Analytical evaluation of uncertainty on active antenna arrays

An analytical method for evaluating the uncertainty of the performance of active antenna arrays in the whole spatial spectrum is presented. Since array processing algorithms based on spatial reference are widely used to track moving targets, it is essential to be aware of the impact of the uncertainty sources on the antenna response. Furthermore, the estimation of the direction of arrival (DOA) depends on the array uncertainty. The aim of the uncertainties analysis is to provide an exhaustive characterization of the behavior of the active antenna array associated with its main uncertainty sources. The result of this analysis helps to select the proper calibration technique to be implemented. An illustrative example for a triangular antenna array used for satellite tracking is presented showing the suitability of the proposed method to carry out an efficient characterization of an active antenna array.

Calibration proposal for new antenna array architectures and technologies for space communications

In large antenna arrays with a large number of antenna elements, the required number of measurements for the characterization of the antenna array is very demanding in cost and time. This letter presents a new offline calibration process for active antenna arrays that reduces the number of measurements by subarray-level characterization. This letter embraces measurements, characterization, and calibration as a global procedure assessing about the most adequate calibration technique and computing of compensation matrices. The procedure has been fully validated with measurements of a 45-element triangular panel array designed for Low Earth Orbit (LEO) satellite tracking that compensates the degradation due to gain and phase imbalances and mutual coupling.

A hands-on education project: antenna design for inter-CubeSat communications

CubeSat platforms have become a de facto standard for universities willing to initiate space-technology activities with students. These small satellite platforms ease the implementation of hands-on education projects and opening the apertures of new research areas. Moreover, due to the limited volume (a 10 cm cube) and power (1 W), the application of imaginative solutions is mandatory. This leads to new innovation processes in the course of CubeSat projects. In this paper, we present a hands-on education project the aim of which is the specification, design, building and measurement of an antenna for communication between nanosatellites and, in particular, CubeSats. The project lies within the framework of ETSIT-UPM innovative education activities in the area of space technology, where students play a leading role in real engineering projects.

Study of an electronic steering antenna with a staggered phase shifter configuration

This paper presents a study of three possible solutions that can be taken into account to control the phase shift between elements in an antenna array. Because commercial digital phase shifters have become a strategic element by U.S. Government, these elements have increased their price. For this reason, it is necessary to adopt some solutions that allow us to deal with the design and construction of antenna arrays.

Novel Gravity Distortion Evaluation on Large Antenna Array for Deep Space Communication

This paper presents a simple gravity evaluation model for large reflector antennas and the experimental example for a case study of one uplink array of 4x35-m antennas at X and Ka band. This model can be used to evaluate the gain reduction as a function of the maximum gravity distortion, and also to specify this at system designer level. The case study consists of one array of 35-m antennas for deep space missions. Main issues due to the gravity effect have been explored with Monte Carlo based simulation analysis.

Analog mitigation of out of band strong interferers in wide band acquisition for multiband HF transmissions

It is clear that in the near future much broader transmissions in the HF band will replace part of the current narrow band links. Our personal view is that a real wide band signal is infeasible in this environment because the usage is typically very intensive and may suffer interferences from all over the world. Therefore, we envision that dynamic multiband transmissions may provide better satisfactory performance. From the very beginning, we observed that real links with our broadband transceiver suffered interferences out of our multiband but within the acquisition bandwidth that degrade the expected performance. Therefore, we concluded that a mitigation structure is required that operates on severely saturated signals as the interference may be of much higher power. In this paper we address a procedure based on Higher Order Crossings (HOC) statistics that are able to extract most of the signal structure in the case where the amplitude is severely distorted and allows the estimation of the interference carrier frequency to command a variable notch filter that mitigates its effect in the analog domain.

Calibration process on the study of new antenna array architectures for space communications

This paper introduces novel calibration processes applied to antenna arrays with new architectures and technologies designed to improve the performance of traditional earth stations for satellite communications due to the increasing requirement of data capacity during last decades. Besides, the Radiation Group from the Technical University of Madrid has been working on the development of new antenna arrays based on novel architecture and technologies along many projects as a solution for the ground segment in the early future. Nowadays, the calibration process is an interesting and cutting edge research field in a period of expansion with a lot of work to do for calibration in transmission and also for reception of these novel antennas under development.

