Electromagnetically coupled microstrip ring-type antennas of arbitrary shape

Microstrip antennas have been used widely with advanced MIC/MMIC technology. This paper focuses on the modeling of microstrip elements of arbitrary shape in multilayered media. Emphasis is placed on the impact of the excitation mechanism on the circuit performance. To avoid the soldered probe-feed excitation, electromagnetically coupled (EMC) microstrip feedlines are preferred in this analysis. The change in resonant frequency due to the presence of proximity coupling from the embedded microstrip line is presented. Several microstrip ring-type antennas of arbitrary configuration are considered including circular, elliptical, polygonal and other arbitrarily-shaped rings. The mixed potential integral equation (MPIE) method combined with the triangular angular expansion function is developed to model general microstrip geometries. This method starts from meshing the whole microstrip geometry with small triangular faces. An evolution of the algorithm developed by McKinzie (see Ph.D. dissertation, UCLA, 1992) is used in this analysis. Both spatial-domain Green´s functions, as obtained from vector and scalar potentials respectively, are evaluated by computing a Sommerfeld-type integral. By means of the moment method (MM) a matrix equation can be set up. Several numerical techniques are applied to speed up calculation. They are discussed and several examples are shown.