1446 PIERS Proceedings, Beijing, China, March 23–27, 2009 Planar Antenna Array Mutual Coupling Identification: A Direct Method Applied to Quasi-Yagi Elements C. E. Capovilla 1 , A. Tavora A. S. 1 , S. E. Barbin 2,3 , and L. C. Kretly 1 1 Department of Microwaves and Optics, School of Electrical and Computer Engineering University of Campinas, Brazil 2 Department of Telecommunications and Control Engineering, Polytechnic School University of Sao Paulo, Brazil 3 Center for Information Technology Renato Archer, Campinas, Brazil Abstract— Mutual coupling between adjacent elements is a critical issue for the design of antenna arrays. In this way, it is important to know the influence that each type of coupling mechanism represents in the total mutual coupling. With this objective for a quasi-Yagi antenna array, four prototypes with special details were built and tested. Surface waves and free space coupling were analyzed aiming at proposing a better optimization procedure for the structure. Concluding, FDTD simulation results for the currents distribution on the surface of the array are presented. 1. INTRODUCTION Modern wireless communication systems demand antennas with small dimensions, reasonable gain over a wide band, and offering the possibility of multi-band operation. Satisfying all these requirements, the quasi-Yagi antenna is a serious candidate for this kind of application. It was introduced as a class of antennas, which presents better characteristics than many others [1]. These characteristics include both, the compactness of resonant-type antennas and the broadband behavior of a travelling-wave radiator. These attributes strongly suggest the application of quasi-Yagi elements in antenna arrays. A simple quasi-Yagi element operating alone in free space presents a wideband, high efficiency, moderate gain, among other characteristics [2]. Its radiation pattern shows an excellent stability over the entire operational frequency band. These characteristics together denote it as an ideal element for applications in systems for which directional beams and reconfigurable radiation patterns are needed. All these favorable conditions show that quasi-Yagi antennas have great potential for applications on phased arrays, switched systems, and, consequently, for adaptive systems. Using a variety of processing algorithms, usually managed by a DSP, an adaptive antenna array can adjust and update its radiation pattern to enhance the desired signal, eliminate or reduce interference, and collect correlated multipath signal [3]. The radiation pattern can be configured according to the environment in real time, if control algorithms as MUSIC (Multiple Signal Classification) or ESPRIT (Estimation of Signal Parameters via Rotational Invariance Techniques) are used. The adaptive array is also necessary for capacity and range improvement [4], due to the need of finding users in a cell and directing the main beam to it. In this way, the same channel can be used more than a time in the same cell. Polarization diversity can be used to differentiate two very close users in a cell. Space diversity is fundamental to avoid signal fading due to the multipath, caused by reflections of the signal, mainly when the signal bandwidth is small compared to the coherence channel bandwidth. During a planar antenna array design, it become necessary to analyze the mutual coupling effects between adjacent elements [5], thus determining the way each type of coupling influences the total mutual coupling. This work is organized in five sections. Following this brief introduction, Section 2 presents the quasi-Yagi antenna and the assumptions made for building the array under investigation. Section 3 discusses experimental results of the mutual coupling mechanism analysis applied to two adjacent antennas. In Section 4, a FDTD simulation of the currents that are functions of the mutual coupling is presented. Finally, Section 5 presents the conclusions of the proposed analysis.