The first ABC that tells aerial

The main parameter of token antenna function has direction to pursue, gain, input impedance, standing wave comparing, polarization mode.

The input impedance of 1.1 antenna
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 Ω .

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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The polarization mode of 1.2 antenna
The polarization of alleged antenna, point to the way of electric field intensity that forms when aerial radiate namely. When direction of electric field intensity perpendicular at the ground, this electric wave calls perpendicular polarization wave; When parallel of direction of electric field intensity at the ground, this electric wave calls horizontal polarization wave. As a result of the character of electric wave, the signal that decided horizontal polarization travels can be in when ground of press close to earth surface generates polarization current, because polarization current suffers earth impedance to the influence produces heat energy and make electric field signal rapid damply, and perpendicular polarization mode generates polarization current not easily, avoided energy thereby considerably damply, assured the effective transmission of signal.

Accordingly, in mobile system, all use the transmission means of perpendicular polarization commonly. Additional, as the development of new technology, appeared again recently antenna of a kind of double polarization. With respect to its design train of thought character, general component is perpendicular with horizontal polarization and ± 45 ° polarization two kinds of means, general and latter excel is former on function, what because this is current,use for the most part is ± 45 ° polarization mode. Double polarization antenna was combined + 45 ° and - 45 ° the antenna of mutual orthogonality of direction of two pairs of polarization, work at the same time in send and receive duplex operation mode to fall, saved the aerial amount of every village greatly; As a result of ± at the same time 45 ° are orthogonal polarization, assured effectively to divide the favorable result that collect receives. (gain of market of its polarization component is 5dB about, antenna of the polarization that compare sheet rises make an appointment with 2dB. )

The gain of 1.3 antenna
Aerial gain is to use the ability that measures aerial to send and receive signal toward a specific direction, it is one of parameter with the most important antenna of choice radical station.

Generally speaking, the increases main support to reduce vertical plane Xiang Fu to shoot wave valve breadth of gain, and keep complete on horizontal to radiation function. Aerial gain is very significant to the riding quality of mobile system, because it decides the signal n of beehive brim. Increase gain to be able to be in what the network increases on one orient to cover range, perhaps increase gain surplus inside certain limits. Any beehive systems are a two-way process, the gain that adds aerial can reduce surplus of budget of two-way system gain at the same time. Additional, the parameter of token antenna gain has DBd and DBi. DBi is opposite the gain at point source antenna, the radiate in each direction is even; DBd is opposite the gain DBi=dBd+2.15 at symmetrical streak antenna. Below same condition, gain is taller, the distance that electric wave transmits is further. Popularly, GSM is directional base the aerial gain of the station is 18dBi, complete to for 11dBi.

The wave valve width of 1.4 antenna
Wave valve width is a directional antenna is commonly used very important parameter, it is the width that included angle becomes under location of peak value 3dB in showing the radiate of aerial pursues (the radiation graph of aerial is magnanimity antenna an index that each direction send and receive signal ability, the concern that normally fashion of form of to in an attempt to expresses to be power strength and included angle) .

The wave valve width with perpendicular antenna is general on as corresponding as this antenna place direction enclothe radius to concern. Accordingly, pair of aerial verticality are passed inside certain limits (pitch angle) adjust, can achieve the goal that improves a village to cover mass, this also is us in the network a kind of method that in optimizing, often uses. Basically involve width of valve of wave of two fields level and perpendicular and planar wave valve width. The half power horn of horizontal plane (H - Plane Half Power Beamwidth) : (45 ° , 60 ° , 90 ° ) the beam width that defined aerial level plane. Point of view is older, in fan area boundary it is better to enclothe, but when should raising aerial dip, also jump over incidental beam distortion, form jump over an area to enclothe. Angle is smaller, enclothe in fan area boundary poorer. Raise aerial dip to be able to be in what fan area boundary improves on floating rate to enclothe, and relative to character, produce pair of other villages not easily jump over an area to enclothe. In downtown base the station is apart from as a result of the station small, aerial dip is big, ought to use the antenna with the half power small part of horizontal plane, the suburb chooses the antenna with the half power large part of horizontal plane; The half power horn of perpendicular plane (V - Plane Half Power Beamwidth) : ?8 ° , 33 ° , 15 ° , 8 ° ) defined the beam width with perpendicular and planar antenna. The half power part of perpendicular plane is smaller, deviate advocate attenuation of the signal when beam direction is faster, it is easier to be in through adjusting aerial dip accurate control covers range.

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1.5 around are compared (Front-Back Ratio)
Indicated stand or fall of low-key of the valve after aerial is opposite. Choose around to compare low antenna, of aerial hind possible generation jumps over valve the area is enclothed, cause switch relation disorder, generation drops a word. Be in commonly 25 - between 30dB, should preferential choose around comparing to be the antenna of 30.

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