Aerial standing wave is compared

      The input impedance of aerial is the ratio that aerial feed end inputs voltage and input electric current. The join of aerial and line of make a present of, optimal case is aerial input impedance is pure resistor and the characteristic impedance that is equal to line of make a present of, at this moment terminal of line of make a present of is reflexed without power, there is standing wave on line of make a present of, the inputs impedance to follow frequency change of aerial is gentlier. The in matching to work even if eliminate aerial to input impedance reactance heft of aerial, make resistor heft is close to the characteristic impedance of line of make a present of as far as possible. The actor of low quality that match is measured commonly with 4 parameter reflex coefficient namely, travelling wave coefficient, standing wave comparing and echo loss, there is fixed numeric concern between 4 parameter, use that one pure stem from a habit. Safeguard daily in us in, those who use is more is standing wave comparing and echo loss. The input impedance of general mobile antenna is 50 Europe. Standing wave comparing: It is the reciprocal of travelling wave coefficient, its value is in 1 arrive between infinity. Standing wave comparing is 1, express to match completely; Standing wave expresses total reflection than be infinity, break completely match. In mobile system, ask standing wave comparing is less than commonly 1.5, but the VSWR in applying actually should is less than 1.2. Too big standing wave is reduced than meeting base of the station enclothe and cause the interference inside the system to increase, the service function that influence radical stands.

     Echo loss: It is the reciprocal that reflexes coefficient absolute value, with decibel the value expresses. The value of echo loss is in of 0dB arrive between infinity, echo loss expresses to match to be differred more greatly more, it is better that echo loss expresses to match greatly more. 0 express total reflection, infinity expresses to match completely. In mobile system, loss of general requirement echo is more than 14dB.

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