双馈源偏置卡塞格伦天线研究

文章根据偏置卡塞格伦天线设计原理,通过双馈源、副反射面的正反面将两种不同结构的偏置卡塞格伦天线结合在一起,研究出一种双馈源-单副反射面-双主反射面的新型偏置卡塞格伦天线。该天线充分利用了偏置双反射面天线的扫描特性好、可避免遮挡效应等优点,在两个不同方向上产生双波束,实现双方向扫描,拓宽了卡塞格伦天线的应用领域。     

Bifocal dual reflector antenna

A bifocal dual reflector antenna is similar to and has better scan capability than a classical Cassegrain reflector antenna. The method used in determining the reflector surfaces is a modification of a design method for the dielectric bifocal lens. Computed radiation characteristics of the bifocal reflector system are compared with those of a classical Cassegrain reflector system. The results confirm that the bifocal reflector has superior scanning performance.     

Synthesis of offset dual shaped subreflector antennas for control of Cassegrain aperture distributions

Many existing large ground reflector antennas have been designed as Cassegrain systems-i.e., paraboloid/hyperboloid combinations. Other large ground antennas are simply paraboloid designs. Upgrading the gain of these systems to a gain comparable to that obtainable with a dual shaped reflector antenna system has been an important and costly objective of many such ground stations. A potentially economic method for such an antenna upgrade is presented herein. It involves a redesign of only the subreflector portion of a Cassegrain antenna or the introduction of a subreflector feed system for a parabaloid. A pair of offset subreflectors are synthesized which will give a controllable high gain amplitude distribution in the aperture of the large paraboloid. The synthesis method that is used is based on an approximate formulation for an offset dual shaped high gain antenna that was first presented by Galindo-Israel and Mittra in 1977. In that approximate formulation, the geometrical optics (GO) energy was scattered from a subreflector and then from a second large reflector which reflected a uniform phase distribution. In the present offset dual shaped subreflector (DSS) antenna, the second reflection is from a smaller (sub) reflector and it scatters a spherical wave that feeds a hyperboloid or feeds a large paraboloid directly. Excellent results are shown for the approximate synthesis of the DSS.     

La synthèse d’antennes à deux réflecteurs conformés à alimentation décalée

A potentially economic method for upgrading the gain of the large earth reflector antenna Cassegrain system to a gain comparable to that obtainable with a dualshaped reflector antenna system is presented herein. It involves a redesign of only the subreflector portion of a Cassegrain antenna or the introduction of a subreflector feed system for a paraboloid. A pair of offset subreflectors are synthesized which will give a controllable high gain amplitude distribution in the aperture of the large paraboloid. The synthesis method that is used is based on an approximate formulation for an offset dual shaped high gain antenna where the geometrical optics energy was scattered from a subreflector and then from a second large reflector which reflected a uniform phase distribution. In the present offset dual shaped subreflector (DSS) antenna, the second reflection is from a smaller subreflector and it scatters a spherical wave that feeds a hyperboloid or feeds a large paraboloid directly. Excellent results are shown for the approximate synthesis of the DSS.     

Dual offset reflector multibeam antenna for international communications satellite applications

Dual offset reflector antenna systems offer exciting possibilities for achieving both low scan losses and low cross polarization in geosynchronous communications satellite antennas providing narrow (100 leq D/lambda leq 400) and multiple beam frequency reuse coverages over an18degconical field of view. Novel geometrical configurations for the reflectors are characterized by simultaneously achieving: 1) blockage free apertures for all element beams within the18degconical field of view, 2) compatibility with large planar feed arrays, 3) additional degrees of design freedom by orientation and shaping of reflector surfaces for depolarization and scan loss optimization, and 4) large effectivef/Dratio achieved in compact and foldable geometries. A comparison of new front-fed offset Cassegrain (FFOC) and side-fed offset Cassegrain (SFOC) systems is made.     

