Summary
International Symposium on Antennas and Propagation
2009
Session Number:1C2
Session:
Number:1C2-6
Matched Antenna Design based on Spherical Mode Expansion
Masashi Iwabuchi, Maki Arai, Kei Sakaguchi, Kiyomichi Araki,
pp.137-140
Publication Date:2009/10/21
Online ISSN:2188-5079
Summary:
In Multiple-Input Multiple-Output (MIMO) communications, receivers and transmitters have multiple antennas. Smaller size of array antenna is required in the MIMO system, while efficiency of MIMO transmission should be maintained. Generally, mutual coupling between the antenna elements increases if the size of array antenna decreases, and it results in inefficiency of the MIMO system. In a conventional approach to make smaller array antenna, a decoupling element to remove the effect of mutual coupling and a polarization antenna have been used. However, these approaches have been considered independently, and moreover an optimal array antenna structure to achieve best performance of MIMO communication has not been found yet. In this paper, we will propose a new array antenna design scheme to achieve best performance under a given propagation environment. For that purpose, Spherical Mode Expansion (SME) of antenna directivity is introduced. In SME, an electrical and magnetic field is expanded into orthogonal spherical wave functions with their weights of Spherical Mode Coefficients (SMCs)[1][2]. In a fixed size or volume of array antenna, the number of effective SMCs to be radiated from the volume is limited. Therefore, optimal antenna directivity in a given volume of array antenna can be achieved by designing limited SMCs. If the SMCs are given, current distribution on the antenna surface can be determined. It is completely a new approach of applying SME to antenna design compared with conventional schemes of [3] and [4] where SME is used for analysis of antenna directivity. The system model for antenna design using SME is shown in Fig.1. In this model, a propagation environment such as angular profile, and volume of target, in which the array antenna is designed, are given. The optimal SMCs in this environment can be estimated by applying conjugate matching theory in the angular domain. It is called as matched antenna in this paper. In the following, we will explain about the details of antenna design based on SME for Single-Input Single-Output (SISO) system and Single-Input Multiple-Output (SIMO) system. Antenna design for MIMO system is our future work.