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Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes/issues, but are citable by Digital Object Identifier (DOI).
Display Method:
Measurement Methods and Techniques
Abstract:
To address the calibration needs of Frequency Modulated Continuous Wave (FMCW) signal testing equipment in millimeter-wave automotive radar applications and enhance measurement capabilities for complex analog-modulated signals in millimeter-wave broadband, we developed a hybrid measurement system. This system combines a frequency-domain full waveform metrology setup with FMCW testing equipment under calibration. By conducting in-situ, synchronous measurements of custom millimeter-wave FMCW signals, we achieved calibration and performance verification of commercial instruments. We thoroughly compared the performance of different measurement methods and equipment in the typical millimeter-wave radar frequency bands of 24 GHz and 60 GHz. Experimental results demonstrate that the frequency-domain full waveform metrology method outperforms relevant commercial instruments. The FMCW chirp deviation measurements under both 200 MHz narrowband and 2 GHz wideband conditions were an order of magnitude more precise, meeting the technical requirements for calibration and performance verification.
Abstract:
Traditional stepped frequency (SF) systems synthesize a large measurement bandwidth using a series of equidistant discrete frequency signals. However, due to sampling theorem limitations, time-domain signals corresponding to fixed frequency intervals exhibit periodicity. Consequently, background and multipath interference in the measurement environment may alias into the target area, adversely affecting imaging and scattering measurements. This paper explores rapid measurement methods for frequency-stepped systems and proposes a near-field scattering measurement technique based on nonuniform sampling. We analyze the impact of range ambiguity on scattering measurements and design optimization principles for the sampling function based on practical application requirements. The signal envelope is shaped using Poisson's formula and the principle of stationary phase (POSP). To address scattering image degradation caused by traditional nonuniform sampling reconstruction methods, we propose a weighted method compatible with the nonuniform sampling strategy. This method effectively suppresses aliasing interference, achieves high-resolution imaging, and improves the accuracy of near-field to far-field (NF-FF) transformations.
Research Progress
Abstract:
The equivalent source reflection coefficient plays a crucial role in microwave power measurement and uncertainty evaluation. This paper first discusses the relationship between the source reflection coefficient in amplitude-stabilized signal source systems and the equivalent source reflection coefficient when measuring power ratios using three-port devices. The concept of "equivalent" in the equivalent source reflection coefficient is explained from the perspective of the mismatch factor. Next, the working principle and limitations of K. Shimaoka's method for measuring equivalent source reflection coefficient using a network analyzer and three-port devices are briefly introduced. Finally, experiments and comparisons are conducted using N-type power dividers and directional couplers as measurement objects, based on K. Shimaoka's method and the traditional formula method in the 1-18 GHz frequency range. Results indicate that K. Shimaoka's method for measuring equivalent source reflection coefficient has certain limitations. Due to the small difference in transmission coefficients obtained in this calculation method, it is sensitive to minor changes and thus unsuitable for measuring equivalent source reflection coefficients when using three-port devices with good directionality (such as directional couplers).
Abstract:
The calibration factor is a parameter used to characterize the reading accuracy of RF power sensors, defined as the ratio of the power displayed by the sensor to the incident power. It is the object of power value transfer. This paper introduces the composition and measurement principles of the direct comparison method and the VNA-based direct comparison method. It describes the application of the equivalent source reflection coefficient in the direct calibration method. The calibration factor of the Rohde & Schwarz NRP50T power sensor was measured using both the direct calibration method and the VNA-based direct comparison method. Results show that the maximum difference between the corrected calibration factors measured by the two methods is 3.056%. The equivalent source reflection coefficient of the VNA-based direct comparison method is generally larger than that of the direct comparison method. The uncertainty evaluation method for the direct comparison method is well-established, making it currently the most prevalent RF power sensor calibration method.
Abstract:
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.
Measuring Instruments and Systems
Abstract:
Due to the varying quality of probes produced by different manufacturers, the development of electric field standard devices has become particularly important. To meet the calibration requirements of low-frequency, high-field-strength electric field probes, a low-frequency electric field standard device was developed using the parallel plate method. The device consists of two square aluminum plates with a side length of 1 m and a plate spacing of 0.5 m. The frequency range is DC to 10 kHz, with an electric field strength range of 0 to 3000 V/m. Through theoretical analysis, software simulation, and experimental measurements, the effects of edge effects, plate material, structure shape, operating frequency, and other factors on the standard electric field generated by parallel plates were studied, and an uncertainty evaluation was conducted. A new measurement model was proposed, and uncertainty components caused by seven factors were evaluated separately: plate voltage, plate spacing, field uniformity within the parallel plates, probe fixture, probe alignment, finite size of parallel plates, and probe influence. The resulting expanded uncertainty is U=6.84% (k=2). The results show that the developed electric field standard device can meet the calibration requirements for low-frequency electric field probes.
Impact Studies in Metrology
Abstract:
Thermistor-type power meters use DC substitution to measure microwave and millimeter wave power. To compensate for environmental temperature changes, these power meters typically employ both measurement and compensation bridges, operating in a dual-bridge mode. When calibrating a coaxial thermistor-type power sensor using a microcalorimeter power standard, the measurement bridge alone cannot be used, even with stable environmental temperatures. To ensure valid calibration results, both environmental temperature compensation and ceramic core temperature variation compensation (due to dual-element errors) are necessary. Experiments show that at 18 GHz and 10 mW power level, the substituted power deviation for an N-type coaxial thermistor power sensor is 0.38% when measured with single versus dual-bridge power meters. For waveguide thermistor-type power sensors with single-element structures, calibrating effective efficiency does not require consideration of single versus dual-bridge measurement issues.
