Abstract
This thesis reports the results of the investigation on the practical implementation of the intelligent Quadrifilar Helix Antenna (IQHA). The research work has covered many aspects on practical issues for utilising the IQHA at the mobile terminal. The investigations were carried out through simulations and measurements, with main emphasis on the measurement results such that mobile phone manufacturers can utilise and progress directly to product development. The research work is divided into three parts, namely, the QHA structure, the intelligent algorithm and the development and performance evaluation of the IQHA demonstrator. One of the challenges was to reduce the physical size of the conventional Quadrifilar Helix Antenna (QHA) structure, such that it is small enough to be implemented onto a mobile terminal device. The QHA structure also needs to be able to operate in more than one frequency band. The QHA structure was successfully reduced by more than 50% using the meander line technique with slight reduction in efficiency and tremendous increase in operating bandwidth. The spur-line band-stop filter technique is used to create dual resonance for the reduced size QHA structure. These two techniques have been patented and can both be applied independently. The intelligent algorithm for the IQHA is studied through simulations. An adaptive combining algorithm based on Least Means Squares (LMS) is proposed to perform real-time diversity combining and is implemented into the micro-controller of the IQHA demonstrator. It was observed through measurements in the downlink that the IQHA is able to perform diversity combining and cancellation of deep fades in realtime. In the uplink, the real time demonstrator uses the micro-controller to feed the appropriate weights through the digital phase shifters on the individual branches of the IQHA system to perform beam steering. The approach relies on producing a variable radiation pattern by adjusting the phase relationship between the individual elements of the IQHA. Beam steering gains relative to the standard QHA configuration were observed using the optimised weighting configurations.