Research Team Incorporates Photonics into Radar System

A photonic radar system, characterized by its developers as so sensitive that it can detect an object’s location, speed, and angle down to the millimeter level, could be used for applications including autopilot assistance, gesture identification, environmental sensing, and medical imaging. Researchers at the University of Sydney developed the photonic wideband stepped-frequency (P-WSF) radar system. Tests showed that the system successfully handled a broad range of frequencies without requiring high-speed electronics.

The use of photonics enabled the system to generate high-resolution images in a format that is simpler and potentially less expensive than conventional electronic radar systems, the researchers said. The system uses analog photonic generation and processes ultrawideband signals using only megahertz (MHz)-level electronics for detection and imaging. It synthesizes stepped-frequency (SF), continuous-wave radar signals using a frequency-shifted optical modulation that is driven by a low-frequency electronic oscillator.

The optical mixing of a broadband radar signal and its echoes at the receiver produces a demodulated signal with a bandwidth that is much smaller than the frequency step. This signal could be processed by low-bandwidth devices with high precision to enable real-time radar ranging and imaging.

Because the bandwidth of the radar is driven and processed by MHz-level-electronics-based, acoustic-optic modulation, the need for high-speed, complex electronics for wideband radar signal generation and processing is eliminated. The radar’s signal bandwidth is more than 11 GHz and can exceed 20 GHz without radio frequency (RF) antenna bandwidth limitations.

The P-WSF radar provides high spatial resolution at the centimeter level and a real-time imaging rate of 200 frames/s⁻¹. It combines high resolution and rapid response, which enables it to detect rapidly moving objects, like the blades of an unmanned aerial vehicle (UAV), at high resolution. The researchers demonstrated the use of the P-WSF radar system for high-resolution range detection and 2D radar imaging. They achieved high spatial resolution down to 1.3 cm and an ultralarge time-bandwidth product exceeding 5 × 10⁵.

Ziqian Zhang and professor Benjamin Eggleton optimize the photonic system that is the basis of the high-frequency radar mechanism the team introduced in a Laser & Photonics Review paper. Courtesy of the University of Sydney.

One such application for the technology could be to monitor vital signs; it could unobtrusively monitor respiratory rate in a patient with sensitive skin, or in an infant by continuously detecting the rise and fall of the patient’s chest. Respiratory rate is typically monitored by a strap around the person’s chest. Unlike traditional health surveillance methods, which use cameras to monitor patients, a radar system would automatically protect the patient’s privacy.

The researchers plan to test their system on cane toads and, ultimately, human participants. The technology is safe, and the research is undergoing ethics approval to proceed. Once the team has developed an advanced prototype, the radar could be miniaturized onto a photonic chip that would be small enough to build into a mobile phone.

The P-WSF radar could lead to next-generation broadband radars with reduced system complexity — a necessity for ubiquitous sensing applications such as autonomous driving, environmental surveillance, and vital sign detection.

The research was published in Laser & Photonics Review (www.doi.org/10.1002/lpor.202100549).