Re: S-parameters of coax-to-waveguide transition

[Brian Frank <FrankB@EE.QueensU.CA>]

Yes, I used a similar approach to that used in the application "Analysis
of a Coaxially-Fed Patch Antenna" on the LC website whereby a reference
model was used to determine the incident wave which was then subtracted
from the total voltage and current.  Everything looks fine in the time
domain, but the reflected signal looks wrong in the frequency domain.



-- 
Brian Frank
ECE Department
Queen's University

On Mon, 17 Sep 2001, Ian Rumsey wrote:

> From: Ian Rumsey <rumsey@ucsub.colorado.edu>
> To: lc-users@maori.colorado.edu
> Date: Mon, 17 Sep 2001 14:23:44 -0600 (MDT)
> Subject: Re: S-parameters of coax-to-waveguide transition
> Reply-To: lc-users@maori.colorado.edu
>
> Did you subtract out the incident voltage from the total (incident +
> reflected) before using the S-parameter calculator?  If you're using the
> total voltage as the reflected input you might see a problem like you're
> describing.
>
> -Ian Rumsey
> Univ. Colorado - Boulder
>
> On Mon, 17 Sep 2001, Brian Frank wrote:
>
> >
> > The S-parameter calculator was indeed used. The magnitude of S11 spikes
> > above 1 (i.e. S11 in dB spikes above 0 dB) periodically due to the fact
> > that the reflected voltage spikes above that of the incident voltage. I
> > have run the simulation many times with different cell sizes and time
> > steps, and haven't been able to eliminate this problem.
> >
> > Thanks,
> >
> > BF
> >
> >
> > > From: Kevin Thomas <kjt@cray.com>
> > > To: lc-users@maori.colorado.edu
> > > Date: Wed, 12 Sep 2001 10:39:54 -0500
> > > Subject: Re: S-parameters of coax-to-waveguide transition
> > > Reply-To: lc-users@maori.colorado.edu
> > >
> > > The problem may lie in the interpretation of the results,
> > > rather than the results themselves.  You mention that the
> > > frequency domain result is unusually large, but do not mention
> > > the time domain result.  I assume then that the time domain
> > > result looks fine.
> > >
> > > The frequency domain plots of voltage, current, and power produced
> > > by LC are not normalized, and thus don't relect normal units
> > > (volts, etc.).  To normalize the plots, divide by the input
> > > source in the frequency domain.  This can be done via the
> > > LC "Plot Calculator" or with another tool, such as Matlab.
> > > You may want to express this result in dB (10*log10 or 20*log10,
> > > which can also be done in the Plot Calculator).
> > >
> > > Of course these plots can be fed directly into the S-parameter
> > > calculation as well, which automatically normalizes the
> > > results to the incident source.  Since each plot includes the
> > > same scale factor, then the resulting S-parameter plot will
> > > have the scale factor removed.
> > >
> > >
> >
>