Baoqiang Du

To address the quantization phase accumulation effect caused by different frequency signals during phase comparison, an accurate frequency detection technology is presented. Through quantized phase analysis, statistics, and processing of the phase difference between the different frequency signals, high-precision measurement of the measured signal is realized. This detection method uses any phase difference within a group period as the switch signal of the counter, overcoming the ±1-word quantization error in traditional frequency measurement and improving measurement accuracy and detection speed. By integrating FPGA technology, the volume of the measurement equipment has been simplified, and the cost and power consumption have been reduced. The experimental results and analysis show that the method is advanced and scientific, and the actual measurement uncertainty reaches the level of 10 ⁻¹³ at 1 s. Compared with traditional frequency measurement technology, this frequency detection technology offers significant advantages in power consumption, device size, and detection rate. It is crucial for Beidou satellite time synchronization, radar detection, high-precision space positioning, and other high-tech applications.

A precise frequency stability measurement technology is proposed that utilises group periodic phase synchronisation of signals with varying frequencies. By quantifying the results of phase comparisons between different frequency signals and analysing these quantised outcomes, high-precision frequency measurements can be achieved. The phase coincidence points between the two comparison signals serve as the start and stop signals for the counter, where the time interval between identical phase coincidence points represents a complete cycle. Through the detection and analysis of phase coincidence points, the ±1 word counting error is eliminated, thereby enhancing the speed of frequency measurement. Employing the Field-Programmable Gate Array (FPGA) technology simplifies the measurement apparatus and reduces development costs. Experimental results demonstrate that this method achieves a frequency stability of 10−13 at 1s. Compared to traditional frequency measurement technologies, this approach offers significant advantages in terms of power consumption, equipment size, and measurement rate, making it crucial for high-tech applications such as Beidou satellite positioning, precision timing, high-precision time-frequency transmission and comparison, and scientific metrology.

To meet the requirements of high-precision measurement of time-frequency multiparameters, a high-accuracy frequency standard comparison technology combining adaptive frequency and Lissajous figure is proposed. This technology uses only one reference frequency source to realize the frequency standard comparison and frequency measurement between any frequency signals without frequency normalization. First, a new frequency standard comparison signal is obtained by using an adaptive frequency standard generation module to roughly measure the measured frequency. Second, the turning period is measured by observing the Lissajous figure. Third, via the turning period and the function relation of frequency deviation, the relative frequency difference between the measured and frequency standard signals can be obtained. Finally, the phase relation between the measured and frequency standard signals is determined by oscilloscope, and then the high-accuracy measurement of the measured frequency can be realized. The testing results indicate that the accuracy of the frequency measurement in the radiofrequency range can achieve the $10^{-12}$ order of magnitude. Compared with the traditional frequency standard comparison technology, this technology has many characteristics, such as simple operation, low cost, low noise, and high measurement accuracy.

Precise frequency detection is one of the key problems to be solved in a high‐accuracy transfer of time and frequency. The solution to this problem is helpful in improving the precision of the phase noise measurement, atomic frequency standard, and time synchronization, which plays a strong role in the whole precision measurement physics fields. A high‐accuracy frequency detection and analysis based on adaptive frequency standard tracking are proposed for time–frequency signal processing without frequency normalization. First, an adaptive frequency standard signal is generated by using an FPGA to control the DDS based on the measured signal. This signal can achieve phase comparison with the measured signal under any frequency relationships including complex and large‐frequency difference relationships, widening a frequency measurement range. Second, the frequency standard signal is put off by the delay chains. The rough time delaying can generate many phase coincidences, which can shorten the gate switch time to achieve fast time response. The finer delaying can provide a very high measurement resolution without transforming the frequency relationships between the measured and reference signals. And then, a differential synchronization is performed between the measured and reference signals after shaping and conditioning the two signals. The obtained optimal phase coincidences, that is, fuzzy zone edge pulses, are used as the gate signals. A precise frequency measurement for the measured signals can then be realized by counting the measured and reference signals without gap in the gate time. The testing results show that the frequency measurement accuracy of the system can reach 1.7 × 10 ⁻¹³ /s.

