Überblick
Millimeter wave: Electromagnetic waves with a wavelength of 1 Zu 10 millimeters are called millimeter waves. They are located in the wavelength range where microwaves and far-infrared waves overlap, so they have the characteristics of both spectra. The theory and technology of millimeter wave are the extension of microwave to high frequency and the development of light wave to low frequency.
Introduction to mmWave
Definition
There is no precise definition of the millimeter wave frequency band. Normalerweise, the electromagnetic wave in the frequency domain of 30300GHz (Wellenlänge 110mm) is called millimeter wave. It is located in the wavelength range where microwave and far infrared wave overlap, so there are two kinds of characteristics of the spectrum. The theory and technology of millimeter wave are the extension of microwave to high frequency and the development of light wave to low frequency.
Entwicklung
On June 15, 2020, Liu Yunjie, an academician of the Chinese Academy of Engineering, said that Nanjing Network Communication and Security Purple Mountain Laboratory has developed a CMOS millimeter wave fully integrated 4-channel phased array chip.
Millimeter Wave Characteristics
Vorteile
- Extremely Wide Bandwidth: It is generally believed that the millimeter wave frequency range is 26.5-300GHz, and the bandwidth is as high as 273.5GHz. Mehr als 10 times the full bandwidth from DC to microwave. Even considering atmospheric absorption, only four main windows can be used when propagating in the atmosphere, but the total bandwidth of these four windows can reach 135GHz, Welches ist 5 times the sum of the bandwidths of the microwave bands below. This is undoubtedly very attractive in today’s tight frequency resources.
- Narrow Beam: The millimeter wave beam is much narrower than the microwave beam under the same antenna size. Zum Beispiel, a 12cm antenna has a beam width of 18 degrees at 9.4 GHz, but only 1.8 degrees at 94 GHz. daher, it is possible to distinguish small objects that are closer together or to observe the details of objects more clearly.
- All-Weather Characteristics: Compared with lasers, the propagation of millimeter waves is much less affected by climate.
- Easy Miniaturization: Compared with microwaves, millimeter wave components are much smaller in size. So mmWave systems are easier to miniaturize.
Shortcomings
- Propagation Attenuation in Atmosphere: The propagation attenuation is serious in the atmosphere.
- High Processing Precision: The processing precision of the device is high.
Millimeter Wave Propagation Characteristics
Millimeter waves have a large number of applications in the fields of communication, Radar, remote sensing, and astronomy. In order to successfully design and develop a millimeter-wave system with excellent performance, it is necessary to understand the atmospheric propagation characteristics of millimeter-wave under different meteorological conditions. Factors affecting the propagation characteristics of millimeter waves mainly include: molecular absorption (oxygen, water vapor, usw.), and the environment (including vegetation, ground, obstacles, usw.). The combined effect of these factors will cause the millimeter wave signal to be attenuated, scattered, change the polarization and propagation path, and then introduce new noise in the millimeter wave system. These factors will greatly affect the operation of mmWave systems, so we must study the propagation characteristics of mmWave in detail.
Overview of Millimeter Wave Radar
In den letzten Jahren, with the increasing demand for millimeter-wave systems, millimeter-wave technology has made major breakthroughs in the development of transmitters, receivers, Antennen, and millimeter-wave devices. Infolge, millimeter-wave radar has entered a new stage of various applications.
Characteristics of Millimeter Wave Radar
Key Benefits
- Extremely Wide Frequency Band: Suitable for various broadband signal processing.
- Narrow Beam with Good Directivity: Provides extremely high spatial resolution and high tracking accuracy.
- Wide Doppler Bandwidth: Offers good Doppler resolution and high speed measurement accuracy.
- Low Impact from Ground Clutter: Results in good low-altitude tracking performance.
- Sensitive Scattering Characteristics: Improves multi-target discrimination and target recognition abilities and imaging quality.
- Difficult to Intercept: Narrow beam emission makes it hard for enemies to intercept in electronic countermeasures.
- Anti-Stealth Function: Due to angular reflection caused by uneven parts of stealth aircraft, increasing the effective reflection area.
- Penetration Ability: Compared to laser and infrared, millimeter wave can penetrate smoke, dust, and fog, and operate around the clock.
Einschränkungen
The disadvantage of millimeter-wave radar is mainly affected by atmospheric attenuation and absorption, limiting the current operating range to mostly within 10 kilometers. Zusätzlich, compared to microwave radar, the components and parts of millimeter wave radar are currently mass-produced with low yield. Many devices also need to be coated with gold or silver in the millimeter wave frequency band, increasing the cost.
Millimeter Wave Antennas
Horn Antenna
Horn antennas are formed by gradually enlarging and extending the opening of a metal waveguide. They are widely used in microwave and millimeter wave bands due to their simple structure, wide frequency band, easy manufacture, and convenient adjustment. Horn antennas are also utilized in millimeter wave therapeutic equipment.
Microstrip Antenna
Microstrip -Antennen, or printed antennas, were first widely used in the centimeter wave band and later extended to the millimeter wave band. This expansion is not a mere proportional reduction but represents a new concept and development. Jedoch, millimeter-wave microstrip antennas face two key problems: increased transmission line loss and stringent dimensional tolerance.
Leaky Wave Antenna
This type of antenna radiates energy due to discontinuous structures when the electromagnetic wave is transmitted along the open structure.
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