Showing papers on "Cassegrain antenna published in 2012"

Reflector arrangement for attachment to a wireless communications terminal

Abstract: A reflector arrangement (20, 22) is configured for attachment to a wireless communications terminal (4) having a patch antenna. The patch antenna includes a patch radiator(28)in a substantially parallel relationship with a ground plane(42), and the patch antenna produces a radiation beam of a predetermined beamwidth. The reflector arrangement is configured, when attached to the terminal, to produce a radiation beam of reduced beamwidth relative to the predetermined beamwidth. The reflector arrangement comprises a main reflector(20)and a sub-reflector (22) for reflecting radiation towards the main reflector(20), and the reflector arrangement is configured such that, when attached to the terminal, the patch antenna acts as a feed antenna for the sub-reflector(22). The sub-reflector (22) is arranged to collect the radiation from the patch antenna and to reflect the beam towards the main reflector (20) such that the main reflector (20) produces the radiated beam of reduced beamwidth.

CPW-Fed Cavity-Backed Slot Radiator Loaded With an AMC Reflector

Abstract: A low profile coplanar waveguide (CPW) fed printed slot antenna is presented with uni-directional radiation properties. The slot antenna radiates above a closely spaced artificial magnetic conducting (AMC) reflector consisting of an array of rectangular patches, a substrate and an electric ground plane. The electromagnetic bandgap (EBG) performance of the cavity structure between the upper conducting surface in which the slot is etched, and the ground plane at the bottom of the reflector, is investigated using an equivalent waveguide feed in the place of a half-wavelength section of the slot antenna. From the reflection coefficient of the equivalent waveguide feed one can determine the frequency band where minimum energy will be lost due to unwanted radiation from the cavity sides. The dimensions of the cavity were found to be very important for minimum energy loss. Experimental results for the final antenna design (with a size of 1.02λ0×0.82λ0×0.063λ0), mounted on a 1.5λ0×1.5λ0 back plate, exhibit a 5% impedance bandwidth, maximum gain in excess of 10 dBi, low cross-polarization, and a front-to-back ratio of approximately 25 dB. This low-profile antenna with relatively high gain could be a good candidate for a 2.4 GHz WLAN application.

A Bifocal Ellipsoidal Gregorian Reflector System for THz Imaging Applications

Abstract: Current terahertz imagers rely on reflector systems for the beam quality and imaging speed because the cross-range span that the system can cover is limited by the beam aberrations when the antenna scans. We present the design of a Bifocal reflector system that can rapidly scan a terahertz beam for standoff imaging applications while increasing the field of view of previous designs up to 50%. The design is based in a confocal Gregorian system where the nominal reflector surfaces are substituted by shaped surfaces to reduce the beam aberrations, while not increasing the manufacture cost of the reflector antenna. We also provide a set of useful design formulas for the design of this kind of reflector systems. The beam patterns obtained by the proposed designs are numerically calculated with the commercial software GRASP and compared with those obtained with previous approaches to the same problem, showing the better performance of the proposed solution.

A Simplified Feed Model for Investigating the Cross Polarization Reduction in Circular- and Elliptical-Rim Offset Reflector Antennas

Abstract: An analytic model for the primary feed of offset reflector antennas is presented that facilitates a more general investigation of the cross polarization reduction in both asymmetric and inter-cardinal planes. It includes both first and second order azimuthal modes, primarily the TE11 and TE21 type modes, and allows selection of symmetric and asymmetrical patterns, with different field tapers in the principal planes. Using this model first the influence of the second order TE21 mode on the cross polarization of an offset reflector with a circular rim is investigated. Then, the problem for an offset reflector with an elliptic rim is also studied. It is shown that minimizing the cross polarization in the asymmetric plane does not necessarily reduce it globally, as in the inter-cardinal plane it remains high. The procedure for reduction of the cross polarization globally and its effects on the sidelobe levels of the reflector antenna are also investigated. With the proposed feed model, the aperture efficiency of the reflector antenna is improved compared with a standard Gaussian feed with the same edge taper. Based on this study, a dual-mode circular waveguide horn is also proposed and designed. Its performance on an offset reflector antenna is studied and shown that the cross polarization levels are reduced quite satisfactorily within a respectable frequency band.

