This disclosure generally relates to imaging sensors, and more particularly, to an antenna-coupled radiation sensor.
Radiation imaging devices, such as digital sensors or cameras, are useful for many applications, including scientific equipment, surveillance equipment, targeting equipment, and other military applications. These devices may detect radiation such as infrared radiation or microwave radiation.
According to one embodiment, a radiation sensor comprises a first pixel and a second pixel. The first pixel comprises a first plurality of antenna elements, a first photodetector, and one or more first feed lines coupling the first plurality of antenna elements to the first photodetector. The second pixel comprises a second plurality of antenna elements, a second photodetector, and one or more second feed lines coupling the second plurality of antenna elements to the second photodetector. The second pixel is an off-axis pixel. Signals feeding each of the second plurality of antenna elements are varied such that an effective radiation pattern of the second plurality of antenna elements is reinforced in a desired direction and suppressed in an undesired direction.
Some embodiments of the present disclosure may provide numerous technical advantages. A technical advantage of one embodiment may include the ability to align pixel antenna gain with optical field angle for optimal detection of incoming radiation. A technical advantage of one embodiment may also include the capability to provide pixels that maximize antenna gain in the direction at which electromagnetic energy from the scene is sampled. A technical advantage of one embodiment may also include the capability to provide a cold-shielding effect without using temperature control and cooling, which may provide additional benefits such as reduced size, weight, cost, and power requirements. A technical advantage of one embodiment may also include the capability to reduce lens design constraints and improve tolerance of lens interchange due to the elimination of a physical coldshield outside the lens.
Although specific advantages have been disclosed hereinabove, it will be understood that various embodiments may include all, some, or none of the disclosed advantages. Additionally, other technical advantages not specifically cited may become apparent to one of ordinary skill in the art following review of the ensuing drawings and their associated detailed description.
A more complete understanding of embodiments of the disclosure will be apparent from the detailed description taken in conjunction with the accompanying drawings in which:
It should be understood at the outset that, although example implementations of embodiments of the invention are illustrated below, the present invention may be implemented using any number of techniques, whether currently known or not. The present invention should in no way be limited to the example implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale.
Examples of energy detector 130A may include any device operable to measure detected radiative input 110, such as infrared or high-frequency microwave radiation. Teachings of certain embodiments recognize two separate categories of energy detectors 130A. The first category is rectifiers, such as diode rectifiers. The second category is photodectors, including photovoltaic, photoconductive, and pyroelectric detectors, and example of which is shown in
Sensor electronics 140A may include any device operable to receive measurements from energy detector 130A and produce a sensor output 150. Sensor electronics 140A may include, but are not limited to, preamplifier and multiplexer circuits.
Antenna-coupled radiation sensor 100B features one or more antennas 120 and electronics 125B. In this example, electronics 125B include a rectifier 130B and sensor electronics 140B. Examples of sensor electronics 140B may include, but are not limited to, preamplifier and multiplexer circuits. In one example, antenna-coupled radiation sensor 100B feeds infrared or microwave waveforms into rectifier 130B, which captures the magnitude of ultra-high frequency infrared or microwave signals and passes that magnitude, then into a preamplifier and multiplexer circuit. In some examples, diode rectifier 130B is a Schottky diode.
Teachings of certain embodiments recognize the capability to use multiple antenna-elements in individual image pixels to increase sensitivity by increasing collection area. For example, antenna dimensions for an imaging system may be smaller than pixel size because diffraction effects create a blur width of 2.44λF, where λ is the wavelength and F is the f-number of the imaging lens. As an example, the diffraction blur limit of F/2 optics is approximately 5 wavelengths, which may be approximately the size of a pixel in some infrared imaging systems. However, teachings of certain embodiments recognize the capability to provide multiple antenna-coupled detectors in a single pixel for shorter and longer wavelengths.
In some embodiments, a radiation sensor may include multiple pixels, each pixel including one or more antenna elements. In these embodiments, pixels may include both on-axis and off-axis pixels. An on-axis pixel is a pixel centered on the optical axis of a lens. An off-axis pixel is a pixel not centered on the optical axis of a lens.
In some embodiments, pixels may be arranged in one-dimensional, two-dimensional, or three-dimensional arrays. For example, in one embodiment, a two-dimensional array has one on-axis pixel centered on or very near the optical axis of a lens and a plurality of off-axis pixels not centered on the optical axis of a lens. In another embodiment, the optical axis of a lens may not align with any pixels, and all of the pixels of an array may be off-axis pixels.
In yet another exemplary embodiment, the alignment of the optical axis and pixels is approximated such that an on-axis pixel is only approximately aligned with the optical axis. For example, an array may actually have multiple pixels located relatively near the optical axis and multiple off-axis pixels located further away from the optical axis.
Accordingly, teachings of certain embodiments recognize the capability to adjust the antenna gain pattern of the antenna array for off-axis pixel 200b.
