3. Characteristics of microwave (II)
Microwave wavelength is very short, which is much smaller than the size of ordinary objects on the earth (such as aircrafts, ships, cars, buildings, etc.), or in the same order of magnitude. When microwave irradiates certain objects, it will produce significant reflection and refraction, just like the reflection and refraction of light. At the same time, the characteristics of microwave propagation are similar to that of geometric optics, which can propagate in a straight line and easily concentrate like light, which makes the characteristics of microwave similar to geometric optics, that is the so-called quasi-optical. Therefore, working in microwave frequency band can reduce the size of circuit components and make the system more compact. The antenna system with small size, narrow beam, strong directivity and high gain can be made to receive weak signals from various objects on the ground or in space, so as to determine the orientation and distance of the object and analyze the characteristics of the target.
Because the microwave wavelength and the size of the object have the same order of magnitude, the characteristics of microwave and sound wave are similar, that is the so-called quasi-acoustic. For example, microwave waveguide is similar to microphone in acoustics; horn antenna and slot antenna are similar to acoustic horn; microwave cavity is similar to acoustic resonant cavity.
Due to the high frequency of microwave, the available frequency band is very wide, up to hundreds or even up to gigahertz in a small relative bandwidth. This is incomparable to low-frequency radio waves. Using the large information capacity of microwave, modern multi-channel communication systems, including satellite communication system, almost all work in microwave band. In addition, microwave signal can also provide phase information, polarization information and Doppler frequency information. These characteristics play an important role in target detection, remote sensing target feature analysis and other applications.
The quantum energy of microwave is not big enough, it will not change the internal structure of matter molecules or destroy the chemical bonds between molecules. So the interaction between microwave and object is non-ionized. From the physical point of view, many resonance phenomena of molecular atoms under the action of external electromagnetic field occur in the microwave range, so microwave provides an effective research means for exploring the internal structure and basic characteristics of matter. Using this characteristic, many microwave devices can be made.
Microwave also has non-thermal effects, such as electric effect, magnetic effect and chemical effect. Using these effects, more applications of microwave can be developed.
(Translated from Elecfans Forum)
(To be continued)