A high aperture efficiency, wide-angle scanning offset reflectorantenna

A unique single offset reflector antenna has been designed which provides as much as ±30° of scanning in azimuth while maintaining a much higher aperture efficiency than a torus antenna. Like a torus antenna, different portions of the reflector are illuminated for each scanned beam. The reflector profile curve in the plane of scan is found by least squares to minimize the error for the beams with the greatest scan angle, and then polynomial terms of up to sixth order which minimize nonplanar phase errors are added to produce a three-dimensional reflector surface. Numerical simulation indicates very good results for all 0.5° beams in the ±30° azimuth field of view, with peak gain no more than 0.3 dB below ideal and highest side-lobe levels no worse than 13.3 dB below the peak gain. Additionally, comparable performance can be extended to the elevation plane out to 15°/-30°, although full azimuth performance becomes compromised at extreme elevation scan angles. By using an offset design, there is no blockage of the outgoing beam by the feed array assembly for azimuth scanning. With better feed performance than comparably sized paraboloids, and being more compact than similar torus reflectors, this novel antenna should find numerous uses in spacecraft and terrestrial applications     

An offset bifocal reflector antenna design for wide-angle beam scanning

A synthesis procedure and performance results for an offset dual reflector with perfect focusing atpm 8degof beam scan are presented. This bifocal antenna extends the theory of the previously reported symmetric system to an offset design. Approximations, such as the smearing of focal points into a "focal ring," are eliminated, as is blockage. The offset design affords greater design flexibility, although the synthesis is more complex. Computed and experimental results demonstrate the improved beam-scanning performance of this antenna.     

The effects of reflector antenna diffraction on the interference cancellation performance of coherent sidelobe cancellers

While adaptive antenna technology has undergone significant development, little attention has been given to the impact of antenna design on the performance of the adaptive system. A need exists to factor the details of the antenna system response into the analysis of adaptive system performance, particularly in the case where adaptive cancellation is required over a broad bandwidth. At extremely high frequency (EHF) where wide bandwidth allocations exist, reflector antenna technology used with an adaptive sidelobe canceller design is appropriate. This paper uses a simple diffraction model to compare the adaptive performance differences between Cassegrain and offset reflector designs. The reduced diffraction of the offset reflector design results in improved cancellation performance. These analyses also provide the opportunity to explore the impacts of antenna design parameters and interference power levels and arrival directions.     

Designing classical offset Cassegrain or Gregorian dual-reflector antennas from combinations of prescribed geometric parameters

This paper proposes a simple procedure for the design of classical offset Cassegrain or Gregorian dual-reflector antennas from combinations of prescribed geometric parameters. This procedure has already been applied to classical Cassegrain and Gregorian antennas, to classical displaced-axis Cassegrain and Gregorian antennas, and to classical offset Dragonian antennas. The antenna systems can be fully characterized by 21 parameters, of which only five need to be provided by the antenna designer, as the remaining 16 parameters can be derived in closed form using the procedure described here. In this paper, we assume that the main reflector has a circular aperture, while the subreflector has an elliptical aperture All the antenna geometries presented satisfy the Mizugutch condition (1976), which is the geometric-optics condition for zero cross-polarized radiation. This procedure is very close to the one used for offset Dragonian systems, but all the relevant information is repeated here for completeness.     

偏馈赋形紧缩场天线电气设计研究

本文对偏馈赋形紧缩场天线设计进行系统研究。提出一种新的偏馈双反射器天线几何光学综合的方法。该法便于理解、推导和用计算机作数值计算。文中提出了一种计算紧缩场交叉极化的新技术。经深入分析，得出了若干具有普遍性的结论。讨论了赋形紧缩场工程设计中的一个重要问题－交叉极化与绕射效应间的矛盾，并由此阐明了布局优化的重要性。     

Equivalent hyperboloid (ellipsoid) and its application

Analogous to the equivalent paraboloid, the equivalent hyperboloid (ellipsoid) for dual quadratic surface reflector antennas is derived. The condition that the equivalent reflector is center fed is also derived. The numerical example shows that a reflector geometry that satisfies this center fed condition is a good initial antenna geometry to design a shaped dual reflector antenna     

Subreflector shaping to improve multiple-beam performance of a Cassegrain antenna

A method of designing multiple-beam antennas based on shaping the subreflector of an offset Cassegrain antenna is described. It is applied to a compact system having a diameter of 300? that is required to produce beams up to 4-6°either side of boresight. The performance is shown to be only slightly less than that obtainable by also shaping the main reflector, indicating that efficient multiple-satellite-access antennas can be designed without specially shaped main reflectors.     

