One, aerial efficiency
Height of erect of length of frequency of appearance of qualitative, antenna, job, antenna, antenna concerns the conductor material of aerial efficiency and erect antenna.
1, aerial material is qualitative
Choose electric property as far as possible the metallic stuff with low rate of good, resistor, wait like silver-colored, copper, aluminium. Because the cost of silver-colored wire is too high, electrical engineering pure copper cash had better choose in applying actually so. Seductively dressed or made up by copper mine stone after refine, eliminate impurity, want to reduce oxide especially, cathode copper gets after repass electroanalysises, pull silk next. The foreign matter of pure copper of this kind of electrician is little, resistor rate is very low. The wire that factory of electrical wiring of a few normal state-operated produces and enamel-insulated wire belong to this kind of wire. After often still seeing a few town enterprises or SOHO use smelt of reclaiming useless old copper in the market now (second birth copper) manufacturing electrical wiring, place of material of this kind of copper cash contains impurity more, resistor rate is older also, if use this kind of wire to make when aerial, the effect of aerial won't be very good, past contact can increase the white noise when receiving, go against the reception of weak signal. When making antenna with all sorts of wire, sectional it is good that big wire receives the result at sectional small wire. As a result of the collect skin effect of high frequency signal, likewise sectional when, of material of much plied yarn it is good to receive the result at material of odd plied yarn. Aluminous material is in what when making 8 wood antenna, use commonly more.
2, the appearance of aerial
To improve the efficiency of aerial, often use the antenna of different figure in different wave band, LW paragraph with long term aerial is given priority to, MW paragraph with long term aerial and cricoid antenna are given priority to, SW paragraph with long term aerial, occasionally extremely aerial and 8 wood antenna are given priority to, FM paragraph give priority to with antenna of 8 wood antenna and whip shape with V/U wave band, the small wave band of 800M above is given priority to with board shape antenna and paraboloid antenna.
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3, working frequency
The job the antenna at different frequency, its efficiency also is different, the efficiency of aerial follows the job to rise and increase of frequency commonly, the efficiency of high frequency antenna is general prep above
Low frequency antenna. The data makes clear: The efficiency of long wave antenna is 10% , 40% , the efficiency of medium wave antenna is 70% , 80% , the efficiency of shortwave antenna is 90% , 95% , ultrashort (FM, V, U) it is with the efficiency of microwave antennae 95% , 99% .
4, the length of aerial
Be close to its job frequency when the effective length of aerial half (1/2 wavelengh) rectifying multiple when, the efficiency of aerial is taller, when be like this multiple to increase, the efficiency of aerial
Still can rise further, dan Bo grows number (aerial length) increase with efficiency rising is not to become direct ratio to concern. When the diameter of annulus antenna increases, aerial efficiency can rise, when the pen number of annulus antenna increases, the efficiency of aerial also can rise further. When the diameter of paraboloid antenna increases, of aerial efficiency rise the meeting is more apparent.
5, erect height
Generally speaking, aerial erect must jump over Gao Jixiao to had been jumped over if really, of course this height is opposite, mix according to the environment even when actual erect the cost investment of erect will accept or reject.
But receving antenna is in V paragraph when above frequency is used, not be erect jump over Gao Yue is good, because,this is V paragraph the frequency of above, its field is in by force of the space perpendicular distributinging is inhomogenous, sometimes it is good instead that aerial position erect gets a bit lower result the effect at altitude.
2, of aerial directional
When we judge the actor of low quality that an antenna is blasting off and receives electromagnetic wave performance, another parameter that knows aerial function index even -- of aerial directional, aerial blasts off to each direction in the space of 360 ° and receive the ability of electromagnetic wave namely. In applying actually, what we basically care is the ability that blast off and receives electromagnetic wave what aerial makes the same score direction to go up in water, perhaps ask to there is the capacity that blast off and receives electromagnetic wave greatly as far as possible on the certain way that aerial hopes in us.
The theoretical foundation of aerial is electromagnetism field theory, it is OK to impose simplified attrib border requirement through maxwell equation the outcome that computation goes out and determines aerial to blast off and receive electromagnetic wave on each direction, this one aerial direction intention that as a result we can express with polar coordinates will describe. This one result that gets through computation often too Utopian, still have bigger error with actual antenna sometimes. So, produce the product of aerial manufacturer normally, often be the directional picture that the method that those who pass actual measurement is in in electromagnetism anechoic room gets this type antenna, we can choose the finished product antenna that right way pursues according to our need. Below spare condition, contain the directional figure of aerial, can consult foregone the directional graph that is the same as type antenna.
