Showing papers on "Cassegrain antenna published in 2007"

The Paraboloidal Reflector Antenna in Radio Astronomy and Communication 348

Abstract: p. 51 Fig. 3.9 this is not the correct three-dimensional picture of the Fourier Transformation of a square aperture distribution. Rather, as the Mathematica routine on page 54 indicates, it is the "azimuthal revolution" of the one-dimensional block-function. The FT of a square, uniformly illuminated aperture can be obtained from the following Mathematica routine (to replace Mat.3.6), showing the well-known "cross-shaped" sidelobes of the "Sinc" function.

Design and Test of a Mobile Antenna System With Tri-Band Operation for Broadband Satellite Communications and DBS Reception

Abstract: The tri-band mobile antenna system for broadband multimedia services in the Ka/K-band and a simultaneous direct broadcast service in the Ku-band has been developed. The radiating part of the antenna consists of a shaped dual reflector system and a tri-band feed of circular polarization. The low-profile offset main reflector has an aperture size of 60 cm 20 cm; therefore, a fan beam is formed which is sharp in azimuth and wide in elevation. The feed system contains a protruding dielectric rod for Ka/K-band and 2 2 active phased array. The latter provides the beam for Ku-band along with four fast electrical beams for stable satellite tracking. The new tracking algorithm based on a fusion technique involving various sensors and fast electrical beams has also been introduced. The antenna system was mounted on a large ship and a test car, and successfully operated via Koreasat-3.

The ALMA Front End Optics—System Aspects and European Measurement Results

Abstract: The Atacama large millimeter/submillimeter array (ALMA) is a radio telescope array with 50 Cassegrain style antennas that is currently being built in the Atacama desert in Chile. The telescopes are designed for a frequency range from 30 to 960 GHz with two orthogonal linear polarizations. Due to the extremely wide range, ten receivers are needed to cover the band, the divisions coinciding with the atmospheric windows. All receivers are built into a common cryostat on separate cartridges. The front end optics include the optical elements between the mixers and the secondary reflector. There are three different generic optical layouts. The two lower frequency bands use lenses that double as vacuum breaks. The next two frequency bands use ambient-temperature mirror systema and the upper six frequency bands have their complete optics cooled to cryogenic temperatures. In addition to the very demanding performance requirements, the optics design needs to take into account the constructional and operational aspects. As a large number of front ends will be built, the design must be robust with respect to mechanical and alignment tolerances. The exchange of receivers must be easy and should require as few alignments as possible. During operation, no mechanical adjustments are allowed. Measurement results are shown for the ALMA baseline bands. These measurements were made for single cartridges with the IRAM near-field measurement system and at SRON. The results of these measurements validate the design approach.

W-Band Fresnel Zone Plate Reflector for Helicopter Collision Avoidance Radar

Abstract: A high gain Fresnel zone plate reflector is presented for helicopter collision avoidance radar at 94 GHz. The antenna system consists of a compact, airtightness and low return loss primary source illuminating a printed reflector with Fresnel plate zone phase correction. In order to increase the overall efficiency, the reflector combines 8 correcting zones in its center and 4 on the border. Reflected phase of over 360deg is achieved by means of circular ring or combined circular and ring patches. The reflector is fabricated using standard photolithographic techniques. The primary source consists of a small FSS made by a double slot array antenna pasted on the aperture of a standard WR-10 waveguide. Antenna measurements were conducted using a compact base arrangement. The antenna performs 37.8 dBi at the center frequency of 94 GHz with a maximum value of the return loss value not exceeding -25 dB. The frequency bandwidth at -3 dB in gain and return loss is of 9%

Phase Center Study of the Electromagnetic Band Gap Antenna: Application to Reflector Antennas

Abstract: Recent studies have shown that the electromagnetic band gap (EBG) antenna can be used to feed a reflector, especially to realize multibeam coverage with geostationary satellite. However, it is necessary to evaluate its performances in terms of aperture efficiency to compare this solution to the classical ones. Among all the parameters which contribute to the aperture efficiency, one of the most important is the phase center, which has never been determined for EBG antennas. This is the aim of this letter. After defining a simple method to calculate the phase center of the EBG antennas, the position and the frequency evolution of this parameter will be studied. Then, the performances of such a feed associated with a Side Fed Offset Cassegrain Antenna (SFOCA) will be evaluated and compared with a classical feed for reflector, a Potter horn

Integrated waveguide cavity antenna and reflector RF feed

Abstract: An integrated antenna and reflector feed is provided which is structured as a waveguide cavity antenna or array having a curved reflector coupled to a sidewall of the waveguide cavity. A radiation source is situated facing the curved reflector and one or more radiating elements are provided on a top surface of the waveguide cavity. Several curved reflector feeds may be used, operating in the same or different frequencies.