Teachings of certain embodiments recognize the capability to align lens and antenna gain for optimal detection of incoming radiation. For example,
Teachings of certain embodiments also recognize that reducing antenna gain for angles not subtended by the aperture minimizes detection of flux emanating from sensor internal parts. In this way, a cold-shielding effect may block unwanted flux from hot sensor parts that otherwise would might flood the focal plane and dilute image contrast. Thus, teachings of certain embodiments recognize the capability to provide a cold-shielding effect without using temperature control and cooling, which may provide additional benefits such as reduced size, weight, and power requirements.
As explained above, teachings of certain embodiments recognize the capability to use multiple antenna-elements in individual image pixels to increase sensitivity by increasing collection area.
In some embodiments, antenna elements 310a includes a metalized coating, formed photolithographically, and separated from ground plane 320a by a dielectric coating. In this example, antenna elements 310a are patch shapes. However, antenna elements 310a may be of any suitable shape, including but not limited to rectangular patches, dipoles, folded dipoles, or any element suited to be placed in an array. For example, teachings of certain embodiments recognize that dipoles may be used to detect infrared radiation.
Antenna elements 310a may be dimensioned to any suitable size. For example, dimensions may depend on signal frequency, substrate dielectric, array layout, and other parameters. In this example, the width and length of antenna elements 310a represents one-third of the wavelength of the radiation being sensed. Thus, for 300 GHz microwave sensing, each individual element 300a will be 1 millimeter square; for 2.5 THz thermal sensing (12 micrometer wavelength), each element will be 4 micrometers square. Teachings of certain embodiments recognize that such antenna element sizes are within the capabilities of modern photolithography, which can maintain 0.25 micrometer or smaller dimensional accuracy.
In the exemplary pixel 300c′, rear feed lines 314c′ provide an equal path length between each antenna element 310c and detector 340c. Teachings of certain embodiments recognize that providing an equal path length to each antenna element may optimize antenna gain for incoming rays perpendicular to the antenna plane. For example, the feed-line structure of pixel 300c′ may correspond to the on-axis pixel 200a of
In this example, rear feed lines 314c″ do not provide an equal path length between each antenna element 310c and detector 340c. Rather, in this example, rear feed lines 314c″ have uniformly different path lengths between antenna elements 310c and detector 340c. This example optimizes incoming rays at a 30-degree angle to the antenna plane. Thus, in this example, the feed-line structure of pixel 300c″ may correspond to the off-axis pixel 200b of
In this example, the length of rear feed lines 314c″ to each antenna element 310c increases two grid spaces moving away from detector 340c, whereas actual distance increases four grid spaces. In this example, increasing the length of rear feed lines 314c″ in this manner creates a squint of 30 degrees in one plane. Similar teachings may be applied to create squint angles in two planes and/or three planes.
In these examples of pixel 300c′ and 300c″, antenna sensitivity as a function of direction is fixed by the design of antenna feed lines within the antenna array of the pixel. Teachings of certain embodiments recognize that delineation of feed lines may be accomplished through any suitable method, including but not limited to photolithography, such as done in fabrication of integrated circuit chips. Teachings of certain embodiments also show that realization of these desired feed line lengths in practical hardware may require consideration of additional well-understood design parameters like transmission line losses and propagation velocity, particularly for wavelengths as short as mid-wave infrared. Consequently, design and shape of feed-length dimensions may need to consider such detailed effects as the microstrip spacing from the ground plane, the dielectric constant of the insulating substrate, the microstrip line width and thickness, and the inductance and capacitance of the feed-line patterns. In addition, teachings of certain embodiments recognize that the front-face feed structure of
Teachings of certain embodiments recognize the capability to reduce or eliminate the need for a coldshield, such as coldshield 504. Accordingly,
In the illustrated embodiment, external lens 501′ creates a scene image on detector array 502′ that is mounted on a cryogenic cooler 503, as before. Coldshield 504′ (not shown) is greatly reduced in size, and is used primarily to block radiative heatload on the cold parts. Optical stop 505′ is located within the optics, rather than within the cryogenic package. Window 506′ is closer to detector 502′, since no space is required for the coldshield. Lens 501′ is smaller, since it is located closer to detector array 502′, and since it is more symmetrically disposed about optical stop 505′.
Comparing
Modifications, additions, or omissions may be made to the systems and apparatuses described herein without departing from the scope of the invention. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. Additionally, operations of the systems and apparatuses may be performed using any suitable logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
Although several embodiments have been illustrated and described in detail, it will be recognized that substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the appended claims.
To aid the Patent Office, and any readers of any patent issued on this application in interpreting the claims appended hereto, applicants wish to note that they do not intend any of the appended claims to invoke paragraph 6 of 35 U.S.C. §12 as it exists on the date of filing hereof unless the words “means for” or “step for” are explicitly used in the particular claim.