Effect of Pointing Errors and Range on Performance of Dual-Pencil-Beam Scatterometers

Short-range FM scatterometers with single antennas are plagued by interference set up by feedthrough and internal reflections. Dual-antenna systems have much lower internal interference, but there are problems associated with pointing the antennas at the same spot. This note quantifies these problems for Gaussian-shaped beams. The use of antennas with beamwidth ratios of up to 5: 1 is shown to improve performance significantly over that obtained with identical beamwidths. For an angle between antenna centers (as viewed from the beam intersection) that is three times the beamwidth of the narrower antenna, the usable spread of range for equal beamwidths is only about 1.85:1, while for an angular ratio of 5, the usable spread of range is > 20:1.     

口径天线方向性系数和增益的快速估算方法

导出了用天线方向图的半功率波束宽度快速计算口径天线方向性系数和增益的简单表达式，分析讨论了这些公式的应用范围。最后，给出了卫星通信天线的增益测量实例，实验结果表明：用半功率波束宽度快速计算的天线增益与其它方法测量的天线增益吻合很好，从而证明了这种方法的正确性。     

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 of a large-aperture lens antenna usable over a±15° scanning sector

A lens antenna design is described which requires the formation of both on-axis and far off-axis beams. The aperture is about 100 wavelengths in diameter, and the off-axis beams are displaced ±20 beamwidths from the axis. The results are indicative of the much greater scan capabilities of lensatic antennas compared to paraboloidal designs when both have single-aperture nonarray feeds     

Submillimeter-wave antennas on thin membranes

Submillimeter-wave antennas have been fabricated on 1-μm thick silicon-oxynitride membranes. This approach results in better patterns than previous lens-coupled antennas, and eliminates the dielectric loss associated with the substrate lens. Measurements on a wideband log-periodic antenna at 700 GHz, 370 GHz and 167 GHz show no sidelobes and 3-dB beamwidths between 40° and 60°. A linear imaging array has similar patterns at 700 GHz. Possible applications for membrane antennas include wideband superconducting tunnel-junction receivers for radio astronomy and imaging arrays for radiometry and plasma diagnostics.     

Scheme for enhancing performance of smart antennas in variableprocessing gain packet CDMA systems

Owing to the finite beamwidths of smart antenna systems, interference exists between signals belonging to different beams in CDMA systems. A new scheme is proposed for reducing the interference between the signals of smart antennas for variable processing gain packet CDMA systems. Numerical results show that the proposed scheme considerably improves the system performance     

Passive Microwave Remote Sensing of Soil Moisture: The Effect of Tilled Row Structure

The tilled row structure is known to be one of the important factors affecting the observations of the microwave emission from a natural surface. Measurements of this effect were carried out with both L-and X-band radiometers mounted on a mobile truck on a bare 40 m × 45 m row tilled field. The soil moisture content during the measurements ranged from ~10 to ~30 percent by dry weight. The results of these measurements showed that the variations of the antenna temperatures with incident angle ? changed with the azimuthal angle ? measured from the row direction. In particular, at ? = 0° and ? ? 45°, the observed horizontally and vertically polarized antenna temperatures, TBH(?, ?) and TBV(?, ?), were not equal. In general, TBH(?°, ?) > TBV(?°, ?) when 0° ? ? < 45° and TBH(?°, ?) < TBV(0°, ?) when 45° < ? ? 90°. The difference between TBH(0°, ?) and TBV(0°, ?) was observed to decrease with ? approaching 45° and/or with soil moisture content. A numerical calculation based on a composite surface roughness-a small-scale RMS height variations superimposed on a large periodic row structure-was made and found to predict the observed features within the model's limit of accuracy. It was concluded that the difference between TBV(0°, ?) and TBH(0°, ?) was due to the change in the local angle of field emission within the antenna field of view caused by the large-scale row structure.     

一种介质埋藏异形微带八木天线的设计

为达到某重点项目性能要求,综合运用微带天线、八木天线和介质埋藏天线理论及设计方法,设计出了一种介质埋藏异形微带八木天线.该天线将传统八木天线的引向振子由一个改变为两个,形成“￥”形,用来规划波束方向和形成双波束;在天线贴片两旁增加“栅栏”,聚集了电磁波的辐射,提高了天线增益,同时还获得了较大的相对阻抗带宽.测试表明:在...     

