The EZNEC antenna modelling software by Roy Lewallen W7EL is now available for free download
The software is available from https://eznec.com/
In 2021 Roy W7EL gave a presentation about EZNEC to the G-QRP club Virtual Convention.
Watch Roy, W7EL, explains antenna modelling using EZNEC
https://www.youtube.com/watch?v=WNPghbiJFbU