I am Awais and I want to design a dual-band antenna in CST studio. My requirement is to design at an operating frequency of 2.45GHz and 5.8GHz. The problem is when I simulated, it was resonating round about 5.3 but have no resonation at 2.45. How I can make it at 2.45 also?
You may tune certain parameters of the design using the 'parametric sweep' in CST MWS. Some of the tunable parameters might include slot dimensions, gap associated with the feed ( such as inset feed, for example), dimensions of the radiating patch, and dimensions of the ground plane.
but have no resonation at 2.45 GHz
Are you using a standard square copper or a defective ground structure? If your antenna has no resonance at 2.45 GHz, this means that the designed ground plane (preferably the defective ground plane) might have provided almost zero transmission at that frequency. You may check the S-parameter plot and check the plots of S11 (reflection coefficient) and S21 (transmission). If you are using a Floquet port model, you can check 'SZmax(1),Zmax(1) for reflection characteristics and 'SZmin(1),Zmax(1) for transmission characteristics.
If the magnitude of reflection is greater than the magnitude of transmission, there will minimum to no transmission.