双圆极化器

本文借助旋转矩阵和矢量叠加原理,详细介绍了能使通信容量加倍的双圆极化器的工作原理和实施方案。从文章中的推导可知分别输入正交模变换器E臂和H臂的两个互相垂直的线极化波,通过两只可旋移相器(90°和180°移相器)之后,变为极化方向彼此垂直的单位复矢量表达的两个椭圆极化波。并且可知,从矢量正交的角度去考虑,(?)与(?),不正交,而(?)与(?)是正交的。此外,考虑到两个移相器有损耗和相位误差,所     

一种带滤波功能的圆极化可控阵列天线

提出了一种带滤波功能的2′2圆极化可控阵列天线,采用探针对每个辐射贴片进行馈电,通过控制辐射贴片的激励相位和极化,实现整个阵列天线的圆极化特性。嵌入在阵列天线馈电网络中的耦合谐振器对保证了馈电网络在幅度响应上呈现滤波特性的同时,在相位上控制每个辐射贴片激励端口处的信号相位在-90°和90°之间变化,同时结合90°移相网络,可实现对整个阵列天线左旋圆极化(LHCP)和右旋圆极化(RHCP)的控制。实测结果表明:该阵列天线能控制辐射的圆极化特性,并获得优异的LHCP和RHCP特性;在两种极化状态下,阵列天线工作频带内均具有较为平坦的增益特性,平均增益为10.4 dBic,带外增益特性呈现较好的滤波特性,在远离通带上、下边带100 MHz 处增益抑制均达到8.6 dB以上。     

机械调整式极化跟踪器

在低剖面动中通天线系统中,辐射器多为平板阵列或柱形抛物面的形式,由于天线高度限制,无法通过旋转天线面板的方式进行极化跟踪,需要独立的极化跟踪调整机构,针对此提出了一种新型机械调整式极化跟踪器,具有结构紧凑和可靠性高的特点。通过电机驱动波导关节及OMT实现上行极化调整。基于极化波合成的工作原理,提出了系统设计方案,并描述了核心器件的设计方法。给出仿真与实测结果,且二者吻合较好。     

交叉极化比对平板天线动中通收发系统性能的影响

交叉极化比是平板天线卫星动中通系统设计和加工的产物,它是衡量系统性能的一项重要参数。针对交叉极化比导致的极化误差,重点研究了交叉极化比对平板天线卫星动中通信号发射和接收系统的影响。通过理论推导和实际测试,结果表明不合理的交叉极化比会导致较大的极化误差,降低发射系统的发射效率,减小接收系统信噪比,导致系统性能恶化。为减小交叉极化的影响,建议等效口径0.6 m的平板天线卫星动中通的交叉极化比指标不小于30 dB。     

电视发射台分米波天线的改造

四偶极子阵列天线是分米波常用的电视发射天线,但大截面塔桅不能满足单一极化(水平或垂直)分米波四偶极子阵列天线的安装条件.为了解决这一难题,在大截面塔桅安装分米波四偶极子阵列天线时,阵列天线单元采用±45°斜极化,并采用电气下倾技术与零点填充技术,使天线系统具有良好的水平面辐射场形和垂直面辐射场形,在水平面和垂直方向都有良好的信号强度,能同时满足移动和固定接收.     

基于图像分类的极化SAR系统的极化误差分析

讨论了极化合成孔径雷达（SAR）系统的极化误差,从分类精度误差的角度分析了极化误差对以基于Wishart分布的最大似然法为分类器的图像分类的影响,并给出计算结果。实验结果表明,出于不影响图像分类的考虑,极化通道幅度失衡应限制在[-3 dB,3 dB]范围内,极化通道的相位失衡应控制在[-13°,13°],极化转换开关的极化隔离度应高于35 dB,天线的极化隔离度应高于30 dB。     

一种新颖的星载SAR无线内定标方法研究

内定标利用雷达系统内部设备和定标通路来测量系统各部分幅度和相位在成像过程中的相对变化,是保证雷达图像辐射精度的重要手段。该文针对传统有线内定标方案定标通路未覆盖相控阵天线TR输出端至无源阵面路径、定标网络庞大且自身误差控制难等不足,提出了一种新颖的利用辅助天线的无线内定标方法,给出了定标原理和分析模型,推导了SAR天线TR通道幅相特性和系统传递函数的标定方法,并在典型星载SAR系统参数下对标定误差进行了仿真分析,仿真结果表明,辅助天线支撑杆位置引起的TR通道幅度标定误差在10–3 dB量级,可以忽略;引起相位标定误差与支撑杆位置偏差密切相关,可依据文中给出的仿真曲线得到。支持杆位置引起的系统传递函数幅度标定误差小于0.1 dB;引起的相位标定误差对支撑杆位置偏差不敏感。最后在实际相控阵天线上对无线内定标方法进行了验证,获取了TR通道幅相特性标定的实测结果,表明了该方案的可行性和有效性。      

