1. Field of the Invention
The present invention relates to apparatus for determining the relative orientation of a missile vis-a-vis a target, but more specifically, the present invention relates to an apparatus for determining the roll angle of the missile vis-a-vis the target
2. Description of the Prior Art
The effectiveness of an anti-aircraft missile against its target can be enhanced by the use of a "shaped" charge in the warhead which explodes as the missile passes by the aircraft. This is because near misses occur more often than direct hits. The use of a "shaped" charge which directs the explosive effect increases the miss distance which allows for a "kill" by a large factor as compared to the use of an ordinary warhead with a spherical charge However, the "shaped" charge can only be effective if it can be detonated when the missile passes by the target and its roll axis has rotated to the proper position. In general, anti-aircraft missiles are not roll-stabilized and are spinning rapidly. Moreover, ordinary radar data only provide information on missile and target position Thus, there is a need in the prior art to monitor missile roll orientation to determine the proper moment for detonation if the improvement offered by the "shaped" charge warhead is to be exploited.
As further background material, in U.S. Pat. No. 4,264,907, filed Apr. 17, 1968, to Durand, Jr. et al, entitled, "Rolling Dual Mode Missile", is disclosed a rolling missile seeker system which is responsive to RF and/or IR energy emanating from a target The system has the capability to switch between guidance modes during the travel of the missile towards its intended target. In U.S. Pat. No. 4,148,028, filed Aug. 2, 1977, to Fujiki, entitled, "Radar System for an Anti-collision System for a Vehicle", is disclosed an anti-collision system for a vehicle wherein a pair of antennas are mounted on the vehicle to receive an echo wave reflected from an obstacle to produce a pair of Doppler signals. The variation of the phase difference of the signals is used to indicate the direction of the relative movement of the obstacle. In U.S. Pat. No. 4,020,339, filed May 19, 1975, to Gustafson, entitled, "System for Determining the Deviation of an Object From a Sight Line", is disclosed a system for determining the deviation of a guided missile form a sight line extending from the missile launcher to a target. In U.S. Pat. No. 3,876,308, filed May 24, 1971, to Alpers, entitled, "Automatic Command Guidance System using Optical Trackers", is disclosed a missile guidance system wherein first and second electro-optical tracking devices are used to track a target and to acquire and track a missile, respectively, by using the angular position data from corrections necessary to bring the missile into line with the target.
The prior art, as indicated hereinabove, include advances in guidance and tracking systems for missiles. However, insofar as can be determined, the prior art does not teach, inter alia, identifying, at a ground receiver the plane of a missile fixed with respect to it body frame by comparing the ratio of signal(s) transmitted from the missile and received at the ground receiver in two cross-polarized directions as taught by the present invention.