天线第十四讲-天线测量

2015/6/8ResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering天线Antennas第14讲天线测量谢泽明华南理工大学电子与信息学院[e-mail]TechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering第14讲内容引言天线测量场地方向图测量增益测量圆极化测量阻抗测量SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering14.1引言天线辐射特性的测量方向图增益主瓣宽度和副瓣电平交叉极化轴比天线电路特性测量输入阻抗（回波损耗、驻波比）阻抗带宽SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering两种测量方法远场测量：收发天线距离满足远场条件，直接测量天线在远场区的辐射场（直接法）近场测量：测量天线近区的场，推算远场的辐射特性（间接法）由互易定理，待测天线可以按照发射SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering天线测试场地的要求符合自由空间的条件，各种杂散的反射足够小；收发天线之间的串扰足够小远场测量时，收发天线之间的距离满足远场条件；SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering14.2微波暗室微波暗室是在一个与外界电磁屏蔽的、内部没有反射的房间；微波暗室模拟无反射的自由空间；微波暗室是在一个电磁屏蔽的房间内贴上电磁吸收材料构成，可以把各种杂散反射和外部干扰降低到最小。SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering微波暗室的形式SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering微波暗室的电特性：静区：各种杂散干扰最小的区域，待测天线按放在静区，静区须大于待测天线；反射率电平：各种反射场与直射场的比值，一般要求小于-40dB，对于低副瓣天线测量要求-60~-70dB交叉极化：电磁波传输过程中与原极化分量正交的分量电平，一般小于-25dB多路损耗均匀性：不同路径和极化的电磁波传输的损耗静区场强均匀性：纵向2dB，横向正负0.25dBSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering14.3远区条件远区条件：远场测量时，收发天线距离足够远，满足远场条件：电磁波照射到待测天线时为均匀平面波一般要求照射到天线孔径时中心和边沿的相位差小于p/8，这时距离应满足：22DRSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering在远场区，方向图与距离无关：SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering14.4方向图测量方向图的远场测量：测量系统组成：微波暗室、天线转台、伺服控制装置、发射天线、参考天线、信号源和接收机（或网络分析仪）、信号采集和计算机、处理软件SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering在远场区，方向图与距离无关：SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineeringSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering方向图的近场扫描测量：近场测量原理：依据等效原理，天线的辐射场可以由包围天线的闭合面上的等效电流和等效磁流计算VS,EH,ssEHn,EH内内天线VS,EH,ssEHn00EH内内sesJnHsmsJnEsnEsnHssessnHJnHHnH内sssmsssnEJnEEnE内SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering方向图的近场测量方法：测量出包围天线的平面、柱面或球面的场分布，利用傅里叶变换可得远场的方向图近场的量的优点：不需要大微波暗室、外部干扰小SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering近场测量系统方法：微波暗室、扫描架、伺服控制系统、网络分析仪、探头、数据采集系统和计算机、控制软件SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering近场测量系统方法：微波暗室、扫描架、伺服控制系统、网络分析仪、探头、数据采集系统和计算机、控制软件SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineeringSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineeringSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering14.5增益测量比较法：用已知增益的天线作参考，通过接收功率进行对比发射天线标准增益天线待测天线tPsGaGsPaPssaaPGPGaassPGGPasasGdBGdBPdBmPdBmSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering同增益双天线法：用相距为R的两副相同的待测天线，用测量的传输损耗和传输损耗公式计算天线增益待测天线aGrP24rtaaPPGGRp41110lg22atrRGdBPdBmPdBmp待测天线tPaGR4ratRPGPpSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering不同增益双天线法：用两副不知增益的待测天线第一步：用对比法测量两付天线增益比第二步：测量待测天线之间的传输损耗，用传输损耗公式计算两付天线的增益2224rtPPAGGRp待测天线22GrP待测天线1tP1GR发射天线待测天线1待测天线2tP1G2G1P2P1122GPAGP24rtRPGAPp12GAG12GAGSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering14.6交叉极化和轴比测量交叉极化测量：分别同极化天线和正交极化天线进行发射，测量待测天线的接收功率进行对比crosscocrosspolarisationdBPdBmPdBm同极化发射天线tP待测天线crossPcoP交叉极化发射天线SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering轴比测量：用线极化天线做发射天线，旋转发射天线或待测天线，测量最大值和最小值，计算轴比maxminARdBPdBmPdBm发射天线tP待测天线rPmaxPminPSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering14.7阻抗阻抗测量可以采用网络分析仪测量，测量出端口的S参数S11，然后转换成阻抗、回波损耗和驻波比，测量时应避免环境反射的影响。111111inCSZZS11()20lgreturnlossdBS111111SVSWRSSouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolofElectronic&InformationEngineering测量步骤：网络分析仪的校正：在电缆末端分别接短路、开路、匹配进行校正用电缆连上天线，测量S11显示驻波比、回波损耗等参数天线应该放在屏蔽、无反射的暗室内测量SouthChinaUniversityofTechnologyResearchInstituteofAntennas&RFTechniquesSchoolo