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The Quiet Zone Performance Evaluation of the Microwave Anechoic Chamber and the Uncertainty Estimation
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摘要: 微波暗室广泛用于天线、目标散射特性测量、雷达成像等领域，是微波频段最重要的测试场地之一。微波暗室建设投入较高，其静区性能取决于其内壁铺设的吸波材料特性及其布置，静区指标直接影响使用该暗室测试的设备测量结果准确度。因此如何测量得到准确的微波暗室静区指标是微波暗室验收中必不可少的环节，也是微波暗室环境对测量结果贡献评估的基础。针对微波暗室静区的关键指标——静区反射率电平的测量方法进行研究，针对中大型微波暗室，建立最大行程4 m的基于三维扫描架的静区测量系统，覆盖频率范围1～40 GHz。利用其开展微波暗室静区的测量，给出静区反射率电平的测量结果，并进行了测量系统影响量的全面分析和测量结果不确定度评定。结果表明，以1.1 GHz为例，该系统静区反射率电平在−33 dB的情况下，测量不确定度为1.72 dB（k=2）。Abstract: Microwave anechoic chamber is one of the most important test sites in the microwave band, which is widely used in antenna measurements, target scattering parameter measurements and radar imaging. The investment construction of the microwave anechoic chamber is relatively high, and the quiet zone performance of the chamber depends on the characteristics and layout of the absorbing materials laid on its inner wall, while the quiet zone parameter of the chamber is closely related to the measurement accuracy of the devices measured in the chamber. Therefore, acquiring the accurate anechoic chamber quiet zone parameter through measurements not only is an essential step for the site validation, but also the basis for estimating the contribution of the anechoic chamber environment to the measurement results. The method to measuring the quiet zone reflectivity level of the chamber, which is the key parameter of the quiet zone, is discussed in this article, and a quiet zone measuring system based on a three-dimensional scanner with a maximum travel of 4 m is established for medium-to-large microwave chamber covering the frequency range of 1 to 40 GHz. An example of reflectivity level measurement for an anechoic chamber is presented, the measured results are shown, and the uncertainties component which effect the results are discussed, and the total uncertainty for the quiet zone reflectivity level is estimated for the first time. The results show that the expanded uncertainty is 1.72 dB (k=2) at 1.1 GHz for reflectivity level of −33dB.
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Key words:
- microwave anechoic chamber /
- quiet zone /
- reflectivity level /
- measurement uncertainty
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图 2 到达暗室静区的直达波信号和反射波信号示意图
Figure 2. Schematic diagram of direct wave signal and reflected wave signal arriving in quite zone of chamber
图 6 扫描架移动范围内地面反射的影响
Figure 6. Influence of ground reflection in the moving range of the scanning frame
表 1 扫描架定位精度测量结果
Table 1. Scanning frame positioning accuracy measurement results
位置
(mm)定位实测值（mm） X轴 差值 Y轴 差值 Z轴 差值 200 199.99 −0.01 200.21 0.21 199.99 −0.01 400 399.98 −0.02 399.70 −0.30 399.95 −0.05 600 599.99 −0.01 600.17 0.17 599.92 −0.08 800 799.99 −0.01 799.71 −0.29 799.92 −0.08 1000 1000.00 0.00 1000.27 0.27 999.93 −0.07 1200 1199.99 −0.01 1199.78 −0.22 1199.93 −0.07 1400 1400.00 0.00 1400.21 0.21 1399.90 −0.10 1600 1600.03 0.03 1599.88 −0.12 1600.00 0.00 1800 1800.07 0.07 1800.14 0.14 1800.01 0.01 2000 2000.10 0.10 1999.92 −0.08 2000.06 0.06 2200 2200.00 0.00 2200.11 0.11 2200.03 0.03 2400 2400.07 0.07 2399.92 −0.08 2400.04 0.04 2600 2600.04 0.04 2600.10 0.10 2600.05 0.05 2800 2800.04 0.04 2799.99 −0.01 2800.04 0.04 3000 3000.04 0.04 2999.96 −0.04 3000.03 0.03 3200 3200.07 0.07 3199.99 −0.01 3200.02 0.02 3400 3400.09 0.09 3400.04 0.04 3400.07 0.07 3600 3600.06 0.06 3599.98 −0.02 3600.07 0.07 3800 3800.06 0.06 3800.03 0.03 3800.00 0.00 4000 4000.04 0.04 3999.99 −0.01 4000.09 0.09 
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表 2 静区反射率电平
Table 2. Quiet zone reflectivity level
(a) 1.1 GHz 行程线 方位角（°） 反射率电平值（dB） 水平极化 垂直极化 X1X2 60 −33.4 −40.6 90 −32.0 −33.6 120 −40.9 −33.4 Z1Z2 150 −42.5 −40.4 180 −46.1 −37.4 210 −49.7 −44.7 Y1Y2 45 −40.2 −46.9 −45 −15.6 −20.8 (b) 26.5 GHz 行程线 方位角（°） 反射率电平值（dB） 水平极化 垂直极化 X1X2 60 −56.3 −56.7 90 −58.1 −57.5 120 −63.1 −65.5 Z1Z2 150 −48.3 −52.3 180 −58.9 −54.6 210 −52.0 −61.3 Y1Y2 45 −58.6 −56.2 −45 −39.0 −45.7 (c) 40 GHz 行程线 方位角（°） 反射率电平值（dB） 水平极化 垂直极化 X1X2 60 −52.3 −52.5 90 −60.6 −60.5 120 −58.4 −68.8 Z1Z2 150 −43.9 −59.1 180 −51.9 −62.3 210 −53.2 −68.7 Y1Y2 45 −46.1 −48.4 −45 −47.4 −41.2
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表 3 静区反射率电平不确定度汇总表
Table 3. Summary of uncertainty of reflectance level in quiet zone
不确定度来源或输入量 $ {x_i} $ 最大允许误差MPE或不确定度U/dB 概率分布 包含因子k 灵敏系数$ {c_i} $ 影响量$ u\left( {{x_i}} \right) $的标准不确定度/dB 天线对准$\delta {A_{{U} } }$ 0.5 正态 2 1 0.25 扫描架自身反射$\delta {S_{ {R} } }$ 0.3 均匀 $ \sqrt 3 $ 1 0.17 移动行程内的地面反射$\delta {R_{{R} } }$ 0.98 均匀 $ \sqrt 3 $ 1 0.57 两天线间互耦$\delta {M_{{R} } }$ 0.43 均匀 $ \sqrt 3 $ 1 0.25 系统漂移$\delta {S_{ {D} } }$ 0.1 均匀 $ \sqrt 3 $ 1 0.06 步长设置$\delta {M_{{S} } }$ 0.2 均匀 $ \sqrt 3 $ 1 0.12 接收天线方向图$\delta {R_{{P} } }$ 0.9 正态 2 1 0.45 测量重复性$ \delta {C_{{R} } }$ 0.18 正态 1 0.18 合成标准不确定度${u_{ \rm{c} } }$ 0.86 扩展不确定度U 1.72
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