'A Modern Wheeler-Cap Method for Measuring Antenna Efficiency'

摘要

A modern method is presented to measure small antenna efficiencies by implementing a variant of the Wheeler-Cap method. As antennas become smaller in size, antenna efficiency typically decreases either because of matching functions or reductions in the antenna radiation resistance. It is important to know while designing small antennas, how much efficiency reduction can be tolerated before a particular design needs changing. Measuring antenna efficiency by integrating radiation functions is not a trivial task and prone to measurement errors. The modern method presented uses a plastic sphere which is internally coated with a highly conductive metallic paint, having low resistivity values (less than 0.1ohms per square), and useful to implement the Wheeler Cap measurements. The measurements are conducted with the use of a modern Agilent Vector Network Analyzer (VNA) which is calibrated to the antenna port (which includes any antenna matching networks). The apparatus was used to measure small "planar" antennas thus producing extremely good results. The paper presents the methodology used for the development of the apparatus and the measurement results.