Multipath Separation-Direction of Arrival (MS-DOA) with Genetic Search Algorithm for HF channels

Cataloged from PDF version of article.Direction-of-Arrival (DOA) defines the estimation of arrival angles of an electromagnetic wave impinging on a set of sensors. For dispersive and time-varying HF channels, where the propagating wave also suffers from the multipath phenomena, estimation of DOA is a very challenging problem. Multipath Separation-Direction of Arrival (MS-DOA), that is developed to estimate both the arrival angles in elevation and azimuth and the incoming signals at the output of the reference antenna with very high accuracy, proves itself as a strong alternative in DOA estimation for HF channels. In MS-DOA, a linear system of equations is formed using the coefficients of the basis vector for the array output vector, the incoming signal vector and the array manifold. The angles of arrival in elevation and azimuth are obtained as the maximizers of the sum of the magnitude squares of the projection of the signal coefficients on the column space of the array manifold. In this study, alternative Genetic Search Algorithms (GA) for the maximizers of the projection sum are investigated using simulated and experimental ionospheric channel data. It is observed that GA combined with MS-DOA is a powerful alternative in online DOA estimation and can be further developed according to the channel characteristics of a specific HF link. (C) 2009 COSPAR. Published by Elsevier Ltd. All rights reserve

Reconfigurable pixel antennas for communications

The explosive growth of wireless communications has brought new requirements in terms of compactness, mobility and multi-functionality that pushes antenna research. In this context, recon gurable antennas have gained a lot of attention due to their ability to adjust dynamically their frequency and radiation properties, providing multiple functionalities and being able to adapt themselves to a changing environment. A pixel antenna is a particular type of recon gurable antenna composed of a grid of metallic patches interconnected by RF-switches which can dynamically reshape its active surface. This capability provides pixel antennas with a recon guration level much higher than in other recon gurable architectures. Despite the outstanding recon guration capabilities of pixel antennas, there are important practical issues related to the performance-complexity balance that must be addressed before they can be implemented in commercial systems. This doctoral work focuses on the minimization of the pixel antenna complexity while maximizing its recon guration capabilities, contributing to the development of pixel antennas from a conceptual structure towards a practical recon gurable antenna architecture. First, the conceptualization of novel pixel geometries is addressed. It is shown that antenna complexity can be signi cantly reduced by using multiple-sized pixels. This multi-size technique allows to design pixel antennas with a number of switches one order of magnitude lower than in common pixel structures, while preserving high multiparameter recon gurability. A new conceptual architecture where the pixel surface acts as a parasitic layer is also proposed. The parasitic nature of the pixel layer leads to important advantages regarding the switch biasing and integration possibilities. Secondly, new pixel recon guration technologies are explored. After investigating the capabilities of semiconductors and RF-MEMS switches, micro uidic technology is proposed as a new technology to create and remove liquid metal pixels rather than interconnecting them. Thirdly, the full multi-parameter recon guration capabilities of pixel antennas is explored, which contrasts with the partial explorations available in the literature. The maximum achievable recon guration ranges (frequency range, beam-steering angular range and polarization modes) as well as the linkage between the di erent parameter under recon guration are studied. Finally, the performance of recon gurable antennas in beam-steering applications is analyzed. Figures-of-merit are derived to quantify radiation pattern recon gurability, enabling the evaluation of the performance of recon gurable antennas, pixel antennas and recon guration algorithms

