Example for Theoretical and conceptual framework for PhD research proposal

I am writing my PhD research proposal at THz antenna.
I need a exsamle for "Theoretical and conceptual framework" at electronics engineering or at antenna engineering.
Can some one post an example for that?
Regards,
Uri

Cellphones used to need an extendable antenna a few inches long. This is no longer the case. It might be interesting to explore and compare circuitry years ago with today's. It might seem like a little thing but someone had to do a lot of research and development to make it possible.