Mutual coupling analyses between conformal microstrip antennas using the full-wave equivalent circuit and the method of moments

Abstract

Mutual coupling is an important parameter in the assessment of the interoperability between two systems located electrically close to each other and operating simultaneously. One example of such a case could be GPS (navigation) and INMARSAT BGAN (communications) installed on a mobile platform (e.g. aircraft). Mutual coupling plays also an important role in the design of arrays of antennas, since it modifies the input impedance of every array element. Among other antennas, conformal microstrip arrays are very suitable for many applications in aeronautics. The cylindrical cross-section, for instance, is quite often found in aircraft and space vehicles, and is, therefore, of great importance. In order to compute accurately mutual coupling between microstrip antennas conformed on cylindrical surfaces, DLR has developed a code called MCAT, which is based on the method of moments (MoM) and uses sub-domain basis functions for the calculation of the current densities on the metallizations. In this approach, the dyadic Green’s functions in cylindrical coordinates and in the spectral domain are needed. These are calculated using a full-wave equivalent circuit (FWEC) under the consideration that the structure is infinite in the axial direction. In this contribution, mutual coupling has been computed between two z-polarized antennas as a function of their separation. Three different configurations have been investigated. For the E-plane coupling, the antennas are moved along the cylinder axis (no azimuthal separation). In the H-plane configuration, the antennas are disposed along the circumference of the cylinder (no axial separation). In the third case, a constant axial displacement is kept, whereas the azimuthal distance is varied. In order to validate the results calculated with MCAT, computations of mutual coupling as a function of the separation between the two patches have been performed with commercial software for the three configurations. Additionally, experiments have been carried out for the third case. The results obtained with MCAT agreed well with the measurements and with the data provided by the other software. Therefore, this code can be used to obtain good engineering predictions of mutual coupling between cylindrical microstrip antennas. Further details concerning the code, the simulations and the measurements will be discussed at the workshop.