9. Compact MIMO Antenna Array Design for Wireless Applications

Design of compact handset antennas to exploit two techniques to increase capacity in mobile systems is reported. Firstly, the use of noise-like signals spread over a very wide frequency band, known as ultrawideband; secondly, MIMO (multiple-input multiple-output) transmission. Methods of achieving MIMO through spatial diversity require array antenna elements to be separated by significant fractions of a wavelength, giving a relatively bulky structure: an alternative is to exploit multiple polarisations in the signal pathways. This requires antenna elements responding principally to each of the orthogonal polarisations and these can be closely located, enabling integration into a mobile handset. The designs presented are very compact and amenable to production by modern printing methods.