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The method of moments (MOM) analysis of probe-fed rectangular microstrip patches requires the inclusion of a probe-to-patch attachment mode-expansion function when the substrate thickness d [is greater than or equal to] O.02??, where ?? is the free-space wavelength. The results for the input impedance showed increased divergence with measurements when the attachment mode was omitted from the full-wave analysis. The attachment mode can be expressed as an infinite eigenfunction series that increases the fill time of the impedance matrix in an MoM analysis. In an earlier investigation, the infinite eigenfunction series was reduced to a residue series that required one or two terms compared to about 55 terms for the eigenfunction series. In this paper, the convergence properties of the eigenfunction and residue series are investigated in view of rigorous MoM analysis. The relative errors resulting from replacing the eigenfunction by the residue series for the attachment mode, are compared by numerically evaluating a class of two-dimensional (2-D) spatial integrals shown to be closely related to the elements of an MoM impedance matrix. Additionally, the computation times for the evaluation of these integrals for the two forms of the attachment mode-expansion function are also included. Based on the superior convergence properties of the residue series for the attachment mode-expansion function, it is mathematically justified that this form can readily be used for analytic reduction of the spatial, reaction integrals from four to 2-D forms. This feature allows further reduction of the fill time of the MoM impedance matrix, suggesting the possibility of developing an efficient space-domain MoM technique for modeling of wide-band microstrip antennas. Index Terms--Method of moments, microstrip antennas.

The Theory of Characteristic Modes (TCM) is proposed as a systematic approach to antenna design to achieve the goal of finding the antenna structure with optimum broadband behavior. This theory provides a physical insight to the radiating nature of microstrip patch antennas and reduces the design optimization time. In this work, the resonant behavior of the highly radiating structure of the single U-slot rectangular patch on a single-layer εr = 4.4 substrate is analyzed using TCM. Modal analysis of this single-layer structure with different single feed excitations concludes that VSWR ≤ 2 impedance bandwidth in the order of 96% can be achieved with a single T-probe feed. Experimental results, included here, show VSWR ≤ 2 impedance bandwidth in the order of 71%. [ABSTRACT FROM AUTHOR]

Ultra-wideband (UWB) phased arrays are increasingly used in radar and medical applications. Mutual coupling reduction between the phased array elements is critical in achieving good scan bandwidth. This study investigates the mutual coupling of a UWB U-slot microstrip patch 2-element array to find the patch orientation and U-slot topology with the least mutual coupling. Electromagnetic (EM) simulation results indicate that, for εr = 2.2 substrate, diamond patch orientation with opposite U-slot topology has the least coupling between the array elements. Results also indicate that the current density distribution on the microstrip patch has an effect on mutual coupling between the array elements. Results show good agreement between MoM and FEM EM solvers. [ABSTRACT FROM AUTHOR]

The need for low-profile and ultra-wideband (UWB) antennas is rising in wireless communication and medical applications. The method of dimensional invariance, which is a class of U-slot patch design methods, is utilized to realize an initial, low-profile, wideband design. Building on this initial wideband design, this study establishes ideal L-probe feed dimensions through extensive parametric study on εr = 2.2 and 4.5 substrates to propose empirical guidelines for the design of L-probe feeds which yield first-pass optimum impedance bandwidth. The established ideal L-probe dimensions, after further extrapolation, are used successfully on other substrates, εr = 3.27, 6.0 and 9.2, for the design of first-pass L-probe feeds which yield impedance bandwidth over 55%, 60%, and 53%, respectively. The results of three commercially available EM simulation solvers show good agreement [ABSTRACT FROM AUTHOR]