An antenna system is a system consisting of a transmitting antenna and a receiving antenna. The former is a transmission mode converter that converts the radio frequency current or electromagnetic wave of the guided wave mode into a spatial electromagnetic wave of the diffusion wave mode; the latter is a transmission mode converter of its inverse transformation.
As a derivative transmitting antenna for conducting wave-diffusion wave mode conversion, as the receiving wave I for the diffusion wave-guided traveling wave mode conversion, the power carrying capacity and voltage withstanding capability of the transmitting antenna are much larger than that of the receiving antenna, both of which are Can be used interchangeably, and the basic characteristic parameters of the antenna are unchanged, which is called the reciprocity theorem. Another important role of the antenna is to concentrate the energy of the electromagnetic wave, that is, to concentrate the energy in the direction of the emission while making the transmitting antenna, and to reduce the energy in other directions; when the receiving antenna is used, more energy can be intercepted from the incoming wave in the receiving direction. For incoming waves in other directions, the input energy is reduced by phase cancellation. This is the directionality of the antenna. The multiplier of the energy concentration is called the gain of the antenna compared to the non-directional antenna. The extension of the antenna directivity is the negative gain (attenuation) of the non-communication direction, which can be used to describe another relevant performance index of the antenna, that is, the side lobe (interference) radiation suppression of the transmitting antenna or the incoming interference of the receiving antenna in the non-communicating direction. Degree of inhibition.
First, the definition of mobile communication antenna system
Definition and scope of the antenna system
In a mobile communication system, a communication antenna is a converter that communicates circuit signals and spatially radiates electromagnetic waves. This paper mainly analyzes the part of the communication antenna feeder system in the mobile communication system, including the base station/room sub-antenna, related feeder cables and other RF devices and related installation services.
Second, the performance parameter description of the base station antenna
General Electric Indicator
1, the working frequency band (Frequency Range)
Operating frequency band: Regardless of the antenna or other communication products, it always works within a certain frequency range (bandwidth), which depends on the requirements of the indicator. Usually, the frequency range that meets the requirements of the indicator can be the operating frequency of the antenna.
The width of the working frequency band is called the working bandwidth. Generally, the working bandwidth of the omnidirectional antenna can reach 3-5% of the center frequency, and the working bandwidth of the directional antenna can reach 5-10% of the center frequency.
2, input impedance (Input Impedance)
Input impedance: The ratio of the signal voltage at the antenna input to the signal current, called the input impedance of the antenna. The input impedance of a typical mobile communication antenna is 50 Ω.
The input impedance is related to the structure, size, and operating wavelength of the antenna. In the required operating frequency range, the imaginary part of the input impedance is small and the real part is quite close to 50 Ω, which is necessary for the antenna to be in good impedance matching with the feeder.
3, voltage standing wave ratio (VSWR)
Voltage standing wave ratio: The voltage standing wave ratio of the antenna is the ratio of the maximum value to the minimum value of the voltage standing wave pattern generated along the transmission line when the antenna is used as the load of the lossless transmission line.
The standing wave ratio is generated by the fact that the incident wave energy is transmitted to the input end of the antenna without being superimposed by the reflected wave generated by the total absorption (radiation). The larger the VSWR, the larger the reflection and the worse the matching. In mobile communication systems, the standing wave ratio is generally required to be less than 1.5.
4, isolation (Isolation)
Isolation represents the proportion of signals that are signaled to one port (a polarization) of a dual-polarized antenna at another port (another polarization).
5, Third Order Intermodulation (Third Order Inter modulation)
Third-order intermodulation signal: refers to two signals in a linear system. Due to nonlinear factors, the second harmonic of one signal is generated by the beat (mixed) of the fundamental wave of the other signal.
The phenomenon of intermodulation is a new frequency component that falls within the frequency band after mixing two or more carrier frequencies outside the band, causing a decline in system performance.
6, power capacity (Power Capacity)
Power Capacity: The power capacity of an antenna is the maximum continuous RF power that can be continuously applied to an antenna for a specified period of time without degrading its performance under specified conditions.
Space radiation index
7, gain (Gain)
The ratio of the radiant power flux density of the antenna in a given direction to the maximum radiant power flux density at the same input power of the reference antenna (usually using an ideal point source);
Antenna gain is a measure of the ability of an antenna to transmit and receive signals in a particular direction. It is one of the important parameters for selecting a base station antenna. The higher the antenna gain, the better the directivity, the more concentrated the energy, and the narrower the lobes.
8, horizontal / vertical half power lobe width (H / V - Plane Half Power Beam Width)
In the main lobe of the power pattern, the angle between the beam widths between two points at which the relative maximum radiation direction power is reduced to half or less than the maximum value is referred to as the half power lobe width.
The half-power beamwidth of the horizontal plane is called the horizontal beamwidth; the half-power beamwidth of the vertical plane is called the vertical beamwidth.
9, Electrical Down Tilt (Electrical Down Tilt)
The electric downtilt angle refers to the angle between the maximum radiation pointing on the vertical radiating surface of the communication antenna and the antenna normal.