Apparatus and method for antenna rf feed

Abstract: An RF feed is provided which is structured as a curved reflector coupled to a sidewall of a waveguide cavity. A radiation source is situated facing the curved reflector. The RF feed may be coupled to a waveguide cavity having radiation elements coupled to top surface thereof, to thereby feed an antenna array. When an antenna array is used, several curved reflector RF feeds may be used, operating in the same or different frequencies.

The Paraboloidal Reflector Antenna in Radio Astronomy and Communication: Theory and Practice

Abstract: and historical development.- Geometry of reflector antennas.- Electromagnetic theory of the reflector antenna.- Antenna characteristics in practical applications.- Measurement of antenna parameters.- Miscellaneous subjects.- Design features of some radio telescopes.

A New Shaped Reflector Antenna for Wide Beam Radiation Patterns

Abstract: This paper presents a new shaped reflector antenna for wide beam azimuthal patterns and a cosecant squared elevation pattern. Elliptical strips instead of parabolic strips are used in horizontal planes of the reflector surface to achieve this purpose. Simulation and measurement results of the shaped reflector fed by a ridged horn antenna are presented.

Back-to-Back Reflector Antennas With Reduced Moment of Inertia for Spacecraft Spinning Platforms

Abstract: A back-to-back reflector antenna system with reduced moment of inertia is proposed in order to address the demanding problem of supporting large reflector antennas on spinning platforms. The configuration provides additional potential advantages, such as reducing the spinning speed by half for a given sampling rate when both back-to-back reflectors are utilized. Geometrical parameters of the reflector are determined such that the moment of inertia of the rotating system is reduced. It is shown that these back-to-back reflectors suffer from a high cross-pol level in the asymmetrical plane due to the large feed offset angle. Two different methods are explored to alleviate the high cross-pol level problem. In the first method, a sub reflector is utilized to minimize the cross-pol level by satisfying the Mizugutchi condition. In the second method, a tri-mode matched feed horn is suggested to achieve a similar result. The suppressed cross-pol level puts forward the gravitationally balanced back-to-back reflector antenna systems as a potential candidate for future spacecraft antennas on spinning platforms.

Optimization of 200-800 MHZ eleven feed for GMRT

Abstract: This paper discusses in brief the electrical design of the Eleven feed for the parabolic reflector antennas of Giant Meterwave Radio Telescope (GMRT-India) optimized for 200 to 800 MHz bandwidth. Paper also gives the comparison between the simulated and measured antenna input reflection coefficient and radiation patterns. The measured S11 of the feed is less than -8 dB and the computed total aperture efficiency including the mismatch losses, is better than -3.2 dB over desired bandwidth for the reflector antennas of GMRT having 62.5° of half subtended angle. (6 pages)

On Analysis and Optimization of an Active Cable-Mesh Main Reflector for a Giant Arecibo-Type Antenna Structural System

Abstract: The active cable-mesh main reflector of a giant Arecibo-type antenna can adjust the illuminated area to a given parabolic surface in time, which is achieved with a flexible cable-mesh structure This paper addresses the feasibility of the active cable-mesh main reflector, including accuracy adjustment and the influence of the panel curvature The illuminate area of the reflector needs to be adjusted to a paraboloid, which is implemented by introducing a bias distribution field vector of mesh surface and least norm solution for under-determined equations Plane panels and spherical panels are investigated Numerical results show that a much more better surface precision can be obtained using spherical panels

Stabilizing mechanism for a deployed reflector antenna in a mobile satellite antenna system and method

Abstract: A stabilizing mechanism and method for a deployed reflector antenna in a mobile satellite system. The stabilizing mechanism has a pair of stabilizing devices with a first end of each stabilizing device connected on a rear support of the reflector antenna. The first ends are positioned on opposite sides of the rear support. A second end of each stabilizing device is connected to a tilt mechanism in the mobile satellite system. The pair of stabilizing devices forms a support angle about the centerline of the reflector antenna and with the tilt mechanism. The pair of stabilizer devices pushes against the opposite sides with a pre-load force when the reflector antenna is deployed to minimize deflection of the reflector antenna due to environmental forces.

