HALF-WAVE DIPOLE WITH AN ACTIVE REFLECTOR BASED ON OPTO-CONTROLLED METAMATERIAL

Для обеспечения радиосвязи применяются различные конструкции антенн, которые могут обладать всенаправленными или узконаправленными диаграммами направленности, при этом наибольшей защитой канала связи от помех и от перехвата обладают направленные антенны. Но их недостатком является то, что для обеспечения связи во всех направлениях требуется или установка группы антенн, или использование поворотных платформ, которые ухудшают показатели надежности системы, а также усложняют ее. Поэтому, как правило, для обеспечения связи применяют всенаправленные антенны, которые имеют диаграмму направленности в виде тороида. Недостаткaми таких антенн являются малый коэффициент направленного действия, а также прием большого числа шумов, что усложняет последующую обработку сигналов. Предлагается конструкция дипольной антенны, помещенной в активный метаматериал, с возможностью формирования луча путем коммутации слоев конструкции, что формирует динамически перестраиваемые рефлекторы. Получаемые в процессе функционирования системы диаграммы направленности обладают высокими значениями КНД, а также высокой помехозащищённостью и защитой от перехвата ввиду направленных свойств. Была получена конструкция антенны, помещенная в кубическую структуру активного метаматериала, с возможностью коммутации проводников с использованием pin-диодов или МЭМС-коммутаторов, что позволяет обеспечить быстрое переключение режимов работы устройства, формирование направленного луча и обеспечение помехозащищенной и защищенной от перехвата связи To ensure radio communication, various antenna designs are used, which can have omnidirectional or narrowly directional radiation patterns, while directional antennas have the greatest protection of the communication channel from interference and interception. However, their disadvantage is that to ensure communication in all directions, either the installation of a group of antennas or the use of turntables are required, which degrade the reliability of the system, as well as complicate it. Therefore, as a rule, to provide communication, omnidirectional antennas are used, which have a radiation pattern in the form of a toroid. The disadvantage of such antennas is, as a rule, a small directional coefficient, as well as the reception of a large number of noises, which complicates the subsequent signal processing. In this work, we propose a design of a dipole antenna placed in an active metamaterial with the possibility of forming a beam by switching the layers of the structure, which forms dynamically tunable reflectors. Directional patterns obtained in the course of system operation have high directivity values, as well as high noise immunity and protection against interception due to directional properties. As a result of the study, we obtained an antenna design, placed in a cubic structure of an active metamaterial with the possibility of switching conductors using pin diodes or MEMS switches, which allows for fast switching of device operating modes, formation of a directed beam and providing noise-immune and interception-proof communication

An Effective Form Analysis Approach for Designing and Optimizing a Cable-Net Structure of a Giant Active Reflector

The cable-net structure of a giant active reflector is a structure with large deformations. The effective form analysis approach can help the active reflector to achieve high surface accuracy. In this paper, a new nonlinear numerical form analysis approach is proposed for the active reflector cable-net structure. The basic principle and calculation flow of the static equilibrium are provided and the calculation program is compiled. This approach does not only achieve a uniform cable tension design based on the idea of “equal-tension replacement” but also simulates the change process from the reference state to the target working state. The obtained final form conforms to the target configuration and achieves the force balance. This, in turn, proves the adaptability of the proposed approach for the design and optimization of active reflector cable-net structure. By employing the form analysis, the length change of actuators and force distribution of all cables can also be simultaneously obtained. This provides an important basis for the actual operation and control optimization of similar active reflectors.

ACTIVE REFLECTORS FOR INTERFEROMETRIC SAR DEFORMATION MEASUREMENT

This paper is focused on the design, implementation and testing of an active reflector, to be used to support deformation monitoring studies based on Synthetic Aperture Radar interferometry. The device is designed to work in C-band with Sentinel-1 data, operating at 5.405 GHz ± 50 MHz. A brief description of the active reflector is provided. It consists of two antennas and an amplifying section. The active reflector has been tested in different experiments. In this paper, we describe the experiment carried out in the Parc Mediterrani de la Tecnologia (Castelldefels, Barcelona). The result shows a strong correlation with temperature. A calibration test was carried out to experimentally derive a calibration curve to correct the effect of temperature on phase stability.

A Low-Cost Active Reflector for Interferometric Monitoring Based on Sentinel-1 SAR Images

The effectiveness of radar interferometric techniques in non-urban areas can often be compromised due to the lack of stable natural targets. This drawback can be partially compensated through the installation of reference targets, characterized by a bright and stable radar response. The installation of passive corner reflectors (PCR) often represents a valid aid, but these objects are usually cumbersome, and suffer from severe weather conditions; furthermore, the installation of a PCR can be difficult and costly, especially in places with hard accessibility. Active reflectors (AR) represent a less cumbersome alternative to PCRs, while still providing a stable phase response. This paper describes the design, implementation, and test of an AR prototype, designed to operate with the Sentinel-1 synthetic aperture radar (SAR), aimed at providing a fair performance/cost benefit. These characteristics, obtained through a tradeoff between the use of off-the-shelf components and a simple architecture, can make the setup of a dense network (i.e., tens of devices) in the monitored areas feasible. The paper reports the design, implementation, and the analysis of different tests carried out in a laboratory, and in a real condition in the field, to illustrate AR reliability and estimate its phase stability.

Adapting Active Reflector Technology for greater sensitivity and sky-coverage in FAST-like Telescopes

The Five-hundred-meter Aperture Spherical radio Telescope (FAST), the largest single dish radio telescope in the world, has implemented an innovative technology for its huge reflector, which changes the shape of the primary reflector from spherical to that of a paraboloid of 300 m aperture. Here we explore how the current FAST sensitivity can potentially be further improved by increasing the illuminated area (i.e., the aperture of the paraboloid embedded in the spherical surface). Alternatively, the maximum zenith angle can be increased to give greater sky coverage by decreasing the illuminated aperture.Different parabolic apertures within the FAST capability are analyzed in terms of how far the spherical surface would have to move to approximate a paraboloid. The sensitivity of FAST can be improved by approximately 10% if the aperture of the paraboloid is increased from 300 m to 315 m. The parabolic aperture lies within the main spherical surface and does not extend beyond its edge. The maximum zenith angle can be increased to approximately 35 degrees from 26.4 degrees, if we decrease the aperture of the paraboloid to 220 m. This would still give a sensitivity similar to the Arecibo 305 m radio telescope. Radial deviations between paraboloids of different apertures and the spherical surfaces of differing radii are also investigated. Maximum zenith angles corresponding to different apertures of the paraboloid are further derived. A spherical surface with a different radius can provide a reference baseline for shape-changing applied through active reflector technology to FAST-like telescopes.

DEFORMATION MONITORING USING SAR INTERFEROMETRY AND ACTIVE AND PASSIVE REFLECTORS

This paper is focused on SAR interferometry for deformation monitoring, based on the use of passive and active reflectors. Such reflectors are needed in all cases where a sufficient response from the ground is not available. In particular, the paper describes the development of a low-cost active reflector. This development was carried out in an EU H2020 project called GIMS. The paper summarizes the key characteristics of the developed active reflector. The reflector was tested in two main experiments: the first one located in the campus of CTTC and the second one in a GIMS test site located in Slovenia. The experiments demonstrate the visibility of the active reflectors and provide the first results concerning the phase stability of such devices.