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This thesis describes the theoretical and practical implementation of a long-range high-resolution millimetre wave imaging radar system to aid with the navigation and guidance of both airborne and ground-based autonomous vehicles. To achieve true autonomy, a vehicle must be able to sense its environment, comprehensively, over a broad range of scales. Objects in the immediate vicinity of the vehicle must be classified at high resolution to ensure that the vehicle can traverse the terrain. At slightly longer ranges, individual features such as trees and low branches must be resolved to allow for short-range path planning. At long range, general terrain characteristics must be known so that the vehicle can plan around difficult or impassable obstructions. Finally, at the largest scale, the vehicle must be aware of the direction to its objective. In the past, short-range sensors based on radar and laser technology have been capable of producing high-resolution maps in the immediate vicinity of the vehicle extending out to a few hundred metres at most. For path planning, and navigation applications where a vehicle must traverse many kilometres of unstructured terrain, a sensor capable of imaging out to at least 3km is required to permit mid and long-range motion planning. This thesis addresses this need by describing the development a high-resolution interrupted frequency modulated continuous wave (FMICW) radar operating at 94GHz. The contributions of this thesis include a comprehensive analysis of both FMCW and FMICW processes leading to an effective implementation of a radar prototype which is capable of producing high-resolution reflectivity images of the ground at low grazing angles. A number of techniques are described that use these images and some a priori knowledge of the area, for both feature and image based navigation. It is shown that sub-pixel registration accuracies can be achieved to achieve navigation accuracies from a single image that are superior to those available from GPS. For a ground vehicle to traverse unknown terrain effectively, it must select an appropriate path from as long a range as possible. This thesis describes a technique to use the reflectivity maps generated by the radar to plan a path up to 3km long over rough terrain. It makes the assumption that any change in the reflectivity characteristics of the terrain being traversed should be avoided if possible, and so, uses a modified form of the gradient-descent algorithm to plan a path to achieve this. The millimetre wave radar described here will improve the performance of autonomous vehicles by extending the range of their high-resolution sensing capability by an order of magnitude to 3km. This will in turn enable significantly enhanced capability and wider future application for these systems.

This thesis describes the theoretical and practical implementation of a long-range high-resolution millimetre wave imaging radar system to aid with the navigation and guidance of both airborne and ground-based autonomous vehicles. To achieve true autonomy, a vehicle must be able to sense its environment, comprehensively, over a broad range of scales. Objects in the immediate vicinity of the vehicle must be classified at high resolution to ensure that the vehicle can traverse the terrain. At slightly longer ranges, individual features such as trees and low branches must be resolved to allow for short-range path planning. At long range, general terrain characteristics must be known so that the vehicle can plan around difficult or impassable obstructions. Finally, at the largest scale, the vehicle must be aware of the direction to its objective. In the past, short-range sensors based on radar and laser technology have been capable of producing high-resolution maps in the immediate vicinity of the vehicle extending out to a few hundred metres at most. For path planning, and navigation applications where a vehicle must traverse many kilometres of unstructured terrain, a sensor capable of imaging out to at least 3km is required to permit mid and long-range motion planning. This thesis addresses this need by describing the development a high-resolution interrupted frequency modulated continuous wave (FMICW) radar operating at 94GHz. The contributions of this thesis include a comprehensive analysis of both FMCW and FMICW processes leading to an effective implementation of a radar prototype which is capable of producing high-resolution reflectivity images of the ground at low grazing angles. A number of techniques are described that use these images and some a priori knowledge of the area, for both feature and image based navigation. It is shown that sub-pixel registration accuracies can be achieved to achieve navigation accuracies from a single image that are superior to those available from GPS. For a ground vehicle to traverse unknown terrain effectively, it must select an appropriate path from as long a range as possible. This thesis describes a technique to use the reflectivity maps generated by the radar to plan a path up to 3km long over rough terrain. It makes the assumption that any change in the reflectivity characteristics of the terrain being traversed should be avoided if possible, and so, uses a modified form of the gradient-descent algorithm to plan a path to achieve this. The millimetre wave radar described here will improve the performance of autonomous vehicles by extending the range of their high-resolution sensing capability by an order of magnitude to 3km. This will in turn enable significantly enhanced capability and wider future application for these systems.

