Aerial is basic knowledge

1 antenna

1.1    The action of aerial and position

      The power of radio frequency signal that radio catapult outputs, through line of make a present of (cable) carry aerial, go out with radiate of electromagnetic wave form by aerial. Electromagnetic wave arrives after receiving a place, by aerial next (receive merely very small very small one part power) , send radio receiver through line of make a present of. Visible, aerial is a when blast off and receive electromagnetic wave important radio equipment, also correspond without radio without aerial.

      Aerial breed is various, wait for different situation in order to feed different frequency, different utility, different situation, diverse demand next use. 

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      To the antenna of numerous breed, undertaking proper classification is necessary:
      Press utility classification, can divide wait for communication antenna, TV antenna, radar antennae; Press working frequency paragraph classification, can divide wait for shortwave antenna, ultrashort antenna, microwave antennae; Press directional classification, can divide wait for omnidirectional antenna, directional antenna; Press appearance classification, can divide for linear aerial, face shape antenna; Wait classification a moment.

*  The radiate of electromagnetic wave

      Have on lead hand in change when electric current flows, with respect to the radiation that can produce electromagnetic wave, the length of radiant ability and lead and appearance are concerned. If place of graph 1.1 A is shown, if the distance of two lead is very close, electric field is manacled to be between two lead, radiation is very consequently faint; Stretch two lead, if place of graph 1.1 B is shown, electric field is in with respect to diffuse all round space, consequently radiation increases.

        Must point out, the length L when lead is far when be less than wavelengh λ , radiation is very faint; When the length L of lead increases to be able to be likened to with wavelengh photograph, guide on-line electric current will increase greatly, can form stronger radiate consequently.
 

1.2  Symmetrical brace up child

        Symmetrical brace up child be a kind classical, use the most extensive antenna up to now, individual half symmetrical Zhen Zike establishs the ground simply to use alone or use the source of make a present of that regards paraboloid as aerial, also can use half many semmetry brace up child compositive antenna blast.

        Two arms length is equal brace up child be called semmetry brace up child. Every arm length is 1/4 wavelengh, full-length be 1/2 wavelengh brace up child, weigh half semmetry brace up child,  see graph 1.2 A .

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