Three long-range 2 GHz radio paths have been established in the British Channel Islands in order to investigate the characteristics of long-range propagation of UHF radio waves over the sea as part of a project supported by Ofcom, UK. The relationship between specific over-sea propagation mechanisms (such as evaporation ducting and super-refraction) in the lower troposphere and signal strength distribution patterns has been examined, modelled and correlated with meteorological parameters. A number of radio meteorological statistics specifically related to evaporation duct propagation in a temperate region such as the English Channel has been presented to confirm the capability of this key propagation mechanism to guide radio waves to distances well beyond the normal radio horizon. Evaporation ducting and diffraction appear to be the dominant propagation mechanisms at most times. Signal strength enhancements have been observed on all three radio paths, primarily in the late afternoon and evening periods, in the spring and summer months. During periods of enhanced propagation, which occur approximately 8% of the time of a 50 km path, the presence of additional higher-level ducting/super-refractive structures has been verified and their influence has been modelled with reasonable success. Additionally, the statistical variation of bulk meteorological parameters in the context of enhanced signal propagation has also been examined. The relatively long-term observations made during this study confirm the fact that the constantly changing weather patterns in the troposphere (e.g. the occurrence of anticyclonic weather) are directly responsible for the occurrence of enhanced signals at certain periods of time. The various issues under investigation are of direct relevance in the planning of radio communication systems operating in the UHF band (e.g. GSM and UMTS) in marine and coastal regions.

The purpose of this project was the study of electrically small material coated antennas. In particular the use of a hybrid dielectric-ferrite material was examined, compared to dielectric alone, and ways it can improve antenna performance. The benefits resulting from the inclusion of ferrite were examined using both analytical and experimental methods. Initially a spherical analytical mathematical model was developed, to examine antenna efficiency, bandwidth and Specific Absorption Rate (SAR) in terms of different mixtures of relative permittivity εr and permeability μr. The theoretical model was then validated through a numerical transmission line matrix (TLM) simulation tool, applied to spherical and rectangular resonator geometries. It was observed that a material with equal values of relative permittivity and permeability in combination with specific positioning of the antenna in relation to the head, can give rise to the definitive small-size, high-efficiency, high-bandwidth, low-SAR antenna.

Dielectric Resonator Antennas (DRAs) propagate electromagnetic waves by setting up resonant modes determined by their physical geometry and excitation feeds. Just as preferential directions of radiation can be designed for conductive antennas; it was thought that far field radiation pattern of DRAs could be manipulated similarly using different dielectrics. Two types of mixed dielectric antennas were investigated i) a variable dielectric discontinuity ii) air and solid dielectric mix.

The performance of ultra wideband (UWB) signals in wireless communication systems depends, primarily, on the knowledge of the propagation channel, interfering signals and the proximity between transmit and receive antennas. This work focuses on the study of the UWB propagation channel and, in particular, on how large scale statistics of the frequency components are affected by the environment. A two-ray UWB model is used to show the effects of magnitude, delay, and phase variations on the power spectrum density of UWB signals. Also, spatial uncertainty in measurements is analysed in two ways. Firstly, by deriving mathematical expressions for the area and volume of uncertainty and, secondly, by measuring the effects of displacements between transmit and receive antennas, when the distance changes are smaller than the spatial resolution of the measuring equipment.

The thesis introduces the concept of the Photonic Active Integrated Antenna (PhAIA) where optical devices are integrated with planar antennas to produce very compact, low cost modules. PhAIAs are applied to the Radio-over-Fibre application area which is a promising approach to improve the coverage of Wireless Local Area Networks (WLANs). Results show that our systems can operate within a room scale without the use of amplification and at much larger wireless ranges with the use of integrated amplifiers chips. Initially, laboratory based setups are developed which prove the system concept and this is followed by the development of fully portable systems which have under gone field trials using live WiFi access points. Initially unamplified systems are developed to understand the fundamental properties of the radio-over-fibre system and impedance matching of the optical devices directly to the antennas has been implemented- To further improve the impedance matching, lossless matching circuits are implemented, in particular for the photodiode which has a large capacitive part to its input impedance. Following this, a fully modular system was developed using packaged lasers and photodiodes which resulted a fully portable. rugged system suitable for a number of commercial applications. Finally the concept of Power-over-Fibre, where by electrical energy is transferred to a remote location via an optical fibre, is used to power the remote PhAIA module. In this case simultaneous transmission of WLAN data and energy was used for the first time.

The increased demand for mobile broadband communications has led to the development of broadband wireless standards such as UMTS, W-CDMA and HSPA. Even though these technologies have been deployed in most of the developed parts of the world, they have not yet achieved the same market penetration as their predecessors, mainly because of their high cost. Additionally, these technologies are incapable of maintaining reliable high-data rates (>1 Mb/s) at vehicular speeds. Both of the above shortcomings are successfully addressed by the latest wireless technologies (for example, IEEE 802.16e) and those expected to enter the market from 2010, such as LTE, LTE-Advanced and 802.16m. Common practice in modem networks is the incorporation of multiple antenna technologies (MIMO) to improve spectral efficiency and reliability (thus reducing cost) through an improved physical layer.