A 36 GHz printed planar array

The performance of a simple, low-cost, centre-fed, efficient planar array aerial for Q band is described. The microstrip radiating pattern is produced by conventional photolithographic techniques. Gains up to 25 dB with beamwidths of 8° and bandwidths of 500 MHz make this `flat? aerial attractive for many industrial applications where space is limited.     

Rigorous TE solution to the dielectric wedge antenna fed by a slab waveguide

A rigorous TE solution to the dielectric wedge antenna fed by a slab waveguide of the same material is presented. The method of solution involves modeling the wedge as a sequence of step discontinuities and uses an iterative procedure to track forward and backward partial wave fields, expressed as modal expansions, to obtain the rigorous field solution. Radiation patterns of directive gain are presented. All patterns smoothly decrease from a maximum in the endfire direction and exhibit extremely low side lobe levels. Longer length wedges or smaller dielectric constant materials are shown to produce higher directivity and smaller half-power beamwidths. For slender, gradually tapered wedges, the reflection coefficient of the guided (surface) wave at the input to the wedge is very small indicating a low VSWR for tapered dielectric antennas and there appears to be no gain limitation with antenna length for these antennas.     

Waveguide-fed spherical dielectric antennas

The results of an experimental investigation into the radiation properties of circular waveguide excited dielectric sphere antennas are reported. The input waveguide had a plain end without a flange or ground plane. The input voltage standing-wave ratio varied from about 1.1 to 2.5 for the sphere sizes used but can usually be reduced to about 1.25 over the 8-12 GHz band by separating the sphere from the waveguide. Separation increases the on-axis gain by 1-3 dB and produces nearly equal beamwidths in bothE- andH- planes. Phase front measurements located a fixed phase center near the end of the waveguide.     

On the use of a conical cornucopia antenna to reduce EMI

The wide-angle radiation form a prime-fed parabolic reflector antenna and the associated EMI (electromagnetic interference) it produces can be greatly reduced by constructing the antenna in the form of an absorber-lined conical cornucopia (CC). Measured RPEs (radiation pattern envelopes) are inspected for the case where all antennas have about a 10-ft diameter and 43-dBi gain at 6 GHz and typify the type of WAR (wide-angle radiation)-RPE improvement achievable if scaled to other bands/sizes. It is shown that the CC's RPEs for angles from about 10 full half-power beamwidths (here 10°) and beyond, and most especially from about 30 full half-power beamwidths (here 30°) and beyond, are vastly superior to those of either the standard or improved (UHX/UMX) parabolic dishes. Indeed, it is seen that the CC's RPE levels are about 95 dB down from on axis for angles greater than about 90°. In other words, the CC's wide-angle RPE is about 40 dB lower than that of a standard parabolic-dish antenna of the same gain. These very low WAR levels then greatly mitigate the EMI to adjacent microwave routes in terrestrial radio relay applications     

Combating sun outage in satellite television distribution systems

Two methods of sun outage avoidance in satellite television transmission are discussed. Each method requires two satellites and dual-beam antennas. The two C-band satellites transmit identical programs at the time when the sun outage period occurs. The separation of the spacecraft is dependent on the dual-feed earth station antenna size. For large television receive-only antennas, the separation must be small; for small antennas, or antennas with large beamwidths, the satellite separation can be large. If the separation is larger than 8° on the geosynchronous arc, only one transmit station is required to transmit program information. Scaling this system for Ku-band use is then considered. It is concluded that in a Ku-band direct-broadcasting system with earth station antenna diameters of 1-m and below, the rise in noise temperature due to sun outage is not significant and can be overcome by a modest amount of system margin, equivalent to that normally provided against rain fades     

幅度固定唯相位实现波束控制的功分器设计

针对传统阵列天线设计流程中功分器繁琐的设计过程, 基于满足-3 dB范围为0°~12°, -10 dB波束宽度为65°, 波束覆盖为65°, 中心频率为9.05 GHz的余割平方扩展波束赋形要求, 设计了一种幅度固定唯相位实现波束控制的新型串馈结构Gysel功分器.该功分器幅度为固定值, 此幅度分布满足余割平方赋形阵列天线幅度的分布特征, 在遗传算法计算出理想赋形激励后只需调整该功分器的输出相位值就能实现高拟合度的余割平方扩展波束赋形, 大为减少了传统设计中功分器所需的设计时间.     

