Reconfigurable antennas with single and multiple reconfigurability functions for wireless communications

Abstract

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 coexistence 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 lowprofile, 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 ...