What does a 1/4 wave transfomer mean?
i am currently designing a microstirip patch antenna and i am using a 1/4 wave transformer to match the feedline to the patch. but however i am not very sure what does 1/4 wave transformer mean? does it matter if i use a 1/2 wave transformer? is size the only thing changed if i used a 1/2 instead of a 1/4? thanks a lot
The line is a quarter wave long and should have an impedance that is the geometric mean between the antenna impedance and the transmission line impedance toward the electronics.
hi
1/4 wave transformer means the length of transmission line is 1/4 the lenght of the operating wave length..
they found that 1/4T.L act as a transformer because it converts the impedance of one side to the other side like a transformer does.
one of its main application is a matching device like match between the feedline and the patch .. means that when the wave is traveling in the feed line there is no a problem because it is in one medium but when it reaches the antenna the medium is not the same so some of the power are reflected back to the source which is undesired so we put a matching device just to let the second medium appears as the first medium to the wave so no reflection happens and all the power transmitt to the antenna
and as said by flatulent
The 1/4line should have a characteristic impedance (Zo) = the geometric mean between the antenna impedance and the transmission line impedance toward the electronics
more information read a book or website about transmission media
mas
Hi, Mohamed:
The following comments might have you to understand why.
Za = antennas impedance (tuned to a real value).
Zs = source impedance (assume real value)
Looking at the input side of the transformer, you have:
Zin = Zc * [ Za + j Zc tan (Beta*L) ] / [ Zc + j Za tan(Beta*L)]
1. If L = lambda/4, tan(beta*L) is approaching infinity.
Zin = Zc * Zc / za
If you choose Zc = sqrt( Zs * Za ), Zin = Zs and you get perfect match.
2. If L = lambda/2, tan(beta*L) = 0. Zin = Za.
Regards.
it means a transformer with electrical length equal to 1/4 th of wavelength
Hi!
I have to use qarter wave transformator to match the feed line to the patch. But my problem is that I have impedance of antenna with imaginar.part (206+j41), and my feedline is 200ohma. So, I know that I have to put transformer , a little bit away of anntena but I don't know how far away? How do I calculate that?
Imped.of transformer is sgrt.200(206+j41)?
Freq.3GHz!
Thanx a lot!
Hi, collie5:
I think you just need to use an open stub to offse the j41 so that the impedance will become 206 from 206+j41 It is already a good match to the 200 ohms feed line. I don't think you need any transformer for it after you offset the j41. Regards.
Thank you very much for your answer.