Millimeter wave and infrared sensor in a common receiving aperture

A millimeter wave and infrared common imaging aperture for transmitting and receiving of MMW energy to and from space and for receiving IR energy for space comprising:

• a primary parabolic reflector for reflecting optical and millimeter wave energy, said primary reflector having a central axis and a focus on the axis opposite the reflector;
• a feed assembly having a feed horn located on the axis in the vicinity of the focus for feeding millimeter wave energy along a path to the primary reflector for transmission to space and for receiving from space millimeter wave energy reflected to the focus from the primary reflector along the path;
• a dichroic element located facing the primary reflector in the path between the feed assembly and the primary reflector having an axis coaxial therewith and a secondary focus on said axis coaxial therewith and a secondary focus on said axis for reflecting optical energy reflected from the primary reflector towards the secondary focus, said dichroic element being substantially transparent to MMW energy and having non-uniformly spaced apart surfaces for allowing said millimeter wave energy to re-focus onto the feed assembly without significant attenuation;
• optical means for relaying the optical energy reflected from the dichroic element to an output focal plane;
• and
• circuit mans responsive to the millimeter wave energy and the optical energy for producing corresponding MMW and optical image signals and correlation means responsive to the circuit means for producing a correlated superimposed image representation of the image signals.

A method for imaging employing a common aperture in diverse spectral regions comprising the steps of:

• transmitting and receiving millimeter wave (MMW) signals along a path by means of a primary reflector, and a MMW transceiver positioned in confronting relation along an optical axis of the primary reflector;
• focusing the MMW signals by means of a transparent millimeter wave focusing element located on the optical axis between the transceiver and the primary reflector said focusing element being formed of a lens element having non-uniformly spaced apart surface;
• and
• receiving optical signals reflected by means of the primary reflector and a dichroic element located on the millimeter wave focusing element, which dichroic element is aligned with the optical axis, faces the primary reflector and supports the MMW focusing element in the same path as the millimeter wave signals without significant attenuation of said millimeter wave signals.

An infrared (IR) and millimeter wave (MMW) common aperture antenna for transmitting MMW energy to space and for receiving MW and IR energy from space through said common aperture comprising:

• a primary parabolic reflector having a reflective surface sized for defining said common aperture, said primary reflector for reflecting infrared and millimeter wave energy impinging thereon, said primary reflector having a central opening, a central axis passing therethrough and a focus spaced from the reflective surface on the axis;
• a millimeter wave feed assembly having a feed horn located on the axis in the vicinity of the focus of the primary reflector for feeding millimeter wave energy for transmission along the path from the feed horn to the primary reflector for reflection therefrom to space and for receiving millimeter wave energy from space reflected from the primary reflector along the path to the feed horn;
• a dichroic element located in the path between the feed horn and the primary reflector having an axis coaxial with the primary reflector, said dichroic element having a selectively reflective surface facing the surface of the primary reflector and a secondary focus on the axis therebetween for reflecting infrared energy from space reflected from the primary reflector towards the secondary focus, said dichroic element being substantially transparent to MMW energy and shaped for focusing said millimeter wave energy towards said millimeter wave feed without significant attenuation;
• and
• optical means including a cylindrical housing extending through the opening int eh primary reflector and being coaxial therewith, and optical elements located in the cylindrical housing along the central axis, said housing having an input opening in spaced relation from the dichroic element, the optical elements being in recessed spaced relationship with respect to the input opening within the housing and the housing includes a tapered end portion extending from the input opening towards the primary reflector for providing clearance for the millimeter wave energy traveling along the path between the primary reflector and the feed horn.