Research activities of Spanish antenna groups

When we look at the history of electricity and electromagnetism in Spain we discover that the most important Spanish researchers are generally out of the official institutions or stable research groups until the 20th century [1] [2]. In the 20th century most of the scientific research is done in stable research institutions and universities and the most important electromagnetism research centres in Spain are located in the Faculty of Physics of the most important universities, the National Scientific Research Council (CSIC) and the School for Telecommunication Engineering created in 1923. But the greatest impulse of research in the antenna and radiowave propagation field is done after 1960 reaching the first national URSI conference in 1980. After that year, the relation between groups and the number of research groups is continuously growing and the relation to industry is also increasing. When Spain joins the European research organizations (COST, ERC...) and the European Union in 1985 the research support experience a fast growing and the participation in the European research structures. In the antenna design field, there exist some specializations although most of the groups have dome specific projects in almost all the antenna analysis and design fields. Here, we have selected the most important and characteristic area related to each of the research groups and institutions. The easiest way to classify the research work in antennas is the selection between antenna analysis, design and measurement. After that the selected frequency bands technology, the type of antennas and the related circuits can be a good criterion to describe the variety of research work and specialization between groups.

Analysis and design of multirate synchronous sampling schemes for sparse multiband signals

We consider the problem of developing efficient sampling schemes for multiband sparse signals. Previous results on multicoset sampling implementations that lead to universal sampling patterns (which guarantee perfect reconstruction), are based on a set of appropriate interleaved analog to digital converters, all of them operating at the same sampling frequency. In this paper we propose an alternative multirate synchronous implementation of multicoset codes, that is, all the analog to digital converters in the sampling scheme operate at different sampling frequencies, without need of introducing any delay. The interleaving is achieved through the usage of different rates, whose sum is significantly lower than the Nyquist rate of the multiband signal. To obtain universal patterns the sampling matrix is formulated and analyzed. Appropriate choices of the parameters, that is the block length and the sampling rates, are also proposed.

Design of universal multicoset sampling patterns for compressed sensing of multiband sparse signals

Many problems in digital communications involve wideband radio signals. As the most recent example, the impressive advances in Cognitive Radio systems make even more necessary the development of sampling schemes for wideband radio signals with spectral holes. This is equivalent to considering a sparse multiband signal in the framework of Compressive Sampling theory. Starting from previous results on multicoset sampling and recent advances in compressive sampling, we analyze the matrix involved in the corresponding reconstruction equation and define a new method for the design of universal multicoset codes, that is, codes guaranteeing perfect reconstruction of the sparse multiband signal.

Application of postprocessing techniques methods for noise reduction in cylindrical near field antenna measurements

Three different methods to reduce the noise power in the far-field pattern of an antenna when it is measured in a cylindrical near field system are presented and compared. The first one is based on a modal filtering while the other two are based on spatial filtering, either on an antenna plane or either on a cylinder of smaller radius. Simulated and measured results will be presented.

Automatized connection of the layers of planar transformers with parallel windings to improve the component behavior

Transformers with parallel windings are commonly used to reduce the losses in the windings. Windings losses depend on the winding positioning and the frequency effects because each winding affects the current sharing of itself and the neighboring windings. In this paper a methodology for determining the connections of the parallel windings that reduces the power losses (and temperature) in the windings of multi-winding transformers is presented. Other applications of the method, such as balanced current sharing and voltage drop reduction are also explored. In this paper a methodology for determining the connections of the parallel windings that reduces the power losses (and temperature) in the windings of multi-winding transformers is presented. Other applications of the method, such as balanced current sharing and voltage drop reduction are also explored.

An alternative for reducing the layers in the construction of three-phase planar transformers

A modified winding layout for three-phase transformers with PCB windings is proposed in this paper. This modified layout can be used in high current transformers with many PCB layers to simplify the fabrication process. One of the key factors that might increase the cost and complexity in the construction of planar transformers is the number of layers of each PCB winding. This issue becomes even more important in medium-high power three-phase transformers, where the number of PCB layers is higher. In addition to that, the proposed method allows the use of commercial core shapes that are commonly used to design single-phase transformers. This fact makes possible the reduction of cost and flexibility of the design solutions. The proposed solution has been validated and compared using the conventional and the proposed methodologies to design a high power (20 kW) transformer.

Bifocal reflector antenna system for radar imaging at 300 GHz

A 300 GHz radar imaging system is presented, including descriptions of the radar sensor and antenna subsystems. The antenna consists of a Bifocal Ellipsoidal Gregorian Reflector whose beam is scanned by a combination of the rotation and vertical tilting of a flat small secondary mirror. A prototype is being mounted and its characterization will be presented.

