QUICK MEASUREMENTS OF THE RADIATION PATTERN OF ANTENNAS USED IN RADIATED EMMISSIONS FOR ELECTROMAGNETIC COMPATIBILITY TESTING AND COMPARISON TO COMPUTED RESULTS

摘要

Antennas have been used in EMC measurements since the early days of EMC testing. Knowledge of the antenna pattern was not a requirement of the standards. While MIL STD 461 [1] and some SAE standards [2] called for the users of the testing antennas to have knowledge of pattern parameters such as the half power beamwidth most standards did not require any knowledge of the antenna radiation characteristics. With the evolution of standards to cover frequencies above lGHz knowledge of the pattern has become more important. Since above lGHz 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. This is important to make sure that large equipment under test is completely covered by the main beam. The present paper shows typical measured patterns for the most common antennas used in EMC. The measured antennas operate in many cases down to 30MHz. The antennas covered are biconicals, log periodic dipole arrays, hybrid antennas (combined bowtie and log), and dual ridge horns. The patterns were measured in a very simplified approach and for lower frequencies the measurements where performed outdoors over a ground plane with minimal absorber coverage. The E and H planes were measured and they are compared with numerical modelled results computed in NEC or using TD based commercial packages. The hope is to demonstrate if this simplified approach is sufficient to provide the users of the antennas with the information they need to satisfy the requirement of regulatory standards.