A Dual-Polarized Parasitic Patch Antenna for MIMO Systems Daniele Pinchera #1 , Fulvio Schettino #2 # DAEIMI, Faculty of Engineering, University of Cassino via G.Di Biasio 43, 03043 CASSINO (FR) ITALY 1 pinchera@unicas.it 2 schettino@unicas.it Abstract— A preliminary analysis of a reconfigurable parasitic patch antenna for MIMO applications is presented. The proposed antenna is able to work on two different polarizations, providing a separate control of the antenna pattern of each of the two polarization. A number of numerical results, showing the adaptive capabilities of the antenna, is given. I. INTRODUCTION MIMO systems can provide a great performance improvement with respect to SISO wireless communication systems [1]; this improvement is mainly due to the capability to spatially multiplex the information over multiple space- time channels. Recently, a number of antenna architectures, exploiting reconfigurability features, especially designed for MIMO approach has been presented [2][3]. Such antennas exhibit better performances due to their capability to adapt the radiating characteristics to the particular realization of the electromagnetic environment in which they have to work. In particular, the architecture presented in [3] uses an high number of MEMS switches in order to change the radiating characteristics, f.i. the polarization, of each element of the array; the solution presented in [2], instead, is based on a number of parasitic elements surrounding the active ones, and connected to electronically controllable impedances. The latter solution can provide an interesting performance improvement, but is not as easily embeddable as the former in small size communication systems (like laptops) due to its size. Moreover it is not suitable for exploiting dual- polarization capability. As a matter of fact, it has been shown [4] that polarization diversity in conjunction with spatial multiplexing allows a better symbol error rate. In this work a 2-port low-profile adaptive parasitic antenna based on the same idea as in [2], but in planar technology is investigated. In addition, the presented antenna provides two radiative modes with orthogonal polarization, the two ports exhibiting a very low cross talking. In section II some details on the proposed architecture will be given, whereas in section III a number of preliminary numerical results will be presented. All the numerical results have been obtained by means of the CST Microwave Studio full-wave electromagnetic simulation software. II. THE ANTENNA ARCHITECTURE In the following the layout of the parasitic patch antenna is given; the substrate thickness is 1.524 mm, and the material used for the simulation was FR4 lossy; the top layer is realized by means of a PEC thin surface 35μm high, whereas for the ground plane a PEC boundary condition has been used. The circuit ports are realized by means of discrete ports, thus simulating the feeding of the patch from a coaxial line. As stated in the introduction, the antenna we are interested in should radiate with a different polarization with each of its two ports. This can be done by means of a properly fed cross patch antenna [5]. This solution has the advantage of being more compact, and it is thus the optimal candidate for becoming the core our parasitic antenna. It is interesting to underline that a proper choice of the positions of the feeding points on the cross patch allows to excite currents in orthogonal directions with the two ports, thus having a very low cross-talk among the ports. If we now surround the cross patch with four parasitic square patch antennas, resonating at the same operation frequency of the cross patch, we obtain the architecture depicted in fig. 1. The proper choice of the distance between the cross and the square patches allows us to maximize the coupling between the currents on the cross and the currents on the squares. Figure 1: geometry of the dual-polarized parasitic patch antenna. The feeding ports are shown in red. All the dimensions of the antenna depicted in fig. 1 are summarized in Table I. In figure 2 the behaviour of the currents on the patches is shown when the antenna is fed from port 1 (and having a 50Ω load on port 2); it is interesting to observe that the direction on the current on the square patches A D C B