Showing papers on "Cassegrain antenna published in 2011"

Beam shaping of rf feed energy for reflector-based antennas

Abstract: A beam-shaping element is provided to shape RF feed energy for reflector-based antennas. The RF beam-shaping element is located between the primary reflector and the antenna feed and configured to direct RF energy from the feed away from a blockage created by the feed itself towards unblocked regions of the primary reflector. The beam-shaping element allows for a simplified feed design. The feed may comprise one or more feed elements, each comprising a radiating element and a feed to the radiating element such as a cavity-backed slot radiator and stripline trace. In a monopulse tracking system, each quadrant may include only a single feed element. In common aperture systems, the RF beam-shaping element may be formed on only the rear surface of the secondary reflector that allows transmission at the predefined RF wavelength while reflecting energy of a second predetermined wavelength to another sensor.

Quad ridge horn antenna with elliptically shaped sidewalls

Abstract: We present a quad-ridge horn antenna as a feed for a reflector antenna for use in radio astronomy applications. The antenna uses elliptically shaped sidewalls to limit the variation of beamwidth over a wide frequency range and to obtain greater radiation pattern rotational symmetry. The antenna is dual-polarized and matched over more than a 4:1 bandwidth. A design procedure is presented and a prototype designed according to this procedure is shown. Measured and simulated results of the prototype agree with each other well. The antenna is analyzed with a prime focus reflector to determine the range of efficiencies that can be expected.

Analysis of a dual-reflect array antenna

Abstract: A modular technique for the analysis of a dual-reflectarray antenna (DRA) configuration is presented. The proposed analysis method has been used to design a DRA that emulates previous dual-reflector antennas in Ku- and W-bands including a reflectarray as a sub-reflector. The results for the DRA compare very well with those of the parabolic reflector and reflectarray sub-reflector; radiation patterns, antenna gain and efficiency are practically the same when the main parabolic reflector is substituted by a flat reflectarray, the gain being reduced by a few tenths of a dB as a result of the ohmic losses in the reflectarray. The phase adjustment on two surfaces provided by the dual-reflectarray configuration can be used to improve the antenna performance in some applications requiring multiple beams, beam scanning or shaped beams.

Elliptically Shaped Quad-Ridge Horn Antennas as Feed for a Reflector

Abstract: Quad-ridge horn antennas of various geometries are considered as possible candidates for a wideband reflector antenna feed. It is demonstrated that shaping the sidewalls of the ridge horns significantly improves the radiation characteristics of the horns. The conical quad-ridge horn with an elliptically shaped sidewall shows the most promise as a wideband reflector antenna feed. The radiation patterns are rotationally symmetric, and the 10-dB beamwidth is reasonably constant over a wide frequency range.

Compact parabolic reflector antenna design with cosecant-squared radiation pattern

Abstract: This paper deals with the parametric analysis and proper design of parabolic reflector antennas to obtain pencil-beam, cosecant-squared and inverse cosecant-squared radiation patterns for air and coastal surveillance radars. A novel design is introduced to obtain both pencil-beam and cosecant-squared radiation patterns by using the same modified parabolic reflector antenna structure fed by an H-plane horn feeder which can be adjusted as symmetric or asymmetric feeder by changing the bottom flare angle. The analytical regularization method (ARM) is used as a fast and accurate way to solve the problem of E-polarized wave diffraction by parabolic shaped perfectly electrical conductive (PEC) cylindrical reflector with finite thickness. The numerical procedure is initially verified by the analytical and numerical methods, and the calculated radiation characteristics are presented for the proposed antenna configurations.

Compact Wideband Unidirectional Antenna With a Reflector Connected to the Ground Using a Stub

Abstract: A compact wideband unidirectional antenna with a reflector connected to the ground using a stub is proposed in this letter. The proposed antenna consists of a pair of stepped-structure patches and a coplanar waveguide feeding line. One stepped-structure patch is used as a monopole radiator, while the other operates as a reflector. As discussed, when the connection area between the reflector and the ground is small, the antenna can provide unidirectional radiation patterns over the operating frequency band ranging from 3.82 to 5.63 GHz for return loss greater than 10 dB. In this investigation, the optimized size of the proposed antenna is 20 × 20 mm2, which is much smaller than most of the current wideband unidirectional antennas. Experimental and simulated results are shown and discussed for practical applications.

