by Fu Kar Kit. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1998. / Includes bibliographical references (leaves 158-160). / Abstract also in Chinese. / Chapter Chapter 1: --- Introduction --- p.1 / Chapter Chapter 2: --- Background and Theories --- p.3 / Chapter 2.1 --- Background History --- p.3 / Chapter 2.2 --- Finite Difference Time Domain Method --- p.4 / Chapter 2.2.1 --- Basic Formulation --- p.4 / Chapter A ) --- Governing Equations --- p.4 / Chapter B ) --- Discretization of Differential Equations --- p.6 / Chapter C ) --- Numerical Stability --- p.7 / Chapter 2.2.2 --- Absorbing Boundary Condition ( PML - Bandlimited ) --- p.8 / Chapter A ) --- Berenger Perfectly Matched Layer --- p.8 / Chapter B ) --- "Theroy, Two-Dimensional TE Case" --- p.10 / Chapter B-1 ) --- Propagation of a Plane Wave in a PML Medium --- p.11 / Chapter B-2 ) --- Transmission of a Wave through PML-PML Interfaces --- p.15 / Chapter B-3 ) --- PML for the FD-TD technique in 2-D domain --- p.18 / Chapter C ) --- Extension to Three-Dimension Case --- p.22 / Chapter 2.2.3 --- Modeling of Source and Passive Lumped-Circuit --- p.25 / Chapter 2.2.4 --- Obtaining the frequency dependent parameters --- p.27 / Chapter 2.2.5 --- Time Domain Extrapolation --- p.29 / Chapter 2.2.6 --- Near-to-Far-Field Transformation --- p.33 / Chapter A ) --- FD-TD implementation of Near-to-Far-Field Transformation --- p.35 / Chapter B ) --- Numerical Techniques to compute the Antenna Directivity --- p.38 / Chapter 2.3 --- Transmission Line Circuit Theories --- p.40 / Chapter 2.3.1 --- Stripline --- p.43 / Chapter 2.3.2 --- Microstrip Line --- p.46 / Chapter 2.3.3 --- Quadrature 90° Hybrid --- p.50 / Chapter 2.3.4 --- Butler Matrices --- p.50 / Chapter A ) --- Types of hybrids --- p.54 / Chapter B ) --- Number of hybrids --- p.51 / Chapter C ) --- Number of fixed phase shifters --- p.51 / Chapter D ) --- Positions and magnitudes of fixed phase shifters --- p.51 / Chapter E ) --- Values of total phase shift at output ports and produced by input ports --- p.53 / Chapter 2.4 --- Antenna Theories --- p.54 / Chapter 2.4.1 --- Microstrip Patch Antenna --- p.54 / Chapter A ) --- Bandwidth Enhancement --- p.55 / Chapter B ) --- Antenna design methodology --- p.55 / Chapter B-1 ) --- Substrate selection --- p.55 / Chapter B-2 ) --- Rectangular element analysis and design --- p.56 / Chapter 1) --- Electromagnetically coupled patch --- p.57 / Chapter 2) --- Aperture coupled patch --- p.61 / Chapter 2.4.2 --- Array Antenna --- p.67 / Chapter Chapter 3: --- Butler Matrix Analysis and Design --- p.73 / Chapter 3.1 --- Circuit Topology --- p.73 / Chapter 3.1.1 --- Basic Operation of the 4x4 Butler Matrix --- p.74 / Chapter 3.2 --- Design Methodology and Circuit Characteristics --- p.75 / Chapter 3.2.1 --- 3 dB branch-line coupler --- p.76 / Chapter 3.2.2 --- 0 dB branch-line coupler --- p.79 / Chapter 3.2.3 --- 4x4 Butler matrix Beamforming network --- p.82 / Chapter Chapter 4: --- Multibeam Array Analysis and Design --- p.90 / Chapter 4.1 --- Antenna Architecture --- p.90 / Chapter 4.2 --- Antenna Design --- p.91 / Chapter 4.2.1 --- Antenna Choice --- p.91 / Chapter A ) --- Microstrip Dipole --- p.91 / Chapter B ) --- Rectangular Microstrip Patch --- p.91 / Chapter C ) --- Circular Patch --- p.92 / Chapter D ) --- Compact Patch --- p.93 / Chapter E ) --- Annular Resonators --- p.94 / Chapter F ) --- Antenna Choice of the 4x4 Butler Matrix Network --- p.94 / Chapter 4.2.2 --- Choice of Feeding and Matching Technique --- p.95 / Chapter 4.2.3 --- Basic Antenna Parameters and Measurement Technique --- p.95 / Chapter A ) --- Radiation Pattern --- p.95 / Chapter B ) --- Radiation Pattern Lobes --- p.96 / Chapter C ) --- Antenna Gain --- p.97 / Chapter D ) --- Input Impedance --- p.97 / Chapter E ) --- Bandwidth --- p.97 / Chapter 4.2.4 --- FDTD Characterization --- p.98 / Chapter 4.3 --- Multibeam Antenna Design and Optimization --- p.104 / Chapter 4.4 --- Stripline Fed - Multibeam Antenna --- p.107 / Chapter 4.4.1 --- Design Methodology of the Stripline 3 dB Hybrid --- p.109 / Chapter 4.4.2 --- Design Methodology of the Stripline 0 dB Hybrid --- p.111 / Chapter 4.4.3 --- Design Methodology of the Stripline 4x4 Butler Matrix Network --- p.113 / Chapter 4.4.4 --- Design Methodology of the Stripline Aperture Coupled Patch --- p.138 / Chapter 4.4.5 --- Design Methodology of the Stripline Multibeam Antenna --- p.142 / Chapter Chapter 5: --- Design Examples and Application of Multibeam Antenna --- p.150 / Chapter 5.1 --- Wireless Local Loop (WLL) System --- p.150 / Chapter Chapter 6: --- Conclusions and Recommendations for Future Work --- p.156 / Chapter 6.1 --- Conclusions --- p.156 / Chapter 6.2 --- Recommendations for Future Work --- p.157 / Bibliography --- p.158 / Publication List --- p.160

