helix antenna design problem in HFSS

hi everybody, I am new at helix antenna. I have been trying to make a helix antenna for 4GHz frequency. I have made the quater-wave transformer by "txline" software. with that i got the width of the stripline to be 16.6 mm. The helix has to be spaced 7.5mm above the ground as lambda=75mm and the resistance is 84 ohms(assuming the helix is 140 ohms). I am having a problem with matching the source (connected through coaxial line of inner dia =0.2mm and outer dia=0.45mm) to the helix antenna.

I want to verify if the stripline is 84 ohms by replacing the antenna by a strip of 140ohms and source with 50 ohms. Now I have the following problems:

¤ how can i make this replacement i.e how can i assure that the strip is 140 ohms
¤ does the length of the coaxial matter? i tried varying it but it doesn't help much

Please help me.......... i am desperate

J. Kraus, "Antennas" has an extensive section on various spirals. Corzine and Mosko has additional information. Start with Kraus.