120GHz radar level gauge, frequency modulated continuous wave radar (FMCW) working principle!

The development history of frequency modulated continuous wave radar can be traced back to the FMCW radar altimeter developed by West Electric in 1938. After years of technological accumulation and innovation, the application of frequency modulated continuous wave radar level gauges has also shone brightly. Today, let's talk about the working principle of frequency modulated continuous wave radar (FMCW).
Radar is divided into two categories based on the type of transmitted signal: pulse radar and continuous wave radar. Conventional pulse radar emits periodic high-frequency pulses, while continuous wave radar emits continuous wave signals.

The signal emitted by continuous wave radar can be single frequency continuous wave (CW) or frequency modulated continuous wave (FMCW), and there are also various frequency modulation methods: common ones include triangular wave, sawtooth wave, coding modulation, or noise frequency modulation. Among them, single frequency continuous wave radar can only be used for speed measurement and cannot measure distance, while FMCW radar can both measure distance and speed, and its advantages in close range measurement are becoming increasingly evident.
FMCW radar emits continuous waves with frequency changes during the scanning period. The echo reflected by an object has a certain frequency difference from the transmitted signal. By measuring the frequency difference, the distance information between the target and the radar can be obtained. The frequency of the difference frequency signal is relatively low, usually in KHz, so the hardware processing is relatively simple and suitable for data acquisition and digital signal processing.
When FMCW radar is transmitting and receiving simultaneously, theoretically there is no blind spot in ranging that pulse radar has, and the average power of the transmitted signal is equal to the peak power. Therefore, only low-power devices are required, thereby reducing the probability of interception and interference; Its disadvantages include a short ranging range, range Doppler coupling, and difficulty in transmitting and receiving isolation.
FMCW radar has the advantages of easy implementation, relatively simple structure, small size, light weight, and low cost, and has been widely used in both civilian and military fields.
It is a frequency modulated continuous wave radar product, and its working principle is to obtain the distance information of the target by comparing the difference between the frequency of the echo signal at any time and the frequency of the transmitted signal at that time. The distance is proportional to the frequency difference between the two. The radial velocity and distance of the target can be obtained by processing the frequency difference between the two measurements. Compared with other ranging and speed measuring radars, the structure of frequency modulated continuous wave radar is simpler. The following is the system diagram of FMCW radar:
We can see that it consists of three parts: the transmitting antenna and receiving antenna, the RF front-end composed of a power divider, power amplifier, and mixer, the modulation signal generator, and the back-end processing part for AD sampling and signal processing. The three parts each perform their own duties and cooperate with each other:
The modulation signal generator provides the required modulation signal, which is controlled by VCO to generate a continuous high-frequency equal amplitude wave with a sawtooth shaped frequency variation in time. Part of it is amplified and radiated out through the transmitting antenna, while the other part is used as the local oscillator signal. After encountering the target, the radio wave returns to the receiving antenna, and the frequency of the echo signal changes compared to the local oscillator signal. After being mixed by a mixer, it becomes a beat signal. The frequency of the beat signal is related to the distance and speed of the target. The main task of signal processing is to extract the frequency of the beat signal and obtain the true distance and speed information of the target through it.

Compared to pulse based radar, this radar level gauge has the following advantages:
(1) According to radar theory, the range resolution is determined by the bandwidth of the radar signal, and FMCW radar has a larger bandwidth, therefore it has a higher range resolution.
(2) Due to the fact that the echo signal delay of FMCW radar is much smaller than the time width of the transmitted signal, the radar transmitter and receiver can work simultaneously without distance blind spots.
(3) Under certain noise power conditions, the detection capability of a radar is determined by the energy of the radar signal. FMCW radar has a very large time band product, which is much larger than pulse radar with the same signal bandwidth and level. Therefore, under the same detection capability conditions, FMCW radar has low transmission power and is not easily intercepted.
(4) Due to the extremely large time bandwidth product of FMCW radar, it does not require high peak power, resulting in a relatively low operating voltage and no need for high-power or high-voltage devices. This makes the entire system structure simple, compact, lightweight, and cost-effective.

Vacorda radar level gauge parameters
Transmission frequency: 120GHz
Equivalent omnidirectional radiation power:<10uW
Measurement range: 0.01 to 30m
Power consumption:<2.4W
Power supply voltage: DC 24V
Power supply current: 70-98mA
Display resolution: 0.1mm
Measurement accuracy: ＜ ± 0.5mm
Output current: 4-20mA
Communication type: RS485, HART
Process pressure: 0-25 bar
Environmental temperature: -30 ℃~+70 ℃
Shell material: POM+SS+HDPE;