Efficiency of electrically small antennas combined with matching networks

In applications where electrically small antennas are necessary and transmitter power is limited, the system efficiency may be a critical parameter in determining the feasibility of the system. The principle of conservation of energy is used to determine the efficiency of an antenna combined with a matching network composed of elements with finite quality factors. It is shown that conditions for maximum efficiency can be met by using a simple L section as the matching network. Illustrative examples concern a cryogenic loop antenna and a ferrite loaded loop antenna.