自由空间单站反射系数测量中校准方法的比较

杨若楠; 梁伟军; 徐浩

doi:10.12338/j.issn.2096-9015.2024.0080

自由空间单站反射系数测量中校准方法的比较

doi: 10.12338/j.issn.2096-9015.2024.0080

中国计量科学研究院，北京 100029

基金项目: 国家重点研发计划（2022YFF0605901）。

详细信息

作者简介:
杨若楠（2001-），中国计量科学研究院在读研究生，研究方向：微波测量技术与计量，邮箱：yangrn@nim.ac.cn

通讯作者:
梁伟军（1978-），中国计量科学研究院副研究员，研究方向：无线电导波基本参数计量与测试技术，邮箱：liangwj@nim.ac.cn

中图分类号: TB973
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出版历程
- 收稿日期: 2024-03-13
- 录用日期: 2024-03-13
- 修回日期: 2024-03-18
- 网络出版日期: 2024-05-30

Comparison of Calibration Methods in Free-Space Monostatic Reflection Coefficient Measurement

National Institute of Metrology, Beijing 100029, China

摘要

摘要: 微波黑体为微波辐射计提供高精度的亮温信号以精确标定观测目标的辐射信号幅度。微波黑体的发射率是影响其辐射特性的重要参数，因此准确测量黑体发射率对于提高辐射计的定标精度和保证量值的溯源性和有效传递具有重要意义，目前黑体发射率主要通过测量反射率来间接计算得到。本文实现了自由空间单站反射系数测量中的两种校准方法：偏移短路校准法和滑动负载校准法，采用时域门技术解决了小反射测量过程中多径反射信号的影响。搭建了反射率测量系统，在75～110 GHz频段内测量了同一黑体目标的反射率，并对测量结果进行了分析和比较。两种校准方法解算的误差项具有很好的一致性，测量发射率均能到达0.999～0.9999量级。当被测黑体满足近似条件时，使用滑动负载校准法具有更高的效率。最后，以偏移短路法为例，采用蒙特卡洛方法对微波黑体反射系数的测量不确定度进行了评定。
- 计量学 /
- 微波黑体 /
- 发射率 /
- 反射率测量 /
- 单端口校准 /
- 偏移短路法 /
- 滑动负载法
Abstract: Microwave blackbodies provide high-precision brightness temperature signals for microwave radiometers to accurately calibrate observed target radiation signals. The emissivity of a microwave blackbody is a crucial parameter affecting its radiative characteristics. Therefore, accurately measuring blackbody emissivity is significant for enhancing radiometer calibration precision and ensuring measurement value traceability and effective transfer. Currently, blackbody emissivity is mainly obtained indirectly by measuring reflectivity. This study implements two calibration methods in free-space monostatic reflection coefficient measurement: the offset-short calibration method and the sliding-load calibration method. Time-domain gating techniques are utilized to address multipath reflection signals during small reflection measurements. A reflectivity measurement system was established, and the reflectivity of the same blackbody target was measured within the 75-110 GHz frequency band, with results analyzed and compared. The error terms solved by the two calibration methods exhibit high consistency, with measured emissivity reaching levels of 0.999-0.9999. When the measurement target satisfies approximation conditions, the sliding-load calibration method proves more efficient. Finally, using the offset-short method as an example, the Monte Carlo method was employed to evaluate the uncertainty of the solved blackbody target reflection coefficient.
- metrology /
- microwave blackbody /
- emissivity /
- reflectivity measurement /
- one-port calibration /
- offset-short method /
- sliding-load method

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图 1 辐射计两点定标原理

Figure 1. Two-point calibration principle of radiometers

下载: 全尺寸图片幻灯片

图 2 反射率测量系统示意图

Figure 2. Schematic diagram of reflectivity measurement system

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图 3 自由空间单端口反射系数测量信号流图

Figure 3. Signal-flow graph for free-space monostatic reflection coefficient measurement

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图 4 半参数圆拟合法拟合$ {\mathit{\varGamma }}_{\mathbf{m}\mathbf{e}\mathbf{a}\mathbf{s}} $

Figure 4. Semi-parametric circular fitting method for $ {\mathit{\varGamma }}_{\mathbf{m}\mathbf{e}\mathbf{a}\mathbf{s}} $

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图 5 自由空间单站反射系数测量系统示意图

Figure 5. Schematic diagram of free-space monostatic reflection coefficient measurement system

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图 6 滑动负载校准法中任意两个频点半参数圆拟合示例

Figure 6. Example of semi-parametric circular fitting for any two frequency points in sliding-load calibration method

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图 7 两种校准方法解算的误差项对比

注：蓝色曲线为测量结果，橘色曲线为差值。

Figure 7. Comparison of error terms calculated using two calibration methods

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图 8 黑体目标两种自由空间单端口反射系数测量结果对比

注：蓝色曲线为测量结果，橘色曲线为差值。

Figure 8. Comparison of free-space one-port reflection coefficient measurement results for the blackbody target

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图 9 偏移短路校准法75.656 GHz反射系数实部单批次MCM概率分布

Figure 9. Single-batch MCM probability distribution of the reflection coefficient real part at 75.656 GHz using the offset-short calibration method

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表 1 两种校准方法在不同测量设置下所需时间对比

Table 1. Comparison of time required for the two calibration methods under different measurement settings

校准方法	频点数	校准件移动次数（负载/金属板）	程序解算时间（秒）
滑动负载校准法	701	4	0.011754
	1601	4	0.036484
		5	0.036092
		8	0.030351
	2500	4	0.059153
偏移短路校准法	701	4	93.747827
	1601	4	319.017061
		5	334.650704
		8	355.390375
	2500	4	447.168423

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表 2 反射系数输入量

Table 2. Reflection coefficient input quantities

输入量	测量值
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{c}\mathrm{h}} $	−0.0012 − 0.0060i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{s}\mathrm{h}\mathrm{o}\mathrm{r}\mathrm{t}} $	−0.0470 − 0.0773i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(1\right)} $	−0.0802 − 0.0350i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(2\right)} $	−0.0830 + 0.0164i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(3\right)} $	−0.0536 + 0.0605i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(5\right)} $	−0.0045 + 0.0780i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(6\right)} $	0.04580 + 0.0641i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(7\right)} $	0.0778 + 0.0210i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(8\right)} $	0.0781 − 0.0318i
$ {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}} $	−0.0019 − 0.0055i

下载: 导出CSV

表 3 测量模型各输入量幅值最大变化值

Table 3. The maximum change value of each input of the measurement model

输入量	均值（$ \times {10}^{-5} $）
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{m}\mathrm{a}\mathrm{t}\mathrm{c}\mathrm{h}}\right\| $	6.4944
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{r}\mathrm{e}\mathrm{a}\mathrm{l}}\right\| $	17.7564
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(1\right)}\right\| $	7.9616
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(2\right)}\right\| $	17.3536
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(3\right)}\right\| $	17.6757
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(4\right)}\right\| $	18.4665
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(5\right)}\right\| $	7.0139
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(6\right)}\right\| $	3.2370
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(7\right)}\right\| $	18.5265
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}^{\mathrm{o}\mathrm{f}\mathrm{f}\left(8\right)}\right\| $	17.7068
$ \left\|\Delta {\varGamma }_{\mathrm{m}\mathrm{e}\mathrm{a}\mathrm{s}}\right\| $	7.1719

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