Electromechanical Coupling Analysis of Ground Reflector Antennas Under Solar Radiation

Abstract: The surface-accuracy design criterion for the next-generation reflector antennas for the deep-space instrumentation project in China was 0.1 mm rms. However, these antennas have no radome or air-conditioned ventilation to protect against solar radiation. Therefore, the effect on the antenna's electromagnetic performance of thermal deformation due to solar radiation must be carefully evaluated. For this engineering problem, a 40-m reflector antenna was selected as the research object. First, the heat fluxes from direct solar radiation, sky-scattering radiation, and ground-reflected radiation on the antenna's surface were calculated, based on the antenna's location, date, and time. Second, the temperature distribution of the whole antenna was obtained with the Finite-Element Method (FEM), considering three methods of heat transfer: conduction, convection, and radiation. A temperature experiment was then designed via a 7.3-m Cassegrain antenna. The results indicated the validity of the previous heat flux and temperature analyses. Engineering knowledge of the thermal impact on the antenna's radiation was essential to improve the overall design and construction of the antenna. Third, a thermal-structural analysis was carried out with ANSYS. Finally, the electromagnetic parameters of the antenna were calculated using a far-field pattern formula, and three main electromagnetic parameters - the gain loss, the sidelobe level, and the pointing error - were considered in detail. The results of the analysis showed that the degradation of the electromagnetic performance was not only dependent on the rms amount of structural deformation, but also on the distribution of the deformation, especially for the sidelobe level and pointing error. The analysis method and results can be referenced for the design of next-generation reflector antennas.

A dual-band multimode monopulse tracking antenna for land-mobile satellite communications in Ka-band

Abstract: The growing interest in bi-directional mobile satellite communications in Ka-band necessitates the development of dedicated antenna systems and feeds. In this paper we describe a mobile satellite communications terminal with a cassegrain reflector antenna fed from a multimode monopulse tracking system for circular polarisation at the satellite downlink frequency of 20 GHz. The structure is operational at 30 GHz as well, to cover the uplink frequency range. The antenna system is mounted on a high-performance mechanical positioner to facilitate a fast compensation of the movements of the carrier vehicle. This work contributes to the development of a satellite terminal for mobile communications in disaster scenarios [1].

Future Architectures for European Space Agency Deep-Space Ground Stations [Antenna Applications Corner]

Abstract: Space communications between distant spacecraft and the Earth are mainly based on large reflector antennas, such as the 35-m Deep-Space Antennas of the European Space Agency. These provide the required G T and EIRP to existing missions, such as, for example, Rosetta, Mars Express, and Venus Express. However, future missions to Mars and to outer planets (Jupiter and Saturn) are going to require higher performance for the ground segment that current stations cannot offer. This paper presents the results carried out in the framework of a strategic feasibility study promoted by the European Space Agency to identify the best architecture for future deep-space ground stations. Technical, economic, and operating aspects are described, deriving high-level specifications for future ground stations, and discussing in detail the antenna options and the subsystem devices. As an outcome, two different ground-station architectures, based on arrays of reflector antennas, are proposed and discussed in detail. These indicate the roadmaps that are going to pave the road to the final implementation.

Wide scan steerable antenna with no key-hole

Abstract: A steerable antenna architecture, or configuration, for optimal steering of transmitting and/or receiving beam over wide scan angles, is capable of steering the beam on a full hemisphere (2 π steradians), with no singularity or key-hole within a coverage area and with only one RF rotary joint. The architecture includes a dual-reflector assembly defining an antenna focal point located close to a main reflector surface and a signal feed chain having a signal source located adjacent to the antenna focal point and defining a feed axis substantially pointing towards a sub-reflector intersection point. A first actuator rotates the feed chain and the dual-reflector assembly about a first rotation axis generally perpendicular to the feed axis and not intersecting with the coverage area. A second actuator rotates one of the main reflector and the dual-reflector assembly about a second rotation axis aligned with the feed axis.

