EP2318878A2

EP2318878A2 - Ir conformal imaging using phased scanning array

Info

Publication number: EP2318878A2
Application number: EP09815440A
Authority: EP
Inventors: Michael A. Gritz; Jar J. Lee
Original assignee: Raytheon Co
Current assignee: Raytheon Co
Priority date: 2008-08-01
Filing date: 2009-07-30
Publication date: 2011-05-11
Also published as: WO2010053608A2; WO2010053608A3; JP2012507691A

Abstract

In one or more embodiments, an uncooled infrared sensor, system, and method include a sensor having an antenna configured to receive infrared radiation, a phase shifting device configured to shift the antenna pattern, and a transducer configured to convert received antenna current into an electrical signal. In various aspects of embodiments, arrays of the infrared sensor can be used for an infrared imaging system with one or more steerable antenna beams that allow for receipt of infrared radiation emitted from a targeted object. By individually controlling the phase shifting device of each sensor in an array, an antenna beam can be scanned over an object, creating one or more pixels with each phase setting. By recording the pixels created from a plurality of phase settings, an IR image corresponding to the object may be created. Such imaging may be accomplished without lenses or other conventional optical devices, and without cryogenic cooling of the sensor housing or sensor components.

Description

IR CONFORMAL IMAGING USING PHASED SCANNING ARRAY

BACKGROUND

[0001] This disclosure relates generally to infrared detection systems. More particularly, to a detector which couples the antenna output directly into the sensor electronics in a phased scanning array, eliminating in one or more embodiments, the need for a photo detector and lens.

[0002] Infrared (IR) detection sensors have a multitude of uses, from military purposes such as missile detection and imaging during nighttime combat operations, to civilian applications such as in the small handheld viewers that are often used by police and fire departments. Two concerns regarding IR imaging are the cost of the IR imaging system, and its weight.

[0003] Traditional "quantum type" IR detectors that have a wide spectral response, such as Ge:Zn, HgCdTe and Si:Ga, generally require cooling systems that bring the detector temperature down to less than 100 K, and sometimes as low as around 4 K. Although these systems offer high detection performance and fast response speed, they are limited by their wavelength-dependent sensitivity, and their cryogenic cooling is both bulky and adds greatly to the detector's cost. The "quantum type" IR detectors which operate without cooling, such as PbS, PbSe, Ge, and InGaAs, are generally limited in their spectral response, and are only sensitive to a narrow range of infrared wavelengths.

[0004] Traditional "thermal type" IR detection sensors can operate at room temperature (around 300 K), over a wide spectrum in the IR range, however these detectors lack fast response times needed for dynamic situations. The slower rate of speed makes "thermal type" IR detectors generally unable to compete in applications relating to missile detection and seeking, for example, and preclude them from many surveillance uses.

[0005] A new "direct detection antenna-coupled" IR sensor disclosed in United States Patent Application Serial No. 11/978,880, filed October 30, 2007 and incorporated in its entirety herein by reference, provides many improvements over

401367712vl "quantum type" and "thermal type" IR detectors. These new "antenna type" IR detectors have a sensitivity reaching that found traditionally only in cryogenically- cooled sensors, without requiring any form of cooling mechanism. This alone dramatically reduces, size, weight, and readiness time. In addition, the "antenna type" detectors are sensitive to polarization and are capable of multicolor sensing. Such sensors can also take advantage of simpler optical systems, as the stop can be positioned for optimum optical performance, instead of having its positioning depend upon the cryogenic cooling system.

[0006] The present application provides improvements over known IR detector systems, by eliminating, in one or more embodiments, the need for the sensor lens and aperture stop all together.

SUMMARY

[0007] One embodiment of this disclosure relates to an IR sensor that is suitable for direct detection of IR radiation, without requiring a lens or optical system. In an embodiment, the IR sensor may include an antenna, an antenna phase shifting device, and a transducer. IR radiation emitted from an object will create an antenna current within the antenna. The controllable phase shifting device will shift the phase of the antenna current, which in turn, will shift an antenna pattern that is associated with the antenna. The transducer will convert the antenna current received by the controlled antenna pattern into an electrical signal, representing at least a portion of an IR image associated with the object emitting the IR radiation.

