Mobile communications antenna technology developed rapidly, initially China mainly use the ordinary directional and omni-directional mobile antenna, and later the widespread use of mechanical antenna, and now some provinces and cities have begun to use the mobile network antenna and dual polarized mobile antenna. Because the frequency, gain and front-to-back ratio of the various antennas used in the mobile communication system are not very different, they meet the requirements of the network index. We will focus on the change of the antenna pattern and the wireless network from the angle of the mobile antenna In this regard, the above-mentioned several antennas are analyzed and compared.
Omnidirectional antenna, that is, in the horizontal pattern shows 360 ° are uniform radiation, that is, usually said non-directional, in the vertical pattern shows a certain width of the beam, in general, the smaller the lobe width, The greater the gain. Omnidirectional antenna in the mobile communication system in general application and suburban county system of the station type, covering a large area.
Directional antenna, in the horizontal direction of the performance of a certain range of radiation, that is, usually has a directional, in the vertical pattern shows a certain width of the beam, with the omni-directional antenna, the smaller the lobe width , The greater the gain. Directional antenna in the mobile communication system is generally used in the urban community system of the station type, covering a small, user density, high frequency utilization.
According to the requirements of the establishment of different types of base stations, and different types of base stations can be selected according to different types of antennas. Selection is based on the above technical parameters. For example, the omnidirectional station is used in the horizontal direction of the gain is basically the same omnidirectional antenna, and the directional station is the use of the horizontal direction of the directional changes have obvious directional antenna. Generally, an antenna with a horizontal beam width B of 65 ° is selected in the urban area, and an antenna with a horizontal beam width B of 65 °, 90 ° or 120 ° can be selected in the suburbs (depending on the station configuration and the local geographical environment) It is most economical to choose an omni-directional antenna that can achieve a wide range of coverage.
The so-called mechanical antenna, refers to the use of mechanical adjustment of the tilt angle of the mobile antenna. After the mechanical antenna is installed vertically with the ground, it is necessary to adjust the inclination of the antenna by adjusting the position of the antenna on the back of the antenna due to the requirement of network optimization. In the adjustment process, although the distance between the main lobe direction of the antenna is significantly changed, the amplitude of the vertical and horizontal components of the antenna is constant, so the antenna pattern is easily deformed. It is proved that the optimum inclination angle of the mechanical antenna is 1 ° -5 °. When the angle of inclination is 5 ° -10 °, the antenna pattern is slightly deformed but does not change greatly. When the inclination angle is 10 ° -15 When the mechanical antenna is tilted by 15 °, the shape of the antenna pattern changes greatly, and the pear shape when there is no tilting is changed into a spindle shape. At this time, although the main lobe direction The coverage distance is obviously shortened, but the entire antenna pattern is not within the base station sector, and the signal of the base station is received within the adjacent base station sector, resulting in severe intra-system interference. In addition, in the daily maintenance, if you want to adjust the mechanical antenna down angle, the entire system to shut down, can not adjust the antenna tilt at the same time to monitor; mechanical antenna adjustment antenna tilt angle is very troublesome, generally need to maintain personnel to climb to the antenna The adjustment angle of the mechanical antenna is the theoretical value calculated by the computer simulation analysis software, and there is some deviation from the actual optimum down angle. The adjustment angle of the mechanical antenna is 1 °, the third-order intermodulation index For -120dBc.
The so-called antenna, refers to the use of electronic adjustment down angle of the mobile antenna. The principle of electronic dip is to change the phase of the co-linear array antenna, change the magnitude of the vertical component and the horizontal component, change the strength of the synthetic component field strength, so that the vertical direction of the antenna diagram down. Due to the increase and decrease of the field strength in each direction of the sky line, it is guaranteed that the antenna pattern does not change greatly after changing the inclination angle, so that the distance of the main lobe direction is shortened, and the whole direction map is reduced in the service area Small coverage area but no interference. It has been proved that the antenna pattern is approximately the same as that of the mechanical antenna when the inclination angle of the ESC is changed at 1 ° -5 °. When the inclination angle changes at 5 ° -10 °, the antenna pattern is larger than that of the mechanical antenna The antenna pattern is larger than that of the mechanical antenna when the inclination angle is 10 ° -15 °. When the mechanical antenna is tilted by 15 °, the antenna pattern is obviously different from that of the mechanical antenna. The direction of the antenna pattern changes little, the main lobe direction to cover the distance significantly shortened, the entire antenna pattern in the base station sector, increase the down angle, you can make the sector coverage area is reduced, but does not produce interference, such a party Figure is what we need, so the use of electric antenna can reduce the call to reduce interference. In addition, the ESC antenna allows the system to adjust the vertical direction diagram under the condition of non-stop, real-time monitoring of the adjustment effect, adjust the inclination of the step precision is also higher (0.1 °), so the network can be fine Adjustment; the third-order intermodulation index of the ESC is -150dBc, which is 30dBc worse than the mechanical antenna, which is helpful to eliminate the adjacent frequency interference and spurious interference.
Dual polarized antenna
Dual polarized antenna is a new type of antenna technology, combined with + 45 ° and -45 ° polarization direction of the antenna orthogonal to each other and work in the transceiver duplex mode, so its most prominent advantage is to save a single orientation Base station antenna number; general GSM digital mobile communication network directional base station (three sectors) to use nine antennas, each fan using three antennas (space diversity, two hairs), if the use of dual polarized antenna, each Only one antenna is required for the sector. At the same time, the polarization of ± 45 ° can ensure that the isolation between + 45 ° and -45 ° is satisfied between the two antennas. (≥30dB), so the space between the dual-polarized antenna spacing only 20-30cm; In addition, the dual-polarized antenna with the advantages of the antenna, in the mobile communication network using dual-polarized antenna with the ESC Antenna, can reduce the call loss, reduce interference, improve the quality of service across the network. If the use of dual-polarized antenna, due to dual-polarized antenna on the erection of the installation requirements are not high, do not need to build the tower, only need to frame a 20cm diameter iron column, the dual polarization antenna fixed in the corresponding direction fixed on the iron You can save infrastructure investment, while making the base station layout more reasonable, the base station site selection easier.
For the choice of the antenna, we should be based on their mobile network coverage, traffic, interference and network quality of service and other practical conditions, select the mobile network for the needs of the mobile antenna: in the base station intensive high traffic area, should try to use Dual polarized antenna and electric antenna; in the edge, the suburbs and other traffic is not high, the base station is not intensive areas and only require coverage of the region, you can use the traditional mechanical antenna. China’s current mobile communication network in the high traffic density area of the call loss is higher, more interference, one of the important reasons is the mechanical antenna down angle is too large, the antenna down angle is too large, the antenna pattern is seriously deformed. To solve the high capacity of the high traffic area, you must shorten the station distance, increase the antenna down angle, but the use of mechanical antenna, down angle greater than 5 °, the antenna pattern began to deform, more than 10 °, the antenna pattern Serious deformation, so the use of mechanical antenna, it is difficult to solve the user high density area call loss is high, interference problems. Therefore, it is recommended to use the antenna or dual polarized antenna in the high traffic density area to replace the mechanical antenna. The replacement mechanical antenna can be installed in areas such as rural areas and suburbs with low traffic density.