Helical Antenna Design in HFSS

I am trying to design a helix antenna at 9 GHz. I used antenna design kit and the design gave me good return loss (-34 db) at 13.22 GHz where as it gave bad results (approx -13 db) for 9 G Hz (which is my design frequency). Why is it so? How can i get a better return loss (more than -30 db) at my design frequency? Which parameter of helix antenna will provide me control over the centre frequency of antenna so that i can optimize my design. Thank You. I am attaching my design and return loss image.

When using Antenna Design Kit for the Helix Antenna- Did you change the Solution freq to 9 GHz and clicked on Synthesize to generate the correct parameters ? And which type of Helix Antenna - Axial mode or Normal mode did you design ?

I synthesized the antenna for 9 ghz by entering 9 ghz in synthesis option. I used the axial mode for my design.