The communication antenna is divided into a fixed downtilt antenna and an electric adjustable antenna according to whether or not the electric downtilt adjustment is supported: the fixed downtilt antenna refers to a fixed downtilt antenna generated by shaping the amplitude and phase of the antenna radiating element array according to the wireless coverage requirement; The electric adjustment antenna refers to changing the phase difference of different radiation units in the array by the phase shifting unit, thereby generating different radiation main lobe down state. Generally, the down state of the electric adjustment antenna is only within a certain adjustable angle range.
10, Front-to-Back Ratio (Front-to-Back Ratio)
The front-to-back ratio of the antenna refers to the ratio of the power flux density of the maximum radiation direction of the main lobe (specified as 0°) to the maximum power flux density in the vicinity of the opposite direction (specified in the range of 180°±30°) F/B= 10log (front and rear power / backward power).
11. Sideflush suppression and zero fill (Elevation Upper Side lobes & Null Fill)
Sidelobe suppression: The side lobes of the main lobe in the vertical plane (ie, in the forward direction toward the zenith angle) are called the upper side lobes. In order to cover the effect, the base station antenna usually adopts a certain mechanical downtilt to the antenna in the network planning. This may cause the side lobes in the first (or within a certain angular range) of the antenna to be in a horizontal position or even lower than the horizontal position, which is likely to cause neighboring area interference, and therefore, it is necessary to suppress it, that is, the upper side lobes are suppressed.
The upper side lobes not only waste the energy radiated by the antenna, but also interfere with the high-rise buildings of adjacent cells, especially adjacent cells, so the upper side lobes should be suppressed as much as possible, especially the first upper side lobes with higher energy.
Zero-fill: It means that in the vertical plane of the antenna, the first zero point of the lower side lobes is filled with beamforming design to improve the coverage of the near-field of the base station and reduce the near-zone coverage dead zone and blind spot.
12, Cross Polarization Ratio (Cross Polarization Ratio)
The difference between the power level of the same-polarized reception (maximum reception level) and the power level of the hetero-polarization reception (minimum reception level) in the 3 dB beamwidth of the pattern
13, the direction of the circularity (Circularity)
The circularity of the omnidirectional antenna refers to the deviation of the maximum or minimum level value from the average value in the horizontal plane pattern.
The average value is the arithmetic mean of the level dB values ​​in the horizontal plane with a maximum interval of no more than 5° in the azimuth.
14, polarization (Polarization)
The direction of the electric field of the electromagnetic wave radiated by the antenna is the polarization direction of the antenna. If the electric field of the electric wave is perpendicular to the ground, we call it a vertically polarized wave; if the electric field of the electric wave is parallel to the ground, it is called a horizontally polarized wave; if the electric field of the electric wave is at an angle of 45° to the ground, then It is called +45° or -45° polarization.
Third, the type of mobile communication base station antenna
There are many types and types of mobile communication antennas. According to their application scenarios, they can be roughly divided into indoor distributed antenna products, outdoor base station antenna products, and beautification antenna products.
I. Indoor distributed and cell coverage antenna products
Ceiling antenna
Ceiling antennas are generally used for indoor wireless coverage scenarios. According to their different radiation forms, they can be divided into directional ceiling antennas and omnidirectional ceiling antennas. Omnidirectional ceiling antennas can be divided into single polarization ceilings and dual polarizations. Suction two kinds.
2. Wall-mounted antenna
The indoor wall-mounted antenna is a typical small-sized antenna. It is mainly used for indoor wireless coverage. It can be divided into single-polarized wall-mounted and double-polarized wall-mounted according to different polarization modes.
3. Yagi antenna
Yagi antenna is mainly used for link transmission and repeater, and the cost is relatively low. The front-back reflection ratio in the two-dimensional plane is better.
4. Logarithmic period antenna
Similar to the Yagi antenna, the log-period antenna is a multi-element bidirectional antenna with wide-band coverage capability and is mainly used for link relay.
5. Parabolic antenna
The parabolic antenna is a high gain bidirectional antenna consisting of a parabolic reflector and a center feed antenna.
II. Outdoor base station antenna products
Omnidirectional base station
The omni-directional base station antenna is mainly used for 360-degree wide coverage, and is mainly used to cover sparse rural wireless scenes.
2. Directional base station antenna
The directional base station antenna is currently the most widely used fully enclosed base station antenna, and is divided into several types, including: vertically polarized antenna, vertical and horizontal polarized antenna, ±45° dual-polarized antenna, multi-band antenna, and the like. According to the difference of the tilting electric mode, it can be divided into a fixed tilt antenna, an electric adjustable antenna, and a three-sector bundle antenna.
3. ESC base station antenna
The electric adjustment antenna refers to changing the phase difference of different radiation units in the array by the phase shifting unit, thereby generating different radiation main lobe down state. Generally, the down state of the electric adjustment antenna is only within a certain adjustable angle range. The ESC downtilt adjustment has manual adjustment and RCU electrical adjustment.
