Computer Aided Design for Printed-Circuit Antennas

Three-dimensional calculations on printed circuit antennas are usually very difficult, especially when normal conductors are involved as boundaries and multiports are used as excitations. We have developed two simple techniques to attack such problems. First, we have modified the traditional Green's dyads to include finite-conductivity value of the ground plane. We have incorporated Wheeler's incremental inductance method in the formulation of Green's dyads. The finite conductivity of the ground plane has been treated as perturbations to the perfect metal boundary. As such, it allows us to calculate the conductor loss arising from an antenna array consisting of a larger number of elements. Secondly, we have established normal mode currents for microstrip patches which serve as basis currents in the expansion of current distribution. The normal mode currents are expressed as gradients of current potentials which satisfy two-dimensional Helmholtz equation. The excitation currents for a microstrip or a coax feeder line can be readily expressed in terms of these normal mode currents. Most importantly, by using current potentials the sixfold integrals required for the calculation of Galerkin elements can be reduced into two-fold ones. This simplifies the calculations significantly. Consequently, the coupling between microstrip patch circuitries can be solved using a personal computer. Radiation patterns as well as radar cross sections associated with normal mode current distributions have also been formulated. Graphic user interface will be developed in Phase I such that the use of our numerical routines can be an easy and an interesting task.