Design of printed dipole with reflector

Abstract: In this paper, a printed dipole antenna with reflector in order to concentrate radiation in half-space is presented. The maximum gain of the antenna achieves 6.5dBi at the cost of a reduced bandwidth. The structure has been simulated and measured with a good agreement. (4 pages)

Mushroom surface cloaks for making struts invisible

Abstract: There are many situations where electromagnetic waves are obstructed by some mechanical structure. If the structure is part of or close to an antenna, the obstruction may represent aperture blockage, causing increased sidelobes and reduced gain. The blocking cylinders can be struts supporting the subreflector in a Cassegrain antenna or the feed in a prime-focus paraboloid. The increased sidelobes and reduced gain for these cases are previously studied in detail in several articles, and some simple analytical expressions and design curves are given in (Kildal et al., 1988). The above mentioned blockage effects are a result of the forward scattered field. This is often characterized in terms of an induced field ratio (IFR). However, the blockage losses and sidelobes caused by forward scattering are proportional to the product of the IFR and the physical width (Kildal et al., 1988). Therefore, the paper (Kildal et al., 1996) chose to characterize the forward scattering in terms of this product, being referred to as the equivalent blockage width or simply the blockage width. Thereby, it is easier to compare struts of different widths and types with respect to their electrical performance and mechanical strength. For opaque objects the blockage width becomes at high frequency equal to the physical width. The blockage width becomes by the definition a complex value, where both the real part and the absolute value are representative for characterizing invisibility. We here choose the absolute value only, to save space. The equivalent blockage width is readily computed by considering a plane wave incident on an infinitely long strut, which is a two-dimensional scattering problem. In this paper we treat for simplicity only normally incident plane waves.

Active reflectarray based on high impedance surface

Abstract: The proposed antenna is composed by an electromagnetic band gap material which acts as active reflector and a waveguide primary feed including sub-reflector placed at the EBG centre. The active control of the reflection coefficient phase, all over the reflector surface, allows obtaining the desired radiation pattern: classic one like parabolic antenna, scanned, sectoral or shaped pattern.

Dynamic Link Improvements using a Reconfigurable Reflector Antenna

Abstract: This paper demonstrates that adapting the reflector surface shape of a spacecraft antenna according to the actual weather situation can reduce the transponder power margin by as much as 6 dB. The computer time required to calculate a new scenario is about 30 seconds. The range of the setting of the actuators to obtain the different surface shapes is within ±10 mm for a typical antenna operating at 12 GHz. (4 pages)

A New Horn Array Feed for Parabolic Cylindrical Reflector Antenna

Abstract: A new horn array for parabolic cylindrical reflector antenna is proposed in this paper. By using the new horns, the linear array can suppress grating lobes when the element spacing is larger than one wavelength. The new array is adopted as the feed of a spatial power combining antenna. The gain of the antenna with new horn array feed is 1.2dB higher than that of the antenna with conventional pyramidal horn array feed.

Dual Polarized UHF/VHF Honeycomb Stacked-Patch Feed Array for a Large-Aperture Space-borne Radar Antenna

Abstract: As penetration depth through vegetation and ground becomes more important in active remote sensing applications, there is a shift toward using lower frequencies. To facilitate imaging of ground water, soil moisture and composition, and penetrating through forest canopies, a dual-band synthetic aperture radar (SAR) has been proposed to operate at VHF and UHF frequencies. To accommodate weekly repeat observations from LEO, a swath of roughly 350 Km is needed, requiring a 30-m long antenna aperture from the SAR design point of view. The beams of the UHF and the VHF antennas must coincide in the cross-track direction, resulting in antenna widths of 3m and 11m, respectively. A stacked, linearly dual-polarized patch array feeding a 30 meter diameter parabolic reflector is proposed for this application, which synthesizes near-rectangular effective apertures on the reflector. Using a mesh reflector technology, the mass of such an antenna configuration is about ten times smaller than a corresponding phased-array antenna. A scaled-frequency version of the feed array was initially designed, built, and tested. It was also integrated with a scaled reflector antenna to verify the performance of the overall system. The actual frequency version was then designed, built, and tested. The design of the dual-band stacked array and the power dividers will be discussed, the fabrication process explained, and the approaches used for optimizing the performance characteristics will be presented. The measurement results for return loss on both transmit and receive, isolation, and radiation pattern will be presented and shown to be in good agreement with the simulated results.