Co-located antenna arrangement

Abstract: An antenna method and arrangement of co-located antennas for wireless communication, includes at least one first antenna having a reflector panel and at least one second antenna utilizing a ground plane, wherein the reflector panel and the ground plane are the same element of the arrangement. The first antenna can be a loop element parallel to the reflector panel and the second antenna can be a monopole element perpendicular to the reflector panel/ground plane.

The blade beam reflector antenna for stacked nearfield millimeter-wave imaging

Abstract: A novel reflector antenna for nearfield millimeter-wave imaging applications has been developed. Combining parabolic curvature in one plane with elliptical curvature in the other, this antenna generates a “blade beam” focusing radiated field at a line. When excited at its focal point, transmitted rays are collimated in the first (horizontal) plane, each passing through the focal line at the second ellipse focus. As such, they illuminate a narrow slice of an object to be imaged. With only this slice illuminated, the scattered field will only be due to this narrow portion of the object, allowing for computationally simple inversion of a one-dimensional contour rather than an entire two-dimensional surface. Stacking the reconstructed contours for various horizontal positions provides the full object image.

The design of the MeerKAT L-band feed

Abstract: The design methodology of the MeerKAT L-band feed which consists of a wide flare angle axially corrugated conical horn, a horn matching section and a compact orthomode transducer (OMT) is presented. The dish is a classical Gregorian offset dual-reflector antenna system. The predicted results show stable radiation patterns over the frequency band with an ideal antenna efficiency above 73 %. The feed has losses below 0.05 dB resulting in very good system sensitivity.

Measurement of the Offset-Cassegrain Antenna of JEM/SMILES Using a Near-Field Phase-Retrieval Method in the 640-GHz Band

Abstract: This communication describes the results of the measurements made for the flight model of the offset Cassegrain antenna of superconducting submillimeter-wave limb-emission sounder (SMILES) aboard the International Space Station. We have employed a near-field phase retrieval method in which the aperture phase distribution is estimated only from the amplitude distribution measurements over two near-field planes. The far-field patterns estimated from the estimated near-field patterns were compared with theoretical calculations based on physical optics in which the surface errors measured for the main and sub reflectors were taken into account. As a result of the comparison, the far-field patterns estimated from the phase retrieval method were found to be in very good agreement with the physical-optics calculations to the sidelobe levels as low as -55 dB. We have also found that patterns of machined flaws on the surface of the main reflector were clearly identified in the retrieved near-field phase pattern. This demonstrates that the phase retrieval is an effective method to evaluate aperture antennas in the submillimeter-wave region, where accurate phase measurement is rather difficult.

Generalized Multilevel Physical Optics (MLPO) for Comprehensive Analysis of Reflector Antennas

Abstract: Recent developments of the multilevel physical optics (MLPO) algorithm aiming at the comprehensive analysis of complex reflector antenna systems are presented. The physical theory of diffraction (PTD) line integral along the rim of a reflector is combined with the physical optics (PO) surface integral within the multilevel algorithm. The multilevel scheme is also generalized to combine fields radiated by various components of different sizes, as encountered in complex antenna systems with multiple feeds and/or reflectors. Comparison with published results demonstrates the ability of the MLPO algorithm to cope accurately and efficiently with realistic reflector antenna problems.

