Wideband and UWB antennas for wireless applications. A comprehensive review

A comprehensive review concerning the geometry, the manufacturing technologies, the materials, and the numerical techniques, adopted for the analysis and design of wideband and ultrawideband (UWB) antennas for wireless applications, is presented. Planar, printed, dielectric, and wearable antennas, achievable on laminate (rigid and flexible), and textile dielectric substrates are taken into account. The performances of small, low-profile, and dielectric resonator antennas are illustrated paying particular attention to the application areas concerning portable devices (mobile phones, tablets, glasses, laptops, wearable computers, etc.) and radio base stations. This information provides a guidance to the selection of the different antenna geometries in terms of bandwidth, gain, field polarization, time-domain response, dimensions, and materials useful for their realization and integration in modern communication systems

HIGH-GAIN ULTRAWIDEBAND DIELECTRIC RESONATOR ANTENNAS FOR WIRELESS APPLICATIONS

The increasing demand for high data rate transmissions in wireless communications and low power consumption, has led to a growing scientific interest concerning wideband and ultrawideband antennas. Besides, the need to integrate more than one service in only one device has made wideband technology very attractive among the scientific community. To this purpose, several kind of techniques have been introduced in literature for increasing the operative bandwidth of well-known radiating structures such as microstrip patch antennas, monopole antennas, printed monopole/dipole antennas, etc. However, all these antenna configurations, which typically are made of metals and dielectric materials, are prone to low antenna radiation efficiencies. Indeed, high efficiency is essential in satellite applications where good link margins are required or in mm-wave communications where the power losses in the system components may be relevant. Besides, high-efficiency antennas are essential for providing a long-range coverage in WLAN access points and base stations, especially in indoor environments where circular polarization is employed to limit multipath effects. For these reasons, an extensive research activity concerning high-efficiency dielectric resonator antennas has been carried out during the past decades. The main goal of this research work, carried out during these three years of Ph.D. studies, is to introduce novel wideband high-efficiency and high-gain dielectric resonator antennas working in both linear and circular polarization and suitable for terrestrial and satellite communications. Besides, an extensive time-domain analysis of the proposed radiating structures, aimed to investigate their suitability to work with UWB pulse signals, has been also carried out. The thesis is organized in five chapters. In the first chapter, after a short description concerning several wireless communication standards and UWB systems, the state-of-art of some of the most important wideband and ultrawideband antennas proposed in literature, is briefly illustrated. A special emphasis is given to dielectric resonator antennas exhibiting broad impedance bandwidths, high gains, pattern stability and good circular polarization performances. In the second chapter, the Singularity Expansion Method (SEM) and the Matrix Pencil Method (MPM), aimed to the extraction of residues and poles of an antenna impulsive response, useful for a better comprehension of the resonating processes taking place into the considered radiating structures, and for computing the antenna time domain response to arbitrary excitation signals, are described. In the third chapter, the main features of the full-wave commercial software CST Microwave Studio™, based on the Finite Integration Technique (FIT), and employed for the analysis and design of the proposed dielectric resonator antennas, are briefly described. In the fourth chapter, a novel wideband multi-level multi-permittivity dielectric resonator antenna working in both linear and circular polarization is introduced. The radiating structure, equipped with a suitable metal reflector, exhibits a maximum gain of about 10 dBi, a high front-to back ratio and a broad impedance bandwidth (between 79% and 82%), resulting suitable for several wireless communications standards (e.g. WLAN and WiMAX) and C-band satellite applications. Besides, a time-domain analysis of the antenna based on FIT and SEM techniques, aimed to the investigation of its relative group delay and fidelity factor, has been also presented. In the fifth chapter, a wideband high-gain mushroom-shaped dielectric resonator antenna, equipped with a suitable metal reflector and a dielectric lens, has been proposed for wireless, C-band radar and UWB applications. Thanks to the dielectric lens the gain of the cylindrical dielectric resonator along the boresight direction is significantly enhanced, while the presence of the metal reflector strongly improve the antenna front-to-back ratio, making the antenna characteristics independent from those of the installation site. The antenna is fed with two/four probes, opportunely disposed around the DR, with the aim of exciting a circular/linear polarization. An antenna prototype was realized to verify the performances predicted by the numerical computations. Measured and numerical results show an antenna radiation efficiency higher than 90% along the antenna operative bandwidth, a fractional bandwidth of about 65% and a maximum achieved gain higher than 15 dBi. Finally, a time domain analysis of the antenna performed by means of the Finite Integration Technique and the SEM procedure showed that the antenna can also operate with UWB pulse signals

A novel wideband multi-permittivity composite dielectric resonator antenna for wireless applications

A novel high-gain dielectric resonator antenna (DRA) for wideband wireless applications is presented. The antenna is composed of a hollow cylindrical dielectric resonator (DR) inside which an assembly of two dielectric truncated cones having different permittivities are inserted. A suitable probe excitation system and an air gap, realized between the base of the first truncated dielectric cone and the ground plane, are used to further increase the antenna bandwidth. A full-wave commercial software based on the finite integration technique (FIT) has been used to analyze and design the antenna, while the singularity-extraction method (SEM) has been adopted to extract information about the main resonant processes taking place in the proposed radiating structure

A high-gain mushroom-shaped dielectric resonator antenna for wideband wireless applications

A high-gain mushroom-shaped dielectric resonator (DR) antenna for wideband wireless applications, featuring 65% fractional bandwidth, is proposed. The antenna consists of a low-permittivity hollow cylindrical DR provided with a top-mount spherical cap lens and a metal reflector, excited by means of coaxial probes. Suitable shaping of lens and reflector yields high gain (exceeding 14 dBi) and limited back radiation. The proposed antenna features a broadside radiation diagram with stable radiation patterns and wideband impedance matching. Its potential applications include access points for indoor/outdoor wireless multimedia systems as well as satellite terminal receivers. CST Microwave Studio, implementing a fullwave locally conformal finite integration technique, is employed to design and characterize the antenna, while the singularity expansion method is adopted to express the antenna response to arbitrary excitation waveforms. The numerical results concerning the antenna parameters are found to be in good agreement with the experimental measurements performed on an antenna prototyp

