The Input Impedance of a Rectangular Microstrip Resonator FED by a Microstrip Network on the Backside of the Substrate

Analytical expressions for the input impedance of rectangular microstrip resonators used in the microstrip array antennas, fed by a microstrip network on the backside of the substrate are derived. Using the feeding-technique from the backside of the substrate, microstrip antenna arrays with unequally spaced elements can be built to reduce the sidelobe levels or to built dual frequency antennas with low side lobe levels. The accuracy of the developed formulas is discussed and applications in microstrip antennas with low sidelobe levels and in dual frequency antennas will be demonstrated.