With the progress and development of contemporary society and science, human society has higher and higher requirements for radar functions. It is not only required that the radar can measure the distance information of the target, but also the speed, phase and acceleration of the target; sometimes It is necessary for the radar to be able to perform one-dimensional, two-dimensional or even three-dimensional imaging of the target. Today, Xunying Zhijian will have an in-depth understanding of this technology with everyone.
Screening Eagle Technologies (Screening Eagle Technologies), formed by the merger of Proceq, a Swiss non-destructive testing instrument brand, and Dreamlab, a Singapore robotics company, Provide a technology platform for intelligent detection in the construction and infrastructure construction industry.
For more information on scanning detection equipment, please contact Guard Eagle Smart Inspection official website: https://www.screeningeagle.com/zh/
At present, radar systems are classified according to the types of their signal sources:
● Pulse frequency radar
● FM CW radar
● Stepped frequency CW radar, etc.
For pulse radar and frequency modulation continuous wave radar, because of its early development of signal source technology, the technology and application are relatively mature. However, the frequency source of stepped frequency continuous wave radar was developed relatively late. It was also at the end of the 1960s that American scholars Ruttenburg K and Chanzi L proposed a new technology to improve the range resolution of radar, which is to use a series of jumping pulse signals to replace the previous common radar frequency source. This is the prototype of the early step frequency signal.
In recent years, with the deepening application of radar wave and integrated circuit technology, step frequency technology has been greatly developed and widely used in the field of civilian radar, such as ground penetrating radar, wall-penetrating radar and even vehicle-mounted radar for intelligent transportation. With its unique feature, it uses a small instantaneous bandwidth and can synthesize a larger working bandwidth due to continuous frequency hopping during operation. This feature can greatly improve the radar resolution and reduce the system. Therefore, the research on the stepped frequency source and its transceiver system has been paid more and more attention by researchers at home and abroad.
In 1997, Cape Town University developed a low-cost, small-volume portable step-frequency radar Mercury-A;
In 2000, Alberti and others in Italy developed the CORISTA remote sensing detection system by using a stepped frequency source, which has achieved great applications in archaeological research;
In 2005, Samsung developed a stepped-frequency UWB radar system with a wide frequency range of 600-5,600 MHz;
In 2009, AKELA Corporation of the United States developed a wall-penetrating radar with a stepping frequency source, with a frequency range of 500-2,000 MHz and a bandwidth of 1.5 GHz. Due to its wide bandwidth, the distance resolution of the radar system can reach 0.1m ;
In 2012, D. Seyfried and others applied the stepped frequency radar technology to the field of underground detection. The frequency range of the radar is 200-1,500 MHz, which can effectively detect the condition of pipelines and cables buried 3-5 m deep underground;
In 2014, Liu and Sato et al. applied step frequency radar to the field of civil engineering. The radar frequency range is 500-6,000 MHz, which is mainly used to detect parameters such as road thickness, layering and dielectric constant.
Stepped frequency continuous radar wave (SFCW), as a continuous wave radar, has certain differences from pulse frequency radar.
First of all, the signal it transmits is a continuous wave, so the design of the required frequency source is much easier, and the length of the wave train is increased at the same time;
Secondly, it does not need to share the transmitting and receiving antennas like the pulse frequency radar, does not need to switch the receiving and receiving state, reduces the switching process of the system, and effectively eliminates the “fog area” of radar detection;
In addition, it also includes ultra-wide band radar wave emission, so It does not require the transmitter to have high peak power, and at the same time the average transmission energy of the signal is large, so that the radar system can realize long-distance detection and have better depth resolution in the full depth range.
Figure 1 SFCW radar: frequency domain plot (left) and spectrogram (right)
From the frequency domain diagram of the SFCW radar wave signal in Figure 1, it can be seen that in the stepped frequency signal, for a single sub-pulse, the instantaneous bandwidth generated by it is very narrow, and the frequency modulation between multiple narrow-band pulses is Larger working bandwidth can be synthesized, and the stepping frequency signal uses this principle to improve the distance resolution of the radar.