双线极化天线极化误差分析

天线的极化纯度是雷达或通信系统中非常重要的技术指标。在实际工程中,双线极化天线的非理想正交,导致天线具有较低的交叉极化水平,从而使得系统性能较差。针对该问题,对双线极化天线的极化误差进行分析,通过理论推导,给出空间合成电磁波的极化角与双线极化天线两正交通道的移相值、相位误差之间的量化关系。最后通过实验验证,证明了该极化误差分析的正确性。     

卫星通信天线极化校准技术

移动载体上的卫星通信天线由于载体姿态变化、雨衰、多径效应等环境因素引起的极化失配通常会导致通信质量差,严重时甚至无法通信等问题。针对该问题,文中通过对极化域的分析与研究,提出了一种电调极化技术,实现了天线的极化校准。该技术通过控制一对正交线极化波的幅度、相位,可实时进行极化调整,使接收天线的极化状态与发射天线的极化状态相匹配,从而能够最大限度地接收发射电磁波的功率,保证通信质量。经测试,采用该技术校准之后的Ku频段0.6 m动中通天线的交叉极化隔离度可达30 d B以上,可满足卫星通信要求。     

基于开关扩展卡尔曼滤波的姿态估计

针对低成本动中通系统中的姿态估计问题,提出一种开关扩展卡尔曼滤波算法。以 无航向角的姿态更新算法为基础,根据微机械陀螺和加速度计分别建立系统状态方程和测量 方程。针对机动加速度的影响,设计了三维开关扩展卡尔曼滤波方程,对载体姿态角和陀螺 零偏进行实时估计。实验结果表明,该算法能够准确估计载体姿态和陀螺零偏,姿态角估计 误差小于0.5°,俯仰角和横滚角估计误差的方差分别为0.130 1°和0.140 5°, 两轴陀螺零偏误差均值均小于(2×10-4) °/s,能够满足动中通的应用要求。     

宽带高性能四脊波导圆极化器设计

在射电望远镜和卫星通信天线中,圆极化器是关键部件之一。传统圆极化器在保证0.75 dB轴比时的相对带宽最多为41%,无法满足日益增长的宽频带应用需求。该文利用四脊波导的宽带特性,通过采用具有不同尺寸的水平脊和垂直脊,使四脊波导两个正交主模的相位常数不同,来实现宽带移相特性,并给出了一种宽带四脊波导圆极化器的设计方法。按照这一方法,设计了一款宽带C波段圆极化器,工作带宽为3.625～7.025 GHz,相对带宽64%。该文还研究了圆极化器主要参数变化对其性能的影响,加工并实测了一个圆极化器样机。实测结果显示出,该圆极化器两个正交极化的反射损耗均小于–21 dB,相差90°±3.8°,相应的轴比小于0.6 dB。测试与仿真结果吻合良好,证明了分析与设计方法的正确性。     

一种双频段正交模耦合器的设计

对水平/垂直极化波模式进行分析,并基于分析设计了一种双频段正交模耦合器。对一个正交模耦合器来说,各个端口的端口匹配和隔离尤为重要,引入模式正交的极化隔离能增加隔离效果。改变金属膜片的尺寸与位置,能够使得正交模耦合器中端口R5.75所输入的水平极化波从端口WR42匹配输出,而不影响端口R5.75所输入的垂直极化波。增加圆波导至波导WR28之间的匹配段,能够匹配加入膜片之后正交模耦合器的垂直极化波的输出。基于上述分析,设计了一种双频段正交模耦合器。     

A circular polarizer designed with a dielectric septum loading

This paper presents a simple method to realize a circular polarizer by inserting a dielectric septum in the middle of the cylindrical waveguide. Since fixing slots are built to precisely locate the septum, dual-compensation slots are made in the orthogonal plane to balance the effects of the fixing slots. The measured axial ratio is smaller than 0.5 dB and the phase difference is flat in the frequency range from 60 to 62.25 GHz. In addition, the return losses are better than -13 dB for both E/sub x/ and E/sub y/ polarizations in the same frequency range. This design has the added advantage that poor phase differences resulting from fabrication error or an inaccurate dielectric constant can easily be improved by adjusting the length of the inserted dielectric septum.     

Airborne imaging microwave radiometer. I. Radiometric analysis

The airborne imaging microwave radiometer (AIMR) was designed and built for regional scale sea ice mapping. It operates at 37 and 90 GHz (nominal), and collects radiance at two orthogonal polarizations from which one can compute horizontal and vertical polarizations. The sensitivity or precision (ΔT) of the radiometric data is on the order of 0.5-0.8 K for the 37 GHz channels and 0.8-1.5 for the 90 GHz channels. A detailed error analysis was conducted to assess the accuracy of the radiometric measurements. The error in the brightness temperatures of the original orthogonal polarizations channels was found to be on the order of 0.35-0.45 K for the 37 GHz channel and 0.55-0.65 K for the 90 GHz channel. The polarization conversion introduces additional errors and these are analyzed and computed for the LIMEX-89 data. The total error due to both calibration and polarization conversion for incidence angles greater than 20° is on the order of 0.65-0.70 K for 37 GHz and 0.75-0.85 K for 90 GHz. For incidence angles between 10° and 20° the error can be up to 1.5 K. As the incidence angle approaches zero the distinction between horizontal and vertical polarization breaks down and the error approaches infinity     

