Monday, December 27, 2010
Weak current College】 【RFID characterization of antenna performance main parameters】.
<br> <br> 1 antenna input impedance <br> Antenna input impedance is the antenna feed end of input voltage and the ratio of the input current. Antenna and feeder connections, the best scenario is antenna input impedance is pure resistance and is equal .to the characteristic impedance of the feeder, the feeder Terminal No power reflection, feeder does not have a standing wave, antenna input impedance with the frequency changes relatively flat. Antenna matching job is to eliminate the antenna input impedance, reactance components in the resistance of .the component as close as possible to the characteristic impedance of the feeder. Match of four parameters typically used to measure the reflection coefficient, traveling wave coefficient, VSWR and return loss, four parameters are fixed values, use a plain out of habit. In our .ongoing maintenance, the more is the standing wave ratio and return loss. General mobile communication antenna input impedance 50 Ω. <br> <br> VSWR: it is the reciprocal of traveling wave coefficient, a value between 1 and infinity. Standing wave ratio .is 1, meaning that an exact match; VSWR to infinity represents total reflection, completely mismatched. In the mobile communication system, VSWR less than 1.5, but the practical application of VSWR less than 1.2. Excessive VSWR will reduce base station coverage and interference within .the system, affect the base station's service performance. <br> <br> Return loss: it is the reciprocal of the absolute value of reflection coefficient to the decibel value. Return loss values in between 0dB to infinity, the return loss is greater that .match the lower, return loss, the larger the better matches. 0 represents internal reflection, infinity represents an exact match. In the mobile communication system, General requirements for the return loss greater than 14dB. <br> <br> 2 antenna polarization < .br> <br> The so-called antenna polarization, antenna radiation electric field strength at the time of formation. When the electric field strength direction perpendicular to the ground, the radio wave is called vertical polarized waves; when the electric field intensity in the .direction parallel to the ground, the radio wave is called horizontal polarized waves. Because the radio waves, determines the level of polarization of the signal transmission in close to the ground surface of the earth when the polarisation currents, polarisation effects due to ground impedance and .the production of heat electric signal attenuation, and rapid vertical polarization mode is difficult to produce the polarisation current to avoid a sharp decline of energy, ensure the effective dissemination of signals. <br> <br> Therefore, in the mobile communication system, generally .adopts vertical polarization mode of transmission. In addition, with the development of new technologies and the recent emergence of a dual-polarized antenna. In terms of their design ideas, generally consists of vertical and horizontal polarization and ± 45 ° polarization in two ways, .performance is better than the former on the latter generally, so most of poling ± 45 °. Dual-polarized antenna combines + 45 ° and 45 ° two pair of mutually orthogonal polarization orientation of the antenna, while working in receiving and duplex mode, significant .savings in each community, the number of antennas; at the same time, due to ± 45 ° for orthogonal polarization, effectively ensure diversity reception for good results. (Its polarization diversity gain approximately 5dB, than single-polarization antenna 2dB increase about.) .<br> <br> 3 antenna gain <br> <br> Antenna gain is used to measure the antenna toward a specific direction and receive signal, it is the choice of base station antenna, one of the most important parameters. <br> .<br> In General, gain increased mainly by reducing vertical facing radiation of the lobe width in the horizontal plane, while maintaining full performance to radiation. Antenna gain on mobile communication system operating quality is extremely important because it determines the castellated edge of signal level .. Increase the gain can be a sure way to increase network coverage, or increase in determines the range of gain. Any cellular system is a two-way process, increase the gain of the antenna can also reduce the bidirectional system gain budget allowance. In .addition, the characterization of the antenna gain parameters have the dBi and dBd. DBi is relative to the point source antenna gain, in the direction of the radiation is uniform; dBd relative to symmetric lattice antenna gain dBi = dBd + 2.15. Under the same .conditions, the higher the gain of wave propagation in the distance. In General, directional GSM base station antenna gain 18dBi, Omni-11dBi. <br> <br> 4 antenna of the lobe width <br> <br> Lobe width is a .directional antenna used a very important parameter, it refers to the antenna radiation diagrams below peak 3dB premises into angle width (antenna radiation pattern is to measure the antenna in all directions and receiving signal indicator, the ability of a typically provides a graphical representation of the .power relationship between the intensity and angle). <br> <br> Antenna vertical width of the lobe and the antenna that generally correspond to the direction of coverage. Therefore, in a certain range of antenna vertical degrees (pitch angle) of the regulation ., to achieve improved cell coverage quality purposes, this is our network optimization is often a means used. Mainly involves two aspects of the level of the lobe width and the width of the vertical plane wave petals. Horizontal plane half power point (H-PlaneHalfPowerbeamwidth .) 45 °, 60 °, 90 °, etc.) defined the antenna beamwidth horizontal plane. The greater the angle, in the sectors covered by the junction of the better, but when you raise the antenna tilt angle, less prone to distortion, .forming more beam area coverage. The smaller the angle, in the sectors covered lower junction. Raise the antenna angle can move on to improve the sector at the junction of coverage, but relatively speaking, not easy to produce more of the other community areas covered .. In the Centre of the base station as a station from the small antenna tilt, should use horizontal plane half power point small antenna selection of horizontal planes in the suburbs of half power, large antenna; vertical plane half power point (V-PlaneHalfPowerbeamwidth) .: (48 °, 33 °, 15 °, 8 °) defines antenna beamwidth vertical plane. Vertical plane of the lower half power point, off the main beam direction signal attenuation, the faster, more easily by adjusting the antenna angle accurately control coverage .. <br> <br> Before and after more than 5 (Front-BackRatio) <br> <br> Indicates that the antenna on the back flap inhibitor is good or bad. Selection of front and rear than the low of antenna, antenna .back flap may have more area coverage, leading to switch between the confusion arising out the words. Generally between 25-30dB, priority should be given before and after more than 30 selected antenna. <br> <br> <br> <br> .<br>.