Millimetre-wave nonreciprocal devices are vital elements in many modern radar and communication systems. Gyromagnetic behaviour in magnetised ferrite materials has been utilised for decades in the design of nonreciprocal devices. However, the effects of ferrite's limited saturation magnetisation and high loss as the frequency of operation exceeds 40 GHz render such devices inadequate for millimetre-wave applications. On the other hand, solid plasma (such as semiconductors) are known to exhibit gyrotropic behaviour when they are biased with a steady magnetic field. This behaviour (which is referred to as gyroelectric) can extend up to the THz frequency ranges. Hence, magnetised semiconductors can be regarded as suitable candidates for realising millimetre-wave, sub-millimetre-wave and even THz nonreciprocal devices. This thesis focuses on analysing different structures containing gyroelectric materials, and proposing millimetre-wave nonreciprocal devices based on the theoretical findings. Measurements and full wave electromagnetic simulation are used to validate and optimise the proposed designs where possible. Before starting the electromagnetic analysis, the physical properties of a semiconductor plasma are studied, then a permittivity tensor is introduced to include the microscopic features of the magnetised semiconductors into a macroscopic model. Different semiconductor candidates for gyroelectric designs are also discussed and analysed. Firstly, Semiconductor Junction Circulators (SJC's) are analysed using a Green's function approach. The same approach is then used to proposed new designs for broadband millimetre-wave SJC's that require low magnetic bias using Indium Antimonide (InSb) cooled down to 77 K. The possibility of realising planar nonreciprocal devices using a Molecular Beam Epitaxy (MBE) grown Two Dimensional Electron Gas (2-DEG) is also studied. Theoretical and simulation results prove the possibility of using this material to realise millimetre-wave resonators and circulators. Then a novel type of circulator is realised by placing an InSb disk at 77 K in the middle of a three port waveguide junction. The structure is analysed by treating the junction as a resonator with a suspended axially magnetised gyroelectric rod placed in the middle. Electromagnetic analysis, simulations and measurements reveal the existence of counter rotating modes that degenerate or split at certain frequencies under specific magnetic bias conditions. Measuring this circulator reveals an isolation of 18 dB at 38.5 GHz when the InSb disk is biased with a D.C. magnetic flux of 0.55 T. This is the first time such a circulator has been demonstrated theoretically and experimentally. In addition to the three port circulator, a model is developed for a rectangular waveguide loaded with layered dielectric and gyroelectric media. Mathematical analysis reveals the dispersion relations and field distributions for such a structure. High nonreciprocity in both phase and attenuation constants is observed from analysing a rectangular waveguide loaded with a transversely biased InSb slab at 77 K. The expected nonreciprocity is then verified, for the first time, by simulation and measurement of similar structures under the same conditions. More than 35 dB of isolation at f=35.6 GHz was obtained when loading a WR-28 rectangular waveguide with an InSb slab at 77 K, transversely biased with a magnetic flux of 0.8 T. Different effects on the isolation behaviour are also discussed theoretically and experimentally, including the effects of the slab's thickness and length, the magnetic bias and the existence of a dielectric layer above the gyroelectric slab. Theoretical and experimental outcomes of this thesis prove the possibility of using gyroelectric materials to develop a new class of component that meets the demands for millimetre-wave nonreciprocal devices. This will provide a significant improvement to the modern high frequency millimetre-wave systems.

