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What is the working principle of the antenna?
Views:597 Date:2018-11-12
First, the reveal of the structure of the flat antenna If we cut the antenna surface of the flat antenna longitudinally, we will see that this antenna surface is composed of five layers. As shown in Figure 1. The first and fifth layers are antenna protection layers, also known as radomes, which are made of corrosion-resistant media. It acts to prevent oxidation, attenuate ultraviolet light on the printed circuit board, and protect against rain and snow. The two layers are not shown in the structural diagram of Figure 1. The second layer is the receiving antenna layer. It is a metal layer of a printed circuit board on which a large number of neatly arranged unit antenna arrays are printed, so it can be called an antenna substrate layer. This layer determines the technical quality of the panel antenna. The unit vibrator antenna can be varied. The third layer is the dielectric layer of the printed circuit board that supports the second layer. The fourth layer is a grounding conductor layer, which is a metal foil plate, which serves as both a reflection to the antenna array and another conductor of the feeder to form a microstrip transmission line. The output of the antenna array is coupled to a tuner mounted behind the planar antenna board. From this we can see that the planar antenna has a more complicated structure and uses the microstrip circuit technology in the microwave technology, which requires a very high process, especially the phase in-phase requirement in the antenna array is extremely strict. It is very different from the structure of the reflective parabolic antenna, so it is difficult to design and manufacture. The theory of the panel antenna has been proposed for more than ten years. So far, no large number of high-quality and low-cost panel antennas have appeared in the domestic market. This is probably the reason.

Second, the panel antenna and its working principle The emergence of satellite live TV, the frequency is increased to 12GHz, the wavelength is shortened to 2.5cm, which provides the possibility of the emergence of the panel antenna. In fact, the panel antenna is transplanted from the array antenna commonly used in radar and communication to the Ku-band satellite TV receiving antenna. The so-called array antenna is formed by regularly arranging a plurality of half-wave oscillator unit antennas in rows and columns. As shown in Figure 2. Typically, each adjacent half-wave oscillator unit, including the line spacing and the column spacing, is separated by an integer multiple of half a wavelength to form an antenna array. The number of cells of a half-wave oscillator depends on the gain requirements of the panel antenna. The higher the gain requirement, the more half-wave oscillator units are used. For example, if the gain of the panel antenna is 34 dB, then the half-wave oscillator unit of the panel antenna has to be 480. Therefore, the more the vibrator unit, the higher the gain, and the larger the area of the panel antenna.

Third, several equivalent radiating elements of the half-wave oscillator unit in the panel antenna In the panel antenna, an array antenna is used, and its basic unit is a half-wave oscillator unit antenna. And this basic unit, we can call it the radiating unit of the antenna. In the Ku band, if the frequency range is 11.7u-12.75GHz, the corresponding wavelength is between 2.353-2.564cm. The 1/2 wavelength is 1.177-1.282cm, and the average value is half. The wavelength is 1.23cm. In actual use, since the antenna has a shortening factor, the actual length of the half-wave oscillator unit is multiplied by the shortening factor. 0.85-0.9, so the actual half-wave oscillator unit length is 1.0455-1.107cm, and the average value is 1.076cm. Above we analyzed that the basic unit or radiating element in the panel antenna is a half-wave vibrator antenna, but since it can only receive linearly polarized waves and has a single form, the size cannot be reduced. Therefore, in actual use, people use various other equivalent forms of radiation elements to replace it. The panel antenna thus produced is not only reduced in area and size, but also can receive circularly polarized waves.

4. Feeding of the radiating element in the feeding plate antenna between the radiating elements is a technical problem with high difficulty. It must be ensured that the radiating elements are fed in phase, so that the flat antenna has higher gain and stronger Directionality. Each radiating element is fed by a microstrip feed line, which solves the problem of circuit impedance matching and phase connection. Since each radiating element vibrator is used in multiple connections, the impedance is continuously paralleled. The impedance is reduced by half every time it is connected in parallel, so the characteristic impedance of the feeder also needs to be changed and matched. The microstrip transmission line is made on the same substrate, and it is impossible to change the impedance by changing the distance between the bands, so only the microstrip width is changed to control the impedance variation. In order to match between different line segments, there are many λ/4 impedance transformers on the line. In order to ensure that the unit vibrators in different parts can receive the same phase of feeding, the microstrip lines between the unit vibrators are not the same length when wiring. In addition, in order to increase the antenna's ability to resist rain and snow, the beam of the electric wave is not perpendicular to the plane of the panel antenna, but is intentionally inclined by 15°-20°. In this way, the antenna surface mounting pair can be vertical and nearly parallel to the wall surface. This is somewhat similar to the biasing antenna commonly used in the Ku-band. When installed, the antenna reflecting surface is inclined at an angle downward relative to the feed-forward antenna. When the panel antenna is used to make the feeder, the length of the feeder lines between the two adjacent rows of vibrators is deliberately unequal, and the phases are different by an angle θ after the current is transmitted. When the radio wave is directed obliquely to the flat plate, the phase of each of the vibrators can be in phase to receive the signal. As shown in Figure 8. Thus, we can see that the electrical angle of the azimuth and elevation can be adjusted by controlling the angle between the beam and the panel antenna by controlling the feeding phase between the unit vibrators of the panel antenna, that is, the radiating elements. This is a major feature of the panel antenna, and it is also a major technical difficulty of the panel antenna, which is also unmatched by the parabolic antenna. However, the angle of adjustment should not be too large, otherwise the effective projected area of the antenna will be reduced, reducing efficiency and gain.

5. The connection between the panel antenna and the tuner head is due to the fact that the radiating elements of the panel antenna are connected by the feeder line, and the electric wave has become an induced current at the vibrator. After the collectors are collectively aggregated, they can be directly transmitted to the tuner in the form of current. Device. It does not require a feed source, and also reduces the loss of the electric field form of the electric wave into a current form, which is advantageous for signal reception. The high frequency head at this time may be a concentrated parameter type or a distributed parameter microstrip type. Moreover, the high-frequency head can be directly mounted behind the panel antenna, or directly through the microstrip type high-frequency head in the panel antenna, so that the antenna-high-frequency head integrated new structure is both beautiful and improved in reliability. Double wins in one fell swoop.

Sixth, the technical key of the flat-panel antenna The flat-panel antenna adopts the manufacturing process of the printed board, the productivity is more convenient than the mechanical processing, the adjustment direction can be solved electrically, and can be integrated into the flat antenna and the high-frequency head. It is the advantage of a flat panel antenna. However, it is not easy to achieve the expected electrical performance of the panel antenna. The key is the loss problem.

7. How to choose a flat panel antenna At present, there is no technical standard for flat panel antennas in China. How to select a flat panel antenna, especially an imported flat panel antenna, is difficult to say accurately. It is not free to use an imported flat panel antenna for domestic use.

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