archimedean spiral mode MSA

i am designing two arm archimedean spiral mode MSA using ie3d software.the ie3d version is 11.05. i simulated the compete model. but the anenna & radiation efficiency is too low. also vswr value is 2 for 1.5 to 1.9 ghz range only . suggest the changes in my model to improve efficinct to 80 to 90 % . also suggest the remedies to improve vswr for wide range.the no. of turns in desinn are 2.5 & the spacing between the conductors & width is 0.5 mm. by changing these parametrs or no. of turns can i get the desired & expected results.or by changing the dielectric constant OR loss tangent results will be improved . kindly suggest the remedies

Low efficiency may be related to the thickness of the trace is too small. If the VSWR is not good, it might be that your normalization impedance is 50-ohms. Most wide band antennas may not work at 50-ohms.