Communications: directive radio wave systems and devices (e.g. – Radar ew – Ecm
Reexamination Certificate
1979-06-27
2001-10-02
Gregory, Bernarr E. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Radar ew
Ecm
C342S013000, C455S001000
Reexamination Certificate
active
06297762
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention pertains generally to electronic counter-measure (ECM) systems and more particularly to an adaptive interferometer for causing errors to be introduced into a tracking radar.
The cost of modern fighter aircraft coupled with the increased effectiveness of ground-to-air missile defense systems has resulted in the development of ECM systems designed to mask such aircraft from ground-based fire control radars. One known type of ECM system designed to protect a penetrating aircraft against a surface-to-air missile which is being guided by a command guidance system is the so-called “Cross-Eye” system. With such a system a portion of the signal transmitted by a control radar, say a ground-based fire control radar, is received at the penetrating aircraft and then is processed to be retransmitted as a pair of equal amplitude, but 180° phase-opposed, signals (referred to hereinafter as the “jamming signals”) in the direction of the ground based fire control radar. The magnitude of the jamming signals is sufficient to mask the skin return from a penetrating aircraft so that the ground-based fire control radar is caused to attempt to track on the jamming signals with the final result that unacceptably large tracking errors are engendered and a guided missile in flight toward the penetrating aircraft is misguided.
Generally, an aircraft employing a “Cross-Eye” system has an appropriate transmitting and receiving antenna located on each of its wings. Thus, a receiving antenna located on a first one of the wings is connected, via an amplifier and requisite transmission lines, to a transmitting antenna disposed on the second wing. In like manner, a receiving antenna located on the second wing is connected, via a 180° phase shifter, an amplifier, and requisite transmission lines, to a transmitting antenna located on the first wing.
It will be appreciated by those of skill in the art that the effectiveness of such “Cross-Eye” systems is dependent upon how well the amplitude and phase of the retransmitted signals are controlled. Unfortunately, however, with transmitting and receiving antennas located on opposite wing tips, it is virtually impossible, even in the best of conditions, to provide the required accuracy in phase and amplitude of the retransmitted, or jamming signals. The problem is even more difficult in the severe vibration environment and over temperature extremes often experienced by any aircraft.
SUMMARY OF THE INVENTION
With this background of the invention in mind, it is an object of this invention to provide an adaptive interferometer which will automatically compensate for differential phase shifts between a pair of receiving and transmitting antennas.
The foregoing and other objects of the invention are attained generally by providing an adaptive interferometer comprising a pair of antennas which may operate as either receiving or transmitting antennas and signal processing means to maintain a desired relationship in phase and amplitude between jamming signals. In the receive mode of operation received signals from a first one of the antennas is split with a first portion thereof being applied, via a quadrature hybrid, to a pair of mixers and a second portion being down-converted to suitable video signals and subsequently applied, via a quadrature hybrid, to a pair of quadrature phase detectors to which reference signals derived from signals received by the second antenna are also applied. After suitable processing, the output signals from the quadrature phase detectors are applied as reference signals to the pair of mixers. The vector sum of the output signals from the mixers, which are proportional-to the product of the input signals, is formed and combined with the signal received by the second antenna, ultimately to cancel that signal. When cancellation of the received signals is achieved, a transmitter is activated. The output signal from the transmitter is passed via a variable attenuator to the second antenna and via a phase shifter, controlled by the microprocessor, to the first antenna, such that the signal radiated by the first antenna is the complex conjugate of the signal that,when combined with the signal received by the second antenna, cancelled that received signal. The variable attenuator, which is also controlled by the microprocessor, is provided in the path between the transmitter and the second antenna to compensate for the insertion loss of the phase shifter to ensure that equal amplitude signals are fed to both antennas.
REFERENCES:
patent: 3072848 (1963-01-01), De Socio
patent: 4117484 (1978-09-01), Shizume
J.H, Dunn et al., “Phenomena of Scintiliation Noise in Radar Tracking Systems,” Proceedings of the IRE, (May 1959 issue), pp. 855-863, May 1955.
Daly, Crowley & Mofford,LLP
Gregory Bernarr E.
Raytheon Company
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