[0008] Another embodiment of this disclosure relates to an IR imaging system containing at least one linear array of IR sensors, wherein each IR sensor acts as a unit cell. In the embodiment, each IR sensor may have a pair of antenna arms, a phase shifting device, and a transducer. The pair of antenna arms are configured to receive IR radiation, where receipt of IR radiation would induce an antenna current. The phase shifting device, coupled to at least one of the antenna arms, is configured to controllably shift a phase of the antenna current. The transducer, coupled to the phase shifting device and at least one of the antenna arms, is configured to convert the antenna current into an electrical signal representing at least a portion of an IR image. Within the embodiment, the pair of antenna arms and the transducer cooperate to directly detect the IR radiation. The unit cells within each linear array are spatially arranged such that at least one antenna beam is formed. A phase controller configured to individually control the phase shifting device of each unit cell, so that the antenna beam or beams are directionally controllable. A readout circuit, configured to process the electrical signal from each of the plurality of unit cells, provides an output representing at least a portion of a pixel of the IR image.

[0009] Yet another embodiment of this disclosure relates to a method for IR imaging. In the embodiment, the method requires forming at least one antenna beam by adjusting a phase of each of a plurality of IR sensors suitable for direct detection. The method then involves receiving IR radiation emitted from an object within the antenna beam or beams, and detecting antenna current or currents responsive to the IR radiation received by each antenna beam. The embodied method additionally contains scanning the antenna beam or beams in either an azimuth or elevation direction, or both. The method also entails converting the antenna current or currents into corresponding electrical signals, representing at least a portion of an IR image of the object. By additionally processing the electrical signal or signals, an output representing at least one pixel of an IR image of the object is created.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Various features of embodiments of this disclosure are shown in the drawings, in which like reference numerals designate like elements. The drawings form part of this original disclosure in which:

[0011] FIG. 1 is a schematic view of an embodiment of a sensor ;

[0012] FIG. 2 is a cutaway schematic view of an embodiment of a linear array of sensors;

[0013] FIG. 3 is a series of diagrams showing an embodiment of the progression of the scanning beam from a single linear array such as the embodiment in FIG. 2 as it is moved over the surface of a target object; [0014] FIG. 4 is a cutaway schematic view of an embodiment of a planar array comprising a plurality of linear arrays of the sensors of the present invention seen in the embodiment of FIG. 2;

[0015] FIG. 5 is a series of diagrams showing an embodiment illustrating the progression of a plurality of scanning beams from a planar array (e.g., the embodiment in FIG. 4), as it is moved over the surface of a target object; and

[0016] FIG. 6 is a series of diagrams showing an embodiment illustrating the progression of a single scanning beam from a planar array (e.g., the embodiment in FIG. 4) as it is moved over the surface of a target object.

DETAILED DESCRIPTION

[0017] FIG. 1 shows a schematic view of an embodiment of an infrared (IR) sensor 100, suitable for direct detection of IR radiation that is being emitted from an object. IR sensor 100 contains an antenna 110, shown in the present embodiment as a dipole antenna with antenna arms. Antenna arms 110 of the illustrated embodiment are configured to receive IR radiation emitted from an object by inducing an antenna current. Although a dipole antenna arrangement is depicted, the antenna can be of any suitable construction or configuration, including but not limited to gold, aluminum, and/or tin.

[0018] In the illustrated embodiment, antenna current is carried from antenna 110 by IR transmission line 115, which may also be of any suitable construction or configuration including but not limited to gold or aluminum. IR sensor 100 additionally contains phase shifting device 120. Phase shifting device 120 is configured to selectively shift a phase of the antenna current, wherein the phase- shifted antenna current is used to shift an antenna pattern associated with antenna 110. Phase shifting device 120 can be of any number of constructions or configurations, including but not limited to a varactor diode, a ferrite, a PIN diode, or a MOS capacitor, for example. Phase shifting device 120 is seen in the illustrated embodiment as having control line 130, receiving commands from a phase controller (not shown). [0019] Also contained in IR sensor 100 is transducer 140 configured to convert antenna current within IR transmission line 115 into an electrical signal representing at least a portion of an IR image of the object. Transducer 140 can be any device suitable for converting antenna current into an electrical signal, and due to present ease of manufacturing and responsiveness, may be a forward biased Schottky diode. Other transducers that are capable of converting high frequency antenna current to an electrical signal may also be used, including but not limited to other such diodes, a thermal detector, a bolometer, a piezoelectric device, a rectifier, or a photo conductor. The electrical signal is carried through readout line 150 to a readout circuit (not shown).

