Doppler FMCW radar module 5.8G sensing solution, with the development of radar technology, the application fields of radar products have become increasingly rich, and it has become a field of smart lighting, smart security, smart home, smart home appliances, assisted driving, energy control, and assisted medical care. one of the important solutions.

Radar is an electronic device that uses electromagnetic waves to detect targets. By emitting electromagnetic waves to illuminate the target and receiving its echoes, it can obtain information such as the distance, distance change rate (radial velocity), azimuth, and altitude from the target to the electromagnetic wave emission point. Currently, there are 5.8GHz, 24GHz, 60GHz and 77GHz. Among them, 5.8GHz radar products are rapidly replacing traditional infrared sensor modules for smart lighting, smart home and other fields. in automotive and other fields. In the application of ADAS (AdvancedDriverAssistanceSystem), the radar needs higher resolution and narrower beam. At this point, mmWave will be the better choice, but with that comes the cost.

For a communication system, an appropriate modulation method can improve the efficiency of spectrum utilization and improve the anti-interference performance of the communication system. For radar, the purpose is not to transmit data like a communication system, but after modulating the radar signal, the dimension of detecting and acquiring information can be increased, and the modulation method can be selected according to the actual use needs. According to different modulation methods, radar can be divided into CW radar, (M)FSK radar and FMCW radar. The intermediate frequency signal (IF) of radar refers to low frequency signal, including useful signal and modulation signal, such as CW Doppler frequency shift signal, and Chirp signal of FMCW belongs to the category of intermediate frequency signal. A radio frequency signal (RF) refers to a signal that mixes an intermediate frequency signal to a high frequency and is radiated into space through electromagnetic waves.

Doppler effect

When a moving object moves at a certain speed, its frequency and phase will change with the speed of movement, which is called Doppler shift. For the observer, the frequency of the moving object increases when the moving object is close to the observer, and the frequency of the moving object decreases when the moving object moves away from the observer.

An antenna is a converter that converts guided waves propagating on a transmission line into electromagnetic waves propagating in an unbounded medium (usually free space) or vice versa. Its basic working principle is that when high-frequency current passes through the conductor, an electric field and a magnetic field are formed in the surrounding space, forming an externally radiated electromagnetic wave, and the antenna acts as a transmitting antenna; on the contrary, when there are electromagnetic waves in the surrounding environment of the conductor, a high-frequency current is formed on the conductor, and the antenna acts as a transmitting antenna. Receive antenna.

Antennas are easy to each other, and their transmit and receive performance are the same. As with any passive antenna, it can be used for transmit or receive. "Transmitting antenna" and "receiving antenna" are delineated according to the actual application, i.e. when an antenna is used for transmitting, it is a transmitting antenna and vice versa.

Constant Frequency Continuous Wave—CW

The continuous wave whose frequency does not change with time belongs to the unmodulated radar signal. The radial velocity is estimated by measuring the Doppler frequency shift of the moving object, but the distance and direction cannot be judged.

Frequency Shift Keying—FSK

The range of the carrier signal remains unchanged, but the frequency changes periodically. For example, FSK switches between two frequency points, which belongs to the binary modulation mode. For the more advanced modulation mode, it is called multi-ary frequency shift keying, that is, MFSK. It can measure the distance and speed of moving objects.

Frequency Modulated Continuous Wave—FMCW

FMCW refers to a continuous signal with a certain bandwidth and linear frequency change, called Chirp signal. If FMCW is combined with a multi-antenna scheme, it can test the distance and speed of multiple objects, and can also measure the azimuth of the object. At present, FMCW is widely used in ADAS vehicle radar.

From a technical point of view, compared with the other two schemes, FMCW and distance test, multi-target test, angle test, CW and FSK have great advantages. Because it has great advantages. Compared with CW technology, FMCW adds multi-dimensional information such as distance and angle, so the accuracy and sensitivity of FMCW micro-motion and presence detection are higher.

Doppler FMCW radar module scheme based on FRZN520

Features of traditional CW solutions

Because the scheme based on CW can only roughly judge the distance of the object by the signal strength reflected by the measured object. Therefore, for the signal strength reflected by the measured object, it is difficult for RCS to ensure the consistency of the farthest trigger distance for different measured objects.

For example, adults have larger RCS than infants and can therefore be detected at greater distances to trigger radar. One problem is that CW radar cannot identify objects in a fixed area. If an object outside the area has a large RCS or movement range, it will become an unnecessary interference signal, causing the radar to trigger falsely.

Advantages of 5.8GHz Doppler FMCW Radar Module Solution

The 5.8GFMCW solution is developed based on FR520, the 5.8GHz radar sensor integrates a digital phase-locked loop, supports FMCW ranging, demarcation of the sensing area, shielding interference outside the area, low power consumption, low cost, typical value less than 0.08W, single-chip integrated high performance 32-bit MCU, in addition to processing the internal signals of the radar, the MCU can also process the internal signals of the radar. OpenCPU replaces part of the host computer system. FR520 has excellent microwave characteristics and strong sensitivity. It can detect weak breathing signals when the human body is inactive. At the same time, with the support of FFT and algorithms on the hardware, it can extract and confirm the effective breathing characteristic information.

Exercise testing support

It can detect movements such as walking, brisk walking, circling, and jumping.

Support micro-motion detection

It can detect small movements such as nodding, shaking your head, waving, raising your hand, flicking, swiping your phone, and flipping a book.

Support micro-motion detection

Detect the human body in static state by grabbing the breathing information.

Support distance detection

Supports multi-target distance measurement function, which can accurately filter targets outside the area.

Application Scenario Example of Doppler FMCW Radar Module Solution

Indoor lighting - shielding interference outside the wall: set a safe distance, shield the office, and people walking outside the meeting room wall.

Bookcase lighting: When the bookcase is near the front of the bookcase, the light is sensed, and the people outside the area work without interference.

Smart Refrigerator: Set the refrigerator screen to be off when people or objects outside the sensing distance move, and the screen will light up when a person approaches the refrigerator.

Smart bathroom: The bathroom scene can include mirror headlights (lights on when people come, lights off when people leave), germicidal lights, smart toilets, sensor trash cans, smart bathroom heaters, sensor hand sanitizers and other usage scenarios to set more accurate sensing distances for different products .