Microcontroller based friend or foe (FoF) detection system (Secondary Radar) is needed in the globe for safekeeping of important locality. The proposed scheme consists of two parts one is aircraft side and other is ground side. Aircraft side is called Transponder and ground side is called Interrogator. Interrogator sends a request from ground to the Transponder through T/R unit. This signal is received by Transponder through T/R unit. Then the signal is received and decoded. Finally Transponder transmits the decoded signal for the reply of Interrogator. If the request is from the friend side...