Don't need particularly large antennas at the Mars end. Basically if you double the size of the antenna at the Mars end you can halve the size of the antenna back here on Earth.
So to establish a link comparable to the Earth-MRO link which has 35m dish here on Earth and 3m antenna at Mars, you could have a 11m antenna at both ends. The hard part is lofting that 11m antenna into Earth orbit in the first place (shipping it to Mars from Earth orbit is easy in comparison).
As an example you could cut the 11m antenna into two pieces, each being a half of a circle with 5.5m radius. That would easily fit into the SpaceX Starship cargo hold. Loft that into orbit, assemble it in orbit, then send it on its way to Mars. The only technical challenges there are flying a spaceship which hasn't reached orbit yet, and performing orbital assembly of a spacecraft (which hasn't been done yet).
Then for completeness put two more of those relay satellites at the leading and trailing Lagrange points for Mars so that we have communication with Mars even when it's on the other side of the Sun.
So to establish a link comparable to the Earth-MRO link which has 35m dish here on Earth and 3m antenna at Mars, you could have a 11m antenna at both ends. The hard part is lofting that 11m antenna into Earth orbit in the first place (shipping it to Mars from Earth orbit is easy in comparison).
As an example you could cut the 11m antenna into two pieces, each being a half of a circle with 5.5m radius. That would easily fit into the SpaceX Starship cargo hold. Loft that into orbit, assemble it in orbit, then send it on its way to Mars. The only technical challenges there are flying a spaceship which hasn't reached orbit yet, and performing orbital assembly of a spacecraft (which hasn't been done yet).
Then for completeness put two more of those relay satellites at the leading and trailing Lagrange points for Mars so that we have communication with Mars even when it's on the other side of the Sun.