刺激视野面积对稳态视觉诱发电位的影响

基于稳态视觉诱发电位（SSVEP）的脑-机接口（BCI）系统通常采用占据较大视野面积的闪烁刺激以诱发更明显的脑电特征,但容易造成使用者疲劳、紧张和头痛,限制了SSVEP-BCI的实际应用。针对此问题,该文以幅值、信噪比、典型相关系数和任务相关系数为指标,探究了不同刺激视野面积（以角度尺寸进行衡量,范围为0.1°至13°）对诱发SSVEP信号特征强度的影响。分析结果表明,SSVEP信号的强度最初随刺激角度尺寸的增大而增大,但在角度尺寸达到3°左右后增长开始变缓并保持平稳。综合考虑系统舒适度和特征强度两个因素后得出结论,SSVEP-BCI系统的刺激角度尺寸约为3°时能够达到最佳性能。该文为SSVEP-BCI的最佳刺激角度尺寸选择提供了依据,相关研究成果在舒适友好型BCI方面具有潜在的应用价值。     

Performance and design procedure of dual parabolic cylindricalantennas

The radiation characteristics of dual parabolic cylindrical antennas are studied, and the dependence of the principal plane beamwidths and the peak cross-polarization on their geometrical parameters is determined. The antenna aperture is rectangular in shape and generates an elliptical beam pattern, with a beamwidth ratio that can be controlled by the main and subreflector focal lengths. The far-field patterns are determined by an extended aperture integration method that includes the contributions of the reflected and the main diffracted rays. It is found that the cross-polarization depends of the offset angle between the axis and the direction of the normal to the subreflector surface and can be minimized by optimizing the relative angle between the reflectors. Other pattern characteristics are controlled by the antenna geometrical parameters and the feed illumination. A procedure for the design of these antennas and the expressions for determining the reflector geometries are provided     

6～18GHz GaAs PHEMT 5位MMIC数字移相器

采用GaAs PHEMT工艺研制开发了一款6～18 GHz五位MMIC数字移相器。通过建立精确的器件模型、选择合理的单位拓扑以及设计优化原理图和版图,并在优化过程中采用性能冗余优化策略,保证了产品各项性能优异和高成品率。测试的电性能典型值表明,在工作频率范围内,11.25°/22.5°移相位的相移误差<2.5°,45°/90°/180°移相位的相移误差<5°,相移均方根误差<4.5°,插入损耗保持在7dB～10.5dB的范围内,32种相移态输入端与输出端的驻波比均小于1.7,最终芯片面积仅为3.555mm×4.055mm×0.1mm,可广泛用于相控阵雷达与电子对抗等系统。     

基于加载线型Ka频段的五位数字移相器

数字移相器广泛应用于相控阵雷达中,本文采用一前一后加载支线的方法设计了 11.25°,22.5°和45°移相单元,以3 dB支线耦合器的形式设计90°和180°移相单元,在Ka频段研制出五位数字移相器。该移相器在30 GHz~31 GHz工作频带内,各移相单元实测相移误差最大为6.5°,最小为0.2°;插入损耗最大为11.8 dB,最小为8.6 dB;输入驻波比小于2,整个电路尺寸为110 mm×55 mm×25 mm。     

Planar three-dimensional constrained lenses

A new design for a beamforming lens is presented. Both faces are planar arrays of radiating elements interconnected by transmission lines whose length varies as a function of radius. While the front face elements are regularly spaced, the back face elements are displaced radially from their corresponding front face elements, the amount of displacement also being a function of radius. We show that such a lens is capable of forming low sidelobe beams over an angular sector 36 beamwidths across in all planes ofphiby switching between clusters of only seven feed elements. Because both faces are planar, construction of lightweight lenses for multibeam antennas should be feasible.     

基于机器视觉的平磨表面粗糙度检测

为了对平磨表面粗糙度进行快速在线检测, 基于机器视觉原理提出了一种平磨表面粗糙度检测方法, 研究了平磨表面粗糙度评定参数。该方法利用CCD提取粗糙度Ra在0.1～1.6 μm之间的平磨表面图像, 运用中值滤波、图像边缘增强和图像二值化等对图像进行预处理, 然后通过特征参数提取平磨表面粗糙度信息。试验结果表明, 在入射光强为0.7×104～1.3×104 lux、入射角为30°～50°时, 均方根(RMS)差随Ra的减小而不断减小。当光源入射角在30°, Ra>0.3 μm的情况下, 陡峭度与Ra具有良好的相关性; 当光源入射角在50°, Ra>0.4 μm的情况下, 陡峭度与Ra具有良好的相关性。