Critical views on present passive radars performance as compared with that of active radars

Passive radars have some renown advantages when used as sources of information for air surveillance and air space control systems. Their main advantage is a concealed operation due to the usage of signals of opportunity and especially signals emitted by commercial broadcasting stations. Many parameters of the passive radars and namely: resolution and estimation of air object coordinates depend on quality of captured signals. Some examples of range resolution achieved using UHF radio and TV broadcasting signals as given in the enclosed references are discussed.. The range uncertainty is explained and its influence on range estimation accuracy is indicated. The influence of air coverage volume on the number and localization of emitters has been explained. A comparison of some fundamental parameters of active radars used nowadays widely as sources of information on situation in the air space used for air traffic control or defense systems with parameters achieved by passive radars (PCL) is then presented. Conclusion resulting from the discussion of both active and passive radars features is that passive radars do not match several of temporary requirements obligatory for the ATC or air defense systems and presently they are not able to replace active radars but can be used only as a supporting sources of information, which can improve the active radar coverage for small RCS objects (“stealth”) and also improve low altitude detection.