Wide-Band Polarizer In Circular Waveguide Loaded with Dielectric Discs

A converter between linear and circular polarization has been designed in circular waveguide by the use of periodic loading with oblong dielectric discs. The disc loading increases the single-mode (TE-11) bandwidth relative to that of homogeneously filled circular waveguide. Moreover, periodic loading gives the designer freedom to adjust the disc thickness and shape to meet certain requirements. With the abutting disc-loaded waveguide as a reference, the dielectric loading is increased in one plane of polarization and decreased in the orthogonal plane. In a wide-band design, this differential loading gives nearly constant 90/spl deg/ difference in time phase between space-quadrature component waves, the condition for circular polarization. Such a polarizer has been constructed with four oblong discs. Across a frequency bandwidth of about 15 percent, the measured phase difference is within 2/spl deg/ of the desired value and the SWR is within 1.5 dB.     

波纹波导极化器的分析

极化器是天线馈电系统中的重要器件,但传统的极化器带宽一般很窄。介绍了一种新型的宽带极化器(波纹波导极化器),其结构是在方波导的两壁加载横槽波纹,使波导中的2个正交模产生了90°的相位差。因而将线极化信号转化成圆极化信号。波纹波导极化器在超过30%的带宽内仍然有很好的相移特性,因此他在宽带反射面天线馈电系统中有着很广阔的应用。     

Arbitrarily polarized slot radiators in bifurcated waveguide arrays

The feasibility of obtaining arbitrary polarization in both one- and two-dimensional arrays of slots in dual mode bifurcated Waveguides has been demonstrated. The radiating element consists of a pair of crossed slots in the sidewall of a bifurcated rectangular waveguide that couple to even and odd waveguide modes. One linear polarization is excited by the even or "sum" mode and the orthogonal linear polarization is excited by the odd or "difference" mode. By superposing the sum and difference modes in the proper amplitude and phase, any arbitrary polarization can be realized. A two-dimensional array consisting of eight waveguide linear arrays, ferrite phase shifters for scanning in the plane normal to the linear arrays, and a feed network for power distribution and polarization control was constructed. Good radiation performance for various polarizations was obtained. In the case of linear polarization, the cross polarization component was on the order of -25 dB and in the case of circular polarization, the axial ratio was on the order of 1 dB. The polarization was controlled with a ferrite phase shifter. Close-in sidelobes of better than 20 dB were obtained for all polarizations. The preceding performance characteristics were obtained over a scan range ofpm20degand over a 6 percent frequency band.     

Single-Fed Microstrip Patch Antenna With Switchable Polarization

A single-fed reconfigurable microstrip antenna that can provide various polarization diversities is presented in this paper. The antenna is excited by a microstrip feed line through aperture coupling. When two PIN diodes are used to respectively reconfigure the coupling slot and the open stub of the feed line, the polarization of the microstrip antenna can be switched between vertical and horizontal polarizations. For the reconfigurable antenna with the linear polarization diversity, it can be converted to a circularly-polarized antenna with switchable polarization sense by introducing a perturbation segment. Moreover, an antenna with the quadri-polarization diversity, including dual orthogonal linear polarizations and two circular polarizations, is also developed from the structure of the switchable circular polarization microstrip antenna, and only three diodes are required. Details of the antenna design are shown, and the measured results for the constructed prototype are also exhibited and discussed.     

一种宽带四脊波导正交模极化耦合器

坐落于贵州天然喀斯特地形的500 米口径球面射电望远镜(FAST),其低噪声接收机系统需要高性能正交模极化耦合器,对此,提出了一种四脊波导形式宽带正交模极化耦合器快速有效的设计方法:首先分别设计四脊波导正交模极化耦合器的两个关键部分,然后进行整体优化,为了改善带内阻抗匹配性能可以在同轴输出端口的内探针引入阶梯匹配环。使用这种方法研制的FAST L 波段极化器工作带宽达到2 颐1,在整个带宽范围内极化器的反射系数小于-20 dB,极化耦合水平低于-43 dB,带内插入损耗优于0. 15 dB,仿真和实测结果有很好的一致性。提出的设计方法适用于各种频率范围的宽带四脊波导正交模极化耦合器的设计。     

W 波段宽带正交模转换器研制

为满足W波段双通道接收系统的需要,实现将天线接收到的线极化或圆极化电磁波分离出正交的垂直极化和水平极化电磁波,研制出了工作频带宽、性能优、结构简单、适合大批量生产的波导正交模转换器(OMT)。在80～102GHz频带内,即相对于中心频率91GHz的24%频带内,测得水平极化传输损耗典型值为0.8dB、垂直极化传输损耗典型值为0.4dB;各端口回波损耗优于15dB;隔离度典型值为21dB。