Wide-band diffraction improved dual-shaped reflectors

Modified dual-shaped reflectors are discussed. These antennas have improved gain and gain over noise temperature (G/T) performance over the conventional uniform illumination design when diffraction effects are considered. A further advantage of the present design approach is its inherent broad-band characteristics. These considerations are vital for ultra-low noise systems as employed in the deep space telemetry service.     

A dual chamber Gregorian subreflector system for compact rangeapplications

A dual-chamber compact range configuration is proposed wherein the main reflector and target zone are located in the main chamber and an oversized Gregorian subreflector and associated feed assemblies in the other. The chambers are isolated by an absorber fence except for a small coupling aperture which is used to transmit signals between them. The absorber fence prevents diffraction by the subreflector and spillover by the feed from illuminating the main reflector and target zone. System performance is analyzed with and without the absorber fence to show how the coupling aperture should be shaped to minimize diffractions     

Comments on "Wide-band diffraction improved dual-shaped reflectors"

It is pointed out that the procedure mentioned in the above paper need not be followed for dual-reflector systems using small subreflectors. In addition, a uniform procedure suitable for both large and small subreflector systems, is presented.     

Uniformity factor of a compact range using dual parabolic cylindrical reflectors

For a dual parabolic cylindrical reflector configuration employed as a compact range, a uniformity factor is defined to indicate the uniformity of the aperture field. The effects of the reflector geometrical parameters on this uniformity factor are studied and some representative results are presented.     

Broadband compact horn feed for prime-focus reflectors

A compact flare angle controlled corrugated horn antenna with a 60° half beamwidth is optimised by using a moment method for bodies of revolution. The horn has corrugations with simple rectangular cross-sections and is excited by a smooth wall circular waveguide. The resulting 15 dB beamwidth varies by <18% and the crosspolar sidelobe levels are more than 26 dB below the mainlobe, both over a 1.8:1 bandwidth. All results are confirmed by measurements. The horn is suited for broadband feeding of e.g. prime-focus reflectors in radioastronomy applications     

Feasibility of compact ranges for near-zone measurements

The purpose of this paper is to demonstrate the feasibility of using compact range reflector systems to make near-zone radiation or scattering measurements. This can be achieved by designing the compact range to provide a uniform spherical wave incident upon the antenna or scatterer under test. The basic design technique is demonstrated using the Scientific Atlanta reflector system which has been modified by adding an elliptic rolled edge to improve the uniformity of the incident wave. The near-zone range design is validated (from around 50 ft range to the far zone) by probing the field in the measurement volume and by comparing measured backscattering patterns from a circular cylinder with those calculated by the geometrical theory of diffraction (GTD). All the advantages of a conventional far-zone compact range are now made available by our demonstrated variable-zone (adjustable continuously from 50 ft to infinity) compact range.     

Some design parameters for point-source compact ranges

Current development efforts with compact ranges are concerned primarily with optimizing the performance of compact ranges. The relationship of the diameter of the test zone to the beamwidth of the feed pattern and to the focal point of a point-source compact range is addressed. Parametric design information is presented in graphical form.     

Exact synthesis of offset dual reflectors

The shaping of offset dual reflector surfaces using geometrical optics can be placed on a firm mathematical basis and solutions can be found for a number of problems hitherto thought to be insoluble except by approximate methods. Examples are given for tapered conical feed cones and circular output aportures with uniform phase and power distributions.     

Compensation for feed crosspolarisation in shaped dual offset reflectors

A re-examination of the problems of shaping dual offset reflectors to produce a zero-crosspolarised parallel beam shows that the shaping can, under geometrical optics, compensate not only for the system asymmetry, but also for a certain amount of crosspolarisation in the feed pattern.     

Offset dual-reflector multiple-beam antennas using circularly symmetric main reflectors

An investigation into the multiple-beam capability of offset antennas using circularly symmetric main reflectors is described. The efficiency and sidelobe performance of systems designed to produce beams up to 4.6° either side of boresight with reflector diameters ranging from 100 to 300 wavelengths are shown to make the antennas suitable for multiple-satellite-access earth stations. Comparison is made with a nonsymmetrical main-reflector antenna designed for the same requirements.     

Design procedure for offset dual reflectors with low crosspolarisation

A simple procedure for designing offset dual reflectors with low crosspolarisation is presented. It provides simple guidelines by which the subdish and the feed parameters can be specified once the main dish geometry is known. The method is most suitable for upgrading existing offset systems with poor crosspolarisation characteristics.     

Stray signal requirements for compact range reflectors based on RCSmeasurement errors

The authors present a performance criterion for compact range reflectors such that their edge diffracted stray signal levels meet a reasonable radar cross section (RCS) measurement error requirement. It is shown by example that one of the significant error sources is the diffracted fields emanating from the edges or junctions of the reflector. This measurement error is demonstrated by placing a diagonal square flat plate in the target zone and rotating it to appropriate angles. These angles are determined by bisecting the plane wave and stray signal directions. This results in a peak bistatic measurement of the edge diffracted stray signal. It is proposed that the diagonal flat plate be used to evaluate new reflector designs as well as existing systems. A reasonable stray signal performance level has been developed so that new reflector systems can be characterized in terms of an RCS measurement error requirement     