Low profile dual-band reflector antenna with dual resonant AMC

Abstract: Dual-band reflector antenna with dual resonant artificial magnetic conductor (AMC) operating in WLAN band (2.4 GHz – 2.48 GHz, 5.15 GHz – 5.35 GHz) is proposed. Generally, a flat metal sheet is used with an antenna as a reflector to increase antenna gain. Since the reflection phase of a metal sheet is 180°, the antenna should be placed λ/4 away from the reflector to avoid destructive interference of the reflected wave from the metal sheet and the radiated wave from the antenna. If AMC with 0° reflection phase is used as reflector, the antenna can be closely placed to the AMC without destructive interference. There have been researches on low profile antennas using single layer AMC having 0° reflection phase in single band. In this paper, dual resonant AMC having 0° reflection phase in dual-band is designed as a reflector of dual-band reflector antenna. The dual resonant AMC is designed by adding another metallic patch-substrate layer on the conventional single layer AMC. Dual-band dipole is also designed with parasitic elements as a radiator. The height of the dual-band reflector antenna is 0.08λ which is one-third of 0.25λ, the height of reflector antenna using PEC. In addition, improvements of both gain and front lobe to back lobe ratio are achieved as a result of using dual resonant AMC which has surface wave suppression characteristic. To demonstrate improvement of gain and front lobe to back lobe ratio, comparison between the antenna using dual resonant AMC as reflector and the antenna using PEC as reflector for dual-band dipole is presented. Measured average peak gains of fabricated dual-band reflector antenna are 5.45 dB and 7.9 dB in 2.4 GHz – 2.48 GHz and 5.15 GHz – 5.35 GHz, respectively

Wide band hat-fed reflector antenna for satellite communications

Abstract: This paper presents a new design of a hat-fed reflector antenna for satellite communication, where low sidelobe and cross polar levels are required over a wideband. The hat feed has been optimized in the design by using the genetic algorithm (GA) through a commercial FDTD solver QuickWave V2D together with own developed Matlab code. The Gaussian vertex plate has been applied at the centre of the reflector for improving the reflection coefficient of the whole hat-fed reflector antenna. A return loss of 15 dB is obtained over a bandwidth of 47.5%. The simulations have been verified by measurements; both of them are presented in the paper.

Wideband QAMC reflector’s antenna for low profile applications

Abstract: A wideband reflector’s antenna based on quasi-artificial magnetic conductor is proposed. To validate the design, an Archimedean spiral has been backed to this new reflector. In comparison to classical solution using absorbent material, the prototype presents a very low thickness of λ/15 at the lowest operating frequency and an improved gain over a 2.4:1 bandwidth. The whole methodology to design this reflector can be applied to other wideband antennas.

Virtual array antenna with displaced phase centers for GMTI applications

Abstract: A novel multi-phase center reflector antenna is introduced for the Ground Moving Target Indicator (GMTI) applications. A single antenna is used to virtually make it more than one antenna by controlling the excitation modes of the dual-mode primary feed. First, the multi-mode primary feed is analytically modeled to study the concept in general. Then, the results are presented for the dual-mode stacked circular microstrip patch antenna placed at the focal point of an offset reflector antenna.

Realistic implementation of ellipsoidal reflector antennas to produce near‐field focused patterns

Abstract: [1] The radiation characteristics of ellipsoidal reflector antennas in the near zone of antenna aperture are investigated using Physical Optics (PO) approximations. This antenna has potential applications in the near-field communications because its radiation focuses in the near zone. Analytical formulations to predict the radiation efficiency and exhibit field phenomena are developed. Its applications as a RFID reader antenna at 2.4 GHz are demonstrated by numerical simulations and measurements over a realistic implementation of offset reflector fed by a microstrip patch antenna. Both numerical and experimental studies are performed to validate this antenna design.

Dual-reflectarray antenna for bidirectional satellite links in Ku-band

Abstract: This paper describes the preliminary design of a Ku-band antenna based on a dual planar reflector configuration that provides electronic beam scanning in a limited angular range. The antenna is characterized by its compact optics and simplicity to be folded and deployed. The system comprises a passive reflectarray as sub-reflector and a reconfigurable reflectarray with 1-bit electronic control as main reflector. The antenna is designed to generate a focused beam in both Rx and Tx frequency bands for Ku-band satellite links, including electronic pointing within a limited angular range.

