Along with the current trend of wireless technology innovation, wideband, compact size,
low-profile, lightweight and multiple functional antenna and array designs are becoming more
attractive in many applications. Conventional wireless systems utilise omni-directional or
sectored antenna systems. The disadvantage of such antenna systems is that the
electromagnetic energy, required by a particular user located in a certain direction, is radiated
unnecessarily in every direction within the entire cell, hence causing interference to other
users in the system. In order to limit this source of interference and direct the energy to the
desired user, smart antenna systems have been investigated and developed. This thesis
presents the design, simulation, fabrication and full implementation of a novel smart antenna
system for future mobile applications.
The design and characterisation of a novel antenna structure and four-element liner array
geometry for smart antenna systems are proposed in the first stage of this study. Firstly, a
miniaturised microstrip-fed planar monopole antenna with Archimedean spiral slots to cover
WiFi/Bluetooth and LTE mobile applications has been demonstrated. The fundamental
structure of the proposed antenna element is a circular patch, which operates in high
frequency range, for the purpose of miniaturising the circuit dimension. In order to achieve a
multi-band performance, Archimedean spiral slots, acting as resonance paths, have been
etched on the circular patch antenna. Different shapes of Archimedean spiral slots have been
investigated and compared. The miniaturised and optimised antenna achieves a bandwidth of
2.2GHz to 2.9GHz covering WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile standards.
Then a four-element linear antenna array geometry utilising the planar monopole elements
with Archimedean spiral slots has been described. All the relevant parameters have been
studied and evaluated. Different phase shifts are excited for the array elements, and the main
beam scanning range has been simulated and analysed.
The second stage of the study presents several feeding network structures, which control
the amplitude and phase excitations of the smart antenna elements. Research begins with the
basic Wilkinson power divider configuration. Then this thesis presents a compact feeding
network for circular antenna array, reconfigurable feeding networks for tuning the operating
frequency and polarisations, a feeding network on high resistivity silicon (HRS), and an ultrawide-band
(UWB) feeding network covering from 0.5GHz to 10GHz. The UWB feeding
network is used to establish the smart antenna array system.
Different topologies of phase shifters are discussed in the third stage, including ferrite
phase shifters and planar phase shifters using switched delay line and loaded transmission line
technologies. Diodes, FETs, MMIC and MEMS are integrated into different configurations.
Based on the comparison, a low loss and high accurate Hittite MMIC analogue phase shifter
has been selected and fully evaluated for this implementation. For the purpose of impedance
matching and field matching, compact and ultra wideband CPW-to-Microstrip transitions are
utilised between the phase shifters, feeding network and antenna elements. Finally, the fully
integrated smart antenna array achieves a 10dB reflection coefficient from 2.25GHz to
2.8GHz, which covers WiFi/Bluetooth (2.45GHz) and LTE (2.6GHz) mobile applications. By
appropriately controlling the voltage on the phase shifters, the main beam of the antenna array
is steered ±50° and ±52°, for 2.45GHz and 2.6GHz, respectively. Furthermore, the smart
antenna array demonstrates a gain of 8.5dBi with 40° 3dB bandwidth in broadside direction,
and has more than 10dB side lobe level suppression across the scan.
The final stage of the study investigates hardware and software automatic control systems
for the smart antenna array. Two microcontrollers PIC18F4550 and LPC1768 are utilised to
build the control PCBs. Using the graphical user interfaces provided in this thesis, it is able to
configure the beam steering of the smart antenna array, which allows the user to analyse and
optimise the signal strength of the received WiFi signals around the mobile device.
The design strategies proposed in this thesis contribute to the realisation of adaptable and
autonomous smart phone systems