Abstract:
Electromagnetic reverberation chambers are typically calibrated for characteristic parameters such as field uniformity and normalized field strength under low input power conditions. However, in practical applications like electromagnetic compatibility immunity testing, these chambers operate under high input power conditions. Currently, relevant international and domestic standards ignore this difference, providing no specific theoretical or experimental evidence. This paper presents a designed experimental study to investigate the influence of input power on the characteristic parameters of electromagnetic reverberation chambers. A rapid calibration technique using 3D photoelectric field probes was employed for low input power calibration, while high input power parameter measurements were conducted under conditions consistent with actual automotive component immunity tests. Results show that the impact of different input power levels on field uniformity is generally within ±0.5 dB, and the effect on normalized field strength is within 2 dB. Based on these findings, recommendations are provided for calibrating field uniformity and normalized field strength during electromagnetic reverberation chamber calibration and testing processes.
Abstract:
Spectrum analyzers are key instruments widely used in radio electronics. The long-term stability of their critical parameters has been a significant concern for users and manufacturers. Accurate tracking of technical specifications plays a crucial role in the research, development, improvement, usage, and maintenance of these instruments. The National Institute of Metrology has accumulated calibration data for spectrum analyzers spanning over a decade. These metrological scientific data are characterized by traceability and accuracy. Based on these data, this paper introduces the operational principles, key performance specifications, and measurement calibration systems and methods of spectrum analyzers. It focuses on analyzing variations in the displayed average noise level and input frequency response during long-term usage of typical spectrum analyzers among representative domestic users. This study aims to provide a more reliable basis for the development, production, testing, and maintenance of spectrum analyzers.
Abstract:
[Abstract]In this paper, a three-axis fiber optic gyro detection system based on superradiant LED light source is designed.Synchronous use of temperature control and constant current drive circuit to ensure the normal operation of the SLD in the full temperature range, the power part of the surge protection design, effectively avoid the transient impact caused by switching power supply or environmental changes, to achieve the protection effect of the device.The detection system monitors the output bias voltage of the photodetector in light and no light, and calculates the system loss of the assembled optical path through numerical analysis, so as to judge whether the technical specifications of the optical path of the fiber optic gyroscope meet the design requirements.Finally, the experiment verifies the function of the three-axis fiber optic gyro combined optical path detection system in the batch production process, the accuracy stability of the fiber optic gyro reaches 87%, and the qualified rate of the finished product is increased to 96%.
Abstract:
In the process of periodic verification of measuring instruments, a large number of verification data will be generated by measuring institutions, and the huge economic and social value is hidden. At present, it is still in the stage of analyzing and utilizing the quality or metrological performance of a single instrument. This paper puts forward a method of performance evaluation and failure early warning of measuring instruments according to the verification data of total station. Firstly, the verification data of total station are analyzed and processed, then the performance of total station measuring instruments is evaluated comprehensively by Topsis method, and then the product quality of total station manufacturers is evaluated by Vague set decision theory. Finally carry on the early warning analysis to the measuring instruments of the total station according to the limit difference and slope method, and finally build the performance evaluation and failure early warning system of the measuring instruments based on this method. Numerical experiments are carried out on the verification data of the total station, and the performance evaluation and failure early warning of the total station are effectively realized.
Abstract:
An isotope dilution-gas chromatography-mass spectrometry method for the determination of lactic acid concentration in serum was established, and the uncertainty of the measurement results was evaluated. Sodium lactate isotope label was added to the serum sample as internal standard. After pretreatment and silanization derivatization, samples were detected by gas chromatography-tandem mass spectrometry in selected ion monitoring mode. The established quantitative analysis method was used to analyze five different concentrations of lactic acid in serum. The results showed that the method had good linearity, and the correlation coefficient was r>0.999. The average spike recovery rate was 101.2%~102.6%, and the relative standard deviation was 0.16%~0.59 % (n = 6). The concentration of lactic acid in five different serum was 1.16 mmol/L, 2.01 mmol/L, 5.50 mmol/L, 10.02 mmol/L, and 15.63 mmol/L, and the related expanded uncertainty Urel of the results was less than 3.0% (k = 2). The method had good repeatability, high accuracy, reliable results, which could be used for accurate detection of lactic acid concentration in clinical serum sample.
Abstract:
Fugitive emission of benzene series and total hydrocarbons has irreversible harm to the ecological environment and human health. The quick and accurate analysis of benzene series and total hydrocarbons has always been a research focus of ambient air monitoring. A quick method for the analysis of total hydrocarbons, methane, benzene, toluene, ethylbenzene, p-xylene, m-xylene, o-xylene and styrene was developed based on the multi-dimensional gas chromatograph with double FID detector. The results show that the target components can be analyzed accurately and quickly in 12 minutes by one injection, and the components show good linearity and repeatability over the measurement range. This method has excellent detection limit and the accuracy ranged from −7.7% to 0.2%. This method can be used for on-line calibration of analytical instruments in different spatiotemporal scenarios, and has potential application value in field navigation monitoring of ambient air.