The handset product has been styled in successive years to reach more compact sizes
and there has as a result been a reduction in volume available to house antennas;
therefore size/performance trade-offs have had to become accommodated. Some of the
issues antenna engineers are currently confronted with include; frequency shifting due
to the antenna not being isolated from the handset, far field pattern deformation due to
close proximity effects from the energy absorbing human tissues, distortion caused by
noise from electronic components that share the handheld platform. What is required is
antenna technology, which maintains a high enough performance despite the escalating
restrictions imposed by the demands of the market. Research is performed on a twisted
loop antenna topology that possesses an integral balun as part of its structure. Two
rudimentary designs are utilised in the research, a simple bifilar structure that can be
adapted for GSM, peN, Bluetooth and W-LAN applications, and a quadrifilar helix
structure for use in GPS. Both structures are based on existing industrial dielectricloaded
antenna structures but are modelled as novel air-loaded structures using a
commercially available Method of Moments (MoM) electromagnetic simulator. In this
fashion, the antennas could be generated quickly with low computational requirements.
A parametric study is performed on the bifilar antenna structure to gain an enhanced
understanding of the twisted loop topology. Once this understanding is achieved
proposed modifications to the structure are implemented to improve the performance of
the antenna. The main subject of improvement is the broadening of bandwidth as
normally dielectric-loaded antennas have inherent narrow bandwidth. Any
improvements made on the air-loaded structures could be tested on dielectric structures
in future research. The most successful novel approach attempted to increase the
bandwidth in the twisted loop structure was the insertion of parasitic helices to create a
coupled multi-pole filter response. In conjunction with the work performed on the
bifilar, an air-loaded GPS quadrifilar helix antenna was also modelled. A method for
inducing circular polarisation is proposed and then by the insertion of parasitics into
the quadrifilar helix design a novel dual-band dual-polarised antenna is presented.
Finally measurements are made to demonstrate the advantageous properties the
dielectric-loaded GPS antenna has over conventional GPS antennas.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University.