【School】 RFID characterization of weak performance of the main parameters of the antenna..

<br> <BR> 1, the antenna input impedance <BR> antenna input impedance is the antenna feed-ended input voltage and input current ratio.. Antenna and feeder connections, the best scenario is the antenna input impedance is purely .resistive and equal to the characteristic impedance of feed line, then there is no power feeder terminal reflection, not standing on the feeder, antenna input impedance changes with frequency relatively gentle.. Job is to match the antenna, antenna input impedance to eliminate the reactance .component of the resistance of feeder components as close as possible the characteristic impedance.. Match the general merits of the four parameters used to measure the reflection coefficient, wave coefficient, VSWR and return loss, four parameters have a fixed numerical relationship between the use of .it a pure habit.. In our daily maintenance, is more used than the standing wave and the return loss.. General mobile communication antenna input impedance is 50Ω.. <BR> <BR> Standing wave ratio: it is the reciprocal .traveling wave coefficient, its value between 1 and infinity.. Standing wave ratio of 1 means an exact match; standing wave ratio is infinite, said total reflection, total mismatch.. In the mobile communication system, general requirements VSWR less than 1.5, but .the actual application of VSWR should be less than 1.2.. VSWR is too large will reduce the coverage of base stations and interference caused by the system increased, the performance of the service station.. <BR> <BR> Return loss: .it is the reciprocal of the absolute value of reflection coefficient, the value expressed in decibels.. 0dB return loss of the value of the infinite, between that match the bigger the worse return loss, return loss, which matches the bigger the better.. .0 total reflection, infinity that match exactly.. In the mobile communication system, the return loss is greater than the general requirements of 14dB.. <BR> <BR> 2, the antenna polarization <BR> <BR> .the so-called antenna polarization, antenna radiation refers to the formation of the direction of electric field strength.. When the electric field perpendicular to the ground, this wave is called the vertically polarized wave; when the electric field parallel to the ground, this .wave is called the horizontal polarization wave.. Because the characteristics of waves, determines the horizontal polarization signal is transmitted to the ground surface of the earth when the polarization current, polarization current due to the production of heat leaving the earth impedance of the rapid decay .of the electric field signal, while the vertical polarization is not easy. the polarization current, thus avoiding the significant energy attenuation and ensure effective dissemination of the signal.. <BR> <BR> Therefore, in the mobile communication system, generally .vertical polarization mode of transmission.. In addition, with the development of new technologies, more recently, the emergence of a dual-polarized antenna.. In terms of its design ideas, usually divided into vertical and horizontal polarization, and ± 45 ° polarization .in two ways, the general performance of the latter than the former, it is currently used mostly ± 45 ° polarization.. Dual-polarized antenna combination of the +45 ° and -45 ° two mutually orthogonal polarization antenna, and simultaneously send and receive .duplex mode, significant savings in the number of antennas for each district; the same time as the ± 45 °. orthogonal polarization diversity reception effectively guarantee good results.. (The polarization diversity gain is about 5dB, compared with unipolar antenna by about 2dB. .) <BR> <BR> 3, the antenna gain <BR> <BR> antenna gain is used to measure the antenna receive signals in one particular direction. the ability to select the base station antenna is the most important parameters ... <BR> <BR> In general, the improvement mainly depends on the gain for reducing the vertical beam width of radiation, and in the horizontal plane to keep all the radiation performance.. Antenna gain on the operation of the quality .of mobile communication systems is extremely important because it determines the signal level cell edge.. Increase the gain to a definite direction in the network coverage increases, or increases in determining the gain margin range.. Any cellular system is a two-way process and .increase the antenna gain can also reduce the two-way system gain budget margin.. In addition, the characterization parameters dBd antenna gain and dBi.. DBi point source antenna is relative to the gain in the direction of the radiation is uniform; dBd symmetric .time around compared to the antenna gain dBi = dBd +2.15.. Under the same conditions, the higher the gain, the farther the distance radio wave propagation.. In general, GSM base station antenna directional gain of 18dBi, for all to 11dBi. .. <BR> <BR> 4, the antenna beam width <BR> <BR> directional antenna beam width is commonly used in a very important parameter, which refers to the antenna radiation pattern 3dB below the peak in the angle .between the premises into. width (antenna antenna radiation pattern is a measure of ability to send and receive signals in all directions an indicator, usually expressed as a power graphically the relationship between strength and angle).. <BR> <BR> .Antenna vertical beam width generally corresponding with the direction of the antenna coverage radius.. Thus, within a certain range of the antenna through the vertical (pitch angle) of the regulation, can achieve the purpose of improving the quality of cell coverage, which we .often used in network optimization as a means.. Mainly related to the level of both beam width and the vertical plane lobe width.. Horizontal plane of the half-power angle (H-PlaneHalfPowerbeamwidth) 45 °, 60 °, 90 °, etc ..) define the horizontal plane of the antenna beam width.. Angle increases, the coverage of the junction in the sector as possible, but to improve the antenna angle, the beam is also more prone to distortion, the formation of cross-district coverage ... The smaller the angle, covering the junction of the worse in the sector.. Increase in the mobile antenna inclination to improve the sector at the junction of the extent of coverage, but relatively speaking, not prone to the more area of coverage of .other cells.. Because the base station away from the station in the city center is small, the antenna angle large, horizontal plane should be half-power angle of the antenna small, rural use of the half-power angle of the horizontal plane large .antenna; vertical plane of the half-power angle (V-PlaneHalfPowerbeamwidth): (.48 °, 33 °, 15 °, 8 °) define the vertical plane of the antenna beam width.. Vertical plane of the half-power angle smaller ., off the main beam direction of the faster signal attenuation in the antenna by adjusting the angle of the more accurate and easier to control the coverage.. <BR> <BR> 5, after more than (Front-BackRatio) < .BR> <BR> showed that inhibition of the antenna on the flap of the good or bad.. Lower than before and after selection of the antenna, the antenna flap may have more area coverage, leading to confusion switching between, resulting in dropped .calls.. Generally between 25-30dB, preference should be given before and after the ratio of 30 antennas.. <BR>..