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This paper deals with the design of matching and decoupling network for a 4-port MIMO antenna system operating in the TV white spaces from 470 MHz to 790 MHz. After stating the limitations on the classical design based on hybrids, we consider a new approach in order to optimize the MIMO antenna performance, in terms of bandwidth, by taking advantage of some degrees of freedom in the matching and decoupling network. The maximum attainable bandwidth will be reported as a function of the network elements.

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Cognitive radio constitutes a very promising solution to improve spectrum usage of communication systems. However, being equipped with MIMO antennas, the design of CR devices poses tremendous challenges. In this paper, antennas requirements as well as the limitations imposed on the system performance are reviewed. Well decoupled and reconfigurable antennas guarantee the flexibility needed during spectrum scanning and data transmission. Nevertheless to achieve the desired performance, many challenges have to be overcome. The different aspects are illustrated by an example of a 4-port MIMO antenna in the frequency range [470, 790] MHz, or the so-called TV white spaces.