Contribución a los arrays de antenas activos en microondas = Contribution to active array antennas at microwave bands

Esta tesis que tiene por título "Contribución a los arrays de antenas activos en banda X", ha sido desarrollada por el estudiante de doctorado Gonzalo Expósito Domínguez, ingeniero de telecomunicación en el Grupo de Radiación del Departamento de Señales, Sistemas y Radiocomunicaciones de la ETSI de Telecomunicación de la Universidad Politécnica de Madrid bajo la dirección de los doctores Manuel Sierra Castañer y José Manuel Fernández González. Esta tesis contiene un profundo estudio del arte en materia de antenas activas en el campo de apuntamiento electrónico. Este estudio comprende desde los fundamentos de este tipo de antenas, problemas de operación y limitaciones hasta los sistemas actuales más avanzados. En ella se identifican las partes críticas en el diseño y posteriormente se llevan a la práctica con el diseño, simulación y construcción de un subarray de una antena integrada en el fuselaje de un avión para comunicaciones multimedia por satélite que funciona en banda X. El prototipo consta de una red de distribución multihaz de banda ancha y una antena planar. El objetivo de esta tesis es el de aplicar nuevas técnicas al diseño de antenas de apuntamiento electrónico. Es por eso que las contribuciones originales son la aplicación de barreras electromagnéticas entre elementos radiantes para reducir los acoplamientos mutuos en arrays de exploración electrónica y el diseño de redes desfasadoras sencillas en las que no son necesarios complejos desfasadores para antenas multihaz. Hasta la fecha, las barreras electromagnéticas, Electronic Band Gap (EBG), se construyen en sustratos de permitividad alta con el fin de aumentar el espacio disponible entre elementos radiantes y reducir el tamaño de estas estructuras. Sin embargo, la utilización de sustratos de alta permitividad aumenta la propagación por ondas de superficie y con ellas el acoplo mutuo. Utilizando sustratos multicapa y colocando la vía de las estructuras en su borde, en vez de en su centro, se consigue reducir el tamaño sin necesidad de usar sustratos de alta permitividad, reducir la eficiencia de radiación de la antena o aumentar la propagación por ondas de superficie. La última parte de la tesis se dedica a las redes conmutadoras y desfasadoras para antenas multihaz. El diseño de las redes de distribución para antenas son una parte crítica ya que se comportan como un atenuador a la entrada de la cadena receptora, modificando en gran medida la figura de ruido del sistema. Las pérdidas de un desfasador digital varían con el desfase introducido, por ese motivo es necesario caracterizar y calibrar los dispositivos correctamente. Los trabajos presentados en este manuscrito constan de un desfasador reflectivo con un conmutador doble serie paralelo para igualar las pérdidas de inserción en los dos estados y también un conmutador de una entrada y dos salidas cuyos puertos están adaptados en todo momento independientemente del camino del conmutador para evitar las reflexiones y fugas entre redes o elementos radiantes. El tomo finaliza con un resumen de las publicaciones en revistas científicas y ponencias en congresos, nacionales e internacionales, el marco de trabajo en el que se ha desarrollado, las colaboraciones que se han realizado y las líneas de investigación futuras. ABSTRACT This thesis was carried out in the Radiation Group of the Signals, Systems and Radiocomunications department of ETSI de Telecomunicación from Technical University of Madrid. Its title is "Contribution to active array antennas at X band" and it is developed by Gonzalo Expósito Domínguez, Electrical Engineer MsC. under the supervision of Prof. Dr. Manuel Sierra Castañer and Dr. José Manuel Fernández González. This thesis is focused on active antennas, specifically multibeam and electronic steering antenas. In the first part of the thesis a thorough description of the state of the art is presented. This study compiles the fundamentals of this antennas, operation problems and limits, up to the breakthrough applications. The critical design problems are described to use them eventually in the design, simulation and prototyping of an airborne steering array antenna for satellite communication at X band. The main objective of this thesis is to apply new techniques to the design of electronically steering antennas. Therefore the new original contributions are the application of Electromagnetic Band Gap materials (EBG) between radiating elements to reduce the mutual coupling when phase shift between elements exist and phase shifting networks where special characteristics are required. So far, the EBG structures have been constructed with high permitivity substrates in order to increase the available space between radiating elements and reduce the size of the structures. However, the surface wave propagation modes are enhanced and therefore the mutual coupling increases when high permitivity substrates are used. By using multilayered substrates and edge location via, the size is reduced meanwhile low permitivity substrates are used without reducing the radiation efficiency or enhancing the surface propagation modes. The last part of the thesis is focused on the phase shifting distribution networks for multibeam antennas. This is a critical part in the antenna design because the insertion loss in the distribution network behaves as an attenuator located in the first place in a receiver chain. The insertion loss will affect directly to the receiver noise figure and the insertion loss in a phase shifter vary with the phase shift. Therefore the devices must be well characterized and calibrated in order to obtain a properly operation. The work developed in this thesis are a reflective phase shifter with a series-shunt switch in order to make symmetrical the insertion loss for the two states and a complex Single Pole Double Through (SPDT) with matched ports in order to reduce the reflections and leakage between feeding networks and radiating elements. The end of this Ph D. dissertation concludes with a summary of the publications in national and international conferences and scientific journals, the collaborations carried out along the thesis and the future research lines.