Novel decoupling networks for small antenna arrays

Abstract

Antenna arrays with multiple ports are widely used in space-time techniques like diversity reception, MIMO technique, adaptive beamforming or nulling, and direction finding. In the case of size-limited platforms, multiport antenna arrays have element spacing significantly smaller than half wavelength. A small element spacing introduces strong mutual coupling between the array elements. The strong mutual coupling effect causes significant system performance degradation. A decoupling network can compensate for the mutual coupling effect to yield decoupled ports and fixed input impedances. In this thesis, a systematic design approach for decoupling networks of circular symmetric arrays is formulated by using a step-by-step decoupling of the characteristic eigenmodes of the array. An alternative approach to achieve port decoupling is also proposed. It involves a modal feeding network which makes use of the orthogonality of the eigenmodes of the array to achieve decoupling. The input ports to the feeding network and array combination can then be matched independently. Design procedures and equations for the decoupling networks and experimental results are presented.