Abstract
This thesis examines existing and novel antennas suitable for application to user terminals for mobile satellite systems. The requirements for such antennas are reviewed, and existing configurations are critically compared. One of the challenges in designing these antennas is computational techniques suitable for analysing their performance in the presence of the human body, so various techniques are explained and compared. Parallel computing techniques are applied to the finite difference time domain (FDTD) algorithm, and are found to yield significant benefits in computation time and memory usage. Several new antenna designs are introduced. These are all based on a patented element configuration which is evolved from the crossed-dipole antenna, and known as the ELES (Easy, Low cost, Effective, low SAR) antenna. In its basic form, operating over a ground plane, the ELES produces circular polarisation with a wide bandwidth (around 20%), and is suitable for production in printed form. Its performance is analysed through simulation and through measurement. It is also shown by analysis to have excellent potential for application as a polarisation diversity antenna due to its low envelope correlation coefficient and mean power ratio in a multipath environment. An alternative configuration of the ELES, the ELES array, is proposed and shown to give similar performance to the basic ELES without the need for a ground plane. In this form the ELES is particularly suitable for application to handheld terminals. The interaction of mobile satellite antennas with the human head and hand are studied through numerical experiments using the transmission line method (TLM). The monopole antenna, the quadrifilar helix (QHA) and the ELES are included in the study, which evaluates the perturbation of the free space radiation pattern and the specific absorption rate (SAR) in the head. Several techniques for reducing the peak SAR are examined and found to produce much lower absorption than a monopole radiating the same power.