antennas used for radiated emission measurement is stipulated in CISPR16-1-6 or ANSI C63.S. The AFFS value is calculated from the value (AFNFS) obtained in a near free-space (metal reference plane, horizontal polarization, antenna height 2 m, distance 10m) by correcting the correction factor. No correction factor to the free-space factor using is provided for log-periodic dipole array (LPDA) antennas and hybrid antennas that are frequently used in recent years. We measured the AFFS and AFNFS of a typical hybrid antenna used for radiated emission measurement in a frequency range of 30 MHz to 1 GHz using the three-antenna method at an antenna height of 10m from the ground, and then compared these values. We further tried the method of removing floor-reflected waves by gating using the time domain function because an effect of the ground plane was found even at an antenna height of 10m. This paper describes these results. And, the phase center of the antenna position of LPDA is planned in the future with reference to Mr. Kurokawa's paper.