HFSS Problem. Any ideas?

Hello all. I have been browsing this board the last couple of days and found the information very useful. I would like to solicit your input for the following problem. I am fairly new to HFSS and have been using it to replicate some results from published papers. I am fairly comfortable in most cases when using a microstrip feed, but I am now trying to simulate a coax fed spiral antenna (see attachment spiral.pdf). I think that I have the geometry correct but the results I am getting are not very good. Any thoughts on how to improve them. I am no expert with coaxial feed antennas having spent most my research looking into microstrip feeds. Any help would be greatly appreciated. I have attached my HFSS file and the pdf so that if anyone has any extra time and would like to help I would be very grateful. Thanks in advance and have a good one.

P.S. I am trying to simulate the entire spiral with all the switches in the "On" position (L5 on their results chart). Thanks.