Multiport network modeling of electro magnetically coupled microstrip patches

Electromagnetically coupled (EM fed) microstrip patches have their feed structure fabricated on a thin substrate located between the patch antenna and its ground plane as shown in Figure 1. This dual layer design has two main advantages over conventional single layer microstrip antennas. First, spurious radiation from the feed network can be reduced by decreasing the height and increasing the dielectric constant of the lower substrate. Secondly, patch bandwidth can be increased by using a thicker upper dielectric material and also by adjusting the feed configuration under the patch. Previous methods of designing EM fed patches have included experimental iteration, transmission line model [1], and full wave analysis [2] [3]. Unfortunately, experimental iteration is time consuming and costly; the transmission line model only works for feeds under the radiating edge of the patch; and full wave analysis is computationally intensive.