Right coaxial feed for planar antenna in HFSS

May be, anybody known how to describy coax cable for [3.1-10.6]GHz bandwidth for microstirp antenna? The following parameters, that i've been used give me the best results. R=0.5cm, r=0.1cm, length = 0.01cm

Hello :

If you want to use coax cable for feeding of mic-antanna you should consider these points:
1-the length of coax cable doesn't have any effect on you'r analysis , in fact it's length does not any necessarilly limitation . but the position of input port has an important effect in computing S parameter .
2-If you want analyse your structure in a wide frequency domain you must design a BALUN or chang the dimentions of your feeding cable in any frequency .

hi
if you want to use coax feeding for planar patch antenna you should know that Z0 for coax cable opproximately is [60*ln(R/r)]/μr as well as real world parameters of coax cable.