Reconfigurable pixel antennas for communications

Premi extraordinari doctorat curs 2012-2013, àmbit Enginyeria de les TICThe explosive growth of wireless communications has brought new requirements in terms of compactness, mobility and multi-functionality that pushes antenna research. In this context, recon gurable antennas have gained a lot of attention due to their ability to adjust dynamically their frequency and radiation properties, providing multiple functionalities and being able to adapt themselves to a changing environment. A pixel antenna is a particular type of recon gurable antenna composed of a grid of metallic patches interconnected by RF-switches which can dynamically reshape its active surface. This capability provides pixel antennas with a recon guration level much higher than in other recon gurable architectures. Despite the outstanding recon guration capabilities of pixel antennas, there are important practical issues related to the performance-complexity balance that must be addressed before they can be implemented in commercial systems. This doctoral work focuses on the minimization of the pixel antenna complexity while maximizing its recon guration capabilities, contributing to the development of pixel antennas from a conceptual structure towards a practical recon gurable antenna architecture. First, the conceptualization of novel pixel geometries is addressed. It is shown that antenna complexity can be signi cantly reduced by using multiple-sized pixels. This multi-size technique allows to design pixel antennas with a number of switches one order of magnitude lower than in common pixel structures, while preserving high multiparameter recon gurability. A new conceptual architecture where the pixel surface acts as a parasitic layer is also proposed. The parasitic nature of the pixel layer leads to important advantages regarding the switch biasing and integration possibilities. Secondly, new pixel recon guration technologies are explored. After investigating the capabilities of semiconductors and RF-MEMS switches, micro uidic technology is proposed as a new technology to create and remove liquid metal pixels rather than interconnecting them. Thirdly, the full multi-parameter recon guration capabilities of pixel antennas is explored, which contrasts with the partial explorations available in the literature. The maximum achievable recon guration ranges (frequency range, beam-steering angular range and polarization modes) as well as the linkage between the di erent parameter under recon guration are studied. Finally, the performance of recon gurable antennas in beam-steering applications is analyzed. Figures-of-merit are derived to quantify radiation pattern recon gurability, enabling the evaluation of the performance of recon gurable antennas, pixel antennas and recon guration algorithms.Award-winningPostprint (published version

Analysis and design of smart antenna arrays (SAAs) for improved directivity at GHz range for wireless communication systems.

Doctor of Philosophy in Electronic Engineering. University of KwaZulu-Natal, Durban 2018.Abstract available in PDF file

Adaptive array antenna design for wireless communication systems

Adaptive array antennas use has been limited to non-commercial applications due to their high cost and hardware complexity. The implementation cost of adaptive array antennas can be kept to a minimum by using cost effective antennas, reducing the number of elements in the array and implementing efficient beamforming techniques. This thesis presents techniques for the design of adaptive array antennas which will enable their cost effective implementation in wireless communication systems. The techniques are investigated from three perspectives, namely, reconfigurable antenna design, wide scan array design and single-port beamforming technique. A novel single-feed polarisation reconfigurable antenna design is proposed in the first stage of this study. Different polarisation states, namely, linear polarisation (LP), left-hand circular polarisation (LHCP) and right-hand circular polarisation (RHCP), are achieved by perturbing the shape of the main radiating structure of the antenna. The proposed antenna exhibits good axial ratio (< 3 dB at 2.4 GHz) and has high radiation efficiency in both polarisation modes (91.5 % - LHCP and 86.9 % - RHCP). With a compact single feeding structure, the antenna is suitable for implementation in wireless communication devices. The second stage of the study presents the design procedure of wide scan adaptive array antennas with reduced number of elements. Adaptive array antennas with limited number of elements have limited scanning range, reduced angular scanning resolution and high sidelobe levels. To date, design synthesis of adaptive array antennas has been targeted on arrays with a large number of elements. This thesis presents a comprehensive analysis of adaptive array antennas with less than 10 elements. Different array configurations are analysed and various array design parameters such as number of elements, separation between elements and orientation of the elements are analysed in terms of their 3 dB scan range. The proposed array, the 3-faceted array, achieves a scanning range up to ±70°, which is higher than ±56° obtained from the Uniform Linear Array. The faceted arrays are then evaluated in the context of adaptive beamforming properties. It was shown that the 3-faceted array is suitable for adaptive array applications in wireless communication systems as it achieves the highest directivity compared to other faceted structures. The 3-faceted array is then synthesised for low sidelobe level. Phase correction together with amplitude tapering technique is applied to the 3-faceted array. The use of conventional and tuneable windowing techniques on the 3- faceted array is also analysed. The final stage of the study investigates beamforming techniques for the adaptive array antenna. In the first part, beamforming algorithms using different performance criteria, which include maximum signal-to noise-ratio (SINR), minimum (mean-square Error) MSE and power minimisation, are evaluated. In the second part, single-port beamforming techniques are explored. In previous single-port beamforming methods, the spatial information of the signals is not fully recovered and this limits the use of conventional adaptive beamforming algorithms. In this thesis, a novel signal estimation technique using pseudo-inverse function for single-port beamforming is proposed. The proposed polarisation reconfigurable antenna, the 3-faceted array antenna and the single-port beamforming technique achieve the required performance, which suggests the potential of adaptive array antennas to be deployed commercially, especially in wireless communication industry

