Broadband microstrip array antennas

Microstrip antennas and microstrip arrays have several practical features, which could make them interesting candidates for a lot of antenna applications, ranging from mobile communications to phased array radar systems. The required bandwidth of these applications varies from less then a few percent to 30 percent or more for radar applications. Most of the microstrip arrays that have been published in literature are made on electrically thin dielectric materials and are therefore narrow-banded. The bandwidth can be improved if thicker substrates are being used. However, electrically thick substrates give rise to an inductive shift in the input impedance, which means that a good impedance match can only be achieved if a compensating input network is used. A solution for this problem could be the so-called electromagnetically coupled (EMC) microstrip structure. In this case the patches are not physically connected to the feeding coaxial cables. This configuration is shown. The results are presented of a theoretical and experimental study of microstrip array antennas with EMC elements. Mutual coupling between array elements and the input reflection coefficients are investigated and compared with measurements.