Polarization reconfigurable patch antenna for compact and low cost UHF RFID reader

This paper presents a patch antenna designed for Ultra High Frequency (UHF) Radio Frequency IDentification (RFID) reader including a reconfigurable feeding for achieving polarization agility. The switchable polarization improves the polarization efficiency in comparison with standard circular polarized antenna solutions. CMOS switches are used in the reconfigurable feeding network for enabling higher power transmission and uncomplicated control with respect to solutions involving varactors and PIN diodes. Moreover, the designed patch antenna and ground planes have reduced size, for best integration of the reader in the required application. The combination of antenna and reconfigurable feeding network has been tested through simulations, showing good performance over the EU RFID frequency band (865-868 MHz). Due to its flexible and inexpensive structure, the proposed reconfigurable feeding system is a promising alternative to standard circular polarized reader antenna approaches

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

Advances in Antennas and High-Frequency Material Characterization for Wireless Body-Area Networks

The development of the personal body-centric communication system is an essential part of the novel generation of wireless communication systems and one of the communication technology challenges. The versatility of body-centric communication revolutionizes healthcare by allowing continuous and in-all- conditions human health monitoring and human-centered authentication. Recently, with the extra-low power consumption and low-complexity backscatter communications, the passive ultra-high-frequency (UHF) radio-frequency identification (RFID) technology has been considered a promising approach for the wireless body area network. An inevitable part of this system is the wearable antenna, which plays a critical role in ensuring the efficient wireless link of the signal in the presence of the wearer. The wearable antenna should be fabricated with textile materials and equipped with various radiation configurations to enhance robustness and the operation’s versatility for long-term use. The difficulty of the wearable antenna development is to obtain the property information of the unknown textile substrate and conductor. To address the above-mentioned challenges, this thesis starts with the novel textile material characterization method to single out the relative permittivity and loss tangent of the substrate and bulk conductivity of the conductor. Unlike conventional approaches, our method simply applied the testing structure of the microstrip line composed of the textile material and simple data processing with the least square estimation. Then, a variation of the textile wearable antenna development with a low-profile planar in geometry is proposed in the next part of the thesis. The headgear RFID tag and forearm RFID reader antennas were developed based on quasi-Yagi configurations and periodic surface to obtain a directive pattern along the body surface. Another type of antenna configuration developed in this thesis is the circular polarization patch antenna for the wearable RFID tag. This type of antenna significantly reduced the polarization mismatch between the reader and the tag; hence, the detection capability and radiation efficiency are remarkably upgraded. The promising performance of the antennas was rigorously analyzed in simulation and verified with on-body measurement

