Proximity fuse for an artillery projectile of the type having reduced aerodynamic resistance of the base

Claim 1

An improved proximity fuse for an artillery projectile of the kind which emits inflamed gases during launch to achieve reduced aerodynamic resistance at the base of the projectile, such inflamed gases radiating interfering electromagnetic waves, such fuse comprising: an ignition circuit actuated by a trigger device for igniting the projectile upon reaching proximity to a target; a radar circuit which transmits Doppler radar waves and receives corresponding Doppler echo waves, such radar circuit comprising a mixer which produces from the transmitted and received waves beat signals S e within a predetermined Doppler frequency band, said mixer also producing parasitic signals within such Doppler frequency band in response to the interfering electromagnetic waves radiated during launch of said projectile; and a first signal processing circuit chain connected to the output of said mixer for comparing the amplitudes of the beat signals produced thereby with a reference threshold level, and which is further connected to said trigger device for actuating it a predetermined time interval τ 1 after a predetermined number N of such beat signals have exceeded such threshold level, such first signal processing circuit chain having a band-pass characteristic covering said Doppler frequency band; such improvements being characterized in that said proximity fuse further comprises a supplementary signal processing circuit chain connected to the output of said mixer and having a band-pass characteristic corresponding to said Doppler frequency band, such supplementary signal processing circuit chain producing output signals in response to signals from said mixer which are within said Doppler frequency band and which exceed a second predetermined threshold level, said supplementary signal processing circuit chain comprising: first delay means for delaying each of such output signals for a first time interval T 1 following the corresponding signal from said mixer, such interval T 1 being less than said predetermined time interval τ 1 ; and second delay means for maintaining each of such output signals for a second time interval T 2 following termination of the corresponding signal from said mixer; and means connected to said trigger device for inhibiting actuation thereof by said first signal processing circuit chain during the time from the end of said interval T 1 to the end of said interval T 2 .