Quasi-compact range

Abstract: An antenna method and system to implement a quasi-compact range technique/technology in which a reflector antenna is used to produce a test field within a test region at a quasi-compact range, which is within a near-field of the reflector antenna but further from the reflector antenna than a compact range of the reflector antenna.

The reflector design problem

Abstract: In this paper we review the mathematical advances achieved in recent years on a reflector design problem. This problem can be reduced to the solvability of a fully nonlinear partial differential equation of MongeAmpere type, subject to a second boundary condition. In the far field case the existence and regularity of solutions was established in [W1]. In the near field case, the existence of weak solutions was obtained in [KO]. The regularity is a very complicated issue but we found precise conditions for it [KW]. In this paper we also prove the C1 regularity of the reflector, assuming less regular energy distributions. 2000 Mathematics Subject Classification: 35J60, 78A05.

Design and Simulation of Novel Ultra Wideband Planar Reflector Antenna

Abstract: A novel ultra wideband planar reflector antenna is presented in this paper. The proposed antenna is composed of a circular disc dipole and a finite reflector plane. The impedance matching and bandwidth for the presented antenna are mainly affected by the diameter of the disc and feeding separation. The theory of ultra wideband planar reflector antenna is discussed and simulated. By properly choosing adequate dimension and adjusting feeding distance, impedance bandwidth of S11<- 10dB is about from 1.7GHz to 19.8GHz, and relative bandwidth is greater than 160%. The antenna can get broad radiation beam in the low frequency band. The main lobe 3dB width is wider than 65deg at E-plane and H-plane in low frequency. To increase the impedance bandwidth, a changed planar reflector antenna is proposed. The simulation and analysis results are presented.

Dual reflector mechanical pointing low profile antenna

Abstract: Dual reflector offset mechanical pointing low profile telecommunication antenna, to be used above all on vehicles, even high-speed ones. Its reduced physical dimensions facilitate its use, with respect to the known solutions, as it allows its connecting to the receiving system, such as a satellite, though installed on a train or on an aircraft. The invention lies within the technical field of telecommunications and the applicative field of stationary, movable antennas of reduced dimensions, and accordingly within that of telecommunications in general. The original dual reflector antenna is obtained from a second-order polynomial that configurates it in the Cartesian space XYZ.

Multibeam Phased Array Feed System Using Beam Group Concept

Abstract: The concept of beam groups should enable us to obtain a lightweight antenna feed system that offers high antenna gain and high flexibility in radio-frequency (RF) power distribution among the beams of the next-generation multibeam communication satellite. Setting up groups of beams and exciting all the beams in a group using the same amplitude weight improves the antenna gain over the entire coverage area compared with the conventional array-fed reflector antenna and achieves flexible RF power distribution among the beams. The beams shared by different beam groups are combined with appropriate phase and division ratios so as to further improve the RF power distribution flexibility. An antenna feeder that uses these techniques is only half the weight of conventional antenna feed systems.

Deformed Antenna Pattern Compensation Technique for Multi-Beam Antennas in Broadband and Scalable Mobile Communications Satellites

Abstract: To create a next-generation mobile satellite communication system that offers large communication capacity, the onboard antenna system must be a multi-beam system consisting of a light weight 20-m class reflector and a light weight 100-beam class antenna feed system. We clarify that the antenna gain decrease created by the reflector surface distortion expected in orbit is relatively large. This paper presents a deformed antenna pattern compensation method that minimizes circuit scale. Validity of the proposed method is confirmed by antenna pattern calculations and experiments on a fabricated array-fed reflector antenna.