[0020] FIG. 2 illustrates an embodiment in which a plurality of IR sensors 100 are assembled in a linear array, with each of the illustrated plurality distinguished by ',", or * respectively. The center to center spacing of these IR sensors 100 allow for their phase adjusted antenna patterns to add constructively or destructively to form one or more antenna beams, focusing on a particular area of the target object that is emitting IR radiation. By individually controlling phase shifting devices 120 through control lines 130 from the phase controller, the antenna patterns are shifted in either an azimuth direction, an elevation direction, or both, depending on the particular imaging requirements.

[0021] The scanning nature of linear array 200 is depicted in FIG 3, showing a schematic of a single linear array scanning individual areas of target 300, from area 301 to area 304. If linear array 200 is stationary, then the phase of individual antennae may be adjusted to shift the combined antenna pattern to scan elsewhere on target 300, converting the signals from the array for each phase setting into at least a single pixel of an image, and assembling the pixels generated from the scan into an image representing at least a portion of the target object 300 that is emitting the IR radiation. In an alternative embodiment, the linear array may be non-stationary, such as mounted underneath an airplane for ground imaging, wherein the linear array would only need to scan in a linear pattern, utilizing and compensating for the motion of the airplane to combine the repeating linear scans into a two dimensional image. In a hypothesized application, this "push broom" array could constitute the entire wingspan of the airplane for increased image resolving power. [0022] FIG. 4 illustrates an embodiment in which a plurality of linear arrays 200 are assembled as a planar array 400, with each of the illustrated plurality of linear arrays 200 distinguished by ',", or * respectively. In such an embodiment, the direct imaging may be accomplished as depicted by FIG. 5, wherein a plurality of linear arrays 200' to 200* within planar array 400 scan corresponding linear areas 300' and 300* of target object 300 in parallel, with the advantage of decreasing the overall scan time for target object 300. In an alternative embodiment, illustrated in FIG. 6, the IR sensors of planar array 400 can be phase shifted to selectively receive IR radiation from a single area 310 of target object 300. Again, individually controlling the phase of the IR sensors allows converting the combined signals from the array for each phase setting into at least a single pixel of an image, and assembling the pixels generated from the scan into an image representing at least a portion of the target object 300 that is emitting the IR radiation. Such a "super-pixel" embodiment would have the advantage of greater resolving power, and could still make use of the "push broom" array concept when utilizing the sensors on an airplane for ground imaging.

[0023] In one exemplary aspect of an embodiment to illustrate advantages of Applicants' approach, a phased array (e.g., with 4x4 dipole elements in each conventional non-directional pixel) may be supported by a coherent power combiner (i.e., a 16-way power combiner in this example). When the signals from each of the dipole elements are collectively processed into one "super pixel" as discussed above, this pixel, made by the combination of signals from the 16 element array, becomes directional, with an array beam pattern of about 30 degrees beamwidth. Thus, the super pixel only sees a field of view of about ±15 degrees. Signals outside this beamwidth region will not be coherently combined in phase by the power combiner, because the signals are not from the broadside of any of the individual antenna elements or dipoles. In this case, the noise (i.e., IR power) radiated by an uncooled sensor housing in which the antenna array elements are contained cannot be seen by the super pixel beyond ±15 degrees (i.e., the point where power is approximately 10 dB down in the array side lobe region). As a result, the sensor or camera housing and system components do not need to be cooled below an ambient or environmental temperature of the system. This approach provides tremendous advantages in cost savings, weight, and size of the overall sensor package. [0024] While certain embodiments have been shown and described, it is evident that variations and modifications are possible that are within the spirit and scope of the inventive concept as represented by the following claims. The disclosed embodiments have been provided solely to illustrate the principles of the inventive concept and should not be considered limiting in any way.

STATEMENT OF INDUSTRIAL APPLICABILITY

[0025] The above inventive concept finds utility in infrared detection systems. More particularly, utility is found in a detector that couples the antenna output directly into sensor electronics in a lens-less phased scanning array.

Claims

CLAIMSWhat is claimed is:

1. An infrared (IR) sensor suitable for direct detection, wherein the IR sensor comprises:

an antenna configured to receive IR radiation emitted from an object that induces an antenna current in the antenna;

a phase shifting device configured to selectively shift a phase of the antenna current, wherein the phase-shifted antenna current is used to shift an antenna pattern associated with the antenna; and

a transducer configured to convert the antenna current into an electrical signal representing at least a portion of an IR image of the object.