This thesis presents a new approach to the hardware test environment for a twist reflector monopulse antenna system with a radome extending current measurement practice. New research is presented on the optimisation of the design of a twist reflector monopulse antenna system with a radome, significantly improving the design and the design process. A unique extension to current measurement practice, for single channel antennas, is presented to determine the best practice method on phase stable measurements of a multi-channel antenna on a moving positioner. A novel axis transform for a 3 axis positioner system located within an anechoic chamber is derived. It allows for true performance measurement of a twist reflector antenna with a radome. This progresses the field of antenna measurement as, uniquely, this axis transform allows the aberration caused by the antenna radome to be measured and included. Design improvements have been made on polarisation selective grids, the matched thickness of the radome and a new software method that removes the need for a comparator and increases the robustness of the antenna system. Polarisation selective grids, constructed from a set of parallel conductors, have a wide range of uses in antenna systems. This thesis shows that the depth of a copper grid line can be reduced to 15 m and still provide better than -25 dB cross-polar isolation. This is contrary to current understanding at 30 times the skin depth. A new combined approach to radome thickness optimisation is presented that reduces the time taken to calculate the optimal thickness by over 3 orders of magnitude and the computer memory by over 2 orders of magnitude without compromising accuracy. The use of a digital comparator is described and leads to a novel method to compensate for a failed feed element, verifified in both simulation and anechoic chamber measurements.

Breast cancer is one of the most widespread types of cancer in the world. The key factor in treatment is to reliably diagnose the cancer in the early stages. Moreover, currently used clinical diagnostic methods, such as X-ray, ultra-sound and MRI, are limited by cost and reliability issues. These limitations have motivated researchers to develop a more effective, low-cost diagnostic method and involving lower ionization for cancer detection. In this thesis, radar based microwave imaging is proposed as a method for early breast cancer detection. This imaging system has advantages such as low cost, being non- invasive and easy to use, with high image resolution and its thus good potential for early cancer detection. In the first stage, an ultra-wideband Vivaldi antenna and a slot Vivaldi antenna are proposed, simulated and fabricated for breast cancer detection. The designed antennas exhibit an ultra-wideband working frequency. The radiation patterns also achieve the desired directional radiation patterns. The second stage of this study presents a planar breast phantom and a hemisphere breast phantom. These two breast phantoms are simulated and fabricated using CST microwave studio and tissue-mimicking materials respectively. Mono-static radar systems based on a single antenna configuration and an antenna pair configuration are then proposed. These two systems are used to measure the planar breast phantom and hemi- sphere breast phantom, with the scattering signals measured in the frequency and time domains. Based on the measurement results, it is concluded that the reflected energy increases when the antenna moves close to the tumour; otherwise, the reflected energy is reduced when the antenna moves away from the tumour. The received time domain scattering signals are processed first and then used to create microwave images to indicate tumour position. A clutter removal method is proposed to extract the tumour response from the received signals. The microwave images are then created using the tumour response based on the simulation and experimental results. The imaging results indicate that a 5 mm radius tumour can be detected. The tumour burial depth is also studied. A multi bio- layer phantom which contains deep and shallow buried tumours is simulated and measured using the Vivaldi antenna. A spectrum analysis method is proposed to distinguish between different tumour depths. The results indicate that a difference in depth of 15 mm results in a mean change of 0.3 dB in the magnitude of the spectrum. Discrimination between benign and malignant tumours is also considered in this study. The singularity expansion method (SEM) for breast cancer is proposed to discriminate between benign and malignant tumours based on their morphology. Two cancerous breast phantoms are developed in CST. The benign tumour is a 5mm radius sphere and the malignant tumour is a spiny sphere with an average radius of 5mm. The use of the SEM leads to the successful discrimination of these two tumours. This method provides a solution to discriminate between benign and malignant tumours similar size when the resulting images cannot provide sufficient resolution. A preliminary study of brain cancer detection is also concluded. Research in this area has never been implemented. A cancerous brain model is designed and simulated in CST. The antenna pair configuration is then used to measure the cancerous brain, with the scattering signals measured. Microwave images for brain cancer detection are then created based on the measurement results. The tumour is correctly indicated in the resulting images.

