Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Microwave antennas for infrastructure health monitoring

Infrastructure health monitoring (IHM) is a technology that has been developed for the detection and evaluation of changes that affect the performance of built infrastructure systems such as bridges and buildings. One of the employed methods for IHM is wireless sensors method which is based on sensors embedded in concrete or mounted on surface of structure during or after the construction to collect and report valuable monitoring data such as temperature, displacement, pressure, strain and moisture content, and information about defects such as cracks, voids, honeycombs, impact damages and delamination. The data and information can then be used to access the health of a structure during and/or after construction. Wireless embedded sensor technique is also a promising solution for decreasing the high installation and maintenance cost of the conventional wire based monitoring systems. However, several issues should be resolved at research and development stage in order to apply them widely in practice. One of these issues is that wireless sensors cannot operate for a long time due to limited lifetime of batteries. Once the sensors are embedded within a structure, they may not be easily accessible physically without damaging the structure. The main aim of this research is to develop effective antennas for IHM applications such as detection of defects such as gaps representing cracks and delaminations, and wireless powering of embeddable sensors or recharging their batteries. For this purpose, modelling of antennas based on conventional antipodal Vivaldi antennas (CAVA) and parametric studies are performed using a computational tool CST Studio (Studio 2015) including CST Microwave Studio and CST Design Studio, and experimental measurements are conducted using a performance network analyser. Firstly, modified antipodal Vivaldi antenna (MAVA) at frequency range of 0.65 GHz – 6 GHz is designed and applied for numerical and experimental investigations of the reflection and transmission properties of concrete-based samples possessing air gap or rebars. The results of gap detection demonstrate ability of the developed MAVA for detection of air gaps and delivery of power to embeddable antennas and sensors placed at any depth inside 350-mm thick concrete samples. The investigation into the influence of rebars show that the rebar cell can act as a shield for microwaves if mesh period parameter is less than the electrical half wavelength. At higher frequencies of the frequency range, microwaves can penetrate through the reinforced concrete samples. These results are used for the investigating the transmission of microwaves at the single frequency of 2.45 GHz between the MAVA and a microstrip patch antenna embedded inside reinforced concrete samples at the location of the rebar cell. It is shown that -15 dB coupling between the antennas can be achieved for the samples with rebar cell parameters used in practice. Secondly, a relatively small and high-gain resonant antipodal Vivaldi antenna (RAVA) as a transmitting antenna and modified microstrip patch antenna as an embeddable receiving antenna are designed to operate at 2.45 GHz for powering the sensors or recharging their batteries embedded in reinforced concrete members. These members included reinforced dry and saturated concrete slabs and columns with different values of mesh period of rebars and steel ratio, respectively. Parametric study on the most critical parameters, which affect electromagnetic (EM) wave propagation in these members, is performed. It is shown that there is a critical value of mesh period of rebars with respect to reflection and transmission properties of the slabs, which is related to a half wavelength in concrete. The maximum coupling between antennas can be achieved at this value. The investigation into reinforced concrete columns demonstrates that polarisation configuration of the two-antenna setup with respect to rebars and steel ratios as well as losses in concrete are important parameters. It is observed that the coupling between the antennas reduces faster by increasing the value of steel ratio in parallel than in vertical configuration due to the increase of the interaction between electromagnetic waves and the rebars. This effect is more pronounced in the saturated than in dry reinforced concrete columns. Finally, a relatively high gain 4-element RAVA array with a Wilkinson power divider, feeding network and an embeddable rectenna consisting of the microstrip patch antenna and a rectified circuit are developed. Two wireless power transmission systems, one with a single RAVA and another with the RAVA array, are designed for recharging batteries of sensors embedded inside reinforced concrete slabs and columns with different configurations and moisture content. Comparison between these systems shows that the DC output voltage for recharging commonly used batteries can be provided by the systems with the single RAVA and the system with the RAVA array at the distance between the transmitting antenna and the surface of reinforced concrete members of 0.12 m and 0.6 m, respectively, i.e. the distance achieved when the array is 5 times longer that the distance achieved with a single antenna

Flexible skin-contact antenna with artifical magnetic conductor for health monitoring application