Compact Reconfigurable Antennas for Wireless Systems and Wearable Applications

The fast growth of wireless communications has driven the necessity of exploiting technological solutions for the needs of faster connectivity. While bandwidth allocation and effective radiated power (ERP) are subjected to regulatory constrain, alternative solutions have been developed to overcome the challenges that arise in terms of wireless coverage and number of users. Reconfigurable antennas (RAs) technology is one of the hardware solutions developed to enhance the connectivity between wireless devices. These new class of radiating elements are able to adapt their physical characteristics in response to the environmental changes or users density and location. Reconfigurable antennas can be divided into two main categories: frequency reconfigurable antennas and pattern reconfigurable antennas. The former class of RAs are able to switch the operational frequency in order to move the communication within unoccupied channels. The latter category defines those antennas that are able to change their radiation characteristics (radiation pattern or polarization) in response to the dynamics of the surrounding environment. Unlike conventional static antennas where the energy is wasted around the surrounding space, the use of RAs allows for a smarter management of the radiated energy as the beam can be focused toward specific directions. As a result, not only data throughput between two devices can be improved but also the interference between adjacent networks can be reduced significantly. n this PhD thesis we focus on the design, prototyping and system application of compact RAs for wireless base stations and mobile devices. Specifically, the first task focuses on the design of a compact reconfigurable antenna capable of generating omnidirectional and directional beams in a single planar design. Next, we propose to apply a miniaturization technique in order to drastically reduce the size of Composite Right-Left Handed Reconfigurable Leaky Wave Antennas (CRLH RLWAs). The large beam steering capabilities along with the miniaturized dimension open new venues for the integration of this antenna technology into mobile devices such as laptop or tablets. Similarly for electrically reconfigurable antennas, characteristics such as input impedance and radiation properties of a radiating element can vary by mechanically change its physical dimension. In other words, instead of changing the metallic geometry through electrical components, the characteristics of an antenna can be changed through physical deformation of its geometry. This principle addresses the second main application of reconfigurable antennas this PhD thesis. Wearable technologies are gaining a lot of attentions due to their strong potential for sensing, communication and tactile interaction applications. Thanks to the progress in knitting facilities and techniques, smart fabrics are generally implemented through sewn-in sensors especially in the fields of medical and athletic applications. Such wearable sensors provide a means to monitor the wearers health through physiological measurements in a natural setting or can be used to detect or alert care providers to potential hazards around the wearer. The feasibility of building electrical devices using conductive fabrics has been analyzed through electrical characterization of textile transmission lines and antennas where conductive fabrics have been applied onto woven fabrics have been demonstrated in recent literature. Previous works show conductive copper foils or fabrics bonded to a flexible substrate. However, these techniques show limitations in terms of electrical losses caused by adhesives or glue chemicals. It is desirable to address these drawbacks by knitting conductive and non-conductive yarns in a single process resulting in smart textiles that are unobtrusively integrated into the host garment so as to eliminate the need for chemical adhesives that degrade electrical performance. The characteristics variations of a fabric-based antenna under physical deformations can be exploited to provide a fully wireless sensing of certain body movements. The second task of this PhD thesis, focuses on the design and testing of these purely textile wireless sensors for biomedical applications. The Radio-Frequency Identification (RFID) technology will be applied fordesigning fabric-based strain sensors through the use of novel inductively-coupled RFID microchips (MAGICSTRAP). As opposed to conventional surface-mount microchips, the MAGICSTRAP does not require any physical soldering connection as the RF energy is inductively coupled from the microchip pads to the antenna arms. A separate interrogator unit can communicate with this knit passive RFID architecture by sending a probing signal; the backscattered component received from the knit tag will indicate the level of stretch, and this information will be translated in the physical phenomenon being monitored. The change in the electrical characteristics of the textile antenna, along with the decoupling of the MAGICTRAP chip allow for more reliable detection of contraction/elongation movements. This study will include comprehensive design and characterization of the textile tag sensor along with performance analysis using a mechanical human mannequin.Ph.D., Electrical Engineering -- Drexel University, 201

A Review on Antenna Technologies for Ambient RF Energy Harvesting and Wireless Power Transfer: Designs, Challenges and Applications

Radio frequency energy harvesting (RFEH) and wireless power transmission (WPT) are two emerging alternative energy technologies that have the potential to offer wireless energy delivery in the future. One of the key components of RFEH or WPT system is the receiving antenna. The receiving antenna's performance has a considerable impact on the power delivery capability of an RFEH or WPT system. This paper provides a well-rounded review of recent advancements of receiving antennas for RFEH and WPT. Antennas discussed in this paper are categorized as low-profile antennas, multi-band antennas, circularly polarized antennas, and array antennas. A number of contemporary antennas from each category are presented, compared, and discussed with particular emphasis on design approach and performance. Current design and fabrication challenges, future development, open research issues of the antennas and visions for RFEH and WPT are also discussed in this review

Antenna Designs for 5G/IoT and Space Applications

This book is intended to shed some light on recent advances in antenna design for these new emerging applications and identify further research areas in this exciting field of communications technologies. Considering the specificity of the operational environment, e.g., huge distance, moving support (satellite), huge temperature drift, small dimension with respect to the distance, etc, antennas, are the fundamental device allowing to maintain a constant interoperability between ground station and satellite, or different satellites. High gain, stable (in temperature, and time) performances, long lifecycle are some of the requirements that necessitates special attention with respect to standard designs. The chapters of this book discuss various aspects of the above-mentioned list presenting the view of the authors. Some of the contributors are working strictly in the field (space), so they have a very targeted view on the subjects, while others with a more academic background, proposes futuristic solutions. We hope that interested reader, will find a fertile source of information, that combined with their interest/background will allow efficiently exploiting the combination of these two perspectives

