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Show you the characteristics of the antenna
Category：Industry News Publish：2019-7-18 11:45:38 Browse：2694
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Today to introduce the basic knowledge of antenna, so that we have a preliminary understanding of the antenna. Let's start with a few concepts.
Resonance: any antenna resonates at a certain frequency. We want to receive the signal at that frequency. Antenna resonance is the most basic requirements of the antenna, otherwise, there is no so much attention, casually throw a wire out is not antenna. The main data involved in the antenna resonance problem is the wavelength and a quarter of it. The formula for calculating the wavelength is very simple, 300/f. Where the unit of f is MHz, and the unit of the result is meters. The 1/4 wavelength is called the fundamental oscillator. For example, the dipole antenna is a pair of fundamental oscillators, and the vertical antenna is a fundamental oscillator. But the length of the oscillator in the antenna is not exactly a quarter of the wavelength, because the wave travels through the wire at a different speed than it would in a vacuum, and is generally shorter, so there is a shortening factor. This factor depends on the material.
Bandwidth: this is also an important but overlooked issue. The antenna has a certain bandwidth, which means that although the resonant frequency is a frequency point, the performance of the antenna is about the same within a certain range of the frequency point. This range is the bandwidth. We certainly want the bandwidth of an antenna to cover a certain range, preferably the entire FM radio band we listen to. Otherwise, it would be too troublesome to change the station and change the antenna or adjust the antenna. Antenna bandwidth and antenna type, structure, material are related. Generally speaking, the thicker the tube and line used by the oscillator, the wider the bandwidth. The higher the antenna gain, the narrower the bandwidth.
Impedance: the antenna can be viewed as a resonant loop. A resonant circuit certainly has its impedance. The impedance requirement is matching: the circuit connected to the antenna must have the same impedance as the antenna. Connected to the antenna is the feeder, and the impedance of the feeder is determined, so we want the impedance of the antenna to be the same as that of the feeder. Generally produced feeders are mainly 300 ohms, 75 ohms and 50 ohms, and there are 450 ohms and 600 ohms in the past abroad. The impedance of basic dipole antenna is about 75 ohms, v-type dipole antenna is about 50 ohms, and the impedance of basic vertical antenna is about 50 ohms. Other antennas do not normally have impedance of 50 or 75 ohms, so some means of impedance transformation is needed before connecting them to the feeder.
Balance: symmetrical antenna is balanced, such as dipole antenna, yagi antenna, and coaxial cable is unbalanced, connecting the two, the need to solve the problem of balance imbalance conversion.
Gain: the antenna is a passive device, but the antenna can have gain. This gain is of course relative gain, relative to the basic dipole antenna. The antenna used by FM DX, of course, wants to gain as high as possible. Remember, however, that high gain is often accompanied by narrow band width.
Directional: not all antennas are directional. A pull-rod antenna on a portable radio is directionless. Dipole antenna has weak directivity, yagi antenna can get better directivity. Good directionality provides the ability to concentrate radio waves in the desired direction, and an important ability to partially mitigate the effects of local radio signals. But directional antennas are not always good. When waiting without a target, the directional antenna may cause you to miss the signal on the back of the antenna. So the more reasonable way, is to use a vertical antenna and a pair of directional antenna, with the vertical antenna to wait, hear the signal, and then use the directional antenna turned to the listening.
Elevation Angle: the elevation Angle of the antenna is the elevation Angle of the wave, not the mechanical elevation Angle of the antenna oscillator itself. The elevation Angle reflects which altitude Angle the antenna receives the strongest waves from. For the F layer, we want the elevation to be low, so we want it to be far away, and for the Es layer, we want it to be high, so we want it to be high. The elevation Angle depends on the antenna type and erection height. Generally speaking, the vertical antenna has a low elevation Angle, and the elevation Angle of other antennas varies with the erection height.
Erection height: the antenna has one erection height. This height is actually two heights, one height let's think about its horizontal height, and this height is useful for the local signal, not so useful for DX. The second height, which is often overlooked, is the height from the antenna to the electrical ground. For example, the antenna erected in the reinforced concrete roof, although the house is 20 meters high, but the antenna is only 1 meter away from the roof, so the height of the antenna is only 1 meter. Antenna height has different effects on different antennas, generally affecting antenna impedance and elevation Angle. Generally, we think that the height of the antenna should be above 0.4 wavelength, so it is relatively unaffected by the ground.