At the same time, it can be seen from the spectrum diagram of the SFCW radar wave that the radar spectrum is discrete (that is, the amplitude of each center frequency is very high, and the background noise amplitude of other spurious frequencies is very weak), which can effectively suppress the external noise. Interference frequency, reduce the noise interference during system detection, and improve the detection sensitivity of the system.
Eagle Patrol uses SFCWground-penetrating radar measured data
01
Figure 2. Ground-penetrating radar actual measurement map of a place in Guangzhou: SFCW (left) and dual-frequency pulse (right)
Figure 2 is a ground-penetrating radar measurement map of a certain place in Guangzhou. The picture on the left is the detection map of GS8000 ground penetrating radar using SFCW technology, and the picture on the right is the detection map of ground penetrating radar using high and low dual-frequency pulse antennas on the market.
It can be seen from the picture on the right: Antennas with specific frequencies only have the best imaging effect at specific depths. In this picture, the high-frequency pulse antenna (upper right) can clearly see the gas pipeline, but the detection of the steel mesh below is not clear enough; low-frequency pulse The antenna (lower right) detects both the pipe and the steel mesh, but the signal from the steel mesh is weak and there are heavy coherent noise streaks at the bottom.
You can see from the picture on the left: SFCW stepped broadband, which can be understood as radar waves with many center frequencies in the full broadband range, and each center frequency has the best imaging effect at its corresponding depth, and at this depth Coherent noise generated here at other frequencies can also be suppressed. Therefore, high-resolution imaging can be achieved at the full depth range, and pipes with strong signals, steel mesh, local voids and very weak coherent noise can be seen at the same time.
02
Figure 3 Ground-penetrating radar actual measurement map of a place in Guangzhou: -10 ultra-wideband SFCW (left), wideband SFCW (middle), narrowband SFCW (right)
Among them, the left picture is 40-3,440 MHz ultra-wideband SFCW antenna collection, the middle picture is 40-1,000 MHz wideband SFCW antenna collection, and the right picture is 220-740 MHz narrowband SFCW antenna collection.
As can be seen from the left image: shallow imaging with ultra-wideband SFCW antennas. The interface of the target void is very clear, and the end of the boundary is also relatively steep.
As can be seen from the middle picture: full-depth imaging is performed using a broadband SFCW antenna. Select the default widest frequency range of 40-1,000 MHz, and you can find that the target void signal is very obvious and ends with a clear boundary, but the second excitation signal appears below the void.
As you can see from the image on the right: Full depth imaging with a narrowband SFCW antenna. Simulate the SFCW antenna as a single-frequency or dual-frequency antenna, narrow the frequency range to 220-740 MHz, and you can see that there are two, three, four, and five excitations below the target. The image is similar to conventional single-frequency or dual-frequency pulse radar images.
In summary
The new SFCW ground penetrating radar adopts progressive narrowband pulse frequency to synthesize ultra-wideband frequency continuous radar waves, which can perform one-time high-definition imaging in the full depth range while ensuring excellent depth resolution and signal-to-noise ratio. In addition, since it comes with multiple single sub-pulse radar waves with better discreteness, it can be used to simulate traditional pulse frequency antennas for effective detection of underground structures.
About Patrol Eagle
Screening Eagle Technologies, formed by the merger of Proceq, a Swiss non-destructive testing instrument brand, and Dreamlab, a Singapore robotics company, provides a technology platform for intelligent testing in the construction and infrastructure construction industries.
“Protect the built world” (Protect the built world) – Patrol Eagle’s mission is to use intuitive software, portable sensors and reliable data to protect fixed assets and infrastructure in the construction field, and implement decisions for construction and asset maintenance Defect detection, data collection and condition assessment, and enable effective preventive diagnosis and maintenance recommendations, thereby prolonging the life of fixed assets and infrastructure and increasing the long-term value of the owner.
