Mismatched polarization can yield a 30 db signal loss (per the Getting Started column on antenna polarization, by W1ZR, in the July 2010 issue of QST). Since this antenna may be used to communicate with mobile radios that typically use vertical antennas, we need to find out how it behaves when oriented vertically.
By changing one number on the GM card we can rotate the antenna 90 degrees around the Y-axis:
The results are very similar : (click images to enlarge)
Most of the differences are minor and probably due to the precision of the calculations, however the vertical polarization has a significant gain loss of almost 4db vs horizontal polarization. Still, compared to a mismatch in polarization, 4db is minor.
Max Vertical Gain vs Max Horizontal Gain
(click image to enlarge)
The variation in theta is less than when the antenna was horizontal, but the pattern is the same.