| This research in computational electromagnetics addressed the problem of predicting the near-field mutual coupling effects in phased array antennas. It developed and demonstrated a new analysis technique that uses the finite element method (FEM) in combination with integral equations. Due to FEM's inherent ability to model inhomogeneous dielectrics, the new capability encompasses many radiator types that were not amenable to analysis by previously-existing methods. The analysis considers the general case of a radiator in an infinite array that is fed through a ground plane by one of three types of waveguides: rectangular; circular; or circular coaxial. Accurate feed modeling is accomplished by enforcing continuity, between the FEM solution and an arbitrary number of waveguide modes, across the ground plane aperture. A periodic integral equation is imposed at a plane above the antenna's physical structure to enforce the radiation condition and to confine the analysis to a single array unit cell. The electric field is expanded in terms of vector finite elements, and Galerkin's method is used to write the problem as a matrix equation. The Floquet condition is imposed as a transformation of the matrix, which is equivalent to wrapping opposing unit cell side walls onto each other with a phase shift appropriate to the scan angle and lattice spacings. The solution of the linear system, accomplished using the conjugate gradient method, gives the electric field, from which the active reflection coefficient and active element gain are calculated.;The theory and formulation were used to develop a general-purpose computer code. The use of commercial CAD (computer-aided design) software for geometry and mesh generation makes the code geometry independent. It was validated by comparing its results to published data for arrays of open-ended waveguides, monopoles and microstrip patches. Predictions for dielectric-clad monopoles were validated by a hardware experiment. Finally, the code was used to predict the scanning properties of arrays of printed dipoles and printed flared notches. |
