Green’s Functions for Probe-Fed Arbitrary-Shaped Cylindrical Microstrip Antennas

The efficiency of a method of moments procedure for microstrip antennas is strongly dependent on the convergence of the inverse Fourier transformation (IFT) from the spectral to the spatial domain. This is especially true when considering cylindrical microstrip antennas (CMAs). In the cylindrical case, the calculation of the two-dimensional Green´s functions stays inherently time-consuming. In the planar case, Green´s function can be reduced to a one-dimensional function. The problem, however, becomes a real bottle-neck when probe feeding of a CMA is considered, as the traditional IFT used to calculate the excitation in the spatial domain results in a huge IFT time. In this paper, this problem is explicitly treated. The asymptotical behavior of the probe-related spectral Green´s functions (GFs) is rigorously derived, subtracted, and the corresponding reaction integrals are inverse Fourier transformed without the occurrence of any cylindrical functions. This results in a much improved calculation efficiency for this type of feeding, evident for both thin and thick substrates. Numerical results for CMAs with complex-shaped patches are presented, applicable to both smaller and larger bandwidths. Several structures are fabricated and measurements are in good agreement with simulations.