Reconfigurable Antennas

In this new book, we present a collection of the advanced developments in reconfigurable antennas and metasurfaces. It begins with a review of reconfigurability technologies, and proceeds to the presentation of a series of reconfigurable antennas, UWB MIMO antennas and reconfigurable arrays. Then, reconfigurable metasurfaces are introduced and the latest advances are presented and discussed

Reconfigurable Microwave Semiconductor Plasma Antenna

Reconfigurable antennas have been a subject of rapidly increased interest during the past decades. This has been prompted by the increased demand on new wireless communications technology in both civilian and military directions. Moreover, different types of reconfigurations have been identified and investigated to keep up with the demand for new technologies. In this research, the possibility of designing reconfigurable Dielectric Resonator Antennas (DRAs) have been explored with different types of reconfigurability directions, especially with the increased interest in the area of DRAs during the past three decades. These results have been satisfactory in general. The main aim of this research is to experiment with different reconfigurability designs, each purpose is to achieve one type of reconfigurability or more. This includes, polarisation reconfigurability in Chapter Three, frequency agility in Chapters Four and Five, beam steering and gain agility in Chapter Five. Furthermore, this research main aim has been to investigate new ways to exploit the advantages of the semiconductor plasma in reconfigurable antennas. However, research’s limited resources led to reduce the efforts in this area to only one experiment, which is presented in Chapter Six, based on a similar design presented in Chapter Four. Although the results have been conflicted for the last experiment, the results shown that the used reconfigurability medium (AlGaN/GaN HFETs) can be benefitted better from it in other application. Two models have been introduced for polarisation reconfigurability, a hemispherical DRA couple with reconfigurable annular slot excitation, and a notched rectangular DRA with reconfigurable parasitic strip(s). Both designs shown the possibility of achieving LP/CP radiations. In addition, rectangular DRAs that are excited with single, as well as multiple, slot have been studied. Prototypes have been built and measured with reasonable agreement between practical and simulated results. Furthermore, the work has been extended to study a reconfigurable DRA linear array where several designs have been investigated including single and dual-slot for two and four-element linear arrays. The single-slot model reconfiguration resulted in the expected beam steering alongside the array direction. On the other hand, both frequency tuning and beam steering have been achieved with the dual-slots models. Finally, the semiconductor plasma reconfigurable antennas have been considered with the investigation of AlGaN/GaN HFETs as a replacement for the well investigated and presented silicon SPIN diodes. The prototype has been measure and discrepancies between measurements and simulations have been discussed

High-Resolution Quantitative Phase Imaging of Plasmonic Metasurfaces with Sensitivity down to a Single Nanoantenna

Optical metasurfaces have emerged as a new generation of building blocks for multifunctional optics. Design and realization of metasurface elements place everincreasing demands on accurate assessment of phase alterations introduced by complex nanoantenna arrays, a process referred to as quantitative phase imaging. Despite considerable effort, the widefield (nonscanning) phase imaging that would approach resolution limits of optical microscopy and indicate the response of a single nanoantenna still remains a challenge. Here, we report on a new strategy in incoherent holographic imaging of metasurfaces, in which unprecedented spatial resolution and light sensitivity are achieved by taking full advantage of the polarization selective control of light through the geometric (PancharatnamBerry) phase. The measurement is carried out in an inherently stable common-path setup composed of a standard optical microscope and an add-on imaging module. Phase information is acquired from the mutual coherence function attainable in records created in broadband spatially incoherent light by the self-interference of scattered and leakage light coming from the metasurface. In calibration measurements, the phase was mapped with the precision and spatial background noise better than 0.01 and 0.05 rad, respectively. The imaging excels at the high spatial resolution that was demonstrated experimentally by the precise amplitude and phase restoration of vortex metalenses and a metasurface grating with 833 lines/mm. Thanks to superior light sensitivity of the method, we demonstrated for the first time to our knowledge the widefield measurement of the phase altered by a single nanoantenna while maintaining the precision well below 0.15 rad

Design and Implementation of High Gain 60 GHz Antennas for Imaging/Detection Systems

