Aeronautics and astronautics – Missile stabilization or trajectory control – Automatic guidance
Patent
1989-09-11
1991-02-12
Jordan, Charles T.
Aeronautics and astronautics
Missile stabilization or trajectory control
Automatic guidance
F41G 722
Patent
active
049917943
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to transient suppressors for radar seekers in homing missiles.
2. Description of Related Art
With a radar-guided missile, the seeker output is generally not very smooth. During mid-course, the target signal strength may be low and the receiver output is then rather noisy. Near intercept, the signal is strong, but there may still be substantial irregular spikes on the output due to glint effects, i.e. sudden changes of the point of reflection of the radar signal.
With the seeker output being used to steer the missile, these disturbances cause corresponding disturbances to the missile body motion and to the trajectory itself. During mid-course, the transient noise can seriously disturb the trajectory and can cause a significant amount of induced drag on the missile (and perhaps also use up hydraulic fluid because of fluctuating fin deflection). Nearer intercept, the glint `spikes` may well increase the miss distance.
It is known to incorporate a "mid-course filter" in the system, to smooth out the noise due to low target signal strength. The lag associated with this filter has a slugging effect on the overall system response to guidance signals, but this does not matter until the missile is fairly close to the target, i.e. during the terminal phase. Then, the filter is generally removed, or the lag is drastically reduced.
In the terminal phase, the glint spikes may be clipped by incorporating some limiting in the signal processing.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide suppression of such glint transients throughout the missile flight.
According to the present invention, a radar seeker transient suppressor for a missile in which a control signal is derived from the seeker to control the missile steering and which is substantially independent of pitch and yaw motion of the missile, includes parallel paths for the signal including a filtered path and a relatively unfiltered path and means for selecting the filtered path when the difference between the instantaneous values of the filtered and unfiltered signals exceeds a threshold value and selecting the relatively unfiltered path when the signal difference does not exceed the threshold value.
The filtered and unfiltered paths may be included in each of azimuth and elevation channels, the two channels being switched to the filtered paths in the presence of the above signal difference exceeding the threshold value in either channel.
The filtered path preferably includes a filter comprising a double integrator such as to avoid displacement of the output signal from a linearly varying input signal.
The control signal may be the target sightline angle or target sightline rate.
There are preferably included means for selecting a reduced value of time constant for the filtered path in a terminal phase of the missile flight.
BRIEF DESCRIPTION OF THE DRAWINGS
A transient suppressor for a radar seeker in a homing missile will now be described, by way of example, with reference to the accompanying drawings, of which:
FIG. 1 is a circuit diagram of a filter system built into the azimuth and elevation output channels of the seeker;
FIGS. 2(a) and 2(b) are diagrams of the filtered and unfiltered seeker output signals;
FIG. 2(c) is a diagram of the corresponding switch conditions, selecting between filtered and unfiltered signals; and
FIG. 3 is a circuit diagram of a Type 2 filter system built into the azimuth and elevation channels of the seeker.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, azimuth and elevation output signals from the seeker, .psi..sub.S and .theta..sub.s, represent the sightline angles in space and may be obtained by subtracting body movement signals (from inertial devices) from look-angle signals the immediate output of the seeker. These signals .psi..sub.s and .theta..sub.s are each applied to parallel paths, a filtered path 5 and an unfiltered path 7. The filtered path contains an integrator 6 having a c
REFERENCES:
patent: 3897917 (1975-08-01), Johnson
patent: 4090250 (1978-05-01), Carlson et al.
patent: 4107678 (1978-08-01), Powell
patent: 4160974 (1979-07-01), Stavis
patent: 4198015 (1980-04-01), Yates et al.
patent: 4337427 (1982-06-01), Maudal
patent: 4350983 (1982-09-01), Blaha et al.
patent: 4465249 (1984-08-01), Selince
IEEE Transactions on Aerospace and Electronics Systems, vol. AES-20, No. 6, Nov. 1984, pp. 736-741, "Missile Guidance Based on Kalman Filter Estimation of Target Maneuver", by Y. M. Tang et al.
Benson Anthony J.
Jones Michael A.
Pew Frederick L.
Walter Oliver H. D.
Warman Geoffrey
Jordan Charles T.
Lieberman Rochelle
The Marconi Company Limited
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