Mutual coupling analyses for small GPS adaptive arrays

Aircraft in an ECM environment require high performance antenna arrays that are compact in size, and easy to manufacture. Modern microstrip antennas are suitable candidates for GPS arrays. A critical issue is how small can these antenna arrays be configured without compromising the performance of the GPS receivers. The closer the antenna elements are spaced, the stronger the mutual coupling between the elements. This can result in impedance mismatch of the individual elements to their feeds, distortion of the radiation patterns of the array, degradation of polarization and adaptive nulling performance. Mutual coupling studies are, therefore, essential in determining the overall characteristic behavior of small GPS antenna arrays. GPS arrays use right-hand circularly polarized (RHCP) elements to match the element polarization to the satellite signal polarization. In this paper, a theoretical study of the mutual coupling between RHCP microstrip antenna elements is presented.