Design and analysis of a low-profile directive antenna array for multi-element terminals

The authors verify the benefits of directivity for a 4 × 4 multiple-input multiple-output (MIMO) system in a non-line-of-sight indoor propagation environment. A novel prototype with four directive antennas has been designed to have full aggregate azimuth coverage, which is conveniently achieved without the need for electronic or mechanical beam-steering. In this way, it captures similar multipath content to that of an equivalent omnidirectional device as confirmed by the field measurements. This coupled with the inherently larger gain of directive antennas renders the prototype a better choice for multi-antenna receivers. The prototype design makes it possible to use a simple but effective power-based antenna selection algorithm. Importantly, this algorithm achieves close to the theoretical maximum channel capacity when only two radio frequency chains are available at the receiver. For the first time, these results show that in an MIMO indoor environment directive receive antennas are a viable option.