Dual parabolic cylindrical reflectors employed as a compact range

Compact ranges using dual parabolic cylindrical reflectors are investigated, and the dependence of the aperture field on the feed pattern and system geometrical parameters is studied. A uniformity factor is defined to indicate the aperture field uniformity and the significance of the diffracted fields is explored. Offset configurations are also considered and studied. It is shown that their feed location and orientation can be optimized to minimize the geometrical-optics cross polarization. The effects of offset angle on the edge diffraction and aperture shape are also studied     

一种双金属板加载的水平极化全向天线

设计了一种双金属板加载水平极化全向天线,包括顶端反射板、微带天线、支撑介质柱和底端反射板等4个部分。微带天线由4个弧形微带偶极子沿圆周排列组成;介质柱的法兰固定天线;顶端和底端金属板对称地放置于微带天线上下两侧,调整顶端和底端金属板的尺寸可以改变波瓣仰角。仿真结果表明,天线在10%的相对频带内端口驻波小于1.5;方位面内增益高于2.3 dB,增益起伏小于1 dB,交叉极化电平低于-30 dB。测试结果表明,在频带内端口驻波小于1.7;方位面波瓣起伏约2.1 dB。     

A feed scanning based APC technique for compact antenna test ranges

The measurement accuracy of a compact antenna test range (CATR) depends on the level of spurious signals. To improve the measurement accuracy, several error compensation methods have been developed, but most of them are not feasible at submillimeter wavelengths. This paper introduces an error compensation technique for compact antenna test ranges, which is especially suitable at submillimeter wavelengths. The method is based on antenna pattern comparison (APC). In the original APC technique the antenna pattern is recorded several times at different positions of the quiet-zone field, and the corrected pattern is obtained by averaging the measured patterns. In the proposed method, the lightweight transmitter is moved instead of moving the heavy combination of the antenna under test (AUT) and the rotation stage. The feasibility of the method is studied and the method is tested with measurements in a hologram based compact antenna test range at 310 GHz. The accuracy provided by the proposed method is compared to the accuracy provided by the conventional APC. The accuracies provided by both methods are practically equal.     

Broadband and compact 2-D photonic crystal reflectors with controllable polarization dependence

Two-dimensional (2-D) compact photonic crystal reflectors on suspended InP membranes were studied under normal incidence. We report the first experimental demonstration of 2-D broadband reflectors (experimental stopband superior to 200 nm, theoretical stopband of 350 nm). They are based on the coupling of free space waves with two slow Bloch modes of the crystal. Moreover, they present a very strong sensitivity of the polarization dependence, when modifying their geometry. A compact (50/spl times/50 /spl mu/m/sup 2/) demonstrator was realized and characterized, behaving either as a broadband reflector or as a broadband transmitter, depending on the polarization of the incident wave. Experimental results are in good agreement with numerical simulations.     

A compact Q-K-band dual frequency feed horn

A millimeter-wave dual frequency circularly polarized feed for an offset reflector antenna is being developed for a portable satellite ground terminal. The two frequency bands areQ- andK-bands for transmit and receive, respectively. A compact feed design consisting of a single corrugated horn with two circular waveguide concentric openings at the horn throat is described. Good aperture efficiency and low sidelobes in both of the frequency bands are achieved.     

A compact wide slot antenna with dual band-notch characteristic for ultra-wideband applications

A new type of ultra-wideband (UWB) antenna with a dual-notched frequency band, compact size of 21?×?28?mm² and a coplanar waveguide (CPW) fed is proposed in this article. Two notched frequency bands are obtained by embedding two U-shaped slots in the radiation patch and a rectangle slot in the ground plane, which can be controlled by adjusting the length of the responding slots. The frequency domain characteristics are investigated and measured. Both the experimental and numerical results show that the proposed antenna has an impedance bandwidth ranging from 3.1?GHz to more than 11.0?GHz in which voltage standing wave ratio is less than 2, expect two notch frequency band, 5–6?GHz (WLAN) and 7.7–8.5?GHz (X-band for satellite communications in China).     

A compact tubular chamber for impedance and power testing of VHF whip antennas

A small-diameter tubular test chamber lined with lossy material (ferrite) has been developed for indoor tuning and testing of the base-isolation and impedance-correcting networks of a VHF whip antenna covering the frequency band from 30 to 76 MHz. Results of experimental evaluation of the chamber which attest to its usefulness in production tuning, power testing, and field maintenance servicing of the antenna assembly are presented.     

Single chamber compact two-phase heat spreaders withmicrofabricated boiling enhancement structures

Presents the thermal performance evaluation of a compact single-chamber two-phase heat spreader. The heat spreader setup has a central evaporator section with integrated fins for cooling along the edges. The evaporator employs a micro-fabricated three-dimensional (3-D) copper structure for enhancing boiling heat transfer. The thermal performance of the system was characterized at various power levels and condenser cooling conditions. The size of the boiling enhancement structure and effects of liquid fill volumes on performance were also investigated. Incorporation of the enhancement structure resulted in an improvement in the spreader thermal performance by decreasing the wall temperature at the evaporator by 8°C, for a power dissipation of 36 W/cm² at an air speed of 1 m/s. The maximum heat flux obtained based on a maximum evaporator temperature of 75°C for an air speed of 1 m/s was 42.5 W/cm². Variation in the liquid fill volume showed negligible effect on the maximum temperature at the evaporator, as long as the enhanced structure was fully flooded