Theoretical research show that wireless communication systems using multiple-input multiple-output (MIMO) antennas can provide a very high spectral efficiency in rich scattering environments. This thesis investigates issues of antenna selection in MIMO systems with an emphasis on the criteria and algorithms of receive antenna selection in layered spatial multiplexing architectures.

Radio over Fibre (RoF) is being considered for indoor and outdoor distributed antenna systems for the support of IEEE 802.11 wireless networks. The 802.11 Medium Access Control (MAC) protocol, however, has not been designed to account for the optical distribution network. The research work presented in this thesis has focused on the analysis of protocol effects in 802.11 over fibre networks and the application of new features in order to improve the protocol's performance. This study is based on numerical analysis, supported in part by analytical approximations, and experimental measurements.

Radio over Fibre (RoF) Distributed Antenna Systems can be deployed in combination with pre-4G and 4G technologies, proposed by the IEEE 802.16 and 3GPP LTE standards, in order to support the increased demand for capacity and coverage for various outdoor, inbuilding and underground scenarios. However, the Physical and Medium Access Control (MAC) protocols have not been designed to account for the additional propagation delay that the optical distribution network inserts. This thesis presents a detailed theoretical analysis of protocol effects in Time Division Duplex (TOO) IEEE 802.16 and 3GPP LTE RoF networks, supported by mathematical analyses. The round trip delays and the timing boundaries of the wireless technologies under investigation might be affected when the optical propagation delay is not taken into account. The analysis indicates that the default durations of the TransmitIReceive Transition Gap (TTG) and the Guard Period, which allow for the downlink-uplink timing synchronisation between the Base Station (BS)Evolved Node B (eNB) and the users, can accommodate fibre lengths up to 14.4 km, 27 km and 69.7 km for legacy IEEE 802.16, IEEE 802.16m and 3GPP TD-LTE systems, respectively. Also, the initial Ranging (IR) slot and the Physical Random Access Channel duration, used for the estimation of the user's distance from the BS/eNE, can accommodate fibre lengths up to 13.2 km, 93 km and 69 Ian for legacy IEEE 802.16, IEEE 802.16m and 3GPP TD-LTE systems, respectively. Furthennore, the OFDM symbol's CP duration has to be chosen based on the maximum difference in fibre lengths between the Remote Antenna Units that needs to be supported in the RoF network. The maximum fibre length differences allowed by the default CP in legacy IEEE 802.16, IEEE 802.l6m and 3GPP TD-LTE systems are equal to 2.2 km, 2.2 km and 1.15 km, respectively. However, it is shown that the system perfonnance deteriorates when these parameters are adapted in order to accommodate longer optical propagation delays and greater fibre length differences. The required protocol and parameter changes for the alleviation of the limitation imposed on the maximum fibre link length are presented. The proposed solutions concern the IR procedure and the MAC management Medium Access Protocol (MAP) messages' timing relevance. The optical propagation delay is compensated and the downlink-uplink timing synchronization between the as and the users is maintained. Thus, the wireless propagation delay estimation (ranging) is successfully carried out, even when the optical propagation delay is greater than what the IR slot and/or the TTG duration can accommodate, and the system's performance is improved, without the need of increased overhead.

The research carried out and detailed in this thesis presents several techniques applied to frequency selective surfaces (FSS) with an emphasis on propagation control in the built environment. Issues are explored such as interference reduction and frequency reuse, security applications or propagation enhancement by reducing the effects of multi path and the wireless black spots or nulls that it produces. A band-stop active FSS (AFSS) has been designed operating in the WLAN band of 2.45GHz. The structure consists of annular ring. elements with PIN diodes as the semiconductor switches. The surface is two-state, being reflective with the diodes forward biased and transparent when zero biased. The design is single sided and includes an efficient distribution method of the de biasing by employing RP chokes. A prototype surface is constructed and its transmission response measured for a range of angles of electromagnetic wave incidence. A dual-band passive band-stop FSS is designed operating in the WLAN bands of 2.45GHz and 5GHz. The annular ring design introduces "traps" to FSS, where a trap is a parallel tuned circuit and behaves as a frequency selective switch, presenting a low or high impedance state depending upon the band of operation. Similarly the technique is applied to an annular slot design where the parallel tuned circuit is replaced with a series tuned circuit. For both designs prototype surfaces were constructed and evaluated for dual-band operation, with transmission response measurements carried out over a range of angles of electromagnetic wave incidence. A new AFSS structure known as the "phase plate" is introduced. A phase plate is a AFSS backed by a solid rear reflective surface spaced some distance away and modulated at a rate to modify wireless coverage nulls in enclosed environments, improving signal distribution in that space. A 2.45GHz experimental phase plate is constructed and evaluated, both by static phase shift measurements and observing its operation in a multi path environment with the successful filling of a wireless null. To demonstrate its performance a just discernible signal in the noise floor of the measurement receiver is brought some 20dB above it.