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This thesis presents a number of design methodologies and a cost-effective measurement methodology of low-cost, low-power consumption smart antennas for applications in wireless and satellite communications. To reduce cost, the Electronically Steerable Parasitic Array Radiator (ESPAR) antennas, which are low-cost solutions compared with traditional smart antennas, are employed. To reduce the antenna size, the methods, in which both the driven element and the parasitic elements can be made small, are developed. Then these small components are used to construct different compact smart antennas for different applications. The contributions to the design methodologies are focused on: (1) compactness (i.e. small size both on antenna height and radius whilst achieving reasonable directionality and beam-forming abilities); (2) high-gain (i.e. low-profile whilst still achieving higher antenna gain by using the novel designed small directors); (3) broad-bandwidth; (4) dual-band; (5) polarisation re- configurability; (7) antenna array (i.e. using Multiple-Input-Multiple-Output (MIMO) technologies to improve channel capacity); (8) adoption of electromagnetic band-gap (EBG) Metarnaterials realizing steerable beams; (9) integration into other antennas such as the Yagi-Uda antenna, circularly-polarised (Cl') antenna, and a reconfigurable reflectarray antenna. Furthermore, the application to Wireless Sensor Network (WSN) communications within a multipath environment is assessed where significant improvement over system throughput is demonstrated against commonly used omni-directional antennas. All the antenna designs are characterised numerically ar1d also, where possible, experimentally. The contributions to the measurement methodology are focused on developing cost-effective measurement approaches for direct smart antenna Signal-to-Interference Ratio (SIR) and radiation pattern characterisation prior to input to a transceiver. Several kinds of low-profile and low-cost ESP AR antennas have been designed, constructed and measured for the first time and specific advances are: Low-profile folded monopole ESPAR Low-profile Yagi-Uda antenna where, for the first time, the height of the Yagi-Uda antenna has been reduced by 50%. Low-profile folded monopole ESP AR with the small director array achieving higher antenna gain where, for the first time, the antenna height of the ESPAR antenna has been reduced from typically 0.25 ~ to 0.1 ~. ii

In this thesis, we have investigated antenna elements that allow broadband operation and are relatively compact, while determining methods by which their geometry may be adapted, or various points in their structure loaded, in order to form reconfigurable antennas that may allow their polarisation or matching characteristics to be electronically altered. Much of the work undertaken has involved evanescent open-ended waveguide antennas, whereby the waveguide is operated below its cutoff frequency. Various novel matching methods have been developed, involving: (i) Using the Imaginary Smith Chart to design a match to the aperture admittance of an open-ended wave guide, and thereby to free space, with the match made reconfigurable through loading of the structure using a varactor diode. (ii) Use of capacitive coupling between an open-ended waveguide antenna's coaxial input feed and capacitive obstacles placed across the aperture of the antenna to obtain a broadband match, with polarisation-agile performance possible through varying the ex citations supplied at the input ports of the antenna. (iii) Application of band-pass filter techniques to design a match to the aperture admittance of an open-ended waveguide, through the use of alternating propagating/evanescent sections or by loading the antenna with capacitive obstacles. Radar cross-section reconfigurability is demonstrated, through a printed obstacle with switch implemented at the aperture of the waveguide. The Vivaldi antenna has also been the subject of investigation in the project, with the most notable result obtained being the design of an antipodal Vivaldi antenna loaded by shorted slotline stubs that have a variable capacitor placed across them; this allows wideband operation but with a tuneable rejection band, which enables rejection of cellular and ISM bands.

The subject of this this has been to produce new antermas suitable for use in Radio-over- Fibre Remote Antenna Units or in Mobile Equi pment which might be used at the other end of the link. Several new antennas have been developed and assessed for their suitable application to RoF systems. The antennas were: (i) a multiband PIFA developed previously in the ROSETTE project and modified here to exhibit an improved match when integrated with a ground plane for ceiling mounting. (ii) A cost effective microstrip array directive antenna for street illumination in the Manhattan Scenario. Beam coverage was controlled by electronic shaping and mechanical tilting. (iii) A new compact PIFA design for use in mobile equipment or sectorized base stations where a slotted structure is used to achieve a sharp edge defined operating bandwidth which allows the antenna to act as a filter, thus reducing component count and insertion loss in the transceiver front end. The antenna has been integrated with a larger handset sized ground plane and its insensitivity to this mounting has been demonstrated. (iv) the antenna in (iii) has been implemented in a 3 sector cluster and interference between sector beams by pattern overlap has been characterized. (v) A new compact PIFA working in the 3-5GHz sub-bands of the FCC UWB band has been described and demonstrated to offer useful performance and exhi bit a useful band pass fil tering characteristic reducing the need for a frontend filter in UW8 systems. (vi) A size reduced PIFA has been presented and studied where the rear ground plane was replaced by a strip element FSS tuned to 450Hz. This was demonstrated to improve performance at that band and the antenna was shown to offer a gain that compared well to a standard PlFA between I and 100Hz. The work described has been undertaken over 3 EU funded projects and the thesis begins with a brief overview of the relevant parts of those projects, particularly how antenna match is of importance at the Remote Antenna Unit of a Radio-over-Fibre system as poor input isolation and reflection can cause ringing in the bidirectional amplifiers associated with the duplex transmission. The new antennas developed for application in mobile equipment are shown to be compact (in relation to electrical size) and are considered in terms of their input bandwidth and efficiency.

The proliferation of mobile communications technology increases the demands for faster and more robust services, in addition to the ever decreasing sizes of antennas. These demands can be satisfied using circularly polarized (CP) dielectric resonator antennas (DRAs) exhibiting wide operational bandwidth capability. By utilizing such antennas, the probability of linking the transmitted and received signals is higher, and the system is more reliable since the CP wave is transmitted in all planes and less susceptible to unwanted reflections and absorptions. As CP system is insensitive to the transmitter and receiver orientation, the time consuming practice of continuously aligning the antennas can be avoided. Furthermore, the antennas profile can be reduced simply by using dielectric material with higher permittivity. The thesis focuses on the design and analysis of singly-fed regular-shaped DRAs with a wideband circular polarization. Two new single-point excitation schemes that can be easily used to excite an arbitrarily shaped DRA are introduced, where a square spiral and a rectangular open half-loop are used for DRA excitation. These proposed feeding methods are based on employing conformal conducting metal strips that are placed on the DRA surface. Additionally, two different approaches are employed onto the DRA design to enhance the CP bandwidth. The first approach is based on using a multilayer dielectric, and the second introduces a parasitic half-loop inside the feeding element. The generated broad CP bands have been achieved in conjunction with sufficient impedance matching bandwidths. The studied geometries have been modeled using a comprehensive self developed MoM code that employs the volume surface integral equation (VSIE). The computed results have been validated against those obtained from measurements as well as CST microwave studio simulations. Theoretical and experimental results demonstrate a several folds enhancement in the CP bandwidths compared to those reported in the literature for identical DRA geometries.