A Wideband Unbalanced-To-Unbalanced Choke for Return Current Suppression in Antenna Measurements

In the measurement process of electrically small or compact antennas, return currents may exist on the outer conductor of the coaxial cable connected to the antenna under test. This undesired phenomenon degrades the quality of the measurement results. A main cause for these return currents in unbalanced-to-unbalanced transitions can be traced to a small ground plane size. In order to suppress return currents, a two-port wideband choke based on two baluns in back-toback configuration is proposed for operation from 100 MHz to 2500 MHz. As an application example, two compact coplanarwaveguide-fed (CPW-fed) antennas affected by return currents on their feeding coaxial cables, are used as test beds for the proposed unbalanced-to-unbalanced choke. The excellent return current suppression for these two antennas demonstrates the practicability of this wideband choke in antenna measurements.