A dual beam monopulse antenna system includes a flat plate antenna (10). The antenna (10) comprises a plurality of slotted waveguides (20) which transmit radiation through slots (28). The antenna is divided into quadrants (12, 14, 16, 18) for monopulse operation. Each of the quadrants is provided with primary and secondary feed lines which are connected through directional couplers (42-136) to connecting lines (146-192) to the slotted waveguides (20). The primary feed lines (26, 28, 30, 32) are connected to a primary monopulse comparator network and the secondary feed lines (34, 36, 38, 40) are connected to a secondary monopulse comparator network. The summation terminals of the monopulse comparator networks are connected to a switch network (322). The azimuth differential terminals of the monopulse comparator networks are connected to a switch network (332). The elevation differential terminals of the monopulse comparator networks are connected to a switch network (342). The switch networks are set to a first state to generate a pencil beam in which the slotted waveguides (20) are connected to the system summation terminal (330), system azimuth terminal (340) and system elevation terminal (350). In a second state the switch networks are set such that the slotted waveguides (20) are connected to both the primary and secondary feed assemblies and therefore to the primary and secondary monopulse comparator networks. In the second state the slotted waveguides (20) produce a shaped search beam which has a greater vertical dimension than horizontal dimension. The antenna system, however, operates in the monopulse mode with both antenna beams. The system can be rapidly switched from one beam shape to the other. Polarization discs (458, 460) are positioned parallel to and spaced apart from antenna (10) to select a polarization desired for the beam produced by the antenna system by rotation of the polarization disc (458, 460).
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