Deep Sequencing Data and Infectivity Assays Indicate that Chickpea Chlorotic Dwarf Virus is the Etiological Agent of the “Hard Fruit Syndrome” of Watermelon

Chickpea chlorotic dwarf virus (CpCDV), a polyphagous mastrevirus, family Geminiviridae, has been recently linked to the onset of the “hard fruit syndrome” of watermelon, first described in Tunisia, that makes fruits unmarketable due to the presence of white hard portions in the flesh, chlorotic mottling on the rind, and an unpleasant taste. To investigate the etiological agent of this disease, total RNA extracted from symptomatic watermelon fruits was subjected to small RNA sequencing through next generation sequencing (NGS) techniques. Data obtained showed the presence of CpCDV and two other viral species. However, following validation through polymerase chain reaction (PCR), CpCDV was the only viral species consistently detected in all samples. Watermelon seedlings were then challenged by an agroinfectious CpCDV clone; several plants proved to be CpCDV-infected, and were able to produce fruits. CpCDV infected and replicated in watermelon fruits and leaves, leading to abnormality in fruits and in seed production, similar to those described in field. These results indicate that CpCDV is the etiological agent of the “hard fruit syndrome” of watermelon

Nondestructive Raman Spectroscopy as a Tool for Early Detection and Discrimination of the Infection of Tomato Plants by Two Economically Important Viruses

Global population forecasts dictate a rapid adoption of multifaceted approaches to fulfill increasing food requirements, ameliorate food dietary value and security using sustainable and economically feasible agricultural processes. Plant pathogens induce up to 25% losses in vegetable crops and their early detection would contribute to limit their spread and economic impact. As an alternative to time-consuming, destructive, and expensive diagnostic procedures, such as immunological assays and nucleic acid-based techniques, Raman spectroscopy (RS) is a nondestructive rapid technique that generates a chemical fingerprinting of a sample, at low operating costs. Here, we assessed the suitability of RS combined to chemometric analysis to monitor the infection of an important vegetable crop plant, tomato, by two dangerous and peculiarly different viral pathogens, Tomato yellow leaf curl Sardinia virus (TYLCSV) and Tomato spotted wilt virus (TSWV). Experimentally inoculated plants were monitored over 28 days for symptom occurrence and subjected to RS analysis, alongside with measuring the virus amount by quantitative real-time PCR. RS allowed to discriminate mock inoculated (healthy) from virus-infected specimens, reaching an accuracy of >70% after only 14 days after inoculation for TYLCSV and >85% only after 8 days for TSWV, demonstrating its suitability for early detection of virus infection. Importantly, RS also highlighted spectral differences induced by the two viruses, providing specific information on the infecting agent

Pyramiding Ty-1/Ty-3 and Ty-2 in tomato hybrids dramatically inhibits symptom expression and accumulation of tomato yellow leaf curl disease inducing viruses

Tomato yellow leaf curl disease is a major constraint for tomato production worldwide and availability of new resistant materials is of great importance for breeding programmes. A phenotypic survey was undertaken to evaluate the level of resistance to the main tomato yellow leaf curl disease-inducing viruses Tomato yellow leaf curl virus and Tomato yellow leaf curl Sardinia virus, in several commercial tomato cultivars, never characterised before. Seven weeks post inoculation, two cultivars resulted in high resistant phenotypes to both begomoviruses, and four were tolerant to at least one of them. In the two highly resistant hybrids (SJ12, RFT112), symptoms were completely absent and viral DNA was from 102to 105fold lower than in susceptible plants. Molecular marker analysis revealed that these genotypes harbour the resistant genes Ty-1/Ty-3 and Ty-2. Given their high resistance, they can be considered good candidates for cultivation and breeding in areas where incidence of TYLCD is very elevated

The Induction of an Effective dsRNA-Mediated Resistance Against Tomato Spotted Wilt Virus by Exogenous Application of Double-Stranded RNA Largely Depends on the Selection of the Viral RNA Target Region

Tomato spotted wilt virus (TSWV) is a devastating plant pathogen, causing huge crop losses worldwide. Unfortunately, due to its wide host range and emergence of resistance breaking strains, its management is challenging. Up to now, resistance to TSWV infection based on RNA interference (RNAi) has been achieved only in transgenic plants expressing parts of the viral genome or artificial microRNAs targeting it. Exogenous application of double-stranded RNAs (dsRNAs) for inducing virus resistance in plants, namely RNAi-based vaccination, represents an attractive and promising alternative, already shown to be effective against different positive-sense RNA viruses and viroids. In the present study, the protection efficacy of exogenous application of dsRNAs targeting the nucleocapsid (N) or the movement protein (NSm) coding genes of the negative-sense RNA virus TSWV was evaluated in Nicotiana benthamiana as model plant and in tomato as economically important crop. Most of the plants treated with N-targeting dsRNAs, but not with NSm-targeting dsRNAs, remained asymptomatic until 40 (N. benthamiana) and 63 (tomato) dpi, while the remaining ones showed a significant delay in systemic symptoms appearance. The different efficacy of N- and NSm-targeting dsRNAs in protecting plants is discussed in the light of their processing, mobility and biological role. These results indicate that the RNAi-based vaccination is effective also against negative-sense RNA viruses but emphasize that the choice of the target viral sequence in designing RNAi-based vaccines is crucial for its success.</p