The millimetre-wave (mm-wave) spectrum offers considerable advantages in terms of antenna form factor and spectrum availability. However, use of this region often requires reconfigurable antennas and systems. Initially, a review of the various applications which are taking hold in the lower regions of the mm-wave spectrum (30 to 100 GHz) is undertaken. Specifically, reconfigurable reflectarray technologies are selected for further research, and critical analysis of the reconfiguration techniques for including these in antennas is considered. Silicon as an optically activated semiconductor is chosen as the reconfiguration mechanism due to its low cost and the scope for improvement in this area. A new form of illumination is used, replacing traditional infra-red (IR) lasers with high power IR-LEDs enclosed in a cavity, increasing the efficiency of the silicon illumination. However, to make use of this novel illumination source, and subsequently integrate it into an antenna, the silicon response has to be characterised within Ka-band. This is done through measurements in a waveguide-based characterisation test cell, from which the complex electromagnetic properties of silicon under IR-LED illumination are retrieved with the aid of full-wave simulations. Using the measured conductivity properties of the illuminated silicon, reflectarrays with non-uniform amplitude distributions can be designed. Through variation of illumination intensities of IR-LEDs throughout the array, it is shown through measurements and full-wave simulations that unit cell reflections can be modified while phases are kept relatively constant. This theoretically allows switching between, for example a low side-lobe pattern binomial array, or a narrow beamwidth pattern Chebyshev array. To implement this, a novel multilayer unit-cell is designed, integrating the IR-LED. This is then used in a full reflectarray design which is measured. The key contributions of this work include the novel illumination mechanism and its integration into a reflectarray antenna, and the use of reconfigurable photoconductive materials to provide a mechanism for beam shaping and pattern synthesis at Ka-band.

The aim of this work is to design and realise millimetre-wave low profile on-chip antennas for 60 GHz short-range wireless communication systems. For this application, it is highly desirable that the antenna can be compatible with standard silicon complementary metal oxide semiconductor (Si CMOS) technology for high level integration and mass production a low cost. Firstly, millimetre-wave antennas on normal dielectric substrates and cavities were studied in detail in order to better understand how the antenna parameters could have effects on their performance at millimetre-wave spectrum. On-chip 60 GHz antennas based on Si CMOS technology were then proposed, designed, fabricated and characterised. A millimetre-wave U-shaped slot antenna with wide bandwidth was first investigated, simulated and designed. The simulation results reveal that this antenna can operate at millimetre-wave frequencies with 1 GHz bandwidth at 73.5 GHz and 76.5 GHz, respectively. A 60 GHz folded dipole antenna was also studied and designed. A metal cavity was added on the back of a folded dipole antenna to act as reflector. Simulated results show that a folded dipole antenna with a metal cavity can achieve a radiation efficiency of 97.9% at its resonant frequency. Compared to the gain obtained for the folded dipole antenna without a cavity, the antenna gain with metal cavity can be enhanced by 3.58 dB. The main challenges of making high gain and high efficiency Si CMOS on-chip antennas at millimetre-wave spectrum come from two sources; the thin silicon dioxide (SiO2) layer (maximum 10 micrometre) and silicon substrate loss (10 ohmscm). The thin SiO2 layer prevents the use of an elevated ground plane, which could significantly reduce the silicon substrate loss, due to the imaging current effect. Si CMOS substrates normally have resistivity of 10 ohmscm, which is very lossy at millimetre-wave spectrum. To tackle these challenges, metamaterial structures, named artificial magnetic conductor (AMC) structures, were studied and utilised for low profile Si CMOS on-chip antenna design and realisation. AMC forms high impedance on its surface, reflecting the incident wave without phase reversal so as to enhance the radiation efficiency. The AMC folded dipole antenna was designed with a mushroom-shaped structured metamaterial cavity. Simulation results show that the gain increased 1.5 dB in the antenna with AMC structure, while the distance to the metamaterial surface was reduced by 90% compared to that of the pure metal cavity. Additionally, two low profile Si CMOS on-chip antennas with novel planar AMC structures were designed, fabricated and characterised. They were manufactured by 0.13 μm Si CMOS technology from Chartered foundry and 0.18 μm Si CMOS technology from TSMC, respectively. The techniques proposed in these two antennas provide valuable alternatives to the existing approaches. The measurement results show that bandwidth of the on-chip antenna with a micro-patterned artificial lattice is approximately 10 GHz. The one with a dog-bone shape and uniplanar compact photonic band gap (UC-PBG) structures managed a 1.6 dB gain and 1 GHz bandwidth enhancement compared to that without AMC structures.

