I have read in many authentic books that a ½ wavelength has 75 ohms impedance (i.e. SWR for 75 ohm system is 1), and gain of 2.2 dBi. The groundplane antennas (horizontal disk, horizontal radials, and slanting radials) are all theoretically close, but inferior to dipole. The main reason ground plane are popular over plain dipole is convinience of bottom fed arrangement used by all types of groundplanes, over side fed arrangement used by dipole.Thanks so much for doing this.
Don't you think is realy strange that dipole has better SWR than the spider? Maybe there are some considerations about the feeding point that the program does not count
Remember, all Yagis have only one driven element - a dipole (or folded dipole). Those who remember rooftop TV antennas, can easily realize success of dipole or folded dipole. Th folded dipole was used with twin-lead (300 ohms), and the straight dipole was used with coax (75 ohms). The directivity was imparted to omni dipole by elements placed in front & back of dipole (but not connected to dipole or feed cable), making a typical TV antenna.