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    Of cross emissive antenna deserve to receive


    Of cross emissive antenna deserve to receiveFstx1.gif (1450 byte)
       Fstx2.gif (2799 byte)Be in a few in in the high frequency emissive equipment of small-power, use normally multilayer cross half twists and turns adds up to Zhen Zifa to shoot aerial. The characteristic of this kind of antenna is a structure simple erect is convenient, its defect is gain inferior and bandwidth is opposite narrower, it is a specification with double deck cross antenna here its deserve to accept a principle. Graph the 1 knot composition of a picture that is this kind of antenna, we know half brace up child the input is hired fight to balance type 300 Europe, and the output impedance of emissive equipment often is 50 Europe lopsided pattern, want above all so amount to brace up child commutation of 300 Europe balance becomes 75 Europe lopsided form (the concerned article that commutation principle can consult publish before me) , it is two length λ next (wavelengh) 75 Europe coaxial cable (line of make a present of weighing cent) will fluctuate two things to Zhen Zihe uses two length to be λ + λ / the 75 Europe cable of 4 will fluctuate, the impedance of 1 is node 75/4=18.75 Europe, because launch the output impedance of equipment to be 50 Europe, still must


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     impedance alternates so, we are usedGs5.gif (182 byte) This formula has consideration, the λ that the Z0 in type needs for place / an impedance of distribution cable character of 4 length, z1 is node the impedance of 1, the output impedance that Z2 is emissive equipment (node 2) . CalculateGs6.gif (278 byte) For this we can be λ with a length / the paralell connection of 75 Europe cable of the 50 Europe cable of 4 and a same length will be replaced approximately.
       Why thing Xiang Hena north to should the line that divide make a present of differ λ / 4? This is to make inside horizontal electromagnetic wave receives even radiation, if divide the length of line of make a present of if pursue,its pursue in the radiate inside horizontal 3, it is thus clear that from inside the graph its radiate field is in southwest, Fstx3.gif (1284 byte)Northeast, southeast, northwest just is weaker up, if north and south to brace up child with the thing to brace up child differ on feed π / of 2 phasic, the radiation field that its form that end is one rotates magnetic field, if the graph is shown 4 times,its radiate pursues, from inside the graph visible radiate field is in all-around on evener. Should produce π according to the principle of transmission line / the phasic difference of 2 needs to get on some direction only (like north and south to) the line that divide make a present of adds λ / 4 OK, this is why Xiang Hedong of north and south differs to the line that divide make a present of on the west λ / the reason of 4. Thinking stalks of grain

    Zbb.gif (2822 byte)



    The measurement technique that aerial standing wave compares
       In aerial system, aerial and equipment deserve to receive good the parameter that we often call standing wave to compare with is measured to its, it is when standing wave comparing of 1 when, state this antenna system matchs good without reflection, such number is meant greatly more match a state to jump over difference, the existence in the system jumps over big reflection wave. How does that end measure the standing wave of aerial to compare? Here I introduce a kind of relatively simple and easy measure to everybody.
       Want to measure standing wave comparing to need a sweep generator, receive a law to be like graph 2-1, first the terminal line of make a present of (one aspect of the matter of close antenna system) short circuit, the signal that outputs as a result of sweep generator right now forms total reflection in the terminal of line of make a present of, observe weaveform of its total reflection is like graph 2-2 curve most it is A substantially, receive aerial the terminal of line of make a present of next, observe inside working frequency limits on sweep generator right now most be like graph 2-3 for B substantially, beg a reflection coefficient P=b/a first, can beg a standing wave comparing with type S=1+P/1-P next, the S in type states standing wave is compared. Thinking stalks of grain

    The electric length of cable 

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       Dldcd.gif (718 byte)





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