The scope of this work is the development of a 60 GHz flexible transceiver frontend by adopting an economic prototyping approach. Such a platform can validate the proposed protocols for the 60 GHz band in a real wireless environment, especially the physical layer security concept. The development course uses the hybrid architecture with off-the-shelf components and custom-designed RF chain blocks on printed circuit technology. Challenge in this approach is the coarse resolution of the selected manufacturing technology and higher process tolerance. This work extends the state-of-the-art by proposing etching-resilient RF chain blocks on wide bandwidths. It presents the design validation of each block and performance analysis for various manufacturing conditions. The study also reviews and proposes a high-frequency interconnect model for bondwires, vital in a frontend design. Parasitics' compensation of the interconnects at millimeter-wave operation is proposed, compatible with printed circuit technology. The 60 GHz frontend is realized by packaging the designed RF blocks and off-the-shelf components with optimized and characterized high-frequency interconnects. The frontend, equipped with a tailor-made antenna duplexer, is reconfigurable for frequency, power, and modulation scheme. The developed frontend is characterized for local oscillator, transmitter, and receiver operations. The adaptability of the frontend allows it to be used as an agent in a heterogeneous network. Two units of the developed frontends are used in a network for frequency domain channel sounding. The antenna duplexer ensures channel reciprocity in bidirectional sounding campaigns. Matched two-way channel response is achieved in various indoor environments, which endorses the frontend for channel reciprocity key generation. Finally, the frontend units are successfully deployed in a physical layer security demonstrator.:Abstract Chapter1: Introduction Chapter 2: Fundamentals and state-of-the-art Chapter 3: The design Chapter 4: Integration and characterization Chapter 5: Application example: Channel sounder Chapter 6: Summary and future work Appendices Bibliography

Multiple-input multiple-output (MIMO) systems are a mature technology that has been incorporated into current wireless broadband standards to improve the channel capacity and link reliability. Nevertheless, due to the continuous increasing demand for wireless data traffic new strategies are to be adopted. Very large MIMO antenna arrays represents a paradigm shift in terms of theory and implementation, where the use of tens or hundreds of antennas provides significant improvements in throughput and radiated energy efficiency compared to single antennas setups. Since design constraints limit the number of usable antennas, virtual systems can be seen as a promising technique due to their ability to mimic and exploit the gains of multi-antenna systems by means of wireless cooperation. Considering these arguments, in this work, energy efficient coding and network design for large virtual MIMO systems are presented. Firstly, a cooperative virtual MIMO (V-MIMO) system that uses a large multi-antenna transmitter and implements compress-and-forward (CF) relay cooperation is investigated. Since constructing a reliable codebook is the most computationally complex task performed by the relay nodes in CF cooperation, reduced complexity quantisation techniques are introduced. The analysis is focused on the block error probability (BLER) and the computational complexity for the uniform scalar quantiser (U-SQ) and the Lloyd-Max algorithm (LM-SQ). Numerical results show that the LM-SQ is simpler to design and can achieve a BLER performance comparable to the optimal vector quantiser. Furthermore, due to its low complexity, U-SQ could be consider particularly suitable for very large wireless systems. Even though very large MIMO systems enhance the spectral efficiency of wireless networks, this comes at the expense of linearly increasing the power consumption due to the use of multiple radio frequency chains to support the antennas. Thus, the energy efficiency and throughput of the cooperative V-MIMO system are analysed and the impact of the imperfect channel state information (CSI) on the system's performance is studied. Finally, a power allocation algorithm is implemented to reduce the total power consumption. Simulation results show that wireless cooperation between users is more energy efficient than using a high modulation order transmission and that the larger the number of transmit antennas the lower the impact of the imperfect CSI on the system's performance. Finally, the application of cooperative systems is extended to wireless self-backhauling heterogeneous networks, where the decode-and-forward (DF) protocol is employed to provide a cost-effective and reliable backhaul. The associated trade-offs for a heterogeneous network with inhomogeneous user distributions are investigated through the use of sleeping strategies. Three different policies for switching-off base stations are considered: random, load-based and greedy algorithms. The probability of coverage for the random and load-based sleeping policies is derived. Moreover, an energy efficient base station deployment and operation approach is presented. Numerical results show that the average number of base stations required to support the traffic load at peak-time can be reduced by using the greedy algorithm for base station deployment and that highly clustered networks exhibit a smaller average serving distance and thus, a better probability of coverage.