Miniature MEMS-Based Adaptive Antennas on Flexible Substrates

Current trends in technology are moving to increased use of wireless communication with rapidly increasing data transmission rates and higher frequencies. Miniaturization is essential to allow electronics of increasing complexity to fit into smaller devices. Adaptive technologies allow a single system to operate across multiple wireless protocols, adjusting to changing conditions to minimize interference and enhance performance. Flexibility is essential as the use of wireless technology increases and spreads to new industries. The objective of this research is twofold: to develop novel reconfigurable electromagnetic structures and a novel process to fabricate microelectromechanical systems (MEMS) devices on flexible substrates. The novel electromagnetic structures are passive frequency-switchable parasitic antennas, conformal MEMS-tunable frequency selective surfaces (FSS) and MEMS-tunable electromagnetic bandgap (EBG) structures. Fabricating the reconfigurable conformal FSS and EBG structures requires the development of a new fabrication process to produce MEMS devices monolithically integrated onto a flexible substrate. Novel frequency-switchable parasitic antenna arrays are developed, fabricated and measured. The structure radiates efficiently when placed over metal and absorbing material, improving the range of conventional RFID systems, as well as minimizing blind spots to provide continuous coverage in a hemisphere. A novel analysis method is developed to characterize frequency-switchable parasitic patch arrays. The purpose of the analysis is to provide an approximation of the input impedance and variation of the radiation pattern with frequency. The analysis combines models based on electromagnetic theory and circuit theory to provide a fast and yet reasonable approximation of the parasitic array characteristics. The analysis also provides a good deal of physical insight into the operation of multi-mode parasitic patch arrays. The end result is an initial array design which provides a good starting point for full EM simulation and optimization. The new analysis method is validated alongside measured and simulated results, with good correlation for both impedance characteristics and far-field radiation patterns. A MEMS-based switched parasitic antenna array is designed, fabricated and measured with good correlation between simulated and measured results. The structure is a direct-coupled parasitic patch array which is capable of frequency steering and has additional MEMS-enabled beam-steering capabilities at each frequency. An EBG-based multi-mode radiating structure design is presented, which is capable of frequency-switchable beam steering. The antenna area is significantly reduced compared to the parasitic patch array structure, but at a considerable cost in terms of gain and efficiency. A novel MEMS process is developed to fabricate large numbers of high-performance MEMS devices monolithically integrated onto a rigid-flex organic substrate using low-temperature processes. The rigid-flex substrate is all dielectric, which is amenable to low-loss electromagnetic structures. The substrate provides mechanical support to the MEMS devices while maintaining overall flexibility. The adaptation of each fabrication process step to handle flexible substrates is analyzed and documented in detail. The newly-developed MEMS process is used to fabricate a MEMS reconfigurable frequency-selective surface. A practical bias network is incorporated into the structure design to ensure that all devices are actuated simultaneously. FSS structures operating in the Ku and Ka bands are fabricated and tested, with good correlation between simulated and measured results for individual devices as well as the entire FSS structures. The newly-developed MEMS process is also used to fabricate a MEMS reconfigurable electromagnetic bandgap structure. An EBG structure operating in the Ka band is fabricated and tested to verify the validity of the proposed concept

Wideband Circularly Polarized Elements and Arrays for Wireless Systems

Circularly polarized (CP) antennas have received increasing interest during recent decades due to their unique features such as the mitigation of multi-path fading, reduction of the "Faraday rotation" effect when signals propagate through the ionosphere and immunity of the polarization mismatching between transmitting and receiving antennas. Due to the requirements of high date rate and large system capacity, CP antennas deployed in various wireless systems are always demanded to have wide bandwidth. Furthermore, other system requirements such as polarization diversity, wide-angle beam scanning and low power consumption impose additional requirements to CP antennas. Therefore, it is becoming a more stringent requirement to design wideband CP antennas with diverse features to fulfil the requirements of various wireless systems. In this thesis, six different types of wideband CP antenna elements and arrays are designed, fabricated and characterized to meet the different demands of wireless systems. Chapters 3-5 investigate three different types of wideband CP antenna elements while Chapters 6-8 investigate three different kinds of wideband CP array antennas. In Chapter 3, an ultra-wideband CP element with a bandwidth of 100% (3:1) is proposed. It over-comes the problem of limited 3 dB axial ratio (AR) bandwidth for single-feed CP antennas and achieves high front-to-back ratio (FBR) by using a novel ground plane with simple configuration, which makes it a good candidate for high-performance Global Navigation Satellite System (GNSS) receivers. Chapter 4 presents a wideband loop antenna with electronically switchable circular polarizations. It solves the issue of narrow overlapped bandwidth under different polarization states for a polarization reconfigurable CP antenna. Because of the available orthogonal polarizations across a wide bandwidth, this antenna can be deployed in wireless communications which implement polarization diversity. The third antenna element investigated in Chapter 5 tackles the difficulty of designing wide-band wide AR beamwidth CP antennas. It achieves wide AR beamwidth within a 42% bandwidth, which is suitable for wideband wide-angle CP beam-scanning applications. The second main part of this thesis focuses on the investigation of wideband CP arrays. In Chapter 6, a dual-CP beam-scanning array is investigated, which can scan its beam independently in right-hand circular polarization (RHCP) and left-hand polarization (LHCP) from 27 GHz to 30 GHz. It tackles the problem of low isolation between the two orthogonally polarized ports across a wide bandwidth at Ka-band. A single-layer high-efficiency CP reflectarray is proposed in the following Chapter. The proposed design solves the issues of bandwidth limitation and low aperture efficiency for single-layer CP reflectarrays. It achieves the widest bandwidth compared with other CP reflectarrays reported in terms of 3 dB AR bandwidth, 3 dB gain bandwidth, larger than 50% aperture efficiency and undistorted radiation pattern bandwidth. In Chapter 8, we investigate the first application of tightly coupled array (TCA) concept into ultra-wideband arrays with CP radiation. Instead of trying to reduce the mutual coupling among the elements, it exploits the strong mutual coupling to improve the bandwidth of a CP array. By using the strong coupling in a constructive way, it overcomes the bandwidth limitation of CP arrays which are constituted by narrow-band elements

