A conventional narrow beam scanning antenna radar systems are inept in detection of small RCS drones. A wide-beam choke horn antennas are proposed for the surveillance system in order to detect and track a small object like drones. The proposed choke horn antenna is derived from sector beam pattern synthesis. The designed antenna has a wide beam width of ±70° and has a low field level in the horizontal plane (-40dB w.r.t. main beam), which is crucial for high isolation among Rx and between Tx and Rx as well.