Flexible antenna plays a significant role to ensure efficient wireless communication in wearable devices. The choice of the dielectric substrate material of the antenna is one of the important factors to ensure good antenna performance while being tolerant to mechanical deformation. In addition, the size of the antenna becomes the main issue in designing the antenna for on-body applications. Furthermore, the radiation and transmissions performance of the on-body antenna suffers from performance degradation due to several factors such as dielectric properties of the human body as well as line of sight (LOS) and non line of sight (NLOS) transmission conditions. Therefore, this study presents a flexible Skin-Contact Antenna with Artificial Magnetic Conductor surface (SCA-AMC) made from medical-friendly material. Initially, three different types of medical materials which include transdermal cotton patch, semi-transparent film, and self-adhesive bandage were proposed for investigation as the antenna’s dielectric substrate. The dielectric properties of the proposed materials were measured prior to the antenna design. For preliminary design investigation, a conventional bowtie antenna was designed using the proposed medical materials and optimized to operate at frequency of 2.4 GHz. To achieve the objectives, the feasibility of medical material usage for the antenna’s substrate was explored based on wetness and repeatability test. The proposed SCA is intended for on-body wireless communication devices where there is a significant limitation on the overall size of the antenna. In order to develop a compact flexible antenna, a meandering technique is applied to the conventional bowtie antenna. By employing the meandering technique, the total length of the antenna can be reduced by 20 %. As the body protection against electromagnetic absorption is important, a dipole-like AMC structure was designed at frequency of 2.4 GHz and integrated with the meandered bowtie antenna. The proposed SCA-AMC is made of flexible material for the substrate and conducting parts, making it suitable for wearable applications. Furthermore, the factors that influence the antenna’s radiation and transmission performance have been determined. The experiments have been carried out considering various conditions such as body movements and the presence of either human body or obstacle in between the SCAAMC transmitter and the receiver. The results indicate that the human body introduces an additional 20 dBm power loss when present between the transmitter and receiver. Also, the presence o f the book causes 6 dBm reduction in received power while sweatshirts and cotton polo shirts contribute to a small variation of approximately from 0.5 to 1 dBm. Besides, wetness measurements were also carried out using tap water and sweat-like solution. The sweat-like solution had been developed using a mixture of sodium chloride, sodium bicarbonate, and water. The material characterization of the developed sweat-like solution was then performed. The developed sweat-like solution has a measured permittivity and loss tangent of 75.8 and 0.13, respectively at the frequency of 2.4 GHz. The proposed SCA-AMC was also tested in a real-life situation by merging it with an electrocardiogram (ECG) sensor node. The results obtained show that the wireless ECG pattern is comparable to the ECG pattern measured using a conventional ECG machine. The findings in this research have profound implications for future studies to develop an efficient wireless device, especially for on-body applications

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

Design of new wearable antennas and textile-based transmission lines

Flexible wearable antennas and their components are a fast growing research topic in modern communication systems. They are developed for various wearable applica tions, such as health monitoring, fitness tracking, rescuing, and telecommunications. Wearable antennas need to be compact, lightweight, flexible, and robust. In this thesis, two dual-band wearable antennas were developed, each with a differ ent design approach. The first antenna is a dual-band flexible folded shorted patch (FSP) antenna which operates at 400 MHz and 2.4 GHz. It uses polydimethylsilox ane (PDMS), which is low cost, flexible and robust, and is used as a substrate for wearable the FSP antenna. In addition, the FSP antenna also exploits the TM010 and TM001 modes. A comparative study was carried out to analyze the far-field radiation and directivity at the TM010 and TM001 modes between the FSP antenna and a conventional patch antenna using cavity model analysis. The proposed FSP antenna is suitable for military search and rescue operations and emergency services. The second antenna is a dual-band flexible circular polarized (CP) patch antenna operational at 1.575 GHz and 2.45 GHz. Kevlar was used as a substrate for the proposed antenna. The patch consists of truncated corners and four diagonal slits. An artificial magnetic conductor (AMC) plane was integrated within the design in order to reduce the backward scattered radiation towards the human body and also to improve the realized gain of the antenna. The AMC unit cell design consists of square slits, a square ring and was integrated as a 3 × 3 array of square patch AMC unit cells. The proposed antenna developed is suitable for WBAN and WLAN applications. A circular polarized (CP) patch antenna with a PDMS substrate was also designed and fabricated to test the durability and resiliency of PDMS as a polymer-based material suitable for use in wearable antennas. Robustness tests such as bent, wet, and temperature tests were performed and reported. Two prototypes of flexible wearable coaxial transmission lines were also designed and fabricated. Polyester (PES) and polytetrafluoroethylene (PTFE) textile materials were used to design prototypes of these cables. Shielding effectiveness and DC losses were measured and compared for the fabricated cables. The cables were also tested for bending, twisting and for suitability in environmental conditions. The highly flexible nature of these cables makes them suitable to use with wearable antennas for various applications. For example, the proposed cables can be used with previously detailed FPS antenna for military search and rescue operations. It should be mentioned that this thesis was done in collaboration with Leonardo, UK and J&D Wilkie, UK

