Measurement and Computational Analysis of the Radiation Patterns of EMC Antennas Used in Radiated-Emissions Measurements [Measurements Corner]

Recently, several standards related to measurements of unintentional radiated emissions of electrical and electronic devices have introduced the need to have a knowledge of the half-power beamwidths (HPBW) of the antennas used during the measurements. Since above 1 GHz most antennas are very directive, information on the pattern has become very important, especially when it comes to understanding how much area the main beam is covering. The standards are extending the need to understand the radiation parameters of the antennas to frequencies in the 30 MHz to 1 GHz range. The present paper is intended as a reference to give information to the EMC engineer and technician on the radiation patterns of the most common EMC antennas used for radiated immunity. The paper also looks at simple methods of measuring the patterns of these antennas. The goal is to propose a simple approach to measure the patterns that will provide results that will be adequate for the EMC community at a low cost. The antennas covered are biconical antennas, log-periodic dipole arrays, hybrid antennas, and dual-ridge horns. As a quick check of the validity of the measured data, computational results are presented for the antennas measured. The Numerical Electromagnetics Code (NEG) and CST Studio Suite™ were used to generate data to compare with the measured results. These experiments give the EMC engineer the information needed to understand the radiation patterns and the half-power beamwidths of the antennas used to perform EMC measurements.