| A rectangular microstrip patch which is excited by an electromagnetically coupled microstripline is analyzed and modeled. Moment method analysis is employed to obtain approximate representations for the patch and feedline current distributions, and input impedances are found by examining the current standing wave pattern along a portion of the feedline where the fields are quasi-transverse electromagnetic (quasi-TEM). Through this procedure, the computed input impedances are uniquely and meaningfully defined and are essentially independent of the properties of any connector or transition which may be utilized to excite the feedline. Thus, it is unnecessary to theoretically account for the presence of such connectors or transitions when performing input impedance calculations. In the analytical model, a fictitious excitation device which is simple to evaluate in the numerical analysis is used in lieu of a connector to launch an incident wave along the microstripline.An experimental method of characterizing a coax-to-microstrip transition is described. The transition, which is used to connect the actual antenna and feedline to a source or network analyzer, is modeled as a reciprocal, two-port device using an S-parameter matrix representation. This S-parameter description provides a simple means of relating measured and computed values of input impedance.The accuracy of the impedance computations and the utility of the experimental characterization of the transition are demonstrated through comparison of theoretical and experimental data. Excellent agreement between calculated and measured results is obtained.The formulation of the theoretical analysis is accomplished through the use of a plane wave spectrum representation of the Green's function for a grounded dielectric slab. An integral equation for the unknown patch and feedline electric current distributions is obtained by enforcing boundary conditions on both the patch and feedline, and Galerkin's method is applied to obtain the desired moment matrix equation. A method of improving the convergence of the resulting spectral integrals is described and illustrated. |
