Radio frequency detection method and apparatus

Abstract

Detection systems and methods using multiple detector arrays and polarized beam elements for single frequency or multi-frequency imaging of objects or scenes.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE This disclosure relates to high frequency electronic systems, and more particularly to detection systems and methods of making and using same. [Background technology]

[0002] Radio frequency systems can be used to detect radiation received from an object or scene and then generate an image by processing the detected radiation. There are both active and passive imaging systems. In active imaging, a radiation source (e.g., a terahertz source) can be used to illuminate the object or field of view and provide radiation for detection. In passive imaging, there is no illumination source. Instead, the system receives radiation emitted from the object or scene itself. The radiation detected can be a single frequency (e.g., a band centered around a single frequency) or, in some cases, multiple frequencies (e.g., multiple separate or overlapping bands).

[0003] A method and apparatus for multi-frequency imaging is provided in US Pat. No. 5,399,633, which describes an imaging system having at least one terahertz receiver adapted to receive radiation of different frequencies over the same time period, an image processor, and a composite image generator, the image processor providing image data relating to a field of view at each of the respective frequencies, and the composite image generator generating composite image data relating to a common field from at least a portion of the image data provided by the image processor.

[0004] Additionally, the field of view can be scanned, for example using a scanning mirror or reflector, to direct radiation towards one or more detector arrays. As described in UK patent application no. 2006 / 023991, a terahertz detection apparatus may include one or more detectors and a scanning mechanism for scanning the field of view, the scanning mechanism including (i) a detection system for determining a position of an object of interest, and (ii) a steering mechanism capable of receiving control signals based at least in part on an output of the detection system, and transmitting steering signals for use in steering the scanning mechanism.

[0005] However, there remains a need for improved detection systems and methods that can fully utilize the radiation available from a source or scene to provide optimized imaging in an efficient and scalable arrangement while maintaining any necessary spatial alignment requirements. In addition, there remains a need for systems that have layouts and components that can be efficiently machined. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2013 / 117920 [Patent Document 2] UK Patent Application Publication No. 2519233 Summary of the Invention [Means for solving the problem]

[0007] According to embodiments, a detection system is provided that includes a first detector array, a second detector array, and a polarizing element, such as a polarizing plate, located between the first and second detector arrays. The polarizing plate is positioned to pass a first radiation signal having a first polarization toward the first detector array and to reflect a second radiation signal having a second polarization toward the second detector array. In some embodiments, the polarizing plate includes a wire grid at a 45 degree angle with respect to the first and second detector arrays, the first polarization being vertically polarized and the second polarization being horizontally polarized.

[0008] According to some embodiments, a system is provided that includes a first electronic device, a second electronic device, a power source, and an unequal power splitter. In a particular aspect, the power source is coupled to an input of the unequal power splitter via a waveguide and sends a power signal (e.g., a local oscillator signal) to the unequal power splitter. In addition, a first output of the unequal power splitter is coupled to the first electronic device via the waveguide, and a second output of the unequal power splitter is coupled to the second electronic device via the waveguide. In some embodiments, the unequal power splitter is configured to provide a first portion of the power signal through the first output and a second portion of the power signal through the second output, where the first portion is greater than the second portion. The unequal power signals may be used to drive one or more frequency multipliers having different levels of efficiency.

[0009] According to some embodiments, a detection system is provided. The detection system includes, for example, a first detector block, a local oscillator (LO) source, and one or more intermediate frequency (IF) processing circuits. In some embodiments, the first detector block includes one or more heterodyne mixer elements, one or more LO input waveguide channels configured to provide an LO signal from the LO source to the one or more heterodyne mixer elements, one or more waveguide feed horns configured to provide a detected radio frequency (RF) signal to the one or more heterodyne mixer elements, and one or more IF output channels configured to provide an IF signal from the one or more heterodyne mixer elements to the one or more IF processing circuits. The one or more waveguide feed horns and the one or more LO input waveguide channels extend along a first axis of the first detector block, and the one or more IF output channels extend along a second axis of the first detector block, the first axis and the second axis being perpendicular. According to an embodiment, the input channel and the output channel are in orthogonal planes. Although described as vertical in some examples, some embodiments may include an IF output channel that is in a different non-orthogonal plane than the waveguide feed horn and / or the LO input.