This thesis presents solutions and studies related to the design of reconfigurable and wideband receiver circuits for system-on-chip (SoC) radiometer front-ends within the millimetre-wave (mm-wave) range. Whereas many of today’s mm-wave front-ends are bulky and costly due to having discrete RF components, single-chip receiver modules could potentially result in a wider use for emerging applications such as wireless communication, short range radar and passive imaging security sensors if realised with adequate performances and at a lower cost. Three main topics are considered in this thesis, monolithic integration of low-loss RF-MEMS (Dicke) switch networks and switched LNAs in MMIC/RFIC foundry processes, designs of SiGe wideband (IF) amplifier and broadband power detectors up to W-band (75-110 GHz). Low-loss and high isolation GaAs and SiGe RF-MEMS switch networks were designed and characterised for the 30-110 GHz range. A GaAs MEMS Dicke switch network has a measured minimum loss of 1 dB and maximum isolation of 19 dB at 70-96 GHz, respectively, making it a potential candidate in Dicke switched radiometer receivers. Furthermore, single-chip 30 GHz and W-band MEMS Dicke switched LNA designs have been realised for the first time in SiGe BiCMOS and GaAs mHEMT processes, respectively. For a targeted 94 GHz passive imaging application two different receiver topologies have been investigated based on direct-detection and direct-conversion (heterodyne) architectures. An optimised detector design fabricated in a 0.13 μm SiGe process achieves a more wideband input matching than earlier silicon W-band detectors and is competitive with reported III-V W-band detectors in terms of a higher responsivity and similar NEP. A SiGe 2-37 GHz high-gain differential (IF) amplifier design achieves a more wideband matching and an order of magnitude higher linearity than a recent single-ended SiGe LNA. The SiGe IF amplifier was integrated on-chip with a power detector in a 5-35 GHz IF section. Their broadband properties compared with other IF amplifier/detector RFICs, make them suitable for W-band down-conversion receivers with a larger pre-detection bandwidth and improved sensitivity. The experimental results successfully demonstrate the feasibility of the SiGe 5-35 GHz IF section for high performance SoC W-band radiometers using a more wideband heterodyne receiver architecture.

As we move towards the sixth generation (6G) of connectivity, satellites have been identified as an indispensable solution to bridge the digital divide. The satellites offer an extensive coverage footprint and can reach the most remote regions with high throughput, fueled by the large bandwidth available in higher frequency bands. As the low earth orbit (LEO) satellites are closer to the earth and therefore have lower latency, we could use a mega-constellation of LEO satellites to complement the terrestrial networks in 6G. However, the satellite and terrestrial networks may compete for the same spectrum band, thereby being a source of interference for each other. The mmWave bands have attracted the attention of LEO satellite networks and terrestrial mobile operators alike. Specifically, the 28-GHz mmWave band (27.5-29.5 GHz) is licensed to Fixed Satellite Services (FSS) for earth-to-satellite uplink transmissions, while the terrestrial networks will use it for downlink operation. The satellite networks are the primary users of the 28 GHz band, while it is also available for licensing to International Mobile Telecommunication (IMT) networks. In some countries, the 28 GHz band is also used for point-to-multipoint (PMP) wireless backhaul links. Therefore, in this work, we aim to understand the impact of the earth station uplink transmissions on the terrestrial users, viz., the cellular users, and the backhaul points, and suggest methods to facilitate the coexistence of these networks in the 28 GHz band through exclusion zones. The average data rate of the networks is derived through stochastic geometry, which results in expressions that are not closed-form. To optimize the data rates of the coexisting networks jointly, we first approximate the coverage probability expressions as closed-form sigmoid curves. This enables us to use gradient descent methods to determine the optimal radii of the exclusion zones.