Half semmetry brace up child with line of make a present of match
General reception equipment (like the television) its input characteristic impedance to be 75 Ω (lopsided pattern) or 300 Ω balance type, half semmetry brace up child output is: M blows?5 Ω to balance type, it is OK to if balance cable join to need to consider impedance only with 300 Ω ,match, we can be used terminal λ is apart from on transmission line / 4 times odder the square that the equivalent impedance of place is equal to impedance of transmission line character is divided with terminal load this one characteristic undertakes impedance matchs character, the mathematical expression Zin=Z0*Z0/ZL of this one character, the Z0 in type is transmission line (match cable) characteristic impedance, zin is the output impedance of aerial, ZL is load (the input impedance that receives facility) impedance, half semmetry brace up child of as parallel as 300 Ω cable deserve to receive computation to be as follows: Xian Jiao persuading porcelain attacks angry box of grandma of busy of Hui of Ao a round flat piece of jade with a hole in its center slaughters M
, also should realize half semmetry namely brace up child of as parallel as 300 Ω cable deserve to receive must want to insert a λ between them / 4 long, characteristic impedance is the parallel cable of 150 Ω , for this, we use two λ / 4 long 300 Ω parallel cable are shunt-wound can, receive a law to be like graph X. Thinking stalks of grain
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Half twists and turns closes brace up child
Zhen Zitian line is using amount to actually in, it is to use amount to like feed Zhen Ziyi brace up child form, its are main the purpose is the bandwidth that increases aerial, amount to brace up child if graph Jk place is shown,the structure is formed, this plants such the frequency band character of aerial is OK coming that prove: of confused ability of of young Chi of Da of a surname danger illuminate this? can regard haw is two λ / the series connection of photograph of short circuit line of 4, to λ of L= of syntonic frequency wavelengh / 4, occasionally extremely aerial and short circuit line do not have reactance composition, should add amount to brace up child on the frequency of high frequency electric current is when certain limits change, appear the following 2 kinds of circumstances: Force comfortable? of heart of crazy Jin of attentively of heart arrow smile is equivalent to L> λ / 4, occasionally extremely aerial grows approximately at λ / the short circuit line of 4, its reactance is perceptual, and right now the reactance of short circuit line is look sex, when frequency under syntonic frequency when, be equivalent to L< λ / 4, occasionally extremely aerial is approximate at λ / the open circuit line of 4, its reactance is look sex, and right now short on-line reactance is perceptual; reason when working frequency when unripe deflection, inside certain frequency limits, amount to brace up child on the inductance that appear and capacitive reactance can be compensated each other, make aerial is inside wider frequency range the change of its impedance character is not big, this is amount to brace up child the principle that has more broadband area. -
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- As a result of amount to brace up child two parallel conductor are had phasic and identical, the electric current with equal size (namely so its radiate electric current is I1=I2) I=I1+I2=2I1, its radiate power is P=I*I*Rr=(2I1)* (2I1) *Rr(Rr is half brace up child input impedance) in amount to brace up child the power input P =4*I1*I1*Rr= (Rin that feed carries is amount to brace up child input impedance) because be in,the electric current that feed end inputs is I actually, place I=I1, so we got amount to here brace up child input impedance is 300 Ω . It is symmetrical half brace up child 4 times what input impedance. To solve as coaxial as 75 Ω cable and antenna brace up child connection, use length to be λ / of the coaxial line make it of 2 phasic, impedance shift device, the U form ring that often makes namely, can solve above the Jk2 of knot composition of a picture of annulus of form of two problems.U is shown as follows.
From the graph knowable, after the B when feed nods electric current to pass U form annulus, with the electricity that A burns phasic difference is π (180 degrees of) , the outer conductor of U form annulus comprised λ / the short circuit line of 4, make in A, the impedance on B dot is infinity, consequently the electric current on outer conductor won't by inside watch wall flows to outside wall to reach the ground, and U form annulus is returned had the effect that impedance alternates, if electric current is inputted to be I1 in on-line of coaxial line core, input voltage is V1, criterion aerial two brace up child the input electric current that go up is I1 respectively, and coaxial wire outer conductor is ground connection, so A, b was opposite severally at 2 o'clock the voltage of the ground is V1, and A, voltage was B at 2 o'clock instead, reason this A, the voltage between 2 o'clock is B VA+VB=2V1, the impedance that in feed the dot presents is: R==After 4V1/I1 introduces U form link namely, the impedance that makes line of make a present of and day line contact are nodded rose fourfold, if use characteristic impedance to be the coaxial line feed of 75 Ω , the impedance that nods in feed is Ω of 4=300 of 75 Ω × , it is better to can be achieved with amount to booklet in accordion form with a slipcase match. -
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