New solutions for directive antennas and components for millimeter wave-band applications

Mención Internacional en el título de doctorEn las últimas décadas se ha producido un avance tecnológico exponencial en el área de las telecomunicaciones. Cada pocos años surgen sistemas de comunicaciones de nueva generación, siendo el 5G el que, hoy en día, se va implementando y ofreciendo progresivamente a los usuarios de todo el mundo. Los sistemas de comunicaciones 5G permiten tasas de datos mucho más altas, una velocidad ultrarrápida y un mayor ancho de banda que el 4G no soportaba debido a las bandas excesivamente utilizadas por debajo de los 6 GHz. Sin embargo, este aumento de la frecuencia introduce retos que no existen en frecuencias inferiores, como la absorción ambiental. Además, los obstáculos físicos que se interponen en el trayecto entre el emisor y el receptor también son un problema a estas frecuencias y las pérdidas inherentes a la propagación en el espacio libre son muy elevadas. El objetivo de esta tesis ha sido desarrollar e introducir nuevos e innovadores diseños de antenas que puedan ser utilizados en las bandas de frecuencia de las comunicaciones 5G y superiores así como en otras aplicaciones de ondas milimétricas. Los diseños que se presentan tienen como principal objetivo conseguir una alta directividad, manteniendo bajas pérdidas. Estos diseños se pueden agrupar en dos categorías principales: antenas Fabry-Pérot, y antenas gap waveguide. En la primera parte de esta tesis se han desarrollado tres diseños de antena Fabry-Pérot, incluyendo una metodología innovadora para el diseño de una metasuperficie que permite un funcionamiento en doble banda con control de directividad y que también puede ser utilizada también para implementar arrays de antenas en bandas de ondas milimétricas. Además, se muestra que este concepto de antenas Fabry-Pérot, implementado en un rango de frecuencias mucho más bajas, puede utilizarse también en aplicaciones de sistemas radar. En la segunda parte, se han desarrollado e implementado diseños innovadores de antenas y arrays usando la tecnología gap waveguide en particular su versión groove. En ellos, se han diseñado novedosas redes de alimentación y sistemas de corrección de fase que proporcionan bajas pérdidas y alta eficiencia.Programa de Doctorado en Multimedia y Comunicaciones por la Universidad Carlos III de Madrid y la Universidad Rey Juan CarlosPresidente: José Luis Masa Campos.- Secretario: Óscar Quevedo Teruel.- Vocal: Guido Valeri

Improvements to Optical Communication Capabilities Achieved through the Optical Injection of Semiconductor Lasers

Optically injection locked lasers have shown significant improvement in the modulation capabilities of directly modulated lasers. This research creates a direct-modulated optical communications system to investigate the bit-rate distance improvements achievable using optically injected Fabry-Pérot laser diodes. The injection strength and detuning frequency of the injection signal was varied to determine their impact on the optical communication link\u27s characteristics. This research measured a 25 fold increase in bit-rate distance product using optical injection locking as compared to the injected laser\u27s free-running capability. A 57 fold increase was measured in the bit-rate distance product when signal power is considered in a power-penalty measurement. This increased performance is attributed to the injected signals tolerance to dispersion given its reduced linewidth and chirp. This work also investigates the suitability of optical injection for radio over fiber applications using the period-one dynamic of optical injection. The all-optically generated, widely tunable microwave subcarrier frequency, well above the 3-dB cutoff frequency of the laser\u27s packaging electronics, was modulated with the same baseband electronics. This optically carried, ultra-wide spread spectrum signal was transported over 50km of standard-single-mode fiber. After detection at a high-speed photo- detector and the baseband modulation component was removed, the resultant signal was found to be suitable for broadcasting with an antenna or added to a frequency division multiplexed channel