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.

This is an investigation of the proposed ‘Square Kilometer Array’ (SKA) for the next generation radio telescope. A parallel plate system with a circular reflector has been investigated for SKA to achieve wideband performance and beam scanning ability, in particular the theoretical analysis of the fields in the parallel plate structure using a combination of Finite Difference Time Domain method and Physical Optics. This study builds on earlier work, explores the possible limits of extension and develops an analysis of the device, which will allow all possible configurations to be simulated. It is anticipated that the final scanning arrangement will consist of at least a double reflector system, possibly with some re-configurability, where the parallel plates will have two 180 degree bends with the output being some form of directly radiating aperture. Results were obtained for a Re-configurable Monopole, where diodes are used as switches to physically vary the length of the antenna element and hence increase the bandwidth of the antenna. Re-configurable reflectors were also investigated and Geometrical Optics was used for shaping a dual-reflector Cassegrain system for beam scanning. All of these methods have produced satisfactory practical and analytical results / Doctor of Philosophy (PhD) Electrical Engineering

<p>In the latest development in the field of telecommunications it has been observed that a lot is expected from the mobile systems. All kinds of communication standards such as Bluetooth, 3G, W-LAN etc. should be present in the same handset. This requires higher data transmission rates and low bit error probability. One of the major problems in achieving this is fading and multi path environment. The other problem is the growing trend of decreasing size of the electronic devices specially handsets. The handsets are getting smaller and thinner. Due to this the antennas in the device come very close to each other which causes high coupling between the antennas resulting in bad diversity gain. Antenna diversity is considered to be one of easier solution to overcome these problems. This thesis presents an implementation of receiver antenna diversity and suggests different optimised networks between the antenna ports for better diversity gain keeping in view the antenna efficiencies. The thesis involves the following steps: simulating the structures, suggesting different networks between the two antenna ports, optimisation and hardware implementation of the networks and finally measurements in reverberation chamber.</p>

<p><strong>This report presents concepts for a planar active electronically scanned antenna(AESA). The goal of the project was to devlop a low-weight, low profile, thin, S-band antenna with wide-scan angle capabilities. In the final concept the service aspects of the T/R-modules was also taken into acount in order to allow easy and fast replacements of these components. The antenna was designed and optimised using the commercial software Ansoft HFSS. A prototype of the antenna was constructed and later measured and verified. The final concept is a 2m×2m antenna with an estimated weight of around 320 kg, around 11 cm thick (where the thickness of the antenna element is 1.76 cm) and has a maximum scan angle range of more than 45 degrees (with <–10dB active reflection) in the frequency band 3–3.5 GHz. </strong></p>

With the development of the wireless communication system, the antenna has been widely used as an important tool in data transmission. However, there are many characteristic parameters for antenna need to be calculated by complex calculation. For example the mutual input impedance of dipole antenna, the Directivity coefficient and the Gain coefficient. Therefore, it is quite practically hard to implement by hand, especially for student who was studying on it. In order to solve this problem, this thesis has establishes the calculation procedure for the complex parameters of antenna by using MATLAB software.

Radio Frequency Identification (RFID) is a short range radio technology for communication between two objects namely, a reader and a tag. Design of an RFID tag with the best range is always the motive of an RFID designer. In this thesis two RFID tags were simulated, designed and manufactured. The first one is a semi-passive RFID tag, which also serves as a discrete prototype tag for the research group to master RFID tag designs. The user can program and further extend the use of this tag according to the requirements. This RFID tag is provided with JTAG interface to program and debug. The read range of this prototype tag is found to be 1m with reader EIRP of 30dBm. The second design is a passive tag which can be commercialized. It achieves a competitive read range of 2.9m for reader EIRP of 21dBm. The read range when measured in a practical implementation inside a building corridor was 15m.

In this work we investigated a new class of subwavelength focusing device, termed the holographic metallic screen. We first proposed a generalized procedure which takes a holographic record of a subwavelength electromagnetic field distribution. Subsequently we synthesized this record using two types of holographic metallic screen – the slot antenna hologram (SAH) and the resonant slot antenna hologram (RSAH). We designed both holograms and evaluated their performances through full-wave simulations, and experimentally demonstrated subwavelength focusing for the RSAH. Simulations and experiments illustrated various attractive properties of the subwavelength focusing RSAH, which included (a) a tighter focal width than a single subwavelength aperture; (b) a focal field amplitude surpassing the incident field amplitude; and (c) a simple design scalable to a wide range of frequencies from microwave to optical. These properties should serve to motivate further development on the holographic metallic screen towards potential applications such as sensing, imaging and lithography.