Electrically small, ferrite-loaded loop antennas

Approximate formulas have been developed for the impedance, efficiency, and Q of electrically small, ferrite-loaded loop antennas. The formulas are based on an assumed knowledge of these parameters for the antenna without ferrite loading. One set of formulas is based on an assumed internal magnetic field, i.e., the field in the ferrite. It is primarily applicable to ellipsoidal-shaped cores. Another set of formulas is based on assumed internal and external fields. It is primarily applicable to rod-shaped cores. The formulas are derived by using the reaction concept, which makes the result relatively insensitive to the assumed distribution. The results are used to evaluate the effect of ferrite size and shape. The results of a variety of measurements are given for comparison.