A design procedure for classical offset dual reflector antennaswith circular apertures

A geometrical optics procedure for designing electrically optimized classical offset dual reflector antennas with circular apertures is presented. Equations are derived that allow the size and spacing of the main and subreflectors of the antenna system, along with the feed horn subintended angle, to be used as input variables of the design procedure. The procedure, together with these equations, yields an optimized design, starting from general system requirements. The procedure is demonstrated by designing both an offset Cassegrain and an offset Gregorian antenna, and is validated by analyzing their radiation patterns using physical optics surface current integration on both the main and subreflectors     

Subreflector extension for improved efficiencies in Cassegrain antennas--GTD/PO analysis

Both offset and symmetric Cassegrain reflector antennas are used in satellite and ground communication systems. It is known that the subreflector diffraction can degrade the performance of these reflectors. A geometrical theory of diffraction/physical optics (GTD/PO) analysis technique is used to investigate the improving effects of the extended subreflector, beyond its optical rim, on the reflector efficiency and farfield patterns. Representative numerical results are shown for an offset Cassegrain reflector antenna with different feed illumination tapers and subreflector extensions. It is observed that for subreflector extensions as small as1 lambdanoticeable improvements in the overall efficiencies can be expected. Useful design data are generated for the efficiency curves and far-field patterns.     

双弯曲赋形反射面天线的外形选择

对双弯曲赋形反射面外形特征进行了理论分析，研究了不同外形反射面对天线电性能的影响，给出了选择反射面外形的方法，对双弯曲赋形反射面天线的设计有一定的帮助。     

Designing axially symmetric Cassegrain or Gregorian dual-reflectorantennas from combinations of prescribed geometric parameters

A procedure to design axially symmetric Cassegrain or Gregorian dual-reflector antennas from various combinations of prescribed geometric parameters is presented. From these input parameters, the overall geometry of the antenna is derived in closed form. This procedure can be used as the starting point of a synthesis procedure, where both main reflector and subreflector are shaped to create the desired aperture field distribution     

RF characterization of an inflatable parabolic torus reflectorantenna for space-borne applications

Space-borne satellite applications provide a vast array of services extending from global connectivity to Earth observation systems. The soil moisture radiation mission is a proposed space-borne passive microwave system complementary to the existing Earth observing system operating at low microwave frequencies and requiring an antenna with multibeam, high-beam efficiency, and dual polarization capabilities. To achieve both the large reflector size and the multibeam pattern at the operational frequencies an innovative multibeam reflector antenna design was needed. The advances in inflatable antenna technology has been proposed to overcome the launch vehicle size and weight restrictions. This paper describes a novel offset parabolic torus reflector antenna design that produces the desired multibeam pattern and is compatible with the inflatable antenna technology. Using the system requirements of this mission as an example, the design process for an inflatable parabolic torus reflector antenna is outlined, the development of suitable distortion models is given, and representative RF characteristics are presented. These RF characteristics include far-field patterns, beam contour patterns, beam efficiency, and other key performance parameters. The development of an advanced analytical modeling/numerical tool in support of the design effort is also detailed     

Bicollimated Gregorian reflector antenna

A bicollimated Gregorian reflector is structurally similar to a classical confocal Gregorian reflector, but its surfaces are shaped to have better scan capability. A geometrical optics procedure is used in designing the reflector surfaces. A three-dimensional ray tracing procedure is used in analyzing the aperture phase errors as the beam is scanned to different angles. The results show that the bicollimated configuration has about 45 percent greater angular scanning range than the equivalent confocal Gregorian reflector antenna.     

Comparison of the design of a contoured-beam and an elliptical-beamsatellite offset reflector antennas to cover the Taiwan island regionfor satellite communications

For the design of the satellite antenna for the future geostationary (GEO) satellite communication or DBS (direct broadcasting satellite) applications to serve the Taiwan Island region, it may be required to have a antenna beam which effectively covers the Taiwan region and reduces the antenna radiation level in the nearby area of mainland China. Two cases of the Ka-band (20 GHz) satellite antenna, a shaped offset reflector antenna to synthesize a contoured beam and an elliptical offset reflector antenna to generate an elliptical beam, have been studied. This paper presents the comparison and discussion of the antenna coverage performance of the two designs     

Offset Cassegrain Earth Station Antenna for the Japanese Domestic Satellite Communication System

Offset reflector antennas have advantages for communication systems because they are not severely subject to blocking. Difficulties mainly arising from structual asymmetries have inhibited the realization of an offset reflector antenna with a large aperture for commercial use. This paper describes the design of an offset Cassegrain earth station antenna for the Japanese domestic satellite communication system. Antenna measurements showed 76 and 69 percent aperture efficiencies at 20 and 30 GHz, respectively, less than -20 dBi wide angle directivity and an 18 K noise temperature in operating conditions. Performances are far superior to conventional axisymmetrical earth station antennas. The antenna was reassembled on a telephone office building after the measurements. The antenna gain was reconfirmed there, using the sun as a radio frequency source. Experiments show that the earth station antenna and a terrestrial antenna can be placed on the same building without serious interference.