Calculable Dipole Antenna for EMC Measurements with Low-Loss Wide-Band Balun from 30 MHz to 2 GHz

Abstract

A half-wavelength calculable dipole antenna has been developed. The Antenna Factor (AF) of this dipole is evaluated between 30 MHz and 2 GHz. Generally the proposed formula by ANSI-63.5 (ANSI, 1988) method for EMI antenna calibration is for a resonant dipole and assumes a perfect sinusoidal current density along the dipole. Indeed, the mutual effects on AF in this case could be taken into account with some approximate correction factors. The perfect sinusoidal form of current density is not correct for the real thick dipoles. For these dipoles, i.e., nonresonant and thick, assuming a perfect sinusoidal current density introduces errors around 1 dB/m on AF. An alternative method is presented: an analytical method based on a simple new current distribution along the dipoles to evaluate their radiation characteristics, and this is compared with a numerical approach based on MoM (the Method of Moments) by NEC software, to model two dipoles in a standard site. The entire frequency range, 30 MHz to 2 GHz, is covered by only two baluns. For the frequency range, 350 MHz to 2 GHz, we have used for the first time a low-loss wide-band tapered balun. The experimental results are presented where a good agreement is observed with the calculated ones.