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[jagadishvakati]

I have been designing the microstrip antenna in CST for 1.8Ghz with epsilon=5 and Mu=90. So in order to get the resonant frequency i have to check the S11(db) curve and get the dip around 1.8 Ghz where my antenna is resonating. But what i observe is the resonant frequency is largely varying around 4Ghz and 4.5 Ghz. why is it so?. what resonant frequency should i consider?
For the figure of S11 curve go to
https://plus.google.com/photos/116153833174430793517/albums/5832408026823865841?authkey=CMLp_rWdu9-FtAE
or
https://plus.google.com/photos/116153833174430793517/albums/5832408026823865841
thanks in advance.

[bigSteve]

Your simulation looks a little screwed up as you have s11 at -2 dB up to 500 MHz, which is a bit odd.

Generally the curve does not look natural. It should be very high for s11 and hten a sharp rolloff for the first frequency (resonance) at a half wavelength. Then you will end up with a 3rd harmonic that is broader band (5.4 GHz roughly), but it should not look like what you have posted.

[jagadishvakati]

So is it like should the curve be very high at the initial and then should have a V shaped drop? Am i correct?
So where could we have gone wrong during simulation. I am introducing new substrates values like Mu and Epsilon and doing the simulation like S11, Vswr, radiation efficiency, Total efficiency, Bandwidth. and many more...in the CST software..

And do u think that this software is reliable when doing such variation in Mu and Epsilon values?