4. Smart antenna
A dual-polarized radiating element is used to form a directional or omnidirectional array, which can perform beam-sweeping antenna arrays in 360 degrees or in a specific direction; smart antennas can determine spatial information of signals (such as propagation direction) and track and locate signal sources. An intelligent algorithm and an antenna array that performs spatial filtering based on this information.
5. Multimode antenna
The main difference between multimode base station antenna products and ordinary base station antennas is the integration of more than two antennas in different frequency bands in a limited space. Therefore, the focus of this product is to eliminate the interaction between different frequency bands (decoupling effect, isolation). Degree, near field interference)
6. Multi-beam antenna
A multi-beam antenna can generate multiple sharp-beam antennas. These sharp beams (called meta-beams) can be combined into one or several shaped beams to cover a particular airspace. Multi-beam antennas have three basic forms: lens type, reflective surface type and phased array.
III. Active antenna
The passive antenna is combined with the active device to form an integrated receiving antenna.
IV. Beautifying the antenna
1. Indoor coverage beautification antenna
The beautification processing of different indoor distributed antenna products not only solves the problem of indoor signal coverage, but also does not damage the layout of finishing and decoration; the general indoor coverage beautification antenna has beautiful appearance and small invisibility effect, and is suitable for various high-end residential areas. Shopping malls, hotels, hotels, office buildings, hospitals and other public places.
According to the shape of the product, the indoor coverage beautification antenna can be roughly divided into: ceiling lamp type beautification antenna, mural type beautification antenna and exhaust fan type.
2. Outdoor coverage landscaping antenna
The outdoor coverage landscaping antenna is mainly for antenna application products such as cells and base stations. It can camouflage and modify the appearance of the antenna through various materials, structures and patterns without increasing the propagation loss, which not only beautifies the urban vision. The environment also reduces the public's fear and resistance to the wireless electromagnetic environment, while at the same time extending the life of the antenna and ensuring communication quality.
According to the form of the product, the outdoor coverage beautification antenna can be roughly divided into: street lamp type beautification antenna, sign type beautification antenna, monitoring ball type beautification antenna, air conditioning type beautifying antenna, rockery type beautifying antenna, speaker type beautifying antenna, simulation tree beautification Antennas, square-column landscaping antennas, chameleon-type landscaping antennas, water tower landscaping antennas, fence-type landscaping antennas, exhaust pipe landscaping antennas, etc.
Fourth, mobile communication feeder passive components and other
The feeder system is connected between the transmitter, the receiver and the antenna. The feeder system is mainly used to transmit the high frequency power of the transmitter to the antenna, and transmit the target reflected signal received by the antenna to the receiver.
In addition to the base station/room sub-antennas included, the mobile communication system also includes feeder cables, passive components (including other combiners such as combiners, filters, POIs, etc.). These are all indispensable devices for communication systems.
RF feed cable
RF feeder cable can be divided into semi-flexible coaxial cable and semi-rigid coaxial cable; according to its model, it can be divided into 1/4′′, 3/8′′, 1/2′′, 5/8′′, 7/8 ", 1-1/4", 1-5/8" and other different sizes, these are mainly used for the transmission of indoor and outdoor RF signals.
The RF cable inside the mobile communication antenna is also an RF feeder cable, which is mainly used for jumper connector feeding, power distribution network feeding, network impedance matching, and the like.
2. Combiner splitter
The combiner is primarily used to combine multiple system signals into a single indoor distribution system. In engineering applications, a combiner can be used to simultaneously operate an indoor distribution system in different communication bands. The combiner used in the mobile communication system generally has a two-way combiner, a three-way combiner, a four-way combiner, and the like.
3. Filter
The function of the filter is to allow the signal of a part of the frequency to pass smoothly, while the signal of other parts of the frequency is greatly suppressed. The filter is generally divided into an active filter and a passive filter. The cavity filter used in the mobile communication system is generally a cavity filter. The main features are: wide frequency coverage, high reliability, good stability, input and output impedance matching, easy to cascade, and internal bandwidth. The frequency characteristics are flat, the insertion loss is small, and the out-of-band suppression is high.
4.POI
Point Of Interface, multi-system integration platform. It is mainly used for indoor coverage of large buildings such as subways, convention centers, exhibition halls, and airports. The system uses the frequency combiner and the bridge combiner to introduce the antenna feed distribution system after combining the signals of multiple operators and multiple standards to achieve the purpose of making full use of resources and saving investment.
In order to avoid interference, the POI is divided into two platforms: uplink and downlink, and the uplink and downlink signals are separately transmitted. As a bridge connecting the wireless communication donor signal and the distributed coverage signal (leakage cable and antenna array, etc.), the POI is mainly used for combining and splitting the uplink and downlink RF signals of each operator, and filtering out the inter-bands. Interference component. The main function of the upstream part of the POI is to transmit signals from different types of mobile phones through the antenna collection and feeders to the upstream POI, and the POIs detect the signals of different frequency bands and send them to the base stations of different operators. The main function of the downstream part of the POI is to synthesize the carrier signals of each carrier and different frequency bands and send them to the antenna feeder distribution system of the coverage area.
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