positive return loss

Hi,

I have modeled a partch antenna (including the feed structure). But the problem is when I plot the Return Loss (dB) over the frequency range there is a section where the return loss is > 0 db and reaches a peak of 6dB.

Thats doesn't make sence to me. It's a passive structure.

Just wanted to check if that make sence in any way.

thanks

You are right, it shouldn't be more tham 0dB for passive structures.
The problem sounds like the calculation did not converge completly. Furthermore, if my guess is right, the whole S11 plot has many ripples above 0dB.

I'd suggest:
a. Set the energy criterion to a lower level.
b. Allow a longer time simulation, i.e. more time steps.
c. Try solving it also in the frequency domain.

Good luck,
P.

hi
in order to make the solution converge::::
in frequency sweep, choose the solution frequency to be the upper frequency for sweep.
use finer meshing.
if u use ADS, using the current solution (not converged) increse number of points or samples in which adaptive sweep is done.

Hi,

maybe we should chekc first which simulator you use? 3D (CST, HFSS ..) 2.5 D. (Momentum, IE3D....)


F.

Hi,

yes, I have the same experience with some passive circuits, it is the consequence of response interpolation (ABS, AFS, etc. depending on software used). If you can control the parameters of this feature, first you should make sure that the number of frequencies that will be used for interpolation is large enough or decrease the tolerance of the interpolator.

flyhigh

Thanks all.

It seems like it was the "interpolation" alalysis. I am using HFSS and tried the "Fast" analysis. Now the letrun loss is all below 0 db but then my RL is worse over my frequency band of interest. :(