Roy Lewallen, W7EL, the author of the EZNEC antenna modelling software package, has decided to retire.  He will no longer support the product but as a going-away present to the community is offering the EZNEC-Pro+ software package for FREE.

See https://www.eznec.com/

This is a great program to play around with various antenna ideas before cutting a single piece of wire or aluminum.  But like any sophisticated simulation software, it's important to understand how to use it properly to avoid incorrect results.  There are books available and even on-line resources like:

http://www.arrl.org/files/file/Antenna%20Modeling%20for%20Beginners%20Supplemental%20Files/EZNEC%20Modeling%20Tutorial%20by%20W8WWV.pdf

I've used Roy's software for a long time.  A warning ... it can become addictive playing around with antenna models from the comfort of your easy chair.

N3AE