1 research outputs found
Adaptive array antenna design for wireless communication systems
Adaptive array antennas use has been limited to non-commercial applications due to their
high cost and hardware complexity. The implementation cost of adaptive array antennas can
be kept to a minimum by using cost effective antennas, reducing the number of elements in
the array and implementing efficient beamforming techniques. This thesis presents
techniques for the design of adaptive array antennas which will enable their cost effective
implementation in wireless communication systems. The techniques are investigated from
three perspectives, namely, reconfigurable antenna design, wide scan array design and
single-port beamforming technique.
A novel single-feed polarisation reconfigurable antenna design is proposed in the first stage
of this study. Different polarisation states, namely, linear polarisation (LP), left-hand circular
polarisation (LHCP) and right-hand circular polarisation (RHCP), are achieved by perturbing
the shape of the main radiating structure of the antenna. The proposed antenna exhibits good
axial ratio (< 3 dB at 2.4 GHz) and has high radiation efficiency in both polarisation modes
(91.5 % - LHCP and 86.9 % - RHCP). With a compact single feeding structure, the antenna
is suitable for implementation in wireless communication devices.
The second stage of the study presents the design procedure of wide scan adaptive array
antennas with reduced number of elements. Adaptive array antennas with limited number of
elements have limited scanning range, reduced angular scanning resolution and high sidelobe
levels. To date, design synthesis of adaptive array antennas has been targeted on arrays with
a large number of elements. This thesis presents a comprehensive analysis of adaptive array
antennas with less than 10 elements. Different array configurations are analysed and various
array design parameters such as number of elements, separation between elements and
orientation of the elements are analysed in terms of their 3 dB scan range. The proposed
array, the 3-faceted array, achieves a scanning range up to ±70°, which is higher than ±56°
obtained from the Uniform Linear Array. The faceted arrays are then evaluated in the context
of adaptive beamforming properties. It was shown that the 3-faceted array is suitable for
adaptive array applications in wireless communication systems as it achieves the highest
directivity compared to other faceted structures. The 3-faceted array is then synthesised for
low sidelobe level. Phase correction together with amplitude tapering technique is applied to
the 3-faceted array. The use of conventional and tuneable windowing techniques on the 3-
faceted array is also analysed. The final stage of the study investigates beamforming techniques for the adaptive array
antenna. In the first part, beamforming algorithms using different performance criteria,
which include maximum signal-to noise-ratio (SINR), minimum (mean-square Error) MSE
and power minimisation, are evaluated. In the second part, single-port beamforming
techniques are explored. In previous single-port beamforming methods, the spatial
information of the signals is not fully recovered and this limits the use of conventional
adaptive beamforming algorithms. In this thesis, a novel signal estimation technique using
pseudo-inverse function for single-port beamforming is proposed.
The proposed polarisation reconfigurable antenna, the 3-faceted array antenna and the
single-port beamforming technique achieve the required performance, which suggests the
potential of adaptive array antennas to be deployed commercially, especially in wireless
communication industry