Non-Radiative Calibration of Active Antenna Arrays

Antenna arrays offer significant benefits for modern wireless communication systems but they remain difficult and expensive to produce. One of the impediments of utilising them is to maintain knowledge of the precise amplitude and phase relationships between the elements of the array, which are sensitive to errors particularly when each element of the array is connected to its own transceiver. These errors arise from multiple sources such as manufacturing errors, mutual coupling between the elements, thermal effects, component aging and element location errors. The calibration problem of antenna arrays is primarily the identification of the amplitude and phase mismatch, and then using this information for correction. This thesis will present a novel measurement-based calibration approach, which uses a fixed structure allowing each element of the array to be measured. The measurement structure is based around multiple sensors, which are interleaved with the elements of the array to provide a scalable structure that provides multiple measurement paths to almost all of the elements of the array. This structure is utilised by comparison based calibration algorithms, so that each element of the array can be calibrated while mitigating the impact of the additional measurement hardware on the calibration accuracy. The calibration was proven in the investigation of the experimental test-bed, which represented a typical telecommunications basestation. Calibration accuracies of ±0.5dB and 5o were achieved for all but one amplitude outlier of 0.55dB. The performance is only limited by the quality of the coupler design. This calibration approach has also been demonstrated for wideband signal calibration

Rapid Beam Forming in Smart Antennas Using Smart-Fractal Concepts Employing Combinational Approach Algorithms

Smart antennas offer a broad range of ways to improve wireless system performance. They provide enhanced coverage through range extension, hole filling, and better building penetration. Smart antennas use an array of low gain antenna elements which are connected by a network. Fractal concepts have been used in antenna arrays recently. The important properties of fractal arrays are frequency independent multiband characteristics, schemes for realizing low side lobe designs, systematic approaches to thinning, and the ability to develop rapid beam forming algorithms. In this paper, an attempt has been made to apply assignment of usage time and location tag algorithm for smart antennas combined with the fractal concepts to reduce the computational complexity and enhance resource allocation for rapid beam forming algorithms. Furthermore, two combinational approach algorithms are proposed for peer users within single base station and peer users between different base stations

1-D broadside-radiating leaky-wave antenna based on a numerically synthesized impedance surface

A newly-developed deterministic numerical technique for the automated design of metasurface antennas is applied here for the first time to the design of a 1-D printed Leaky-Wave Antenna (LWA) for broadside radiation. The surface impedance synthesis process does not require any a priori knowledge on the impedance pattern, and starts from a mask constraint on the desired far-field and practical bounds on the unit cell impedance values. The designed reactance surface for broadside radiation exhibits a non conventional patterning; this highlights the merit of using an automated design process for a design well known to be challenging for analytical methods. The antenna is physically implemented with an array of metal strips with varying gap widths and simulation results show very good agreement with the predicted performance

Beam scanning by liquid-crystal biasing in a modified SIW structure

A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium

Applications of Antenna Technology in Sensors

During the past few decades, information technologies have been evolving at a tremendous rate, causing profound changes to our world and to our ways of living. Emerging applications have opened u[ new routes and set new trends for antenna sensors. With the advent of the Internet of Things (IoT), the adaptation of antenna technologies for sensor and sensing applications has become more important. Now, the antennas must be reconfigurable, flexible, low profile, and low-cost, for applications from airborne and vehicles, to machine-to-machine, IoT, 5G, etc. This reprint aims to introduce and treat a series of advanced and emerging topics in the field of antenna sensors