[SI-LIST] Re: balun theory
- From: Mike Brown <bmgman@xxxxxxxxxx>
- To: atifshamimkhan@xxxxxxxxx
- Date: Fri, 09 Jul 2004 14:23:54 -0500
Atif,
I don't have your graphics, either. I'll imagine a slightly different figure
than Paul Levin's, one in which there are two transmission lines in parallel.
The one on the top is driven at the left end; the one on the bottom is grounded
at the left end. They are terminated at the right end with a load between
them, which may or may not have a ground connection at the half-impedance point.
Assume, for the moment, that the two lines are tightly coupled, and share a
homogenous dielectric. The homogenous dielectric results in a forward
crosstalk coeffient of 0. Due to the tight coupling, Kb is greater than 0;
ideally 0.5. This situation couples a half-amplitude signal into the lower
line and attenuates the rightward flowing incident wave to an amplitude of 0.5
The resulting backward crosstalk (left-flowing) wave in the lower line is
reflected at the short with a reflection coefficient of -1. Hence the phase
reversal. This reflected wave now travels to the right, where it is terminated
in the balanced load Z. Thus the incident unbalanced waveform has been
converted to a balanced wrsp ground pair of signals.
Levin's model is a discrete representation of this transmission line
configuration.
Regards
Mike
atifshamim khan wrote:
> Hi all
>
> Following figure is a basic balun structure. I have utilized this to
feed/test an on-chip dipole on bulk Si, but I still dont know how it works in
theory.
> There is an unbalanced signal (Zin) at the input and a balanced signal at the
output(load resistor ZL). Basically one end of the transmission line is
grounded.
At the output (the two ZL terminals) have signal which is equal in magnitude
but
opposite in phase.This means that between the two transmission lines a phase
reversal has taken place. How is this achieved or in other words how can we
explain
the working of this balun in terms of voltages and currents or
electric and magnetic fields? My guess is that we are forcing and odd mode in
the transmission lines? Is that right? what is the difference between odd mode
and even mode impedances here. Any input in terms of explanation or references
will be appreciated.
> Thanks
> Atif
>
>
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