Standing bobbi: finally, introduce this feature which is not familiar to Chinese fans. The standing-wave ratio reflects the matching of antenna feed system. It measures the performance of the antenna by the ratio of the energy emitted and reflected when the antenna is used as the transmitting antenna. The standing wave ratio is determined by the impedance of antenna feed system. The impedance of the antenna and the impedance of the feeder are consistent with that of the receiver, and the VSWR is small. The antenna feeder system with high standing-wave ratio loses a lot of signal in the feeder.
The role of celestial modulation:
1. Match the impedance to make the antenna system (antenna + antenna) match the impedance for the transmitter, so as to maximize the radiation efficiency of the antenna cable in the antenna system
2. Resonant antenna: according to the electromagnetic theory, antenna impedance Z=R+jX is considered as antenna resonance when X = 0. After using the antenna with unnatural resonance, the antenna is adjusted so that Z=R+jX, where X = 0, by adding inductance or capacity.
3. The electrical efficiency of the antenna after day adjustment is relative to the natural resonant antenna. Tuning the antenna to the transmitter is impedance matching, relying on the LC network inside the day adjustment. Since L and C are not ideal elements and consume some energy, the more unnatural resonance of the antenna (especially the farther the equivalent radiation resistance deviates from 50 ohms), the lower the electrical efficiency after the addition of day adjustment.
Fujian jiasida communication technology co., LTD., located in quanzhou city, fujian province, was established in 2009. It is a high-tech company specializing in communication research, development, production and operation of communication antennas and passive devices.
Company has an experienced r&d team, skilled production testers, perfect testing instruments and equipment, committed to the development and production of all kinds of radio antenna, car antenna, omni-directional antenna, power splitters, combiner, road system and platform, and so on related products, and provide personalized custom services according to customer's specific requirements. We in line with take the technology as the core, the science and technology strives for the development, provides the superior high technology product for the user the enterprise culture idea, in fully introduces absorbs the domestic and foreign advanced technology foundation, unceasingly develops the innovation, devotes to the research and development own characteristic new product. At the same time, we will sincerely provide customers with quality service.
Resonance: any antenna resonates at a certain frequency. We want to receive the signal at that frequency. Antenna resonance is the most basic requirements of the antenna, otherwise, there is no so much attention, casually throw a wire out is not antenna. The main data involved in the antenna resonance problem is the wavelength and a quarter of it. The formula for calculating the wavelength is very simple, 300/f. Where the unit of f is MHz, and the unit of the result is meters. The 1/4 wavelength is called the fundamental oscillator. For example, the dipole antenna is a pair of fundamental oscillators, and the vertical antenna is a fundamental oscillator. But the length of the oscillator in the antenna is not exactly a quarter of the wavelength, because the wave travels through the wire at a different speed than it would in a vacuum, and is generally shorter, so there is a shortening factor. This factor depends on the material.
Bandwidth: this is also an important but overlooked issue. The antenna has a certain bandwidth, which means that although the resonant frequency is a frequency point, the performance of the antenna is about the same within a certain range of the frequency point. This range is the bandwidth. We certainly want the bandwidth of an antenna to cover a certain range, preferably the entire FM radio band we listen to. Otherwise, it would be too troublesome to change the station and change the antenna or adjust the antenna. Antenna bandwidth and antenna type, structure, material are related. Generally speaking, the thicker the tube and line used by the oscillator, the wider the bandwidth. The higher the antenna gain, the narrower the bandwidth.
Impedance: the antenna can be viewed as a resonant loop. A resonant circuit certainly has its impedance. The impedance requirement is matching: the circuit connected to the antenna must have the same impedance as the antenna. Connected to the antenna is the feeder, and the impedance of the feeder is determined, so we want the impedance of the antenna to be the same as that of the feeder. Generally produced feeders are mainly 300 ohms, 75 ohms and 50 ohms, and there are 450 ohms and 600 ohms in the past abroad. The impedance of basic dipole antenna is about 75 ohms, v-type dipole antenna is about 50 ohms, and the impedance of basic vertical antenna is about 50 ohms. Other antennas do not normally have impedance of 50 or 75 ohms, so some means of impedance transformation is needed before connecting them to the feeder.
