Design of a small antenna for indoor electronic monitoring
The objective of this project is to design an antenna for use in the electronic monitoring of persons convicted of non-violent crimes. If implemented, electronic monitoring will lighten the load on the South African prison system. Electronic monitoring makes use of an electronic tether connected to the person being monitored. This led to specific performance requirements and size constraints being placed on the antenna. The antenna should be physically small while still being able to perform as specified. It is also necessary to test the design with various frequencies, to determine the best possible frequency to use. It was decided to use a Transformer Coupled Loop (TCL) antenna, after various designs were considered. The TCL antenna can be used in various configurations, with some of these configurations being simulated to determine the best antenna structure to use. After various antenna structures were discarded, a specific antenna structure emerged as a possible solution, which was then optimised to deliver the best possible performance. The optimised antenna model was constructed to test the antenna performance. The receiving antenna was a directional Log-Periodic Dipole Antenna (LPDA), connected to a spectrum analyser. Tests were conducted in an open-field environment to minimise the effect of reflections. The azimuth- and elevation radiation patterns for the antenna could be compared to the simulated results. The same tests were performed with the antenna attached to a saline solution bag, simulating the effects of the human body on the antenna performance. The radiation patterns obtained from the measured results proved to be similar to the simulated results for both frequencies tested. When making use of the human analogue, the radiation pattern tended to be more omnidirectional in both the azimuthand elevation planes. These results are ideal, since omnidirectional communication by the tethering device is required by a security application. The primary objective was achieved, together with the secondary objectives of comparing different frequencies.
- Engineering