Recently, millimeter wave (MMW) imaging detection systems are drawing attention for their relative safety and detection of concealed objects. Such systems use safe non-ionizing radiation and have great potential to be used in several applications such as security scanning and medical screening. Antenna probes, which enhance system performance and increase image resolution contrast, are primarily used in MMW imaging sensors. The unlicensed 60 GHz band is a promising band, due to its wide bandwidth, about 7 GHz (57 - 64 GHz), and lack of cost. However, at 60 GHz the propagation loss is relatively high, creating design challenges for operating this band in MMW screening. A high gain, low profile, affordable, and efficient probe is essential for such applications at 60 GHz. This thesis’s focus is on design and implementation of high gain MMW probes to optimize the performance of detection/imaging systems. First, single-element broadside radiation microstrip antennas and novel probes of endfire tapered slot high efficient antennas are presented. Second, a 57-64 GHz, 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer controlled phase shifter is presented. Then, a mechanical scanner is designed specifically to test proposed antenna probes utilizing low-power 60 GHz active monostatic transceivers. The results for utilizing proposed 60 GHz probes show success in detecting and identifying concealed weapons and explosives in liquids or plastics. As part of the first research theme, a 60 GHz circular patch-fed high gain dielectric lens antenna is presented, where the prototype’s measured impedance bandwidth reaches 3 GHz and a gain of 20 dB. A low cost, 60 GHz printed Yagi antenna array was designed, optimized, fabricated and tested. New models of the antipodal Fermi tapered slot antenna (AFTSA) with a novel sine corrugated (SC) shape are designed, and their measured results are validated with simulated ones. The AFTSA-SC produces a broadband and high efficiency pattern with the capacity for high directivity for all ISM-band. Another new contribution is a novel dual-polarized design for AFTSA-CS, using a single feed with a pair of linearly polarized antennas aligned orthogonally in a cross-shape. Furthermore, a novel 60 GHz single feed circularly polarized (CP) AFTSA-SC is modeled to radiate in the right-hand circularly polarized antenna (RHCP). A RHCP axial ratio bandwidth of < 3dB is maintained from 59 to 63 GHz. In addition, a high gain, low cost 60 GHz Multi Sin-Corrugations AFTSA loaded with a grooved spherical lens and in the form of three elements to operate as the beam steering antenna is presented. These probes show a return loss reduction and sidelobes and backlobe suppression and are optimized for a 20 dB or higher gain and radiation efficiency of ~90% at 60 GHz. The second research theme is implementing a 1 × 16-element beam steering antenna array with a low-cost piezoelectric transducer (PET) controlled phase shifter. A power divider with a triangular feed which reduces discontinuity from feed lines corners is introduced. A 1 × 16-element array is fabricated using 60 GHz AFTSA-SC antenna elements and showed symmetric E-plane and H-plane radiation patterns. The feed network design is surrounded by electromagnetic band-gap (EBG) structures to reduce surface waves and coupling between feed lines. The design of a circularly polarized 1 × 16-element beam steering phased array with and without EBG structures also investigated. A target detection investigation was carried out utilizing the proposed 60GHz antennas and their detection results are compared to those of V-band standard gain horn (SGH). System setup and signal pre-processing principle are introduced. The multi-corrugated MCAFTSA-SC probe is evaluated with the imaging/detection system for weapons and liquids concealed by clothing, plywood, and plastics. Results show that these items are detectable in clear 2D image resolution. It is believed that the 60 GHz imaging/detection system results using the developed probes show potential of detecting threatening objects through screening of materials and public

Leaky waves for near and far field antenna beam shaping

Mención Internacional en el título de doctorThe main purpose of this thesis is to present innovative beam shaping antennas, based on leaky wave antennas LWAs, which can meet fundamental requirements like: low cost, low profile and high gain. Important fields of application switch on from near-field (holographic concept) to far-field (low and high satellite applications). For the near-field application, the objective has been the use of periodic LWAs to synthesize a near-field pattern focusing at a specific point and with also a predetermined polarization. The impact of the circular or radial polarization on the shape of the focal region in these periodic LWAs has been investigated. Also the ability of these antennas to do frequency steering of the focus is studied for all the designs. For the far-field application, we consider two main scenarios: in the first one, we study solutions for Geostationary Satellite (GEO) where thinned arrays are required to scanning at a few degrees. In the second one, we point to LEO satellites, where dense arrays are more suitable for large scanning angles. In these applications, uniform LWAs are more appropriate, since they allow the possibility for overlapping areas between the different array elements. All results are carefully corroborated with commercial software and home-made code as well as with the measurement of the fabricated prototypes.El objetivo principal de esa tesis es presentar soluciones innovadoras para realizar conformación de haz con antenas tipo Leaky Wave. Estas antenas son conocidas por ser de bajo coste, fáciles de diseñar y tener alta ganancia. Los campos de aplicación de este tipo de antenas son muy variados y pueden ir desde aplicaciones en campo cercano (antenas holográficas) hasta campo lejano (aplicaciones para satélites de bajas y altas órbitas). En particular para antenas en campo cercano, esta tesis propone el uso de antenas Leaky Wave periódicas para sintetizar diagramas de radiación que focalizan el campo concentrándolo en un punto con una polarización predeterminada. Se investiga el impacto de los distintos tipos de polarización (circular y lineal) en la forma de la región focal, así como la habilidad de este tipo de antenas para desplazar el foco en función de la frecuencia. Ambos fenómenos se estudian a través de varios diseños y con las medidas de dos prototipos construidos. En campo lejano se consideran dos escenarios. En el primero se presenta un estudio para satélites geoestacionarios donde agrupaciones de antenas con grandes periodicidades son útiles para cubrir unos pocos grados. Por el contrario, el segundo escenario se centra en una aplicación de satélite para baja órbita. Aquí es recomendable utilizar una agrupación de antenas con periodicidad menor que λ para poder cubrir grandes ángulos. En estos dos escenarios las antenas Leaky Wave uniformes son muy adecuadas ya que permiten que las áreas de los diferentes elementos de la agrupación de antenas se solapen. Todos estos diseños se verifican con software comercial y código propio así como a través de medidas de los prototipos fabricados.All the thesis costs have been supported by two grants (UC3M) and two projects (UCM). The initial period of the thesis has been funded by the research project: “Estudio de mecanismos avanzados para el acoplamiento de la radiación del infrarrojo lejano a detectores, superconductores para el instrumento”, from the Spanish Ministry of Science and Innovation (SAFARI/SPICA, 2011-2012). Afterwards the financial support for the final period of the thesis came mainly from the project: “Diseño de Agrupaciones de Antenas con Filtros Angulares Realizados Mediante Estructuras Periódicas Selectivas en Frecuencia”, (EADS CASA ESPACIO (ECE),2012-2013).Programa Oficial de Doctorado en Multimedia y ComunicacionesPresidente: Francisco Luís Mesa Ledesma.- Secretario: Angelo Freni.- Secretario: José Luís Vázquez Ro

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