Problem in S-parameter graph

Please some one help me out. i m getting such attached graph of s-parameter at resonant frequency of 10GHz. please help me out which parameter should i change in cst so that i can get good result of s-parameter.
thank you

Hi,

Are you using a high lossy or a high dielectric substrate ? It could be the reason why your not getting a smooth drop at 10GHz.

i m using FR4 loss free with a dielectric of 4.3 substrate.

have u feed it correctly

what kind of structure are you modeling?

Ur Structure is resonating well for 10 GHz but its bandwidth is High. If u want High Q structure then modifications are to be done but its all depending on ur application. FR4 is a lossy Material. Try giving the value of its loss tangent and simulate the structure again..! Also, If its a 2 port device, see that ur structure is symmetric..!

thanks to all

@spacedust. actually its 1 port device. please can you tell me about lass tangent ? how it could be ?

To me, it looks like you have some other parts resonating near 10GHz, you might need a look of the snapshot and check where in your structure is causing that. To me your 10GHz Q factor is high enough, you almost reached -38 dB. Thus improving resonance at 10GHz has little room, but removing other resonance near 10GHz might be a worth try.

Loss tangent or Tan(D) is a measure of How much losses a dielectric can add..! For FR4 the loss tangent is 0.027 typically..! So ur Structure is an Planar Antenna ? Which software are u using to model it ?

actually i m using CST MWS