engleski

Mutual coupling effects in wideband microstrip antenna arrays

The paper presents theoretical and experimental investigations of mutual coupling between stacked microstrip patch antennas. The numerical modeling of mutual coupling between stacked patch antennas is developed by solving the electric field integral equation (EFIE) in spectral domain using two-dimensional Fourier transform. The required Green's functions in spectral domain were calculated using G1DMULT algorithm [1]. Method of moments (MoM) is applied by expanding the patch currents into a linear combination of sinusoidal entire domain basis functions. For distant antenna elements integrands in MoM matrix are highly oscillating, so the special integration algorithm that applies integration in imaginary directions is developed. Thus the exponential decay instead of oscillations is obtained. The developed software calculates the mutual coupling, radiation pattern and input impedance of arbitrarly polarized stacked patch arrays with arbitrary number of rectangular parasitic patches and arbitrary number of different dielectric layers. The application of the software is demonstrated on the antenna presented in figure 1. Its design consists of driven patch printed on a substrate and parasitic patch printed at the bottom side of a dielectric support that can simultaniously act as a protecting radome. The driven and parasitic patch were center aligned. The antenna is matched to 50 W with standing wave ratio (SWR) of 2 within 3.25-3.99 GHz, i. e. the relative bandwidth is about 20%. The experimental setup for mutual coupling measurements was designed to enable simple change of array configuration, i. e. the relative position of patches can be easily changed. Extensive measurements of mutual coupling between two described identical stacked patch antennas were carried out, at ten distances ranging from 4 cm to 22 cm in both E and H plane, within whole operating bandwidth. These experiments were compared with calculations and are found to be in a good agreement. In order to demonstrate significant influence of neighbouring elements in an array on each array element, a setup presented in figure 2 is constructed and measured. It consisted of one active antenna element and one loaded with its matching impedance. Both antennas are identical as described in figure 1. The comparison between element gain pattern and the one in a presence of neighbouring element is shown in Figure 3 at frequency of 3.6 GHz. The signifciant difference in the patterns shows importance of analysis when applying stacked microstrip arrays.

Microstrip Antennas; Mutal Coupling

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