Low-Cost, Microstrip-Fed Printed Dipole for Prime Focus Reflector Feed

Abstract: A low cost printed dipole antenna is proposed as a feed for prime focus reflectors. Its geometry is arranged such that the two dipole arms are on opposite sides of a dielectric substrate, fed by a microstrip line. A printed dipole-reflector is placed parasitically in front of the radiating dipole arms to make its radiation backward, toward the microstrip line. This allows mounting the feed centrally on a parabolic reflector from its apex, eliminating the needs for supporting struts. The feed antenna offers an impedance bandwidth of 16.5%, when printed on a substrate of dielectric constant 2.5, and an overall dimension of 60 $\,\times\,$ 60 $\,\times\,$ 1.58 ${\rm mm}^{3}$ at 3 GHz. Its impedance bandwidth is enhanced up to 29.1% by modifying the feed line. The pattern symmetry and cross-polarization of the antenna are improved by slightly changing the arms length. Its performance on a small available deep dish, with $f/D=0.25$ and $D=45~{\rm cm}$ , is experimentally calculated at 3 GHz, and overall efficiency of 55% is measured. For further verification, a second feed for operation at 6 GHz is also designed and verified on the same reflector, providing the same level of efficiency.

Assessment of the sensitivity of the South African KAT-7 and MeerKAT/SKA radio telescope reflector antennas

Abstract: This paper assesses and compares the sensitivities of the antenna gain, cross-polarization and sidelobe levels with respect to feed and/or subreflector displacements due to estimated operational conditions as well as manufacturing tolerances. The probabilistic assessment is evaluated with the Unscented Transform, deemed computationally more efficient than other similar techniques, and employs physical optics computer simulations performed with the WebPRAC and GRASP computer codes. The procedure is applied to the KAT-7 prime focus parabolic reflector antenna, and to a proposed design for the MeerKAT offset Gregorian reflector antenna.

Pattern synthesis for multi-feed reflector antenna using IWO algorithm

Abstract: In this paper, a new optimization algorithm to design shaped beam antenna is proposed. It is shown that by using offset parabolic reflector antenna and a linear array of horn antennas with one-wavelength spacing in focal point, Invasive Weed Optimization (IWO) algorithm can be used for amplitude and/or phase of source antennas to provide desired cosecant squared radiation patterns. To achieve a simple cosecant squared radiation pattern, amplitudes and phases of 11 source antennas (22 parameters) are optimized with no constraint by IWO and the results are compared with Particle Swarm Optimization (PSO) algorithm. Convergence diagram and radiation pattern results confirm the capability of IWO algorithm in shaped beam antenna design.

Satellite ground stations with electronic beam steering

Abstract: In this work, we propose electronic beam steering via antenna arrays as a substitute for large parabolic antennas at satellite ground stations. We concentrate on two array geometries, faceted arrays and hemispherical arrays. A thorough analysis is carried out of the radiation characteristics, the array size, as well as the antenna element distribution and spacing. Moreover, in order to fulfill the requirement of the array design, that is, to achieve a higher gain at low elevation angles where the longer spacecraft to ground station distance leads to a larger range loss, we propose to adjust the number of active antenna elements, i.e., some antenna elements are turned on while others are turned off according to the required level of antenna gain. This also contributes to a concept of an optimized array design for this specific application. In the simulations, the array optimization for both array geometries is further investigated and realized with a realistic ephemeris incorporated. The numerical results support the proposal of replacing large reflector antennas by electronic beam steering via antenna arrays at satellite ground stations.

Effect of Boundary Support and Reflector Dimensions on Inflatable Parabolic Antenna Performance

Abstract: For parabolic antennas with sufficient surface accuracy, more power can be radiated with a larger aperture size. This paper explores the performance of antennas of various size and reflector depth. The particular focus is on a large inflatable elastic antenna reflector that is supported about its perimeter by a set of elastic tendons and is subjected to a constant hydrostatic pressure. The surface accuracy of the antenna is measured by an RMS calculation, while the reflector phase error component of the efficiency is determined by computing the power density at boresight. In the analysis, the calculation of antenna efficiency is not based on the Ruze Equation. Hence, no assumption regarding the distribution of the reflector surface distortions is presumed. The reflector surface is modeled as an isotropic elastic membrane using a linear stress-strain constitutive relation. Three types of antenna reflector construction are considered: one molded to an ideal parabolic form and two different flat panel design patterns. The flat panel surfaces are constructed by seaming together panels in a manner that the desired parabolic shape is approximately attained after pressurization. Numerical solutions of the model problem are calculated under a variety of conditions in order to estimate the accuracy and efficiency of these antenna systems. In the case of the flat panel constructions, several different cutting patterns are analyzed in order to determine an optimal cutting strategy.

