Factors affecting the diversity performance of multimode antennas in directive channel scenarios

The tremendous growth rates for bandwidth requirements in wireless communications seek for using multiple antenna techniques even at the mobile device. Prominent examples of multiple-input multiple-output (MIMO) transmission schemes are defined within the standards of HSDPA for cellular networks based on UMTS and IEEE 802.11n in wireless local area networks. Standardization for wide-area networks based on WiMAX are also expected to enclose MIMO extensions for enhanced data rates. Headroom restrictions on the mobile side require multiple antenna techniques with small antenna frontends thus providing sufficient decorrelation in order to yield a certain diversity gain. For that reason predominantly multimode antenna configurations are heavily researched that provide a certain number of independent polarizations and radiation patterns. Compared to antenna configurations with spatially decorrelated antennas, size requirements of multimode operating devices can be reduced to comparatively small rates.