Balance: symmetrical antenna is balanced, such as dipole antenna, yagi antenna, and coaxial cable is unbalanced, connecting the two, the need to solve the problem of balance imbalance conversion.
Gain: the antenna is a passive device, but the antenna can have gain. This gain is of course relative gain, relative to the basic dipole antenna. The antenna used by FM DX, of course, wants to gain as high as possible. Remember, however, that high gain is often accompanied by narrow band width.
Directional: not all antennas are directional. A pull-rod antenna on a portable radio is directionless. Dipole antenna has weak directivity, yagi antenna can get better directivity. Good directionality provides the ability to concentrate radio waves in the desired direction, and an important ability to partially mitigate the effects of local radio signals. But directional antennas are not always good. When waiting without a target, the directional antenna may cause you to miss the signal on the back of the antenna. So the more reasonable way, is to use a vertical antenna and a pair of directional antenna, with the vertical antenna to wait, hear the signal, and then use the directional antenna turned to the listening.
Elevation Angle: the elevation Angle of the antenna is the elevation Angle of the wave, not the mechanical elevation Angle of the antenna oscillator itself. The elevation Angle reflects which altitude Angle the antenna receives the strongest waves from. For the F layer, we want the elevation to be low, so we want it to be far away, and for the Es layer, we want it to be high, so we want it to be high. The elevation Angle depends on the antenna type and erection height. Generally speaking, the vertical antenna has a low elevation Angle, and the elevation Angle of other antennas varies with the erection height.
Erection height: the antenna has one erection height. This height is actually two heights, one height let's think about its horizontal height, and this height is useful for the local signal, not so useful for DX. The second height, which is often overlooked, is the height from the antenna to the electrical ground. For example, the antenna erected in the reinforced concrete roof, although the house is 20 meters high, but the antenna is only 1 meter away from the roof, so the height of the antenna is only 1 meter. Antenna height has different effects on different antennas, generally affecting antenna impedance and elevation Angle. Generally, we think that the height of the antenna should be above 0.4 wavelength, so it is relatively unaffected by the ground.
Standing bobbi: finally, introduce this feature which is not familiar to Chinese fans. The standing-wave ratio reflects the matching of antenna feed system. It measures the performance of the antenna by the ratio of the energy emitted and reflected when the antenna is used as the transmitting antenna. The standing wave ratio is determined by the impedance of antenna feed system. The impedance of the antenna and the impedance of the feeder are consistent with that of the receiver, and the VSWR is small. The antenna feeder system with high standing-wave ratio loses a lot of signal in the feeder.
The role of celestial modulation:
1. Match the impedance to make the antenna system (antenna + antenna) match the impedance for the transmitter, so as to maximize the radiation efficiency of the antenna cable in the antenna system
2. Resonant antenna: according to the electromagnetic theory, antenna impedance Z=R+jX is considered as antenna resonance when X = 0. After using the antenna with unnatural resonance, the antenna is adjusted so that Z=R+jX, where X = 0, by adding inductance or capacity.
3. The electrical efficiency of the antenna after day adjustment is relative to the natural resonant antenna. Tuning the antenna to the transmitter is impedance matching, relying on the LC network inside the day adjustment. Since L and C are not ideal elements and consume some energy, the more unnatural resonance of the antenna (especially the farther the equivalent radiation resistance deviates from 50 ohms), the lower the electrical efficiency after the addition of day adjustment.
Fujian jiasida communication technology co., LTD., located in quanzhou city, fujian province, was established in 2009. It is a high-tech company specializing in communication research, development, production and operation of communication antennas and passive devices.
Company has an experienced r&d team, skilled production testers, perfect testing instruments and equipment, committed to the development and production of all kinds of radio antenna, car antenna, omni-directional antenna, power splitters, combiner, road system and platform, and so on related products, and provide personalized custom services according to customer's specific requirements. We in line with take the technology as the core, the science and technology strives for the development, provides the superior high technology product for the user the enterprise culture idea, in fully introduces absorbs the domestic and foreign advanced technology foundation, unceasingly develops the innovation, devotes to the research and development own characteristic new product. At the same time, we will sincerely provide customers with quality service.
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