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Data Processing Methods for Quiet Zone Reflectivity Level in Microwave Anechoic Chambers
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摘要: 微波暗室是工作在微波频段的暗室，是天线、目标散射特性等领域测量中使用的实验场地，用来模拟自由空间，相比与室外测试场，具有全天候、低反射的优势。实际应用中，由于内部铺设的吸波材料无法完全吸收特定频段电磁波等原因，暗室中的测试区域仍会有干扰的反射信号存在，这些反射信号从各个方向进入测试区域并与收发天线之间的直射波叠加，在测试区域内一定行程上形成空间驻波分布。测试区域内的干扰反射指标用静区反射率电平表征。将微波暗室用于天线辐射方向图等参数测量时，应评估暗室中不同角度的静区反射率电平。微波暗室静区反射率电平测量方法常采用自由空间电压驻波比（Voltage Standing Wave Ratio, VSWR）法。测试区域中直射信号和反射信号的矢量和一定行程上形成空间驻波，空间驻波的数据处理方式决定了静区反射率电平计算结果，实际测试曲线中驻波峰峰值的选择方式直接决定了测量结果。详细讨论了微波暗室内反射率电平的采集数据和处理方法，有助于优化现场测量测试的测试方案，并对静区扫描架的优化设计有积极意义。Abstract: Microwave anechoic chambers are enclosed spaces specifically designed for measurements in the microwave frequency range, used as experimental sites for antenna and target scattering characteristics measurements to simulate free space. Compared to outdoor test sites, these chambers offer advantages of all-weather operation and low reflection. However, due to the imperfect absorption of electromagnetic waves by internal materials in specific frequency bands, interfering reflected signals still exist in the test area. These signals enter from various directions and overlap with direct waves between transceiver antennas, forming spatial standing wave distributions over certain distances. The interference reflection index in the test area is characterized by the quiet zone reflectivity level. When using microwave anechoic chambers to measure parameters such as antenna radiation patterns, the reflectivity level at different angles should be evaluated. The free-space voltage standing wave ratio (VSWR) method is commonly employed to measure this reflectivity level. In the test area, the vector sum of direct and reflected signals forms spatial standing waves along specific paths. The data processing method for these standing waves determines the calculated reflectivity level of the quiet zone, with the selection of peak-to-peak values in actual test curves directly influencing measurement results. This article discusses in detail the collection and processing methods of reflection level data in microwave anechoic chambers, aiming to optimize on-site measurement and testing schemes. Additionally, this research provides valuable insights for the optimal design of quiet zone scanning frames, potentially enhancing the overall accuracy and reliability of microwave measurements in anechoic environments.
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Key words:
- metrology /
- microwave anechoic chamber /
- quiet zone reflectivity level /
- measurement /
- antenna
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图 1 静区中反射信号和直射信号示意图
Figure 1. Schematic diagram of reflected and direct signals in the quiet zone
图 3 驻波曲线及峰峰值D确定
Figure 3. Standing wave curves and determination of peak-to-peak values D
图 4 沿纵向线Z1−Z2方向，方向角90°（1.71 GHz），水平极化
Figure 4. Horizontally polarized measurement along longitudinal line Z1−Z2 direction, direction angle 90° (1.71 GHz)
图 5 沿横向线X1−X2方向，方向角90°（2.69 GHz），垂直极化
Figure 5. Vertically polarized measurement along the transverse line X1−X2 direction, direction angle 90° (2.69 GHz)
图 6 沿纵向线Z1−Z2方向，方向角90°（8 GHz），水平极化
Figure 6. Horizontally polarized measurement along longitudinal line Z1−Z2 direction, direction angle 90° (8 GHz)
图 7 沿横向线X1−X2方向，方向角90°（8 GHz），水平极化
Figure 7. Horizontally polarized measurement along the transverse line X1−X2 direction, direction angle 90° (8 GHz)
表 1 频率 1.71 GHz反射率电平（最大值和平均值）
Table 1. Reflectivity level (maximum and average) at 1.71 GHz
行程线 方位角(°) 最大值得到的反射率电平值（dB） 平均值得到的反射率电平值（dB） 指标（dB） 水平极化（H） 垂直极化（V） 水平极化（H） 垂直极化（V） 沿横向线X1−X2 60 −40.1 −42.5 −48.8 −48.7 ≤−40 dB 沿横向线X1−X2 90 −47 −43.2 −55.5 −52.2 ≤−40 dB 沿纵向线Z1−Z2 60 −43.3 −38.2 −53 −49.2 ≤−38dB 沿纵向线Z1−Z2 90 −43.1 −44.3 −53.5 −51.6 ≤−40 dB 
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表 2 频率 2.69 GHz反射率电平（最大值和平均值）
Table 2. Reflectivity level (maximum and average) at 2.69 GHz
行程线 方位角(°) 最大值得到的反射率电平值（dB） 平均值得到的反射率电平值（dB） 指标（dB） 水平极化（H） 垂直极化（V） 水平极化（H） 垂直极化（V） 沿横向线X1−X2 60 −41.6 −41.8 −48.8 −50.2 ≤−40 dB 沿横向线X1−X2 90 −44.1 −42.6 −53.8 −52.1 ≤−40dB 沿纵向线Z1−Z2 60 −40.4 −40.4 −52.6 −51.4 ≤−40 dB 沿纵向线Z1−Z2 90 −43.8 −43.8 −52.9 −49.8 ≤−40 dB
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表 3 频率 8 GHz反射率电平（最大值和平均值）
Table 3. Reflectivity level (maximum and average) at 8 GHz
行程线 方位角(°) 最大值得到的反射率电平值（dB） 平均值得到的反射率电平值（dB） 指标（dB） 水平极化（H） 垂直极化（V） 水平极化（H） 垂直极化（V） 沿横向线X1-X2 60 −54.4 −51.4 −65.7 −60.3 ≤−50dB 沿横向线X1-X2 90 −58.8 −56.1 −69.0 −66.9 ≤−50 dB 沿纵向线Z1-Z2 60 −59.4 −51.9 −69.0 −64.4 ≤−50 dB 沿纵向线Z1-Z2 90 −56.7 −54.6 −64.5 −62.7 ≤−50 dB
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