Experimental investigation of radiating current distribution and measurement cable interaction on wireless devices

The measurements of small passive antennas often require the connection of a coaxial cable to the Antenna Under test (AUT). If the AUT is electrically small, current flowing back from the radiator to the outer surface of the cable will result in secondary radiation. This causes the measured radiation pattern to be inaccurate. To reduce unwanted radiations, the coaxial cables can be covered with EMI suppressant tubing materials, but this causes the measured efficiency to be inaccurate due to the power loss in the absorbing materials [1]. In this paper, the cable contribution to the measured antenna characteristics of a printed Ultra Wide Band (UWB) antenna and a sleeve electrical dipole have been investigated experimentally. The antenna measurements have been performed using a spherical near field multi-probe system [2]. To investigate the secondary cable radiation, the measurement have been processed by extraction of the equivalent currents/sources on a closed surface conformal to the AUT as described in [3-5].