Reconfigurable antennas with single and multiple reconfigurability functions for wireless communications

Antennas are an important core element of any communication system for transceiving signals in the form of electromagnetic radiation. Traditionally, antenna design and performance are optimised for fixed frequency, radiation and polarisation. However, modern electronic and wireless communication technologies necessitate compact and multifunctional antennas that are suitable for adapting in changing operating scenarios. As an alternative, reconfigurable antennas (RA), which have dynamic adaptability in such operating conditions, are impressive for improving system functionality and operational flexibility. Owing to the advantage of reconfigurability, an RA can be equivalent to several FPAs, thus provides compactness, minimises costs, and simplifies system integration. Antenna reconfiguration can be done with physical or mechanical modification, by electrical control by switching or tuning elements, by change of material properties, and via an optical switching scheme. However, due to the adopted control techniques and the antenna design process, RA performances often become non-uniform/inconsistent in different operating states. Besides, the use of multiple feeding, additional impedance matching networks, and compound controlling mechanisms, increases the antenna volume and control complexity. This research is focused on building compact size and low-profile RAs by means of simplified control mechanisms for achieving single- and multiple-reconfigurability functions and uniform reconfigurability performances in all reconfigurable states. The reconfigurable antenna concepts are developed aiming to avoid complicated feeding structures (external feeding and/or matching network) and lossy biasing arrangements (with a minimum number of active elements), as any mismatches or errors from those can affect the antenna performance.The single-function RAs are investigated for on-demand band-rejection reconfigurability, and 360˚ uniform beam-scanning with stable gain profiles. Due to the co-existence of several commonly used narrow band standards (WiMax and WLAN etc.) within the widely used ultra-wideband (UWB: 3.1-10.6 GHz), devices running simultaneously at these bands may suffer from in-band mutual interferences. To address this, the flexibility of on-demand band-rejection is offered with a low-profile, simple construct and easy to control configuration. Unlike others, this antenna has reversibility and works in four modes - UWB, single and dual band-rejection modes. The operating mechanism of the reconfigurable band-rejection techniques is explained using circuit model and current distribution analysis at each mode to give a clear insight into the developed concept.Beam-steering reconfigurable antennas are desirable for a wide range of applications, such as mobiles, satellite communications, remote sensing, radar etc. While uniform pattern reconfigurability and 360˚ beam-scanning are generally looked for, antennas that lack structural and control symmetry suffer from limited or non-uniform scanning. Here, structural symmetry of circular profiles has been utilised that has proven effective to achieve multi-state uniform reconfigurability, reduce design complexity and make simplified control circuits with the least number of active components. Several compact, low-profile, and simple construct 360˚ beam-scanning antennas having 90˚, 60˚ and 45˚ scanning steps are demonstrated. The 90˚ and 45˚ scanning antennas are loaded with switchable stubs around a micro-circular patch, thus obtaining symmetrical beam-steerability with a stable gain of 5-6 dBi and of 62-78% inefficiency. On the other hand,  a new technique of using a matching disc shorted with a circular patch is investigated on the 60˚ scanning antenna that overcome the impedance matching challenge of a typical centre-fed antenna. This technique enhanced the beam-steering gain profile while miniaturising the antenna (nearly 20%). Moreover, the antenna gain reached above 8 dBi with 84% efficiency without using any reflector.The reported multi-function reconfigurable antenna concepts integrate frequency tunability and beam-scanning capability. An initial wideband 180˚ beam-steering antenna is improved further with added 24.7% frequency tuning range (TR) and nearly 360˚ azimuthal beam-scanning. Additionally, this antenna has a unique capability of tuning to single-, dual- and wide-band operation. Next to this, the dual-polarised tunable patch antenna, built with parasitic dipole-array, obtained 44.94% TR, over 8 dBi gain and ±30° beam-steering range along the two vertical planes of φ = 0° and φ = 90°. Finally, a tunable travelling-wave antenna is demonstrated, featuring both frequency-dependent and fixed-frequency beam-scanning characteristics, which has scarcely been studied so far. It achieved 28.57% TR, 45° total beam-scanning range and 34% to 86% efficiency across 13.42% of bandwidth.The performances of the reported reconfigurable antennas are predicted by full-wave electromagnetic simulators and validated by testing the fabricated prototypes in the measurement lab. To validate the concepts and design performances, they are compared with other state-of-the-art antennas proposed for similar purposes/applications. The demonstrated antenna concepts and the results obtained can be used as design considerations when building new reconfigurable antennas (or antenna arrays) for future communication systems at lower or higher frequency bands, given the availability of suitable switching/tuning components in the target operating bands.