Analysis and Measurement of Reflector Antennas in the MM-Wave Frequency Range

Abstract: For the ADMIRALS study of ESA/ESTEC, performed in 2000 - 2002 and subsequent mm-wave studies in 2003 - 2005, a Representative Test Object (RTO) was designed and built to validate the antenna measurement performance with a high gain reflector antenna at 203, 322 and 503 GHz. The RTO mainly contains out of an offset reflector antenna with 1.5 in reflector diameter and is related to future remote sensing antennas as FIRST, MASTER or HERSCHEL/PLANCK. For assessment of measurement results, the RTO was theoretically analyzed with the simulation tool GRASP. For improvement of the simulation model, primary feed and surface contour data of the reflector - measured at the feed as well as reflector manufacturer - were taken into account within the simulations. Within further simulations, reflector deformation effects due to the mounting configuration regarding the reflector backing structure of the RTO reflector could be identified with additional surface measurements of the RTO reflector. Additional optical measurements were performed with a highly accurate laser tracker system and measurement technology. The accuracy of these measurements could be identified with 10 .. 20 mum. This work was finished in 2005 and the results are described in this paper.

Design and Analysis of 3mm Multimode Monopulse Feed

Abstract: The design and analysis of a monopulse multimode feed used in a Cassegrain antenna at 3 mm waveband is described in this paper. A new combination of higher modes has been given, which will result in a novel structure that is easier to fabricate and more aseismatic. A better way has been proposed to keep the modes in phase at the horn aperture. By adjusting the amplitude and phase of the modes and the length of the phase section, a good performance is achieved with low side lodes, radiation patterns in both the elevation plane and the azimuth plane are in good agreement.

Design of a shaped double-shell lens feed for a quasi-optical reflector system

Abstract: This paper proposes a new shaped double-material lens for this objective and presents its design and performance when integrated into the reflector system. A parabolic reflector is used to prove the lens concept. Reflector optimization is out of the scope of this paper. Experimental results are presented for a fabricated scaled lens prototype at 62.5 GHz.

Design of a Simultaneous Center-Fed X/Ka-Band SATCOM Reflector Antenna with Replacable C-Band Option

Abstract: A 1.5m tri-band (C-, X- and Ka-band) center-fed SAT-COM terminal has been designed for shipboard applications. The terminal has two independent replaceable feeds; C-band and simultaneous X/Ka-band. Offset prime-focus and dual-reflector designs are optimum from a performance standpoint for a reflector of this electrical size, however the scarcity of real estate and other mechanical considerations on shipboard drives the design to a center-fed type. Of the available center-fed reflector types, a shaped ring-focus configuration was chosen since the ring-focus reflector has several advantages over Cassegrain/Gregorian types for reflectors in this electrical size range. The reflector antenna shape is derived numerically utilizing GO shaping techniques while the feeds are designed using the BOR MoM and PO methods. The resulting antenna has been constructed and tested, and results are presented.

Enhanced two level EBG antenna for a high F/D multibeam reflector antenna in Ka band: design and characterization

Abstract: This paper deals with the design of an EBG antenna dedicated to feed a side front offset Cassegrain antenna (SFOCA) for a multibeam coverage of Europe in Ka band. Indeed, the EBG structure which permit to interlace equivalent radiating apertures, represents a new passive technology to realize multi beam coverage with only one reflector at an attractive cost compared to usual systems with beam forming networks or with several reflector antennas. The telecommunication mission studied requires on the one hand a multibeam reflector antenna with large F/D ratio to decrease the parasitic defocusing effects for high scanned beams and on the other hand, a circular polarization concept which reduces the price of the subscriber terminals assembly. These characteristics induce some focal structure specifications which cannot be reached with a classical EBG antenna. Also, the first step has been to improve the EBG antenna performances thanks to a more efficient feed which is a conical horn. The replacement of the patch by the horn permits to double the radiation bandwidth and to decrease the side lobes (-15 dB) of a 24 dB EBG antenna. The second job has been to reduce the parasitic interferences which occur in a multifeed EBG antenna especially that no polarization decoupling is achievable. Consequently, a multihorn two level EBG antenna with corrugations which permit to emplace the feeds outside the EBG cavity has been designed. As the performances of this structure are as well as those obtained with an EBG antenna fed by only one feed, we have study the whole system composed of the SFOCA and the multihorn two level EBG structure. The results obtained agree with the specifications because a EOC gain higher than 43 dB and sideslobes lower than -20 dB have been obtained for 90% of the beams. (7 pages)