The phase difference of the voltages in the coaxial cable between the central conductor and the outer conductor is exactly equal to 180 degrees. If this answer does not suit You, please describe more your problem.

Ok, so If I am designing my spiral with an edge feed. then I can feed the spiral with the co axial cable from the edge and it should work...right? I am attaching a picture of my fabricated spiral with the coaxial cable connecting at the edge. 

If you simulated your antenna with an edge feed port it means the antenna expects a balanced feed. From your picture the feeding is unbalanced, by doing so your antenna will operate under its best performance. You can try (a) to model inside your software a piece of coaxial cable and getting exactly what youve done to check on the results or (b) try another design, based on the infinite balun approach (ref. http://www.antenna-theory.com/definitions/infinite.php).

Thankyou Kamal, but in my application, edge feed is required