A panel array antenna comprises an input layer including a waveguide network coupling an input feed on a first side thereof to a plurality of primary coupling cavities on a second side thereof, and an output layer on the second side of the input layer. The output layer includes an array of horn radiators, respective horn radiator inlet ports in communication with the horn radiators, and respective slot-shaped output ports in communication with the respective horn radiator inlet ports to couple the horn radiators to the primary coupling cavities. The horn radiators, the respective horn radiator inlet ports, and the respective slot-shaped output ports are integrated in a monolithic layer, which is configured to provide respective output signals from the horn radiators having a polarization orientation that is rotated by a desired polarization rotation angle relative to respective input signals received at the respective slot-shaped output ports coupled thereto.