In-depth interpretation of the principles and applications of millimeter wave radar

The hottest industry at present is new energy vehicles, and one of the most important features of new energy vehicles is intelligence, automatic driving, and intelligent perception, which can be said to be a major selling point of new energy vehicles. For example, the latest Xiaomi Su7, Ideal L6 and Wenjie M5, intelligence is their biggest selling point, and in addition to software support, another most important component of intelligence is radar, laser radar, millimeter wave radar, and ultrasonic radar are all important components of new energy vehicle intelligent perception.

In the introduction of the Wenjie M5 intelligent driving version, it uses 1 high-precision laser radar, 3 millimeter-wave radars and 12 ultrasonic radars.

(From the official website of Wenjie, HUAWEI ADS 2.0 advanced intelligent driving system has 27 perception hardware, consisting of 1 long-range high-precision laser radar + 3 millimeter-wave radars + 2 8-megapixel high-perception front cameras + 9 side view, surround view, and rear view cameras + 12 ultrasonic radars. With the support of high-performance computing platform + Huawei's anthropomorphic algorithm, it has become a new model of high-level intelligent driving.)

So what is millimeter wave radar? What are its magical properties? Let's learn about it together today.

No.1

What is radar?

We are used to the word radar, but in fact, radar is a foreign word, a transliteration word, which comes from the English word Radar, pronounced /ˈreɪ.dɑːr/. Radar is not an English word from the beginning. It is an acronym, which stands for Radio Detection and Ranging. This is also the basic meaning of the word radar, using radio to detect targets and measure distances.

With the development of technology, the application and function of radar have long surpassed the basic scope of detection and ranging, such as speed measurement, angle measurement, target identification, target imaging, battlefield reconnaissance, etc. However, as long as the technology uses electromagnetic waves for detection, we still call it radar.

So radar’s name is not “Thunder”, its name is “Radio”, which means radio wave, the most widely used electromagnetic wave frequency band.

The electromagnetic spectrum includes radio waves, infrared, visible light, ultraviolet, and higher frequency x-rays and gamma rays.

Radio waves can be divided into long waves, short waves, meter waves, centimeter waves, millimeter waves and submillimeter waves according to the wavelength of electromagnetic waves, as shown in the figure below.

Millimeter-wave radar is a device that uses millimeter waves in radio waves for detection and ranging. The wavelength of electromagnetic waves is 10mm to 1mm, and the corresponding frequency is 30GHz to 300GHz. In addition to millimeter-wave radar, there are also centimeter-wave radar and meter-wave radar.

The working principle of radar is shown in the figure below

The radar signal generated by the transmitter is transmitted through the antenna. The target intercepts and reflects part of the radar signal, and part of the reflected signal is received by the radar receiver. The radar antenna collects the echo signal, which is amplified and filtered by the receiver and then sent to the signal processor and data processor for processing, and finally input into the display.

Radars can be divided into different categories according to different dimensions. For example, according to the type of electromagnetic wave signal, they can be divided into pulse radar, continuous wave CW radar and frequency modulated continuous wave FMCW radar.

According to the usage scenario, it can be divided into military radar and civilian radar;

According to the antenna configuration, it can be divided into monostatic radar, bistatic radar and electronically scanned array radar;

According to the carrier wave, it can be divided into centimeter wave radar, millimeter wave radar, laser radar, broadband radar, etc.

Different radars have different functions and application scenarios.

No.2

History of Radar

When talking about radar, we have to mention the history of electromagnetic waves.

This kind of invisible and intangible thing really makes people work hard. If it weren't for the prediction of the genius scientist Maxwell, I think we might still be in an era where communication basically relies on shouting.

Magnetism was used quite early. Our ancestor Huangdi used magnet to make Si Nan and defeated Chi You. Dian's cognition was more about the early people's fear of lightning. Electricity and magnetism had their first handshake in Oersted's experiment, and then produced a closer coupling in Faraday's electromagnetic experiment. It was not until the genius physicist Maxwell derived the Maxwell equations that electricity and magnetism really came together, and then the existence of electromagnetic waves was deduced.

It was not until 1885-1889 that Hertz proved the existence of electromagnetic waves through a series of experiments and successfully measured the wavelength and speed of electromagnetic waves. Only then did electromagnetic waves truly come into people's vision and gradually enter people's lives. Until today, they are irreplaceable.

We all know the principle of echo. When we speak loudly to a tall building or a mountain, our sound waves will be reflected back by the building, forming an echo. Using the time difference of the echo, people can roughly estimate the distance of the mountain.

Therefore, after Hertz confirmed the existence of electromagnetic waves, the first thing researchers used was the principle of electromagnetic wave reflection to measure distance.

In 1904, German engineer Christian Hülsmeyer invented an obstacle detector and ship navigation device based on Hertz's principle, which was the earliest radar. The schematic diagram of the invention is shown in the figure below.

Hulsmayer also built a "radar" and publicly demonstrated this amazing device. He successfully transmitted electromagnetic wave signals to an approaching ship and successfully received the reflected signal.

It’s a pity that it was a relatively peaceful time and no one was interested in his equipment.

It wasn’t until 1927 that Dr. Hans E Hollmann further developed the device and built the first centimeter-wavelength transmitter and receiver, the first “microwave” communications system. Hans-Karl von Willsen, working with Hollmann and a third scientist, Gunther Erbsloeh, perfected a device that could detect ships at about 8 kilometers away and aircraft flying at an altitude of 500 meters at about 30 kilometers away. The marine system was called “Seetakt” and the land system was called “Freya” – these three systems arguably created the application we most commonly associate with radar – detecting and assessing the distance of objects.

The real radar was born, and along with the Second World War, the technology and application of radar developed rapidly.

To this day, the most advanced radar technology still serves the needs of warfare.

With the development of autonomous driving technology, millimeter-wave radar has become the most widely used radar equipment in civilian use.

No.3

Principle of millimeter wave radar

Millimeter-wave radar is a device that uses millimeter waves for detection. Let’s first talk about the advantages and disadvantages of millimeter waves.

The operating wavelength of millimeter waves is between 10mm and 1mm, and the corresponding operating frequency is 30GHz to 300GHz. It is a section of the electromagnetic wave spectrum between microwaves and light waves. Therefore, millimeter wave radar has the dual advantages of microwaves and light waves, which can be summarized as follows:

Of course, it also has its disadvantages. For example, the attenuation in highly humid environments such as rain, fog and wet snow, as well as the influence of high-power devices and insertion loss reduce the detection range of millimeter-wave radar; the ability to penetrate trees is poor, and compared with microwaves, the penetration of dense trees is low; the cost of components is high, the processing accuracy requirements are relatively high, and the development of single-chip transceiver integrated circuits is relatively slow.