[0010] According to an embodiment, a detection system is provided, comprising a first detector array block and a second detector array block stacked on the first detector array block. In this example, each of the first and second detector block arrays comprises at least one signal input extending along a first axis, at least one power input extending along the first axis, and at least one signal output extending along a second axis, the first axis and the second axis being perpendicular. In a particular aspect, each of the first and second detector block arrays comprises one or more stacking notches. In addition, the first and second detector block arrays may be identical modular units. In addition, the one or more signal inputs for each of the first and second detector array blocks may comprise at least two rows of feed horns and at least two columns of feed horns (e.g., 2x2 or 2x4 arrays).

[0011] According to an embodiment, a detection module for a scalable imaging system is provided. The module may include one or more signal inputs extending along a first axis, one or more power inputs extending along the first axis, one or more signal outputs extending along a second axis, and a first stacking notch, the first and second axes being perpendicular. In a particular aspect, the signal inputs include one or more radio frequency feed horns, the power inputs include one or more local oscillator channels, and the signal outputs include one or more intermediate frequency output channels. According to an embodiment, the feed horns and oscillator channels are in a first plane, while the IF channels are in a second orthogonal plane. The module may further include a second stacking notch, and both notches may be angled. In some embodiments, the module is a block including a first side, a second side, a third side, a fourth side, a fifth side, and a sixth side, where the first and second sides are opposite the detection module, the third and fourth sides are opposite the detection module, and the fifth and sixth sides are opposite the detection module. Additionally, in some embodiments, one or more signal inputs are located on the first side, one or more power inputs are located on the second side, one or more signal outputs are located on the third or fourth side, a first stacking notch is located on the fifth side, and a second stacking notch is located on the sixth side.

[0012] According to an embodiment, a detection method is provided. The method may include receiving a first radiation signal having a first polarization at a first detector block of a camera, where the first radiation signal is received from a radiation source through a polarizing plate, receiving a second radiation signal having a second polarization at a second detector block of the camera, where the second radiation signal is received from the radiation source as a reflected signal from the polarizing plate, processing the first radiation signal to form first detection information, and processing the second radiation signal to form second detection information. In some embodiments, the method includes passing at least one of the first and second received radiation signals through a polarization rotation element prior to the processing step.

[0013] According to some embodiments, a method for manufacturing a detector block is provided. The method may include machining a first housing component including a first radio frequency (RF) channel portion, a first local oscillator (LO) channel portion, a first intermediate frequency (IF) channel portion, a polarization rotation portion, and a first mixer mounting cavity, and machining a second housing component including a second radio frequency (RF) channel portion, a second local oscillator (LO) channel portion, a second intermediate frequency (IF) channel portion, a polarization rotation portion, and a second mixer mounting cavity. Additional steps may include mounting a heterodyne mixer in at least one of the first and second mounting cavities, and attaching the first housing component to the second housing component to form a first detector block. Additionally, in some cases, the first RF channel portion and the first LO channel portion are machined along a first axis of the first housing component, the first IF channel portion is machined along a second perpendicular axis of the first housing, the second RF channel portion and the second LO channel portion are machined along a first axis of the second housing component, and the second IF channel portion is machined along a second perpendicular axis of the second housing. An integrated array can be formed by attaching a second detector block to the first detector block.