Pattern and Polarization Reconfigurable Antennas for Gain Enhancement

Since the rapid proliferation of the wireless communication systems, the effective use of the allocated spectrum has become vital. The desire for generating equipment that can adopt their characteristics for different and challenging environments where excessive interference and mobile traffic is present has been increased. Pattern reconfigurable antennas have been an ideal candidate with conformal radiating characteristics, low cost and low power consumption features. A pattern reconfigurable dipole antenna placed over a ground plane with parasitic reflectors for continuous beam control has been considered as a starting point of the project where the well known Fabry Pérot resonance modes were utilized. The model was designed to be operating within 1.8GHz frequency band of current wireless communication systems. The continuous beam steering over the azimuth plane has been achieved by manipulating the surface currents along the parasitic strips by varying the capacitance between the conducting strips of the elements. Furthermore, a partially reflecting surface formed of periodic dipoles, was allocated on top of a metallic ground and the radiating structure formed of a half wavelength dipole and two parasitic strips for further gain enhancement and pattern reconfigurability. PIN diodes have been biased to switch between "ON" and "OFF" states and achieve beam switching from a high gain boresight direction to endfire radiation along the azimuth. Latterly the dual polarised version of the model was evaluated for an extra step of freedom where the operating frequency has been increased up to 3.6GHz which will be within the predicted frequency bands of next generation communication systems. Two orthogonally positioned dipole antennas with single parasitic elements have been used as the radiating structure. A total of four PIN diodes have been initialized for achieving pattern reconfiguration in both polarizations where the beam is switched from boresight to endfire directions. The evaluation process of three different models supported with, current curves and polar plots have been extensively studied in the thesis. Prototypes have been generated for each model and tested in a fully anechoic chamber for the proof and validation of the theory and simulation results

Performance Improvement of Dense Dielectric Patch Antenna using Partially Reflective Surfaces

Recently, millimeter-wave (MMW) band is being considered as the spectrum for future wireless communication systems. Several advantages are achieved by utilizing the millimeter-wave range, including high gain with large available bandwidth, compact size, and high security. Nevertheless, attenuation loss may restrict wireless communication systems’ transmission range. Meanwhile, printed antenna technology has gained the attention of antenna designers’ due to its low profile and ease of fabrication. High-gain antennas are very desirable as a critical part of MMW systems. Designing millimeter wave antennas with high gain characteristics would be a significant advantage due to their high sensitivity to atmospheric absorption losses. Moreover, planar configurations are required in many applications, such as for wireless communication. The main goal of this thesis is to design and propose state of the art designs of Fabry Pérot Cavity antenna (FPCA) designs with several types of superstrates to achieve high gain, wide bandwidth, and high efficiency to satisfy the requirements of today’s advanced wireless communication systems. A dense dielectric patch (DD) antenna is used as the main radiator and designed to operate at 28 GHz. The thesis presents several contributions related to the design and analysis of FPC antennas using several types of superstrates. The first research theme of this thesis has two parts. The first part presents a holey dielectric superstrate applied over a 2×2 dense dielectric square patch antenna array to enhance the gain, improve the bandwidth and efficiency, as well as to reduce the side lobe levels (SLLs). A dense dielectric patch replaces the metallic patch and is used as a radiated element. The measured results show a high gain of 16 dBi, with radiation efficiency of about 93 %, wide bandwidth of 15.3 %, and a reduced SLL. The second part focusses on a partially reflective surface (PRS) unit cell composed of two thin perforated dielectric slabs. The effect of the thicknesses of the unit cell dielectric slabs is discussed in detail. An array of the proposed PRS unit cell is applied over a dense dielectric square patch antenna array to broaden the bandwidth and to enhance the gain as well. The measured results exhibit a 3 dB gain bandwidth of 27 % with a high gain of 16.8 dBi. The second research theme presents an effective method to design a tapered superstrate of an FPC antenna with a DD patch element. This type of superstrate is designed to correct the phase above the superstrate to be almost uniform. The proposed single-layer perforated tapered superstrate is constructed by tapering the relative permittivity to be high in the center of the superstrate slab and then decrease gradually as it moves towards the edges. This tapered relative permittivity is then applied over a single DD patch antenna. The proposed antenna exhibits good performance in terms of the antenna gain and bandwidth. The antenna gain becomes flat and as high as 17.6 dBi. The antenna bandwidth is about 16 %, and the side lobe level of the antenna is very promising. A third theme presents the implementation and design of a high gain dense dielectric patch antenna integrated with a frequency-selective surface (FSS) superstrate. A 7×7-unit cell is used to build the superstrate layer, and applied above the high DD patch antenna. A modified unit cell is proposed to generate a positive reflection phase with high reflection magnitude within the frequency design in order to broaden the antenna bandwidth. A bandwidth of 15.3 % with a high gain of 16 dBi is obtained. Finally, a high gain linearly polarized (LP) substrate integrated waveguide (SIW) cavity antenna based on a high-order mode is implemented, fabricated, and tested. A TE440 mode is excited at 28 GHz. In this design, 4×4 slots are cut into the top metal of the cavity, where each slot is placed above each standing wave peak. These slot cuts contributed to a high gain of 16.4 dBi and radiation efficiency of about 96 %. The LP SIW cavity antenna was then integrated with a linear-to-circular polarization converter developed as a high gain circularly polarized (CP) SIW cavity antenna with high gain and high radiation efficiency of 16 dBi and 96 %, respectively

