A matched horn coupler assembly is used in a RF rotational joint for conveying an electromagnetic signal. The coupler assembly includes first and second feed horns defining respective first and second horn longitudinal axes intersecting one another at an intersection point. The first and second feed horns connect to a mirror for conveying the signal there between with the intersection point lying on a reflecting surface of the mirror which defines a normal direction thereof at the intersection point. The normal direction is equally angularly spaced from both the first and second horn longitudinal axes. First and second lenses connect to the respective first and second feed horns and focus the signal there between and at the intersection point. At least one of the first and second feed horns is rotatably connected relative to the mirror about the respective horn longitudinal axis.