[0014] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate various embodiments. [Brief description of the drawings]

[0015] [Figure 1] 1A and 1B are diagrams illustrating a detection system according to some embodiments. [Diagram 2] 2A-2C are diagrams illustrating waveguide sections according to some embodiments. [Diagram 3] FIG. 3 is a schematic diagram illustrating a system according to some embodiments. [Figure 4] 4A and 4B are block diagrams according to some embodiments. [Diagram 5] 5A-5C are diagrams illustrating rotate and divide components according to some embodiments. [Figure 6] FIG. 6 is a diagram illustrating image formation according to an embodiment. [Figure 7] FIG. 7 is a diagram illustrating image formation according to an embodiment. [Figure 8] FIG. 8 is a diagram illustrating image formation according to an embodiment. [Figure 9] FIG. 9 is a diagram illustrating image formation according to an embodiment. [Figure 10] FIG. 10 is a flow diagram illustrating a process according to some embodiments. [Figure 11] FIG. 11 is a flow diagram illustrating a process according to some embodiments. [Figure 12] 12A-12C are diagrams illustrating a detector block and assembly process according to some embodiments. [Figure 13] 13A and 13B are diagrams illustrating a system according to some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] In the security sector, detection and identification of threats posed by people is a key area of ​​concern. There remains a need, particularly for systems that can achieve detection at significant distances, in outdoor environments, and in real time, so that threats can be eliminated before they escalate. However, particularly for passive systems, such detection and identification may require the ability to deal with changes in outdoor weather, atmospheric, geographic, and seasonal conditions. Aspects of the present disclosure address these demands with detector setups and geometries that allow maximum signal capture while maintaining the desired temporal and spatial alignment for real-time threat analysis. The systems and methods described herein can be used for detection and identification of weapons, threats, illegal items, and stolen goods, and may be deployed in both indoor and outdoor environments.

[0017] According to embodiments, a polarization beam combiner is used to align and overlap the fields of view of one or more detectors, along with a waveguide polarization rotator and adjustable local oscillator power to provide a compact and configurable front-end receiver module layout, enabling the use of a wide range of frequencies while simultaneously reducing cost. Aspects of the present disclosure allow for the use of multiple frequencies, or simultaneous capture of dual-polarized single-frequency data, or any combination of the above. For example, some embodiments may be used to capture data using 1-4 frequencies.

[0018] 1A and 1B show a detection system 100 according to some embodiments. For example, the system may be a radio frequency detection system such as a terahertz camera. FIG 1B shows a top view of the system 100 shown in FIG 1A.

[0019] 1A, the system 100 may include a first detector array 102, a second detector array 104, and a polarizing element 106, such as a polarizing plate. As shown in FIG. 1A, the polarizing plate 106 may be placed between the detector arrays 102, 104 to pass and / or reflect a radiation signal 110 from a source 108 to the detector arrays 102, 104. According to an embodiment, a first radiation signal 112 having a first polarization (e.g., vertical polarization) passes through the polarizing plate 106 toward the first detector array 102, and a second radiation signal 114 having a second polarization (e.g., horizontal polarization) is reflected from the polarizing plate 106 toward the second detector array 104. In the illustrations of FIGS. 1A and 1B, both radiation signals originate from a source 108, which may be, for example, one or more humans emitting radiation 110 toward the detection system 100. The other sources may include, for example, a single object of interest, such as a vehicle or structure, or an entire scene having multiple objects. Additionally, the radiation signal 110 from source 108 may actually originate from a secondary source (not shown), similar to an active detection system, in which case the signal 110 may reflect off of source 108 back towards system 100. That is, system 100 may be part of a passive or active detection implementation.

[0020] According to some embodiments, the system 100 does not require any optical elements to be placed between the polarizing plate 106 and either the first or second detector array 102, 104. Although two detector array blocks 102, 104 are shown in FIGS. 1A and 1B, additional array blocks may be used in the system 100, such as on top of or adjacent to the arrays 102, 104. Furthermore, while the system 100 is shown with spaced apart detector array blocks 102, 104, in some embodiments, the arrays may be joined together. For example, in some embodiments, the detector array block 102 may be stacked on top of the array block 104, or may be placed immediately adjacent to and connected to the block 104, as shown in FIGS. 12A-12C. In such cases, the polarizing plate 106 may not be used.

