Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics

Significance 

Electronic warfare systems are critical for national defense because they enable the detection and measurement of signals from potential military threats. However, traditional systems rely heavily on electronic components that suffer from several limitations including bandwidth limitations, hard to achieve high-resolution radar detection and accurate frequency measurement because typically requires high-speed electronic devices, which are expensive and complex to implement. Furthermore, trying to integrate high-speed electronics into radar and frequency measurement systems increases both the cost and the complexity, which make these systems less flexible and harder to maintain and upgrade. To this account, new study published in Optics Communications and conducted by Zhigang Tang, Mingcheng Yang, Jian Zhu, Nianqiang Li, and led by Dr. Pei Zhou from the Soochow University developed a novel photonics-assisted joint radar detection and microwave frequency measurement system.

The researchers generated a broadband dual-chirp linear frequency-modulated (LFM) signal using an optically injected semiconductor laser (OISL). The experimental setup involved a master laser (ML) with a tunable output frequency and a slave laser (SL) operating in the P1 oscillation state. They monitored the optical spectra of the ML, free-running SL, and injected SL using an optical spectral analyzer and showed that the P1 oscillation frequency increased with higher injection power, and confirmed the tunability of the generated LFM signal. Afterward, the authors used a triangular-like electrical control signal V(t) with a 10 μs period to modulate the optical carrier, which resulted in a dual-chirp LFM signal with a 6 GHz bandwidth (from 12 to 18 GHz). The short-time Fourier transform of the temporal waveform verified the linearity of the LFM signal, with a calculated linearity of 0.01303 and a signal-to-noise ratio of 20.37 dB. These findings demonstrated the system’s ability to generate high-linearity LFM signals essential for radar detection and frequency measurement.

The team used aluminum trihedral corner reflector (TCR) placed 25 cm away from the antenna pair to evaluate the radar detection capabilities of the proposed system. The LFM signal transmitted by the radar was reflected by the TCR and received by the system. The de-chirped signal’s electrical spectrum, obtained through fast Fourier transform of the captured waveforms, revealed a spectral peak at 25.45 cm, closely matching the actual distance of the TCR. The 3-dB width of the main peak was 1.25 cm, consistent with the theoretical range resolution. Additionally, the researchers demonstrated the system’s inverse synthetic aperture radar (ISAR) imaging capabilities. A rotating platform was set 80 cm away from the antenna pair, rotating at a speed of 4π rad/s. The ISAR images were reconstructed using a Range-Doppler (RD) algorithm on the de-chirped signals. In one experiment, two targets placed with a cross-range of 13.0 cm were accurately imaged, with a measured distance of 13.27 cm. Another experiment involved imaging six TCRs arranged in a triangle-like shape. The measured lengths of the triangle sides closely matched the actual distances, highlighting the system’s high-resolution imaging capabilities. They also validated microwave frequency measurement capabilities of the system using a single-tone signal under test (SUT) at 4 GHz. The researchers recorded a pair of pulses with a 6.69 μs time interval using an 80-GSa/s real-time oscilloscope. Based on the frequency-to-time mapping relationship, the calculated frequency was 4.010 GHz, with a minor error of 10 MHz. The experiment was repeated with SUT frequencies ranging from 3 to 8 GHz in 1 GHz steps, consistently achieving measurement errors below ±50 MHz. To further test the system’s multi-tone frequency measurement capabilities, a two-tone signal with frequencies of 4 and 6 GHz was used. The calculated frequencies (4.010 GHz and 5.970 GHz) closely matched the actual values, demonstrating the system’s accuracy in multi-tone signal measurement. The authors also tested the frequency resolution using a two-tone signal with a 20 MHz frequency difference (6 GHz and 6.02 GHz). The system accurately identified the two adjacent pulses, indicating a frequency resolution of 20 MHz, primarily determined by the bandwidth of the electrical bandpass filter. According to the authors, the overall frequency measurement range was extended from 1 GHz to 39 GHz by tuning the frequency coverage of the generated LFM signal. The researchers obtained of averaging 50 sets of measurement results a good linear relationship with the actual values, with measurement errors kept below ±50 MHz. Such broad frequency measurement range and high accuracy underscored the system’s potential for practical applications in electronic warfare.

In conclusion, Dr. Pei Zhou and colleagues designed an innovative approach to integrate photonics with traditional electronic systems for radar detection and microwave frequency measurement. The system achieved an excellent radar range resolution of 1.25 cm and a frequency measurement error within ±50 MHz significantly enhances the precision of radar and frequency measurement systems. This high level of accuracy is critical for military applications where precise detection and measurement of signals are vital for strategic decision-making. Moreover, there is no need for high-speed electronic devices, and therefore the overall cost and complexity are much more affordable accessible and scalable. Additionally, the authors designed system to be of dual-function which enhances its resistance to interference, and improves the reliability and robustness of radar operations in contested environments which makes it a valuable asset in electronic warfare. It is worthy to mention, the success in the integration of radar detection and frequency measurement into a single, compact system reduces the hardware footprint and enhances the system’s flexibility which has significant advantage in the deployment on mobile platforms, such as unmanned aerial vehicles and ground-based radar systems, where space and weight are critical considerations. Furthermore, the broad frequency measurement range from 1 GHz to 39 GHz in the new system allows to intercept and analyze a wide variety of signals, and also enhance versatility and applicability in different operational scenarios which can be beneficial for comprehensive electronic intelligence and signal intelligence operations.

Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering Photonics-Assisted Dual-Functional Radar and Microwave Frequency Measurement System: Enhanced Resolution and Accuracy without High-Speed Electronics - Advances in Engineering

About the author

Pei Zhou received the B.S. and Ph.D. degrees from Nanjing University of Aeronautics and Astronautics (NUAA), Nanjing, China, in 2013 and 2019, respectively.

From 2017 to 2018, he was a Visiting Scholar at the University of California, Los Angeles, CA, USA. In July 2019, he joined the School of Optoelectronic Science and Engineering, Soochow University, Suzhou, China, where he is currently an Associate Professor. His main research interests include microwave photonics, and nonlinear laser dynamics.

Reference

Zhigang Tang, Mingcheng Yang, Jian Zhu, Nianqiang Li, Pei Zhou, Photonics-assisted joint radar detection and frequency measurement system, Optics Communications, Volume 550, 2024, 130008,

Go to Optics Communications

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