A planar passive dual band array feed antenna for Ku band satellite communication terminals

Abstract: A planar passive array feed antenna for bidirectional Ku band satellite communication was designed, fabricated and measured. The feed antenna achieved 50 dB isolation between transmit and receive ports across the transmitting band. An on-reflector test was conducted by mounting the array feed with external low noise amplifier and block downconverter (LNB) on a 90 cm dish to verify the feed radiation efficiency and illumination pattern. The measured signal to noise ratio (SNR) with the planar feed including loss in test connectors was within 2 dB of that of a commercial horn feed.

Analytic Transient Analysis of Radiation From Ellipsoidal Reflector Antennas for Impulse-Radiating Antennas Applications

Abstract: A time-domain (TD) analysis of ellipsoidal reflector antennas is presented to predict the transient scattered fields when it is illuminated by a cosine-tapered and transient-step feed radiation whose phase center is located at the nearby focus. A transient-step function of the feed's radiation is considered because it will produce an impulsive response near the second focus of the reflector as interested in the applications of impulse-radiating antennas. This TD solution is in a closed form and remains valid both near and far from the reflector, and can be used via the convolution theorem to efficiently obtain the early time transient fields generated by the same ellipsoidal reflector antenna when it is illuminated by a realistic finite-energy pulse which emanates as a spherical wave from the focus. Numerical results are presented for the transient fields both near and far from the reflector.

Synthesis Technique of Array-Fed Shaped-Reflector Antenna for DBF-SAR Application

Abstract: This letter presents a new approach to synthesize patterns of a phased-array-fed shaped-reflector antenna for digital beamforming (DBF) synthetic aperture radar (SAR). This type of reflector antenna is capable of radiating different broad transmitting beams under phase-only control and can generate narrow receiving beams using DBF technique in the elevation direction, which is applicable to a high-resolution wide swath (HRWS) SAR system. The linear array feed locates at the defocused area of the reflector, which can enhance the beam reconfiguring ability. The elevation patterns are optimized mainly by adjusting the excitation coefficients of the array feed using improved Projection Matrix Algorithm (PMA). The azimuth patterns are optimized mainly by adjusting the reflector shape using Differential Evolution method with Global and Local neighborhood (DEGL). The patterns of the shaped reflector antenna fed by a defocused feed array are effectively synthesized, including scanning and reconfiguring beams. A numerical analysis is performed that validates the effectiveness of the approach. The beam direction, beamwidth, and sidelobe level requirements are all met.

A solar parabolic reflector antenna design for digital satellite communication systems

Abstract: This paper introduces a compact solar parabolic reflector antenna design, with an effective DC solar performance and high gain / pencil beam antenna radiation characteristics, as an alternative to the standalone use of home-based autonomous solar panels and digital satellite antennas. The proposed solar reflector antenna consists of 2 parabolic shaped silicon solar panels with a diameter of 60 cm, each constructed by connecting individual silicon solar cells electrically in appropriate angles in order to create an approximate parabolic surface. The solar panels within the design have been connected in parallel in order to increase the total DC output level for medium and high current appliances. The bottom DC contact layer of the first silicon solar panel, which collects the DC current generated by the electrically connected solar cells within the panel as a result of the photovoltaic effect, also works as a parabolic reflector antenna with an average gain of 32.8 dB at the digital satellite downlink frequency band of 10.70 – 12.75 GHz, allocated by the ITU to the Region 1, including Europe.

