How to interface AX5031 to 400ohm impedance antenna?

The title says it all, there is information regarding the AX5043, but I can’t find anything specific to the AX5031.

Hi Bob, the AX5031, like our other radios, implements a Class-E amplifier and therefore requires a dedicated matching network dependent not only on the frequency of operation, but also on the output power, and of course the antenna. We don’t have a reference design for a 400 Ohm antenna.
You can find more info on how to proceed with this matching process here: FAQ: How to operate AX5043 at 27 MHz