Theoretical and experimental study of mutual coupling between microstrip stacked patch antennas

One of the major challenges that appears in the design of microstrip arrays is the impact of mutual coupling on radiation properties. The mutual coupling between array elements can be calculated using the standard moment method procedure in spectral domain. However, with increased distance between elements, the high-oscillating part of the sub-integral in method of moments (MoM) matrix elements makes standard integration procedures inapplicable. A convenient method for overcoming this problem is to change the integration path towards imaginary values in the complex plane, thus transforming the oscillatory behaviour to an exponentially decaying one. The challenge consists in careful management of the loci of the poles and branch cuts of the Green´s function in the spectral domain (Garino, M.S. et al., 2000; Kitchener, D. et al., 1987), which generally differs for each MoM matrix element and must be tailored differently. A method for calculating these high-oscillating integrals is developed, implemented and compared with experimental results. The developed software can handle either single or stacked rectangular patch configurations with arbitrary number of dielectric layers.