Small Antenna Pattern Testing - The Antenna-to-Range Interface

The antenna-to-range interface can have a large effect when measuring the radiation performance of electrically small antennas for wireless communications. Small antennas, with their almost omni-directional patterns, need to be tested in very low reflection environments. However, the connection of the antenna to the RF measurement subsystem, particularly where cables, or other conducting interfaces, are used can cause problems with external currents flowing on the interfaces. One method of suppressing these currents is by the use of quarter-wave chokes. Also the feeder cable is replaced by optical fibre. This paper examines the use of electro-optic transducers and chokes, and presents measured and modelled results for a small antenna operating within the frequency range 2.4 to 2.5 GHz.