Faculty of Engineering, Built Environment and Information Technology
School of Engineering
Department of Electrical, Electronic and Computer Engineering
Selected Highlights from Research Findings
A simple circuit that is relatively easy to design and implement in microstrip line was proposed to match and increase the VSWR bandwidth of patch antennas. The matching technique is based on the principle that the imaginary admittance of a patch antenna can be reduced at frequencies close to the resonant frequency by adding a parallel-LC resonator, yielding a larger frequency range with a small reactive input impedance. A phase shift, implemented using a matched transmission line, and quarterwave transformer is used to further increase the input impedance of the patch antenna. The overall result is a matched patch antenna with a VSWR bandwidth close to the optimum that can be achieved. The matching circuit is placed behind the ground plane of the probe-fed patch antenna, and thus no coupling or interference was encountered in the main beam direction of the radiation pattern.
Contact person: Prof J Joubert.
The backscattered field of an Airbus A310 model was measured in a compact range and frequency data were used to investigate the statistical properties and dominant statistical dependency of measured radar data as a function of aspect angle. The results indicate that the decision whether to use higher order statistics or second order statistics in radar imaging algorithms must be done with care. Second order statistics may be used most of the time, but the user must be aware that in certain angle regions higher order statistics must be considered. On the other hand, although higher order statistics has many advantages, it is not advisable to use only higher order statistics if most of the measured radar data indicate second order statistics.
A single-layer capacitive feeding mechanism for rectangular, circular and annular-ring probe-fed microstrip antenna elements on thick substrates has been proposed. Through calculated and measured results that agree very well, it has been shown that these elements behave very similar and that 10 dB return-loss bandwidths in excess of 25% can be obtained. Given that this configuration only requires a single substrate layer proves to be suitable for a wide range of applications that require wideband operation at a low cost.
Contact person: Prof JW Odendaal.
In most-to-all (commercially) available high-frequency RF transceivers (available globally) a passive inductor is deployed. The passive inductor suffers from a low quality factor, as well as takes up a large chip-area. Research is indicating good success of an active (transistor-level) implementation for this purpose and has dramatic improvements on both transceiver size, as well as a much higher quality factor. Several publications are possible from this research aspect in future, and a generic active inductor design software has already been developed.
Contact person: Mr S Sinha.
In a joint project with the CSIR, researchers investigated how telephone services can be used to provide information to underserved areas in South Africa. Users from two communities (one in Gauteng, the other in KwaZulu-Natal) were given the opportunity to use a telephone-based system to register insurance claims, and to obtain general information about the Unemployment Insurance Fund. A number of significant conclusions can already be made. Most importantly, it is crucial to provide services in callers' home language: even when users express proficiency in English, most find it much easier to use systems in their first language. It was also found that services that use speech as input mode (rather than key presses) are more usable for technologically inexperienced users - even when they are relatively numerate. More surprisingly, some widely-used measures of task complexity were found to be inappropriate in these settings. For example, the length of a digit string to be entered by users was much less important than its familiarity to the user e.g. id number or phone number.
Contact person: Prof E Barnard.
|
