impedence (S-11) & axial ratio equations for conical hor

Hi,

I am designing conical horn antenna on Ansoft HFSS. Kindly guide if there is any relation between these two because when one improves other gets disturbed. kindly provide with relevant equation so i may get correct results. My demand is to get -15 dB (s-11 parameters) and upto 3dB axial ratio.

Thanks in advance.

S11 and axial ratio are not really related. Axial ratio is a function of the amplitude and phase between orthogonal components of the radiated field while s11 describes reflected power ant the feed port. Interactions between the two (s11 and axial ratio) would be difficult to characterize in an equation.

You might want to run down this reference:

Corrugated Horns for Microwave Antennas (Ieee Electromagnetic Waves Series) (Hardcover)
by P. J. B. Clarricoats (Author)

I saw several references pop up for IEEE as well.