know antenna's s11, how to matching?

know antenna's input s11, I know can calculate antenna impedance from s11, but it is complex form. if using quarter wavelength to match, should use resistive impedance only? thanks

Hi

yes, a quarter wave transformer can only match resistive impedance.
If it is complex then you can use stub-matching.

quater wavelenght tranformer is to transform real impedance (general sense). And for low frequency it is not feasible (very long line needed). In that case better to use lumped element matching, single/double stub tuner.

Why don't you take a look at pozar's book 'Microwave engineering' where impedance matching is very easily and clearly explained.

Regards,
Shameem

thanks. If s11=a+bj and using quarter wavelength to match, then Zin=Z0*(1+a)/(1-a)?

As we have already told you, you cannot match a complex load using quarter wave transformer.

but one ieee paper show they use quarter wave to match each arm of one quadrifilar helix antenna whose s11 is complex. that is why i confused

Hi

What is the name of the paper?

We can have a look.

thanks a lot.
'printed quadrifilar helix: development of a novel antenna for measurement of electro magnetic interference', I simulated this structure, and the s11 is complex

Hi

I have looked at the article.
They say taht a quarter wave transformer(QWT) is used, to transform an input real input impedance of 13 ohm to 50 ohm with a 37 ohm QWT. I cant see where they specify a complex impedance?

But I cannot make sence of their QWT. I think it should have been 25.5 ohm and not 37 ohm.

Article: https://www.edaboard.com/viewtopic.p...drifilar+helix

hi,thanks. I made mistake before, when antenna is resonant, its impedance should be real, so my simulation somewhere wrong.