WHAT IS RADAR ?

 Radar was devised from a radio detection for both ( direction and range ) .

The  radar is consist of 2 main components the main one is the primary radar which is the basic for any radar system , the secondary radar which created to enhance the radar reception and to provide the ATC with more information about the aircraft within its range .

primary radar ( pulse ):

primary radar works on the reflected signal principal , which mean when the radar transmitted the beam of  electromagnetic radio energy encounters any metal object ,its reflected back  to the point from which it was transmitted , this radar is used to detect the aircrafts and it does not required any specific equipment on board the aircraft , the primary radar use ultrahigh and very high frequency that have the minimal static and atmospheric attenuation ,and it use a line of sight path .

there is an external elements which effect the range of the primary radar :

atmospheric attenuation , antena power  and aircraft hight

secondary radar  ( surveillance ) : 

the secondary radar works on the respondent reply signal which is required the active participation of an aircraft which transmits a new return and reply single back to the ground station . when the ground station receive the interrogation single this is to be done by an active onboard device called ( transponder ) .

the transponder also allow the return signal to carry additional information , such as an identification code , aircraft altitude ,etc ……

so do you still believe that aircraft can be disappear from radar screen ?