A Scalable Arrangement Method for Aperiodic Array Antennas to Reduce Peak Sidelobe Level

Peak sidelobe level reduction (PSLR) is crucial in the application of large-scale array antenna, which directly determines the radiation performance of array antenna. We study the PSLR of subarray level aperiodic arrays and propose three array structures: dislocated subarrays with uniform elements (DSUE), uniform subarrays with random elements (USRE), dislocated subarrays with random elements (DSRE). To optimize the dislocation position of subarrays and random position of elements, the improved Bat algorithm (IBA) is applied. To draw the comparison of PSLR effect among these three array structures, we take three size of array antennas from small to large as examples to simulate and calculate the redundancy and peak sidelobe level (PSLL) of them. The results show that DSRE is the optimal array structure by analyzing the dislocation distance of subarray, scanning angle and applicable frequency. The proposed design method is a universal and scalable method, which is of great application value to the design of large-scale aperiodic array antenna

Способ пространственной обработки для радара системы контроля железнодорожного переезда

Introduction. Railway crossing is a source of increased danger for vehicles and pedestrians. To increase the safety of traffic at railway crossings, radar systems based on antenna arrays (AA) can be used. The important requirements for radar at a railway crossing are a wide field of view (up to 90 degrees) and, at the same time, a high accuracy in determining coordinates. Therefore, an analysis of methods for constructing AAs and spatial processing for an automatic traffic control system at a railway crossing seems to be a relevant research task.  Aim. Design of a method for constructing the topology of an AA and spatial processing of a radar system for monitoring traffic at a railway crossing, providing a wide field of view with a high accuracy in determining the coordinates of targets.  Materials and methods. The considered method was developed based on the theory of space-time signal processing. The design of the analyzed AA topologies was carried out by the finite element method (FEM) and the finite differ-ence time domain method (FDTD) based on segments of a microstrip transmission line.  Results. A method for constructing a filled transceiver antenna array and a beamforming algorithm, which provide high angular resolution and unambiguous measurement of the target's angular coordinates in a wide field of view with relatively low computational complexity, was developed. Mathematical and electrodynamic modeling of the designed AA topologies was performed. Adjusted values of the radiation patterns (RP) of the transmitting and receiving AA were obtained, which showed good agreement with the calculated values. The main design solutions regarding the construction of AA radar for a railway crossing control system are presented to provide a wide field of view when determining the coordinates of targets.  Conclusion. It was shown that the width of the resulting RP can be reduced by several times compared to the width of the receiving RP when using two transmitting antennas located at the edges of the aperture. This approach is similar to that used in the MIMO technology, although requiring no coherence of transmission channels and use of a system of orthogonal signals. The findings determine the prospects of using the developed method. Введение. Железнодорожный (ж/д) переезд является источником повышенной опасности как для автомобилей, так и для пешеходов. Для повышения безопасности движения в зоне ж/д переезда могут быть использованы радарные системы. В качестве антенн данных систем зачастую выступают антенные решетки (АР). Основными требованиями, предъявляемыми к радару на ж/д переезде, являются широкий сектор обзора (до 90°) и в то же время высокая точность определения координат целей. Является актуальным анализ способа построения АР и пространственной обработки для автоматической системы контроля движения на ж/д переезде, позволяющий обеспечить выполнение указанных требований.  Цель работы. Разработка способа построения топологии АР и пространственной обработки радара для контроля движения на ж/д переезде, с помощью которого достигается широкий сектор обзора при высокой точности определения координат целей.  Материалы и методы. Для рассматриваемого способа построения АР использованы методы теории пространственно-временной обработки сигналов. Разработка анализируемых топологий АР выполнялась методом конечных элементов и методом конечных разностей на базе отрезков микрополосковой линии передачи.  Результаты. Разработаны способ построения заполненной приемо-передающей АР и алгоритм формирования лучей, обеспечивающие высокое угловое разрешение и однозначное измерение угловых координат цели в широком секторе обзора при относительно низкой вычислительной сложности. Выполнено математическое и электродинамическое моделирование спроектированных топологий АР. Получены уточненные оценки диаграмм направленности (ДН) передающей и приемной АР, которые с высокой степенью точности совпадают с расчетными. Представлены основные конструктивные решения, касающиеся построения АР радара системы безопасности переезда, для обеспечения широкого сектора обзора при определении координат целей.  Заключение. Показано, что ширина результирующей ДН АР может быть уменьшена в несколько раз по сравнению с шириной ДН приемной решетки при использовании двух передающих антенн, расположенных по краям апертуры. Такой подход во многом аналогичен использованию технологии MIMO, но не требует обеспечения когерентности каналов передачи и применения системы ортогональных сигналов, что также определяет перспективность использования разработки

Development of antenna arrays for terrestrial and satellite applications: Feasibility study of different solutions to monitoring the atmospheric pollution, determination of electromagnetic fields in urban scenario and calculation of their dosimetry in small animals

The present work can be summarized as it follows: First of all, it will be held theoretical and numerical studies to improve the performance of antenna arrays by focusing on the isophoric case. Then, different antenna designs are shown and discussed, in order to be integrated within the urban environment. Some of these designs are experimentally tested. On the other hand, a study on the characterization of the electromagnetic fields through urban areas based on an equivalent planar circuit model is highlighted. Moreover and lastly, the influence of the electromagnetic fields in small animals is discussed by using two methods for the SAR level determination

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

Técnicas de simplificación de redes de alimentación para el diseño de agrupaciones de antenas y cálculo dosimétrico de SAR en animales pequeños mediante FDTD

