Dual-frequency millimeter wave and laser radiation receiver

Communications: directive radio wave systems and devices (e.g. – Combined with diverse type radiant energy system – With laser

Reexamination Certificate

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Details

C342S062000, C342S175000, C343S725000, C343S753000

Reexamination Certificate

active

06268822

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to dual-frequency receivers, responsive to both millimeter band radiation and to laser radiation.
Dual-frequency detectors responsive to both microwave and infra-red radiation are found in the target seeking systems of aircraft, both piloted aircraft and guided missiles. To obtain an unrestricted field of view, such sensors are generally located at the nose of the aircraft or missile. The prior art teaches to provide reflector systems to provide directivity and gain for detectors of both wavelengths. Such reflector systems are generally of concave or Cassegrain configuration designed on classical optical principles. To obtain maximum resolution and sensitivity, the aperture of the reflecting system should be as large as possible, and in a missile seeker system generally occupies as much of the missile cross-section as possible. This means that both wavebands have to use the same aperture, and such systems are commonly referred to as common aperture receivers.
In a conventional reflecting system consisting of purely reflecting elements, all wavelengths are brought to focus at the same point. While U.S. Pat. No. 4,282,527 teaches wavelength discrimination by providing a fiber optic cable coaxially with a microwave waveguide at the focus of a reflecting system to guide infra-red radiation and microwave radiation to respective sensors in different locations remote from the focus, the more usual approach is to incorporate one or more dichroic elements in the reflecting system so as to bring different wavelengths to a focus on different detectors at different points in space. Examples of such prior art arrangements are disclosed in U.S. Pat. No. 5,373,302; No. 5,327,149; No. 5,214,438; No. 5,130,718; and No. 3,165,749.
It is also known to provide dual mode detectors where the reflecting system only reflects and focusses infra-red radiation. Microwave radiation is sensed by an array of antennas located either on the surface of a principal infra-red radiation reflector or else behind a principal dichroic reflector which is transparent to microwaves. Such arrangements are disclosed in U.S. Pat. No. 4,477,814 and No. 5,307,077, respectively.
In these prior art arrangements, the component parts of the dual mode detectors, that is to say, the respective detectors responsive to different wavebands and the reflecting systems associated therewith, have been in fixed spatial relationship to each other. Beam steering has involved physically steering the reflecting system and both detectors. This has necessitated the provision of correspondingly robust gimbal arrangements and the need for relatively powerful actuators to overcome the inertia of the reflectors and detectors.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved dual mode tandem seeker configuration in which the disadvantages of the prior art are at least ameliorated.
The present invention provides a tandem laser and millimeter wave receiver for a moving vehicle and for providing directional information of a target to a guidance system for the vehicle. The invention comprises a primary reflector comprising a peripheral region transparent to laser radiation and reflective to millimeter wave radiation; a secondary reflector reflective to millimeter wave radiation and arranged to receive and reflect millimeter waves reflected from the primary reflector; annular laser receiver means comprising a plurality of discrete laser receiver means arranged in a ring behind the peripheral region to receive laser radiation passing through the peripheral region; millimeter wave receiving means arranged to receive the millimeter waves reflected from the secondary reflector; processor means arranged to receive signals from the annular laser receiver means and the millimeter wave receiving means and to generate therefrom target position signals; and means to fasten the primary reflector, the secondary reflector, the annular laser receiver means, the millimeter wave receiving means, and the processor means together within the envelope of the vehicle.
The present invention provides full use of the common receiver aperture areas for the laser and millimeter wave collectors with a common diameter.


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