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### NF2FF Phase

Posted: Tue 18 Dec 2018, 14:33
Dear openEMS-users,
if I do a RCS calculation in the fashion of the sphere-RCS example, how can I determine the correct complex Phase of the RCS?
Is it done by specifying the radius R? If I don't specify anything the default should be R=1 m. Do I get the complex RCS at distance R from the phase-center, if I multiply the outcome of calcNF2FF by $\exp\left(-\mathrm{j} \frac{\omega}{c_0}(R-1)\right)$... I guess the convention $\mathbf{E}(\mathbf{r},t)=\mathbf{E}(\mathbf{r})\exp\left(\mathrm{j} \omega t)\right)$ is used in openEMS, right?

### Re: NF2FF Phase

Posted: Thu 20 Dec 2018, 02:12
I didn't do it in traditional fashion, as in the example. but I did phase extraction with a plane wave box. this instrument extracts the plane wave from itself in the box exterior, so it is zeroed, but leaves the excitation inside the box. If there is something disturbing the field inside it, the the field difference appears outside and on the boundaries, which is dumped and processed by "nf2ff", and if I am not mistaken, the data is complex, or contains phase. I do not have a reference code now to check. You need to explore the resulting structure.
So the trick is that it is very stable when scanning frequency without random phase bias, and you can plot phase walk vs frequency and direction the same time.

### Re: NF2FF Phase

Posted: Thu 20 Dec 2018, 09:14
It's of course "-jwt"
And yes, by default everything is for 1m distance, but you can tell nf2ff to calculate for every other radius instead. But I must confess I have never used it since I was never really interested in the absolute phase and I guess there are more things to consider too, like the phase of the Gaussian pulse and so on?

regards
Thorsten

### Re: NF2FF Phase

Posted: Fri 21 Dec 2018, 00:47
isn't phase of the pulse removed when normalizing the frequency response at the output? Then again, if it is a true synthetic Gaussian pulse, why should there be deviations? AFAIK it should be flat as a board.