Radiation efficiency analysis on small antenna by Wheeler cap method

There have recently been extensive studies of small‐size microstrip antennas. Some of these small antennas maintain gains of 5–6 dBi, whereas others have gains of 0–1.5 dBi. One important antenna parameter is the radiation efficiency. There have been very few studies on this parameter for small microstrip antennas. This letter presents measurements of several of these structures introduced earlier, with the use of the Wheeler cap method. The highest efficiency measured was about 96%.