Evaluation of the Quality Factor, Q, of Electrically Small Microstrip-Patch Antennas [Wireless Corner]

The quality factor, Q, for a number of configurations of a microstrip antenna is evaluated using exact and approximate quality-factor formulas found in the literature. A number of slits parallel to the radiating edges are used to miniaturize the microstrip antenna´s size. The microstrip antenna in use is considered to be electrically small according to Wheeler´s electrically small antenna definition. The Q for each configuration is numerically evaluated using the given expressions, for simulated and measured data, and is compared to the Chu lower bound. There is good agreement between the results, while the Q lower fundamental limitation is not violated. Despite the size reduction, satisfying radiation efficiency is achieved, and the radiation pattern remains unchanged.