Broadband antenna reflector for a circularly-polarized planar wire antenna and method for producing said antenna reflector

Abstract: The invention relates to the field of circularly-polarized planar wire antennas for very broadband telecommunication systems. It relates to an antenna reflector (3) for such an antenna (2), to an antenna device comprising said antenna reflector (3) and the antenna (2), and to a method for producing said antenna reflector (3). The antenna reflector (3) according to the invention is based on a hybrid structure comprising, on the one hand, a first reflecting region (341A) possessing the electromagnetic properties of an electrical conductor in a first frequency sub-band and, on the other hand, a second reflecting region (342A) having electromagnetic properties akin to a magnetic conductor in a second frequency sub-band. Each reflecting region (341A, 342A) is intended to face a region of the antenna able to emit electromagnetic radiation in the corresponding frequency sub-band so as to reflect the electric field of the rear radiation in phase with the electric field of the front radiation.

Beamforming capabilities of array-fed reflector antennas

Abstract: Array-fed reflector antennas are often used on GEO satellites to realize multiple beams with high gain. However, the directivity of these antennas suffers from relatively high scan loss. By utilizing beamforming, the antenna performance can significantly be improved. This paper addresses some of the beamforming capabilities of array-fed reflector antennas and their influence on the antenna performance. Numerical results supporting the discussed topics are given.

A Novel Reflector/Reflectarray Antenna An Enabling Technology for NASA's Dual-Frequency ACE Radar

Abstract: This paper describes a novel dual-frequency shared aperture Ka/W-band antenna design that enables wide-swath Imaging via electronic scanning at Ka-band and Is specifically applicable to NASA's Aerosol, Cloud and Ecosystems (ACE) mission. The innovative antenna design minimizes size and weight via use of a shared aperture and builds upon NASA's investments in large-aperture reflectors and high technology-readiness-level (TRL) W-band radar architectures. The antenna is comprised of a primary cylindrical reflector/reflectarray surface illuminated by a fixed W-band feed and a Ka-band Active Electronically Scanned Array (AESA) line feed. The reflectarray surface provides beam focusing at W-band, but is transparent at Ka-band.

Conical switched beam antenna method and apparatus

Abstract: A switched beam antenna system is provided The antenna system includes a plurality of feed elements arranged radially about a center point A feed switch provides equidistant signal paths between each antenna element and a transceiver The production of an antenna beam in a desired direction is achieved by controlling a switch to selectively operate a feed element associated with a beam coverage area that encompasses the desired steering angle

1.2 m Shielded Cassegrain Antenna for Close-Packed Radio Interferometer

Abstract: Interferometric millimeter observations of the cosmic microwave background and clusters of galaxies with arcminute resolutions require antenna arrays with short spacings. Having all antennas co-mounted on a single steerable platform sets limits to the overall weight. A 25 kg lightweight novel carbon-fiber design for a 1.2 m diameter Cassegrain antenna is presented. The finite element analysis predicts excellent structural behavior under gravity, wind, and thermal load. The primary- and secondary-mirror surfaces are aluminum-coated with a thin TiO2 top layer for protection. A low beam sidelobe level is achieved with a Gaussian feed-illumination pattern with edge taper, designed based on feed-horn antenna simulations and verified in a far-field beam-pattern measurement. A shielding baffle reduces interantenna coupling to below ~-135 dB. The overall antenna efficiency, including a series of efficiency factors, is estimated to be around 60%, with major losses coming from the feed spillover and secondary blocking. With this new antenna, a detection rate of about 50 clusters yr-1 is anticipated in a 13-element array operation.

Design of diffractive Cassegrain antenna at W band

Abstract: In this paper, a diffractive Cassegrain antenna for the monopulse radar at W band is designed. The main-reflector of the antenna is divided into several rings, and the surface in each ring is a part of a parabolic reflector with different focal length. The antenna has a gain of 37.6dB and the first sidelobe level is about −18.9dB. The thickness profile of the antenna is less than 10mm on the edge and 30mm in the center. Its radiation performances are comparable with the traditional Cassegrain antenna, but it has a much lower thickness profile.

Synthesis and rigorous analysis of omnidirectional dual-reflector antennas with shaped main reflector described by local conic sections

Abstract: This work presents a formulation for shaping the main reflector of an axis-symmetric dual reflector antenna designed to offer an omnidirectional coverage with an arbitrary radiation pattern in the vertical plane. The subreflector is generated by an axis-displaced confocal conic and the main reflector is shaped to achieve a prescribed far-field radiation pattern. The shaping procedure is based on geometrical optics (GO) principles. For validation of the antenna designs, the wotk employs technique by the accurate method of moments technique.

