One of basic functions of emissive antenna are an energy that obtains from line of make a present of to all round dimensional radiate goes out, of basic function is the directional radiate that wants place of major energy face. Perpendicular half placement semmetry brace up child have the stereo direction that makes the same score put " biscuit to encircle " form to pursue (graph 1.3.1 A) . Although stereo sense is strong,stereo direction pursues, but scale is difficult, graph 1.3.1 B and graph 1.3.1 C gave out two its advocate planar direction graph, what planar direction graph describes aerial to appoint plane to go up in some is directional. From the graph 1.3.1 B can see, in brace up child the radiate on axes direction is 0, direction of the biggest radiate is on horizontal; And can see from graph 1.3.1 C, the radiate on each direction on horizontal is euqally big.
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Of aerial directional increase
A certain number of symmetrical brace up child group blast, can control radiation, the biscuit with generation compressed " encircles " , go to signal on horizontal direction centrally further. Next graphs are 4 half wave semmetry brace up child edge vertical line arranges up and down perpendicular a stereo direction graph when and graphs of 4 yuan of vertical plane direction.
Also can use baffle-board to be able to control radiant energy to plane of odd side direction what baffle-board puts in array to form sector area to enclothe aerial at the same time. The horizontal direction graph below showed the effect of reflection face- - reflection face reflexes power to odd side direction, increased gain. The basic knowledge of aerial is full to blast (perpendicular array does not take planar baffle-board) . Cast content to reflex the use of the face, can make more the radiate of aerial, the searchlight in resembling optics in that way, go to energy centrally inside a small solid angle, score very tall gain thereby. Self-evident, of paraboloid antenna form include two main essential factor: Face of the reflex that throw thing and set the radiation source on paraboloid focus.
Wave valve width
Directional graph has two normally or many valve, among them the piece with radiation the biggest intensity says to give priority to valve, the valve of the others calls deputy piece or by valve. Refer to a graph 1.3.4 A, be in advocate piece is the biggest radiation direction two side, radiation intensity reduces 3 DB (power density reduces an in part) the included angle definition between 2 o'clock is wave valve width (call beam width again or advocate valve width or half power horn) . Wave valve width is narrower, directional better, action distance is further, interference rejection capability is stronger. Still have breadth of valve of a kind of wave, namely width of 10dB wave valve, just as its name implies it is intensity of the radiate in directional graph reduces 10dB (power density falls to very one of) two included angle between the dot, 1.3.4 B seeing a picture.
Around comparing
Direction pursues medium, of around valve maximum compare than calling from beginning to end, write down for F / B. Around comparing is bigger, of aerial backward radiation (or receive) smaller. Around is very simpler than the computation of F / B---F / B = 10 Lg {(forward power density) / (backward power density) when} has a demand than F / B to the around of aerial, its type cost is (18---30) DB, ask to amount to below special situation (35---40) DB.
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