Broadband linear-to-circular polarizing reflector for space applications in Ka-band

This communication presents a novel low-profile broadband polarizing reflector to convert dual linear polarization (LP) into dual circular polarization (CP). The polarizing cell is based on printed dipole technology and presents a wideband performance in Ka-band. The dimensions of the printed dipoles are adjusted cell by cell to improve the reflection phase performance against variations in the incidence angles or in the cell dimensions. A 25-cm flat polarizing reflector demonstrator has been designed, fabricated and tested. The design has been optimized for transmit (19.2-20.2 GHz) and receive (29-30 GHz) frequencies in Kaband, but the broadband behavior of the cell provides satisfactory results also at the intermediate frequencies. The measured patterns show a good agreement with the simulations, with an axial ratio lower than 1.8 dB within the 19.2-30 GHz band. The proposed polarizing reflector can be used for novel multibeam antenna configurations to produce multi-spot coverage in Ka-band with a smaller number of apertures.Agencia Estatal de Investigación | Ref. TEC2016-75103-C2-1-RMinisterio de Economía y Competitividad | Ref. TEC2015-65353-REuropean Space Agency ESTEC | Ref. 4000117113/16/NL/A

Transmit–receive parabolic reflectarray to generate two beams per feed for multispot satellite antennas in Ka-band

This contribution describes the design of a multibeam parabolic reflectarray to produce two adjacent beams per feed in orthogonal circular Polarization (CP) simultaneously at transmit (Tx) and receive (Rx) frequencies in Ka-band. The Variable Rotation Technique (VRT) has been applied to reflectarray cells based on two types of resonant elements, which makes it possible to provide orthogonal beams at Tx and Rx, as well as to implement an in-band optimization procedure to reduce the cross-polarization. A 90-cm parabolic reflectarray has been designed, manufactured and tested to produce multiple adjacent beams in RHCP and LHCP at both 20 and 30 GHz. The results are satisfactory and validate the concept of generating two spaced beams in orthogonal CP by a single feed, changing the polarization of the beam between Tx and Rx. This concept can be suitable for multispot satellites in Ka-band, enabling to halve the number of onboard antennas and feedsAgencia Estatal de Investigación | Ref. TEC2016-75103-C2-1-RAgencia Estatal de Investigación | Ref. FJCI-2016-29943European Space Agency | Ref. 4000117113/16/NL/A

Uncertainty Determination Methodology, Sampling Maps Generation and Trend Studies with Biomass Thermogravimetric Analysis

This paper investigates a method for the determination of the maximum sampling error and confidence intervals of thermal properties obtained from thermogravimetric analysis (TG analysis) for several lignocellulosic materials (ground olive stone, almond shell, pine pellets and oak pellets), completing previous work of the same authors. A comparison has been made between results of TG analysis and prompt analysis. Levels of uncertainty and errors were obtained, demonstrating that properties evaluated by TG analysis were representative of the overall fuel composition, and no correlation between prompt and TG analysis exists. Additionally, a study of trends and time correlations is indicated. These results are particularly interesting for biomass energy applications

X-Band reflectarray antenna with switching-beam using PIN diodes and gathered elements

An electronically switching-beam reflectarray antenna to be used in X-band has been designed, manufactured and tested, using PIN diodes as switching device. The antenna has 244 elements arranged in a circular aperture. With the aim of saving electronic devices and reducing both manufacturing complexity and cost, the phase control has been implemented at sub-array level, using aperture-coupled patches gathered by pairs to a common delay line. The antenna was designed to switch the beam between +/- 5 degrees, in a scanning plane tilted 18.3 degrees with respect to the YZ plane. Each state was obtained by forward biasing one half of the diodes, while the other half remains in reverse biasing. A third state with the beam pointing to 0 degrees was obtained when all the diodes are in reverse biasing. The concept has been demonstrated by manufacturing and testing a breadboard. The measured radiation patterns fulfill the design requirements

Planar C-Band Antenna with Electronically Controllable Switched Beams

The design, manufacturing, and measurements of a switchable-beam antenna at 3.5 GHz for WLL or Wimax base station antennas in planar technology are presented. This antenna performs a discrete beam scan of a 60∘ sector in azimuth and can be easily upgraded to 5 or more steps. The switching capabilities have been implemented by the inclusion of phase shifters based on PIN diodes in the feed network following a strategy that allows the reduction of the number of switches compared to a classic design. The measurements show that the design objectives have been achieved and encourage the application of the acquired experience in antennas for space applications, such as X-band SAR and Ku-band DBS

Bifocal Dual-Reflectarray Antenna to Generate a Complete Multiple Spot Beam Coverage for Satellite Communications in Ka-Band

This paper presents a novel multibeam transmitting dual-reflectarray antenna able to generate a complete multiple spot coverage from a geostationary satellite in Ka-band (20 GHz). The bifocal design technique has been exploited for the first time to reduce by 50% the beam deviation factor with respect to the equivalent monofocal antenna, allowing to produce adjacent beams separated by only 0.56° in the antenna offset plane. In order to guarantee an acceptable spillover, the main reflectarray has been oversized in the same plane where the beams are compressed, resulting in an elliptical reflectarray of 3.5 m × 1.8 m. The interleaved beams required to provide the complete multi-spot coverage are produced in the orthogonal polarization, using the same aperture and feeds. The proposed antenna requires a smaller main aperture (about half of the area) and a lower number of feeds than other configurations that use a single oversized reflector to generate a complete multi-spot coverage, showing promising results for communication satellite applications in the Ka-band

Dual-Polarization Ku-Band Compact Spaceborne Antenna Based on Dual-Reflectarray Optics

This article demonstrated an accurate analysis technique for dual-reflectarray antennas that take into account the angle of incidence of the impinging electric field on the main reflectarray cells. The reflected field on the sub and the main reflectarray surfaces is computed using Method of Moments in the spectral domain and assuming local periodicity. The sub-reflectarray is divided into groups of elements and the field radiated by each group is used to compute the incident and reflected field on the main reflectarray cells. A 50-cm demonstrator in Ku-band that provides European coverage has been designed, manufactured and tested to validate the analysis technique. The measured radiation patterns match the simulations and they fulfill the coverage requirements, achieving a cross-polar discrimination better than 25 dB in the frequency range: 12.975–14.25 GHz

Millimeter-wave Beam Scanning Antennas using Liquid Crystals

Two Liquid crystal-based reflectarrays that operate at 100 GHz and 125 GHz are presented. The first pro totype (100 GHz) is used to validate the modeling and the design procedure proposed for this class of antenna. Experimental validation of the beam scanning is carried out by measuring the received power in a quasi-optical test bench, which is able to rotate the receiver in the horizontal plane. These results are used to des ign a second prototype antenna (125 GHz) which exhibits 2D beam scanning capabilities with a large bandwidth and scanning range that is sufficient for radar and communications applications