RF-mechanical performance for the Haystack radio telescope

Abstract: The Haystack radio telescope is being upgraded to support imaging radar applications at 96 GHz. The Cassegrain antenna includes a 37 m diameter primary reflector comprising 432 reflector panels and a 2.84 m diameter hexapod mounted subreflector. Top-level antenna performance is based on meeting diffraction-limited performance over an elevation range of 10 - 40° resulting in a maximum RF half pathlength error requirement of 100 μm RMS. RF-mechanical performance analyses were conducted that allocated subsystem requirements for fabrication, alignment, and environmental effects. Key contributors to system level performance are discussed. The environmental allocations include the effects of gravity, thermal gradients, and diurnal thermal variations which are the dominant error source. Finite element methods and integrated optomechanical models were employed to estimate the environmental performance of the antenna and provide insight into thermal management strategies and subreflector compensation. Fabrication and alignment errors include the manufacturing of the reflector surface panels and assembly of overall reflector surface.

A new reflector antenna design providing two different patterns

Abstract: Antennas with cosecant squared pattern are designed for air-surveillance radar systems. These permit an adapted distribution of the radiation in the beam and causing a more ideal space scanning. In the practice a cosecant squared pattern can be achieved by a deformation of a parabolic reflector. Moreover, it can be achieved by using multiple feed antennas with normal parabolic reflector surfaces. A fan beam antenna which is a directional antenna producing a main beam having a narrow beamwidth in one dimension and a wider beamwidth in the other dimension can also be used for similar purposes. This pattern can be achieved by a truncated parabolic reflector or a circular parabolic reflector. Frequency selective surfaces (FSSs) have been used in the reflector antenna designs in recent years. A FSS is an array of periodically arranged patches or apertures, showing a particular filtering behavior. Its selectivity in frequency is obtained by the design and allows the transmission of signals in a certain frequency range only. This work is proposed to design a reflector antenna that provides both fan beam and cosecant squared pattern by using a FSS. For the simulation and optimization of the antenna, high frequency simulation software (HFSS) and SUPERNEC antenna simulation programs are used.

Design and simulation of an ultra-wideband parabolic antenna with three-source based on time reversal method

Abstract: A novel application of the time reversal technique for multi-source reflector antenna design is proposed in this paper. The focus of a shaped reflector and the time sequence of its feeds can be determined by time reversal method, exploiting its spatial-temporal focusing property. Then a designed three-source parabolic antenna was simulated by the FDTD. The radiation properties show that the designed antenna can lead higher peak value of electric field which is 238% compared to a standard parabolic antenna with one-source and same aperture. It means time reversal method for designing multi-source antenna is effective, and can realize the spatial power combination in the far field.

Directional Sensitive Modulation Signal Transmitted by Monopulse Cassegrain Antenna for Physical Layer Secure Communication

Abstract: The broadcast nature of the wireless medium makes the communication over this medium vulnerable to eavesdropping. In this paper, we propose a directional sensitive modulation signal transmitted by Monopulse Cassegrain antenna for physical (PHY) layer security transmission. The main idea is that the sum beam transmit communication signal, simultaneously, and two difierence beams transmit artiflcial noise to guarantee secure transmission of the sum beam. The eavesdropper's channel is degraded by artiflcial noise, but the desired receiver's channel does not afiect because of the spatial orthogonality between the sum beam and two difierence beams. In this way, the desired receiver can demodulate the communication signal while the eavesdroppers learn almost nothing about the information from its observations. A closed-form expression of the secrecy capacity is also derived for this practical transmit scheme from the viewpoint of information theoretic. Finally, simulation results show that the proposed signal can signiflcantly improve the performance of secure wireless communications.

