Mobile Communications Handset Antenna Design

A broad range of new radio-based services is being introduced particularly in the personal communications area.

This includes second-generation mobile phones using frequencies in the 800/900 MHz band (for example, GSM - Global System for Mobile Communications) and more extensive cellular telephone systems operating in the 1.8GHz band (for example DECT - Digital European Cordless Telecommunications).

Current mobile systems suffer from variation in link losses up to 20dB.

There are two key contributing factors: poor antenna performance in the presence of the user, and multipath, where the signal is reflected many times between the handset and the basestation, this is particularly severe in urban areas.

This report details work carried out to design a handset antenna with re-configurable polarization characteristics, so that, in the presence of fading to one polarization, signal continuity can be maintained by utilization of the orthogonal (right-angled) polarization.

The mobile communication environment is discussed and the environmental factors that influence the performance and reliability of mobile systems are highlighted. Antenna diversity schemes, which allow the antenna to "choose" the path that will provide the best reception are reviewed, illustrating techniques, such as space, frequency, polarization and pattern diversity.

Conventional externally-mounted antenna designs are studied, together with more novel approaches using planar antennas.

Measurements conducted on current handset antennas, including return loss and radiation patterns under "free-space" conditions and with operator present, in both vertical and horizontal polarization, are depicted.

The development of a polarization-diverse antenna is described.

The antenna also offers the advantages of planar compact construction low maintenance and the received signal is less affected by the orientation of the phone than conventional antennas.

The factors taken into account during development are outlined, and the radiation patterns of the measurements conducted on it are depicted.

Useful conclusions are drawn and suggestions for future work are included.

An appendix provides a discussion on the issue of interaction of handsets with the human body.