Planar handset antennas with electronically steerable parameters

The primary objective of developments in wireless communications systems is to increase the density of subscribers simultaneously served by the system. Another major objective is to provide services where high rates of data transmission are needed. This can be achieved by extending the multiple access scheme and by improving channel modulation and coding. There are two major approaches to the multiple access scheme problem-the code division multiple access (CDMA) and the spatial division multiple access (SDMA). Their implementation calls for the use of smart antennas not only at the base station site, but also at the terminals, where antennas of an improved design are recommended. However, the functioning of smart antennas is still far from being well defined, and in this context a variety of concepts have been examined. This paper presents some results of our investigations into terminal antennas with improved properties of their radiation patterns. We focused on two properties-the optimized shape of the radiation pattern and the scanning of the main beam. These properties are needed to suppress interference. Furthermore, owing to the achieved antenna directivity it is feasible to suppress the scattered waves and to decrease intersymbol interference, which is a prerequisite to achieve a high data transmission rate. Unfortunately, each terminal antenna design must comply with the tough miniaturization requirements.