Embedded antenna technology in smart polymeric composite structures

One of the fastest-growing uses of sheet moulding compound (SMC) material is in the area of manufacturing of vehicle body components for both structural and non-structural applications. This trend is accelerating, driven by original equipment manufacturers (OEM) and their need for lighter and more fuel-efficient vehicles. In addition, over the last 20 years, the number of entertainment and communication systems in vehicles has also been expanding. The aim of this research is the development of a single wideband antenna that is capable of receiving all of the major services of interest. Taking this approach one step further and embedding such an antenna in a polymeric composite vehicle body panel would combine the benefits of reduced coefficient of drag, lower vehicle weight, reduced assembly complexity and shorter assembly time. These benefits would manifest themselves in the form of lower overall design and manufacturing vehicle cost for the OEMs and lower fuel consumption for customers. This thesis will deal with the development of such an antenna and the challenges faced in embedding it in a polymeric composite vehicle panel to such an extent that it becomes a seamless part of the vehicle body. This application required the development of a detailed understanding of the following three areas. Firstly, understanding of the interactions and effects of SMC material and automotive paint on antenna signal quality and performance through experiments and electromagnetic modelling (EM). Secondly, the development of the manufacturing process and material used to embed the antenna and its impact on the physical properties of the antenna through rheological testing, analytical modelling and experimentation. Lastly, the development of a wideband antenna capable of receiving pre-determined signals, through EM and field testing. The effects of paint application and presence of SMC resulted in a frequency shift of less than 1%. The experiments correlated well with the analytical model developed for compression moulding which incorporates a novel inclusion of the Maxwell’s model to predict the shear forces in the material flow within a confined space. A modular planar inverted conical antenna (PICA) was developed and optimised for the frequency range 700MHz – 9000MHz, which includes the commercial global positioning system (GPS) frequency. This development was then deployed as an embedded prototype in the deck lid of a test vehicle. Comparison against commercial GPS and mobile phone antennas was undertaken. This field test comparison showed that the developed PICA antenna performed better than the commercial antenna by up to 17%, especially in spaces devoid of multi-path signals

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

Electromagnetic characterization of barefaced terrain for oil sand exploration

The scant difference in the electromagnetic (EM) reflectivity of barefaced terrain often imposes challenges in differentiating between such terrain types and deployment of synthetic aperture radar to oil sand exploration. Microwave remote sensing has a proven ability to provide valuable information about targets. However to derive geoscientific information, a profound understanding of the EM interaction with terrain is vital. The challenge is to identify scattering characteristics relevant to oil sand fields. While various terrain identification methods and signature databases have been developed in the optical domain, only few examples of barefaced terrain discrimination in the microwave domain have been reported. In this thesis a three step multi-sensor approach has been used to identify EM signature of barefaced terrain encompassing homogeneous and heterogeneous materials, in the optical and microwave range. The combined method also led to the development of a large database of hyperspectral reflectivity, dielectric and backscattering data relevant to geointelligence analysis. The geochemical signature identification and prediction (GSIP) process required spectral data acquisition, chemometric model implementation and postprocessing to determine the spectral fingerprints and components of two strains of Nigerian oil sands. The results were compared with available hydrocarbon databases and four new features of Nigerian oil sands were observed. The dielectric discrimination statistical model (DDSM) involved three studies of the dielectric properties of oil sands and other barefaced terrain with different weight percentage of moisture and statistical processing of data to identify the 1 – 2 GHz and 5 – 7 GHz as most suitable frequency bands for microwave imaging. The GSIP and DDSM provided new empirical data on the geochemical and electrical behaviour of oil sand particularly the contrasting effects of bitumen, sand and moisture. Finally computer EM (CEM) models of barefaced terrain and sensors were used to identify the backscattering behaviour of the terrain for analysis in 2D/3D format. The results provided good agreement with classical surface roughness models particularly the Surface Perturbation and Kirchoffs Scattering model. They also enabled the investigation of the effect of wide variations in the sensor and terrain parameters on backscattering in order to evolve a radar signature necessary for identification of oil sand terrain for petroleum exploration. A laboratory scatterometer system (LSS) was developed and deployed in three imaging scenarios to verify aspects of the derived microwave EM signature of the terrain. The LSS measurements and the results from the CEMs were complimentary