A Novel Long-Range Passive UHF RFID System over Twisted-pair Cable

Radio Frequency Identification (RFID) is one of the most representative, rapidly growing, and highly extendable technologies, which uses electromagnetic waves in accordance with specific communications standards and regulations to identify, track, or even localise desired objects. However, due to its high cost, limited read range, and uncertain reliability, its adoption still lags, especially in large-scale organisations. Even though an RFID distributed antenna system (DAS) can greatly improve the detection range and read rate of a single reader when system uses different combinations of antenna states with frequency and phase hopping, the lossy and heavy coaxial cables between reader and antennas still limits the system coverage and design flexibility for wide-area passive UHF RFID applications. In order to develop a cost-efficient and flexibly-installed passive RFID DAS, a novel large-range passive UHF RFID system over twisted-pair cable is proposed in this dissertation. This new system consists of one baseband central controller and one antenna subsystem, connected by a commonly used twisted-pair cable. It is shown that transmitting/receiving low frequency baseband signals over a twisted-pair cable can significantly reduce cable attenuation and extend the communication distance. A simulation is conducted to demonstrate that frequency and phase hopping can also be remotely controlled to fit this system structure by slightly varying the frequency or phase of the input reference signal of the frequency synthesis system. The features of twisted-pair cable in terms of its low cost, light weight, and bend radius greatly improve the design and installation flexibility of an RFID system. The implemented system is designed based on the ISO 18000-6C and EPC Class 1 Generation 2 standards, and can operate according to FCC (902-928 MHz) and ETSI (865-868MHz) regulations. The results of the measurement show the reader can achieve a sensitivity of - 94.5 dBm over 30 m Cat5e cable, and its sensitivity can still remain at around -94.2 dBm over 150 m Cat5e cable. The experimental results of tag detection show that the passive tags can be successfully detected over a 6 m wireless range following a 300 m of twisted-pair cable between the central controller and antenna. This detection range cannot be achieved by existing commercial RFID systems. Since the transmission and reception in a RFID system are simultaneous, finite isolation of the circulator/directional coupler and environmentally dependent reflection ratio of the antenna lead to serious leakage problems. Leakage can directly cause sensitivity degradation due to saturation of the RF components. A fast leakage suppression block is developed in efforts to solve this problem. Measurements show that this new canceller can deliver an average suppression of 36.9 dB, and this excellent performance remains when the system uses frequency hopping. With help of an improved scanning algorithm, this canceller can find its optimal status within 38 ms, and this settling time is short enough for most commercial RFID readers. By reducing the number of voltage samples taken, the convergence time can be further improved. To fully investigate this new passive UHF RFID system value, a comparison study between the new system and a commercial system is conducted. This new automatic passive UHF RFID system is confirmed to deliver high performance long-range passive tag detection. Particular advantages are shown in the fast tag read rate and capability of uplink SNR improvement. This novel system is also superior to conventional RFID systems in terms of link distance, link cost, and installation flexibility