High Gain Beam Steering Antenna Arrays with Low Scan Loss for mmWave Applications

In millimeter-wave (mmWave) communications, the antenna gain is a crucial parameter to overcome path loss and atmospheric attenuation. This work presents the design of two cylindrical conformal antenna arrays, made of modified rectangular microstrip patch antenna as a radiating element, working at 28 GHz for mmWave applications providing high gain and beam steering capability. The microstrip patch antenna element uses Rogers RO4232 substrate with a thickness of 0.5 mm and surface area of 5.8 mm × 5.8 mm. The individual antenna element provides a gain of 6.9 dBi with return loss bandwidth of 5.12 GHz. The first antenna array, made by using five conformal antenna elements, achieves a uniform gain of approximately 12 dBi with minimal scan loss for extensive scan angles. In the second antenna array, a dielectric superstrate using Rogers TMM (10i) was used to modify the first antenna array. It enhanced the gain to approximately 16 dBi while still maintaining low scan loss for wide angles. The proposed array design method is very robust and can be applied to any conformal surface. The mathematical equations are also provided to derive the array design, and both array designs are verified by using full-wave simulations

Study on improvement of the performance parameters of a novel 0.41–0.47 THz on-chip antenna based on metasurface concept realized on 50 μm GaAs-layer

A feasibility study is presented on the performance parameters of a novel on-chip antenna based on metasurface technology at terahertz band. The proposed metasurface on-chip antenna is constructed on an electrically thin high-permittivity gallium arsenide (GaAs) substrate layer. Metasurface is implemented by engraving slot-lines on an array of 11 x 11 circular patches fabricated on the top layer of the GaAs substrate and metallic via-holes implemented in the central patch of each row constituting the array, which connects the patch to the leaky-wave open-ended feeding slot-lines running underneath the patches. The slot-lines are connected to each other with a slit. A waveguide port is used to excite the array via slot-lines that couple the electromagnetic energy to the patches. The metasurface on-chip antenna is shown to exhibit an average measured gain in excess of 10 dBi and radiation efficiency above 60% over a wide frequency range from 0.41 to 0.47 THz, which is significant development over other on-chip antenna techniques reported to date. Dimensions of the antenna are 8.6 x 8.6 x 0.0503 mm(3). The results show that the proposed GaAs-based metasurface on-chip antenna is viable for applications in terahertz integrated circuits

A Review of Broadband Low-Cost and High-Gain Low-Terahertz Antennas for Wireless Communications Applications

Low-terahertz (Low-THz, 100 GHz-1.0 THz) technology is expected to provide unprecedented data rates in future generations of wireless system such as the 6th generation (6G) mobile communication system. Increasing the carrier frequencies from millimeter wave to THz is a potential solution to guarantee the transmission rate and channel capacity. Due to the large transmission loss of Low-THz wave in free space, it is particularly urgent to design high-gain antennas to compensate the additional path loss, and to overcome the power limitation of Low-THz source. Recently, with the continuous updating and progress of additive manufacturing (AM) and 3D printing (3DP) technology, antennas with complicated structures can now be easily manufactured with high precision and low cost. In the first part, this paper demonstrates different approaches of recent development on wideband and high gain sub-millimeter-wave and Low-THz antennas as well as their fabrication technologies. In addition, the performances of the state-of-the-art wideband and high-gain antennas are presented. A comparison among these reported antennas is summarized and discussed. In the second part, one case study of a broadband high-gain antenna at 300 GHz is introduced, which is an all-metal model based on the Fabry-Perot cavity (FPC) theory. The proposed FPC antenna is very suitable for manufacturing using AM technology, which provides a low-cost, reliable solution for emerging THz applications

Analysis and design of new electronically reconfigurable periodic leaky-wave antennas

