Mutual coupling in microstrip antenna array: evaluation, reduction, correction or compensation

Mutual coupling between the antenna elements in a microstrip antenna array is a potential source of performance degradation, particularly in a highly congested environment. The degradation includes impedance mismatching, increased side-lobe level, deviation of the radiation pattern from the desired one, and decrease of gain due to the excitation of a surface wave. To deal with these problems, the first thing is to evaluate the mutual coupling and to select the element with low mutual coupling. Then, it is still desired to reduce the mutual coupling further by taking some measures. Finally, in certain critical cases, it is necessary to involve the mutual coupling effects accurately through numerical analysis, such as ultra low side lobe arrays and adaptive nulling arrays. All these issues are discussed and some numerical examples are given. Due to limited space, the paper focuses mainly on the work done in our laboratory.