94 GHz cassegrain reflector antenna performance characterization

Abstract: In this contribution, the measurement procedure of the impedance and radiation characteristics of a cassegrain reflector antenna is presented. Near-field (NF) measurement techniques have been used to obtain the radiation pattern and the directivity of the antenna. The antenna efficiency has been characterized using a calibrated total power radiometer. Moreover, tolerance effects in the return loss (RL) measurements are discussed, providing a solution to overcome the variability of the input impedance of different antenna prototypes.

Reflector and a multi band antenna

Abstract: The present invention relates to a reflector for an antenna comprising a first reflector assembly and at least one second reflector assembly, the first reflector assembly having a first reflector structure adapted for a first antenna frequency band f1 and at least one second antenna frequency band f2; the at least one second reflector assembly having a second reflector structure adapted for the first antenna frequency band f1 and at least one third antenna frequency band f3; and wherein the first reflector assembly and the at least one second reflector assembly are electrically coupled so that the first reflector assembly and the at least one second reflector assembly together form a common reflector structure adapted for the first f1, at least one second f2 and at least one third f3 antenna frequency bands. Furthermore, the invention also relates to a multi band antenna comprising at least one such reflector.

P-band feedarray for BIOMASS

Abstract: This paper deals with feed array suitable to SAR mission employing large reflector antennas (∼10–15m projected diameter). The feed array, in patch technology, is specifically designed to accomplish various mission operative modes in a modular way. A key feature of such feedarray is the capability of cancelling the high cross-polar components at secondary level, intrinsically generated by large reflector with short F/D ratio, allowing the SAR instrument operating in dual linear polarization.

Design and characterization of a simplified planar 16×8 RF MEMS switch matrix for a GEO-stationary data relay

Abstract: This paper presents the design and measurements of a simplified design approach for a 16 × 8 switch matrix based on Radio Frequency Microelectromechanical System (RF MEMS) switches. The operational frequency range is between 25.5 GHz and 26.5 GHz for data links between a Geostationary Earth Orbit (GEO) relay satellite and several Low Earth Orbit (LEO) satellites. The switch matrix implements a key functionality for tracking the incident signals of the LEO satellites on the receive feed antenna array of the GEO satellite's reflector antenna. A maximum insertion loss of 8.5 dB, isolation of higher than 45 dB and a minimum return loss of 18 dB have been measured.

Shaped beam synthesis for shaped reflector antenna using PSO algorithm

Abstract: A new method to design a cosecant squared radiation pattern in a shaped reflector antenna is proposed. Surface of the proposed reflector antenna is expanded by modified Jacobi polynomials. The expansion coefficients are optimized by using particle swarm optimization (PSO) algorithm to achieve desired cosecant squared radiation pattern in elevation plane and a narrow pencil beam radiation pattern in azimuth plane. The antenna is analyzed by physical optics (PO) method.

Synthesis and rigorous analysis of omnidirectional ADE antenna with shaped main reflector described by local conic sections

Abstract: This work investigates the synthesis and analysis of omnidirectional dual-reflector antennas. The body-of-revolution subreflector is generated by a single conic section while the shaped main reflector is generated by a combination local conic sections, sequentially concatenated to each other. The main-reflector is shaped to radiate, under GO principles, a prescribed power density in the elevation. As case studies, four representative axis-displaced ellipse (ADE) configurations are synthesized to provide a sectoral coverage in the elevation plane. Two different ray structures are considered: with a real or a virtual main reflector caustic. For a rigorous analysis of the antenna, a hybrid technique based on Mode Matching and Method of Moments is employed.

Design of multiple feed per beam antenna based on a 3-d directional coupler topology

Abstract: In this paper, an original Multiple-Feed per Beam (MFB) focal array architecture is designed Significant overlapping of the feed clusters is achieved to enhance illumination performances within a size-constrained lattice This focal array is set in front of a reflector to produce multiple beams with frequency and polarization re-use The key component of the focal array is the beam-forming network, composed of polarizers, interleaved three-dimensional directional couplers, phase-shifters, and circular feed horns Design considerations and final simulated radiation patterns are reported for a typical Ka-band multimedia mission