2. The IR sensor of claim 1, wherein the phase shifting device comprises a variable capacitor coupled to the antenna via an IR transmission line.

3. The IR sensor of claim 1, wherein the phase shifting device comprises a PIN diode.

4. The IR sensor of claiml, wherein the phase shifting device comprises a varactor diode.

5. The IR sensor of claim 1, wherein the transducer comprises a Schottky diode.

6. The IR sensor of claim 1, wherein the transducer comprises a thermal detector.

7. The infrared imaging system of claim 1, wherein the transducer comprises a rectifier.

8. The IR sensor of claim 1, wherein the antenna comprises an antenna element having a pair of antenna arms.

9. An infrared (IR) imaging system, comprising:

at least one linear array of IR sensors comprising a plurality of unit cells therein, wherein each of said unit cells comprises:

a pair of antenna arms configured to receive IR radiation and to induce an antenna current in the pair of antenna arms in response thereto;

a phase shifting device coupled to at least one of the antenna arms and configured to controllably shift a phase of the antenna current;

a transducer, coupled to the phase shifting device and said at least one of the antenna arms, the transducer being configured to convert the antenna current into an electrical signal representing at least a portion of an IR image,

wherein said pair of antenna arms and said transducer cooperate to directly detect the IR radiation,

wherein the plurality of unit cells in the at least one linear array are spatially arranged such that at least one antenna beam is formed,

wherein the at least one antenna beam is directionally controllable by a phase controller configured to individually control the phase shifting device of each unit cell in the at least one linear array; and

a readout circuit coupled to the at least one linear array and configured to process the electrical signal from each of the plurality of unit cells and to provide an output representing at least a portion of a pixel of the IR image.

10. The IR imaging system of claim 9, wherein said at least one linear array comprises a plurality of linear arrays of IR sensors, wherein the readout circuit is further configured to provide an output representing at least a portion of a pixel from each of the plurality of linear arrays.

11. The IR imaging system of claim 9, wherein said at least one linear array comprises a plurality of linear arrays of IR sensors, wherein the readout circuit is further configured to combine the electrical signals from each of the plurality of linear arrays of IR sensors to provide an output representing at least a pixel from each of the plurality of linear arrays.

12. The IR imaging system of claim 10, wherein the plurality of linear arrays of IR sensors are arranged as a planar array.

13. The IR imaging system of claim 11 , wherein the plurality of linear arrays of IR sensors are arranged as a planar array.

14. The IR imaging system of claim 9, wherein the antenna is constructed from materials selected from the group consisting of any conductive metal including, but not limited to aluminum, gold, and nickel.

15. The IR imaging system of claim 9 , wherein the phase controller is configured to individually adjust the phase shifting device of each unit cell in the at least one linear array so that the at least one antenna beam scans in either an azimuth direction, or an elevation direction, or both.

16. A method for infrared (IR) imaging, the method comprising:

forming at least one antenna beam by adjusting a phase of each of a plurality of IR sensors suitable for direct detection;

receiving IR radiation emitted from an object, the IR radiation being within the at least one antenna beam, and detecting at least one antenna current responsive to the IR radiation received by each of the at least one antenna beams;

scanning the at least one antenna beam in either an azimuth or elevation direction, or both;

converting the at least one antenna current into at least one electrical signal representing at least a portion of an IR image of the object; and

processing the at least one electrical signal to provide an output representing at least one pixel.

17. The method of claim 16, further comprising processing the output representing the at least one pixel into an image.

18. The IR sensor of claim 1, further comprising an uncooled housing at least partially enclosing one or more of the antenna, the phase shifting device and the transducer.

19. The IR sensor of claim 1, wherein the transducer comprises an uncooled transducer suitable for operation at an ambient temperature.

20. The IR imaging system of claim 9, further comprising an uncooled housing at least partially enclosing the at least one linear array of IR sensors.

21. The IR imaging system of claim 9, wherein the transducer comprises an uncooled transducer suitable for operation at an ambient temperature.

22. The method of claim 16, wherein said forming, receiving, detecting, scanning, converting, and processing steps are carried out without cooling the plurality of IR sensors below an ambient temperature thereof.