Mention the directional plan of aerial, understand the polarization of electromagnetic wave even. So-called polarization, when the electric field heft that is electromagnetic wave is travelling, it is as perpendicular still as what big n goes, such, had the branch of horizontal polarization and perpendicular polarization. Broadcast of the LM of public broadcast broadcasting station, MW, SW, FM, TV basically is to use horizontal polarization mode, spare broadcasting station is in HF paragraph also be to use horizontal polarization mode. The V of business broadcasting station, U paragraph communication (the interphone that we often use, the pager, the V that includes spare broadcasting station, U paragraph communication) , AIR, GSM, CDMA, basically be the means that uses perpendicular polarization, when receiving, to get reception the result best, when receving antenna is being installed actually, the polarization mode that should receive electromagnetic wave with place as far as possible is consistent, namely the effective unit of aerial is to use level or perpendicular means installation. But the frequency of 800 million above, the polarization effect of receving antenna is not apparent, and it is frequency taller, jump over not apparent. Additional, the signal field that receives the seat is strong tall when, the polarization effect of receving antenna is not apparent, field is strong when losing, the polarization effect of receving antenna is apparent. Annulus antenna is an exception, the annulus of low block antenna is the magnetic field weight that receives electromagnetic wave, the reception of tall block annulus antenna holds concurrently to the magnetic field heft of electromagnetic wave and electric field heft and have, as a result of annulus antenna structure and the characteristic that receive a principle, when be being used actually, we need not use the polarization that considers annulus antenna
Effect, what need to consider aerial only is directional.
Additional, radio wave is in transmission process, after passing multipath transmission, often unwarrantable arrive at the polarization mode that when receiving the seat, still keeps strict, total meeting produces a few changes. For example, when shortwave radio signal travels, mix in ionosphere between the earth for many times bounce, radio wave passes the diffraction when tall Shan Dachuan, the tall building to radio wave reflex in the city, etc. Of respecting antenna directional, basically can divide it is two kinds big, omnidirectional antenna and directional antenna.
1, omnidirectional antenna
The directional graph of omnidirectional antenna is a circle that with aerial location position is the centre of a circle one, or it is an irregular circle. Public broadcast broadcasting station covers area to get broadcasting greatly as far as possible, also can regard the communication on the dot that finish as, especially medium wave and FM broadcasting, still have telecast, basically be the our region that finish enclothe, what its emissive antenna uses is omnidirectional antenna. But shortwave broadcast broadcasting station is exceptional however. The interphone that we often see (include all sorts of holding interphone, receiver) used antenna, the car carries the sucking disk antenna that interphone uses on mobile car, clip to hold aerial to belong to omnidirectional antenna, whip shape antenna also is typical omnidirectional antenna. What our lover often uses is long term aerial also can be omnidirectional antenna.
2, directional antenna
The direction of directional antenna pursues, can regard aerial position as to be in those who spend core, a beautiful petaline graph, the petaline likelihood that does not cross this flower has one only, two, or it is to have a few, also these leaf have the likelihood greatly small, have wide have narrow, have long have short, these are petaline, we call it wave valve. The directional antenna of different type, its direction graph also is different. Sometimes, the effect that goes up in some direction to emphasize aerial particularly, we can use wave piece is long and narrow directional antenna. When undertaking interference rejection is received, or be when be being received remotely what undertake medium wave and FM broadcasting, often do so. Broadcasting station of shortwave public broadcast is to be used finish cross a region, cross the national boundaries, broadcast that crosses intercontinental, its emissive antenna often uses directional antenna. Business communication broadcasting station is nodded all right in V/U Duan Jin directional antenna also should be used when bit righter communication. The half wave idol that we often use extremely aerial, amount to is Zhen Zitian line, inclined pull aerial, pouring V antenna, 8 wood antenna, annulus antenna to wait is to belong to directional antenna. Sometimes we are OK also be together an omnidirectional antenna and combination of a directional antenna, will get one has the assorted antenna that special direction pursues, also can have a few the directional antenna that same way pursues is combined together, will get an omnidirectional antenna.
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