Here is a link to Walter Fair's Website on 1/4 wave ground plane verticals. It might be helpful to some that suggest a 1/4 wave radiator with a horizontal 1/4 wave radial at 90* degrees shows a feed point impedance of about 35 ohms.
Antenna Notes
In answer to CK suggestion that the 35 ohms at the feed point comes into play when the antenna is over perfect ground. CK idea here is not supported by the article above, or by my model (.25w 4 HR 32') that I posted earlier.
Below is this same model which I have set over perfect ground plane just like CK suggested, and the impedance changed just a little bit as noted, and it is still not near 35 ohms, but instead down at 23.44 ohms...almost identical to what Walter Fair's article reports.
CK, I also added the wires report, in case you would like to input them into your Eznec program. However, this will not work for you if you have the Demo Version.
I'm off looking for more verification for what I see in my modeling and in my real world testing back in 2006 and 2009.
Here is another Website that again shows what I've claimed is true: http://ve2bmc.com/ANTENNA.htm
Here is another link, but it agrees with CK and others who claim the feed point impedance for a 1/4 wave ground plane is 36 ohms: http://www.chem.hawaii.edu/uham/radials.html
Here is another that CK and others will agree with: http://www.tomthompson.com/radio/EHam_Articles/DipolevsVertical/DV.html
