Controlling the effects of feed cable in small antenna measurements

Ideally, antennas would be measured without any measurement cables to perturb the results. However, most handset and wireless LAN prototype antennas are measured using a coaxial cable to connect the antenna under test (AUT) to the measurement transceiver. This feed cable couples to the currents on the AUT and can affect both the antenna match and also the radiation performance. A new method of suppressing spurious measurement cable currents has been developed. This relies on computer simulation to predict the low electric field regions where the measurement cable can be safely attached, and on comparison between simulation and measurement results to verify that the measurement cable´s spurious surface currents are suppressed. In practice, this method only suppresses currents directly coupled from the AUT to the measurement cable. Other mechanisms such as ferrite beads are still required to suppress currents induced onto the measurement cable from the radiated field. However, using the cable positioning simulation results in much lower spurious currents, and therefore much lower ferrite induced ohmic losses.