Using different frequency group period phase synchronization, a precise frequency detecting technology is presented. On the basis of the phase comparison for different frequencies, a high-accuracy frequency measuring can be achieved by quantization of phase comparison results and analysis of quantization results. Using the phase coincidence points between comparison signals as the counter’s open and close signals, the time interval between the same phase coincidence points is a group period. Via the detection and analysis of the phase coincidence points, the ±1-word counting error can be eliminated, and measuring speed is also improved. By using FPGA technology, the measuring device can be simplified, and the development cost can be reduced. Testing results indicate that the frequency measuring accuracy with 10−13/s level can be achieved. The technology is greater than the common frequency measuring technology in more ways than one, such as power consumption, device volume, measuring rate, etc., so it plays an important role in Beidou satellite positioning, precise timing, high-precision time frequency transfer and comparison, scientific metrology and other fields.

For the time and frequency signals of Beidou satellites, a high-accuracy phase frequency detection technology based on phase group synchronization is proposed. Using the Beidou receiver and satellite signals as the frequency standard and the measured signals, respectively. The Beidou receiver and the satellite signals are sent to the phase coincidence detector of the different frequencies to generate a phase coincidence point pulse, which is sent to the different frequency phase detector as a control signal to generate the phase differences between the Beidou receiver and satellite signals, and then complete the high-accuracy phase synchronization between the Beidou receiver and satellite signals. Experimental results show that when the delay resolution reaches ps level, the phase synchronization accuracy of the system can reach 10 ps, which has the characteristics of small phase noise, low development cost, simple circuit structure, and high synchronization accuracy compared with the traditional phase synchronization technologies. Therefore, it would be widely used in satellite positioning, astrometry, precision navigation, aerospace, satellite launch, power transmission, communications, radar, and other high-tech fields.

The combination of advanced radar sensor technology and smart grid has broad prospects. It is meaningful to monitor the respiration and heartbeat of grid employees under resting state through radar sensors to ensure that they are in a healthy working state. Ultra-wideband (UWB) radar sensor is suitable for this application because of its strong penetration ability, high range resolution and low average power consumption. However, due to weak heartbeat amplitude and measurement noise, the accurate measurement of the target heart rate is a challenge. In this paper, singular spectrum analysis (SSA) is proposed to reconstruct the eigenvalues of noisy vital signs to eliminate noise peaks around the heartbeat rate; combined with the variational modal decomposition (VMD), the target vital signs can be extracted with high accuracy. The experiment confirmed that the target vital sign information can be extracted with high accuracy from ten subjects at different distances, which can play an important role in short distance human detection and vital sign monitoring.

Due to the small size and various types of foreign object debris (FOD), radar detection of FOD on airport runways is a great challenge, and there are often a large number of false alarms in the detection results. Arc-scanning synthetic aperture radar (AS-SAR) is an emerging method for detecting FOD targets, which achieves omnidirectional coverage with a very high azimuth resolution. However, this method faces a similar challenge. A direct way to reduce false alarms is to increase the detection threshold based on enhancing the target signal-to-noise ratio (SNR), and in this paper, the coherent accumulation of multiple images is used to improve the target SNR. The stable phase is also an important feature of the target distinguishing background. Therefore, it is important to maintain the stability of the target phase. Aiming at the systematic phase drift (SPD) caused by atmospheric disturbance and system hardware, a spatial and temporal model is established, a corresponding correction approach is proposed, and the performance of the correction approach is validated by field experiments.

To improve the accuracy of radar ranging and positioning under complex backgrounds, a high-precision synchronization detection method for bistatic radar is proposed based on different-frequency phase processing. First, the transmit signal and receive signal are converted to radio frequency pulses by frequency conversion. Then, the transmit signal is roughly measured with a field-programmable gate array. The obtained rough signal is used as the reference signal under the control of the direct digital synthesizer frequency synthesizer. Second, the transmit signal and receive signal are each synchronized with the reference signal in a different-frequency phase detection. These detection results are used as the starting signal and stopping signal of the counter gate. Finally, all the signals are counted, and the time synchronization between the transmit signal and the receive signal is implemented by processing the counting value. The experimental results show that a time synchronization precision of 1.5 ps and a frequency stability of 6.2 × 10⁻¹³/s can be reached. This method has the advantages of a fast time response, good noise suppression, and high measurement precision and strong system reliability.