PCB Blog - Advantages and disadvantages of millimeter wave radar

Millimeter wave radar concept

The so-called millimeter wave is a section of the radio wave. We call the electromagnetic wave with a wavelength of 1-10 mm millimeter wave, which is located in the wavelength range where microwave and far-infrared wave intersect, so it has the characteristics of two kinds of the wave spectrum. The theory and technology of Millimeter wave radar are respectively the extensions of microwave to high frequency and the development of light wave to low frequency.

The so-called Millimeter wave radar refers to the radar whose working frequency is in the millimeter wave frequency band. The ranging principle is the same as that of ordinary radar, that is, it sends out radio waves (radar waves), receives echoes, and measures the position data of the target according to the time difference between receiving and transmitting. Millimeter wave radar is the radio wave whose frequency is in the millimeter wave band.

Characteristics of Millimeter wave radar

1. In the case of the same antenna aperture, millimeter wave radar has a narrower beam (generally in the order of milliradian), which can improve the angle resolution and angle measurement accuracy of the radar, and is conducive to anti electronic interference, clutter interference and multipath reflection interference.

2. Due to the high working frequency, large signal bandwidth (such as Gigahertz magnitude) and Doppler frequency shift may be obtained, which is conducive to improving the measurement accuracy and resolution of range and speed and analyzing target characteristics.

3. The antenna aperture, components and devices are small and suitable for aircraft, satellite or missile.

Advantages and disadvantages of Millimeter wave radar

Compared with other sensor systems, millimeter wave radar has the following advantages:

(1) High resolution, small size; As the size of antenna and other microwave components is related to frequency, the antenna and microwave components of millimeter wave radar can be smaller, and small antenna size can obtain narrow beam.

(2) Although interference and atmospheric attenuation limit the performance of millimeter wave radar, they help to reduce the mutual influence when many radars work together.

(3) Compared with the infrared system which is often used to compare with the millimeter wave radar, the millimeter wave radar has the advantage that it can directly measure the range and speed information.

Disadvantages:

(1) Compared with microwave radar, the performance of millimeter wave radar has declined for the following reasons: Low power of transmitter; High loss in waveguide devices

(2) It has a lot to do with the weather, especially when it rains;

(3) In the air defense environment, distance ambiguity and velocity ambiguity are inevitable;

(4) Millimeter wave devices are expensive and cannot be mass produced

Millimeter wave radar speed measurement mode

Like ordinary radar, millimeter wave radar has two ways to measure velocity. One is based on the principle of dopler, that is, when the transmitted electromagnetic wave and the detected target have relative movement, the echo frequency will be different from the transmitted wave frequency. By detecting this frequency difference, the moving speed of the target relative to the radar can be measured. However, this method cannot detect the tangential velocity. The second method is to obtain the velocity by tracking the position and differential.

The Principle and Advantages and Disadvantages of Millimeter wave radar

Operating principle of millimeter wave radar

The millimeter wave velocity measuring radar system is mainly composed of a tuner, a preprocessing system, a terminal system, an infrared starter, etc. 

Millimeter wave radar oscillator generates millimeter wave (8mm) oscillation. Set its frequency as f0, add it to the circulator through the isolator, radiate it directionally from the antenna, and propagate it in the form of electromagnetic wave in space. When this electromagnetic wave encounters the target (projectile) in space, it will be reflected back. If the target is moving, the reflected electromagnetic wave frequency is added with a Doppler frequency fd which is proportional to the target's moving speed vr, so that the reverse echo frequency becomes f0 ± fd ("+" is taken when the target is flying close to the target, and "%" is taken when the target is far away from the flight). 

This echo is received by the antenna, added to the mixer through the circulator, and mixed with the signal leaked through the circulator (as the local oscillator signal) f0 in the mixer. The mixer is a nonlinear element, and its output has a variety of sum and difference frequencies, such as fd, f0 ± fd, 2f0 ± fd,..., etc. The Doppler signal (frequency fd) is selected by the preamplifier, and then sent to the main amplifier of the preprocessing system through a long cable (length 50-100m). The main amplifier is equipped with automatic gain control and manual gain control circuits. Manual gain is used to adjust the total gain of the amplifier, and automatic gain control is used to increase the dynamic range of the amplifier.

Generally, automatic gain control is not used in interior ballistic test. The automatic gain control is only suitable for testing the external ballistics, because in order to avoid the interference of muzzle flame, the test should be started after an appropriate delay.

The Principle and Advantages and Disadvantages of Millimeter Wave RadarThe millimeter wave velocity measuring radar system is mainly composed of a tuner, a preprocessing system, a terminal system, an infrared starter, etc. 

Millimeter wave oscillator generates millimeter wave (8mm) oscillation. Set its frequency as f0, add it to the circulator through the isolator, radiate it directionally from the antenna, and propagate it in the form of electromagnetic wave in space. 

When this electromagnetic wave encounters the target (projectile) in space, it will be reflected back. If the target is moving, the reflected electromagnetic wave frequency is added with a Doppler frequency fd which is proportional to the target's moving speed vr, so that the reverse echo frequency becomes f0 ± fd ("+" is taken when the target is flying close to the target, and "%" is taken when the target is far away from the flight). This echo is received by the antenna, added to the mixer through the circulator, and mixed with the signal leaked through the circulator (as the local oscillator signal) f0 in the mixer. Millimeter wave radar is a nonlinear element, and its output has a variety of sum and difference frequencies, such as fd, f0 ± fd, 2f0 ± fd,..., etc.

The Millimeter wave radar signal (frequency fd) is selected by the preamplifier, and then sent to the main amplifier of the preprocessing system through a long cable (length 50-100m). The main amplifier is equipped with automatic gain control and manual gain control circuits. Millimeter wave radar is used to adjust the total gain of the amplifier, and automatic gain control is used to increase the dynamic range of the amplifier.