En esta tesis se presentas dos líneas de investigación distintas, aunque ambas relacionadas estrechamente con el electromagnetismo. Así, en la primera de ellas se hace un estudio profundo de diferentes técnicas que permiten simplificar las redes de alimentación de las agrupaciones de antenas, mientras que en la segunda se presentan distintos sistemas de dosimetría de SAR sobre animales pequeños en los que se utilizan técnicas de FDTD. Las agrupaciones de antenas presentan grandes ventajas como puede ser la capacidad de generar patrones de radiación de altas prestaciones. Además suelen ser antenas compactas, de tamaño reducido y con prestaciones superiores comparativamente a otro tipo de antenas. El inconveniente o desventaja de este tipo de agrupaciones reside en el coste y complejidad de las redes de alimentación necesarias para su funcionamiento. Con esta motivación en esta tesis se desarrollan técnicas que minimicen estas desventajas. Tras una breve introducción, presentada en una de las partes del capítulo 1, de los conceptos básicos de las agrupaciones de antenas, en el segundo capítulo se presenta un estudio minucioso de las ventajas de utilizar la técnica de subarrays para agrupaciones lineales y planas. En el tercer capítulo, se describen dos métodos que hacen posible sintetizar diagramas suma y diferencia compartiendo parte de las excitaciones de los elementos que forman el array. Además uno de los métodos combina la técnica de subarrays para minimizar en mayor medida la complejidad de la red de alimentación. En el cuarto capítulo se presenta una técnica que permite obtener diagramas footprint mediante el uso de elementos dispuestos en anillos concéntricos. En el quinto capítulo se realiza un análisis de tolerancia sobre antenas de haz perfilado. Finalmente, en el sexto capítulo se presentan varias técnicas basadas en la utilización de elementos parásitos para obtener diagramas de radiación de altas prestaciones. Además, se muestran resultados experimentales mediante un prototipo construido con una de las técnicas propuestas. Por otra parte, en los últimos años el uso de tecnologías de comunicación inalámbricas se ha extendido de forma generalizada en nuestro entorno (telefonía móvil, Bluetooth, 3G, ...). Este hecho, hace que exista una preocupación creciente de la población sobre el posible daño de los campos electromagnéticos a los que estamos expuestos de forma cotidiana. Esta ha sido la motivación en esta segunda línea de investigación que se presenta en esta tesis. Así, tras una breve introducción en el capítulo 1 sobre conceptos básicos en los cálculos dosimétricos de SAR, en el séptimo capítulo se presentan 3 sistemas de dosimetría diferentes para obtener valores de SAR sobre animales pequeños. En el primero de los sistemas se utiliza una radiación GSM a 900 MHz en una caja metálica de onda viajera sobre ratas epilépticas. En el segundo, se realiza un estudio a 2,45 GHz en una cámara GTEM en el que se observa la expresión de la proteína HSP-90 en los animales radiados. Finalmente, en el tercer sistema se utilizan dos frecuencias simultáneamente, 900 MHz y 2,45 GHz, sobre los animales. Se pretende observar los efectos de radiaciones eléctricas simultaneas como a las que estamos sometidos cotidianamente. En todos los sistemas presentados se utilizan técnicas de FDTD para obtener los valores de SAR sobre los animales. Finalmente, en el capítulo 8 se enumeran las conclusiones que se derivan de este trabajo

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

DESIGN AND ANALYSIS OF SUBSTRATE INTEGRATED WAVEGUIDE BASED FILTERING ANTENNAS

Ph.DDOCTOR OF PHILOSOPH

SPICA:revealing the hearts of galaxies and forming planetary systems : approach and US contributions

How did the diversity of galaxies we see in the modern Universe come to be? When and where did stars within them forge the heavy elements that give rise to the complex chemistry of life? How do planetary systems, the Universe's home for life, emerge from interstellar material? Answering these questions requires techniques that penetrate dust to reveal the detailed contents and processes in obscured regions. The ESA-JAXA Space Infrared Telescope for Cosmology and Astrophysics (SPICA) mission is designed for this, with a focus on sensitive spectroscopy in the 12 to 230 micron range. SPICA offers massive sensitivity improvements with its 2.5-meter primary mirror actively cooled to below 8 K. SPICA one of 3 candidates for the ESA's Cosmic Visions M5 mission, and JAXA has is committed to their portion of the collaboration. ESA will provide the silicon-carbide telescope, science instrument assembly, satellite integration and testing, and the spacecraft bus. JAXA will provide the passive and active cooling system (supporting the

The Apertif Surveys:The First Six Months

Apertif is a new phased-array feed for the Westerbork Synthesis Radio Telescope (WSRT), greatly increasing its field of view and turning it into a natural survey instrument. In July 2019, the Apertif legacy surveys commenced; these are a time-domain survey and a two-tiered imaging survey, with a shallow and medium-deep component. The time-domain survey searches for new (millisecond) pulsars and fast radio bursts (FRBs). The imaging surveys provide neutral hydrogen (HI), radio continuum and polarization data products. With a bandwidth of 300 MHz, Apertif can detect HI out to a redshift of 0.26. The key science goals to be accomplished by Apertif include localization of FRBs (including real-time public alerts), the role of environment and interaction on galaxy properties and gas removal, finding the smallest galaxies, connecting cold gas to AGN, understanding the faint radio population, and studying magnetic fields in galaxies. After a proprietary period, survey data products will be publicly available through the Apertif Long Term Archive (ALTA, https://alta.astron.nl). I will review the progress of the surveys and present the first results from the Apertif surveys, including highlighting the currently available public data