The antenna cable as a source of error in EMI measurements

Radio-frequency current on the exterior of an antenna cable, which is derived from the signal being measured or transmitted, can significantly alter the results of antenna calibration and EMI (electromagnetic interference) measurements. Two distinct phenomena are observed. The first is related to the behavior of the cable as a parasitic element of the antenna system; the second, which is more serious, is related to leakage between the antenna and cable due to imperfect balance, leaky connectors, and other problems. These phenomena are examined, and a method to measure the leakage between an antenna and its cable is developed. Several types of commonly used antennas are characterized with regard to cable interaction. The use of a ferrite choke on the exterior of the cable is proposed as an effective solution to the problem