Multiband feed using coaxial configuration

Abstract: We present design, analysis and test results of a dual-aperture coaxial multiband feed horn that operates at S, Ku, K and Ka bands. The design objectives are to achieve aperture efficiencies of 85% for S and Ku bands and 60% for K and Ka bands and cross-polarization level of −20 dB within 30 degree off-boresight for all bands. These values are deduced primarily from the reflector geometry, −10 dB reflector edge taper and moderate cross-polarization requirements for the secondary patterns. In our design the Ku, K and Ka bands are launched through a multiflared circular horn while the S band is launched through a coaxial horn. A method of moment based software is developed to analyze the structure including mutual coupling between the apertures. It is found that the aperture impedance significantly affects the S-band performance. For the high frequency bands, the mutual coupling between the circular and coaxial apertures plays an important role. The simulated results including mutual coupling effects agree well with the measured data. The multiband feed design allows a compact, low weight, single offset reflector configuration as opposed to a Cassegrain antenna system that requires two separate feeds and a dichroic subreflector to accommodate such widely separated bands. © 2011 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2011. © 2011 Wiley Periodicals, Inc.

Development of Large Earth-Station Reflector Antennas in Japan

Abstract: This paper reports an overview of the development of large Earth-station reflector antennas for satellite communication systems in Japan. KDD (now, KDDI) developed a Cassegrain reflector antenna 20 m in diameter at KDD Ibaraki Space Communication Laboratory for Japan's first Earth station in 1963. This antenna was the first Earth station using a Cassegrain antenna in the world. It was awarded an IEEE Milestone as the “First Transpacific Reception of a Television (TV) Signal via Satellite, 1963” on November 23, 2009. The authors describe design technologies for large Earth-station reflector antennas, including beam-waveguide feed systems and reflector-shaping techniques. These design technologies have contributed tremendously to the popularization and advancement of satellite communication systems. The shaped Cassegrain antenna, fed by a four-reflector beam-waveguide feed, is symbolic of the standard Earth-station antenna all over the world.

Experimental Model of Array-fed Imaging Reflector Antenna for 21GHz-band Satellite Broadcasting System

Abstract: Satellite broadcasting in the 21GHz-band is expected to transmit large-capacity signals such as ultra high definition TV, called Super Hi-Vision in Japan with more than 4000 scanning lines. However, the 21GHz-band suffers from severe fading due to rain. In order to overcome the large rain attenuation, a reconfigurable antenna with an array-fed reflector is effective for the 21GHz-band satellite system. Therefore, we designed and manufactured an experimental model of an array-fed imaging reflector antenna for the 21GHz-band broadcasting satellite system. We verified the characteristics by measurement. We describe the configuration of the manufactured antenna and the radiation pattern of the imaging reflector calculated by using the measured radiation pattern of the feed array. A 7dB boosted beam has been successfully obtained.

An elliptical dipole antenna with rectangular slot reflector for wideband applications

Abstract: This paper presents an elliptical dipole antenna with rectangular slot reflector for wideband applications. The proposed antenna is designed on the FR4 substrate, resulting in low profile, high gain, and low cost. The antenna composes of an elliptical dipole and a slot rectangular reflector on the same plane. The proposed antenna has been analyzed and simulated by using the CST software package. In order to confirm the results, implementation and measurement of the antenna have been realized. The measured S11 < −10 dB covering a frequency range from 3 to 12 GHz with a relative bandwidth of 123.07 % and the pattern bandwidth from 3 to 6.5 GHz have been obtained. Also, the main lobe gain of 5.3 dB has been found.

On the Possibility of the Application of Axially Displaced Ellipse Antenna Elements for Construction of a Compact Multibeam Antenna System

Abstract: The application of axially displaced ellipse antenna elements in a multibeam antenna system is recommended. It is shown that in an axially displaced ellipse antenna, a simultaneous lateral shift of both the feed and subreflector results in much more beam tilting than does a shift of the feed, alone. The results of calculations and comparisons with known data are given.

Fixed ground stations for multi-satellite geostationary missions

Abstract: Multi-satellite missions, such as the next generation of METEOSAT geostationary satellites, require a ground station able to support an arbitrary number of satellites that can fly wherever within a pre-determined sky region, called control box. The use of high frequencies, around 26 GHz, imposes on the ground station high antenna gains to compensate for the noise temperature collected at those frequencies to obtain the specified G/T. Regardless of the narrow beamwidths that emerged from the adoption of high antenna gains, it is also required to operate with fixed (i.e. without any kind of tracking) antennas. This paper shows how all these specifications drive a new type of ground station with respect to current solutions. The proposed architecture is based on a multi-reflector system able to provide a set of interleaved beams, which generates an almost uniform coverage of the control box. The architecture is analyzed and designed, optimizing all the main antenna parameters, and presenting the analytical results.