[SPA] El principal objetivo de la tesis es el estudio de nuevas tecnologías en el campo de las antenas reconfigurables. En particular, la tesis se centra en explorar y explotar el potencial que presentan un tipo de antenas denominadas como ¿Antenas basadas en Modos de Fuga¿ para controlar electrónicamente su diagrama de radiación. La tesis desarrolla el análisis, diseño y fabricación de tres novedosas antenas basadas en modos de fuga capaces de variar mediante unas pocas señales de control y de forma continua su ángulo de apuntamiento. El mecanismo de reconfiguración electrónica principalmente se basa en el control de la dispersión de los modos de fuga excitados en dichas estructuras, mediante un control electrónico introducido empleando estructuras periódicas resonantes combinadas con elementos activos tales como diodos varactores. La tesis demuestra claramente la utilidad de estas antenas en el campo de la reconfiguración electrónica, proponiendo estas nuevas estructuras como alternativas a otras soluciones más clásicas (como antenas en array de fase reconfigurables o reflectores parabólicos mecánicamente re-orientables mecánicamente) y otras de actualidad (como reflectarrays, transmitarrays, antenas metamateriales o antenas pixeladas), las cuales todas ellas presentan otros problemas en términos de coste, complejidad de diseño o limitaciones de escalabilidad en frecuencia, aportando así esta tesis novedosos conceptos de reconfiguración electrónica.[ENG] The thesis aims the design of novel reconfigurable antennas with electronic beam-scanning. In particular, the antennas analyzed are known as Fabry-Perot Antennas (FPA) and are currently of high interest in the scientific community because of their high-directivity, low-profile and structure simplicity, what allow them to be an interesting alternative to other technologies (e.g. parabolic reflectors, phased arrays, etc.) which require of complex power distribution networks, bulky external sources or costly techniques to achieve reconfigurable capabilities. In this thesis, the integration of active components, such as varactor diodes, with FPRA structures, is exploited to achieve electronic control of their aperture illumination, which in turn results in the electronic steering of the radiation-pattern main beam. A modal analysis based on the leaky-wave theory has allowed to understand and predict the behavior of these structures. An equivalent circuit model was developed to design and optimize the dimensions of theses complex structures, saving computational cost and time. The antennas are based on the control of the frequency dispersion response and the electromagnetic band-gap (EBG) properties of periodic structures, employing specially designed Frequency-Selective Surfaces (FSS) loaded with varactor diodes. Three novel antenna prototypes were manufactured to demonstrate electronic steering capability operating at 5.5GHz. Continuous scanning in elevation (1D scanning) and also in elevation and azimuth simultaneously (2D scanning) have been achieved employing just a few control signals (between 1 and 4 signals). The antenna structures have been implemented in a low-cost technology based on parallel plate waveguides and printed circuit boards which have allowed to design antennas with a reduced profile. Theoretical, simulated and experimental results are shown for each prototype to demonstrate the concepts. Also, some future lines related to novel planar reconfigurable antennas in development are also outlined. One of the main potential advantages of the reconfiguring principles presented for future applications is their frequency scalability. This would allow to apply these concepts to other technologies, such as MEMS or graphene, to build new reconfigurable antennas able to operate at higher frequency bands (e.g. mm-bands) for future applications.Universidad Politécnica de Cartagen

Parametric Optimization of Visible Wavelength Gold Lattice Geometries for Improved Plasmon-Enhanced Fluorescence Spectroscopy

The exploitation of spectro-plasmonics will allow for innovations in optical instrumentation development and the realization of more efficient optical biodetection components. Biosensors have been shown to improve the overall quality of life through real-time detection of various antibody-antigen reactions, biomarkers, infectious diseases, pathogens, toxins, viruses, etc. has led to increased interest in the research and development of these devices. Further advancements in modern biosensor development will be realized through novel electrochemical, electromechanical, bioelectrical, and/or optical transduction methods aimed at reducing the size, cost, and limit of detection (LOD) of these sensor systems. One such method of optical transduction involves the exploitation of the plasmonic resonance of noble metal nanostructures. This thesis presents the optimization of the electric (E) field enhancement granted from localized surface plasmon resonance (LSPR) via parametric variation of periodic gold lattice geometries using finite difference time domain (FDTD) software. Comprehensive analyses of cylindrical, square, star, and triangular lattice feature geometries were performed to determine the largest surface E-field enhancement resulting from LSPR for reducing the LOD of plasmon-enhanced fluorescence (PEF). The design of an optical transducer engineered to yield peak E-field enhancement and, therefore, peak excitation enhancement of fluorescent labels would enable for improved emission enhancement of these labels. The methodology presented in this thesis details the optimization of plasmonic lattice geometries for improving current visible wavelength fluorescence spectroscopy