[0021] Each of the detector arrays 102, 104 may include one or more input channels, such as, for example, feed horns 116, 118, 120. According to an embodiment, the feed horns capture radiation from the source 108 and pass the received signal to other parts of the system for further processing. For example, the feed horn 116 may capture radiation 112 that has passed through the polarizing plate, while the feed horns 118 and 120 may capture radiation 114 that has been reflected from the polarizing plate 106. Although a circular waveguide is shown in this example, other shaped waveguides (e.g., elliptical or rectangular waveguides) may also be used.

[0022] According to some embodiments, the first detector array includes a first plurality of feed horns having a first width and spaced apart by at least the first width, and the second detector array includes a second plurality of feed horns having a second width and spaced apart by at least the second width. That is, the feed horns may be substantially spaced apart. Additionally, a first processing circuit may be located between the feed horns of the first detector array and a second processing circuit may be located between the feed horns of the second detector array.

[0023] Although shown in Figure 1A as 2x2 and 2x4 arrays, respectively, the first detector array 102 may have more than two feed horns in each of the horizontal and vertical directions of the array, and similarly the second detector array 104 may have more than two feed horns in each of the horizontal and vertical directions of the array. According to an embodiment, the detector array blocks 102, 104 may be formed of multiple sub-blocks, as shown, for example, in Figures 4A, 4B, and 12A-12C.

[0024] As shown in FIG. 1B, according to some embodiments, the polarizing plate 106 may be aligned at a 45 degree angle with respect to each of the first and second detector arrays 102, 104. However, the plate 106 may be aligned at a different angle in a particular arrangement, for example depending on the particular alignment or spacing of one or more of the detectors 102, 104. That is, the polarizing plate may be aligned at an angle greater than or less than 45 degrees. In some embodiments, the polarizing plate includes a wire grid structure. In this example, the wire grid operates to pass vertically polarized radiation 112 from the source 108 while reflecting horizontally polarized radiation from the source 108. Although a wire grid and horizontal / vertical polarization are described, multilayer dielectric polarizer plates and frequency selective surfaces may be used in some cases. Although shown as a flat plate, the polarizing plate 106 need not have a flat surface and may take the form of a lens or other curved structure. According to an embodiment, the polarizing element (e.g., 106) has low insertion loss in both pass and reflect modes. In certain embodiments, the polarizing element operates as a free-space polarization duplexer or an ortho-mode transducer.

[0025] As shown in Figures 1A and 1B, the system may further include a scanning mechanism 126. The scanning mechanism 126 may be based on one or more movable mirrors that reflect incoming radiation towards one or more detectors, such as arrays 102, 104. An image may be recovered by scanning (e.g., moving) the mirror(s) so that the detector(s) effectively follows a scan raster for the field of view. The mirror(s) may move to generate a scan raster that includes spaced scan lines, and to generate the scan raster, the mirrors may move in different ways in different directions. For example, the mirror may reciprocate about a first axis to create scan lines combined with a step rotation about a second axis to set the scan line spacing. Structurally, in some embodiments, the scanning mechanism may include (i) a mirror structure mounted for rotation about a first axis, (ii) an intermediate support structure for supporting the mirror structure, which is mounted for rotation about a second axis, (iii) a base support structure for supporting the intermediate support structure, (iv) a mirror drive mechanism mounted in part to the intermediate support structure and in part to the mirror structure for driving the mirror structure to rotate about the first axis, and (v) an intermediate drive mechanism mounted in part to the base support structure and in part to the intermediate support structure for driving the intermediate support structure to rotate about the second axis, whereby the mirror structure may be driven to rotate about either or both of the first and second axes. The mirror itself may be a thin metal (e.g., aluminum) mirror, including a thin (e.g., 0.5 mm) sheet with or without reinforcing ribs.

[0026] An adaptive scanning mirror may be used to scan the field of attention in a continuous detection of the field of view. "Field of view" in this context is intended to indicate the range of the scene seen or detected by either the detection system or one or more detector elements. That is, "field of view" is intended to indicate the range of the scene currently being imaged or detected by the detector, such as by the movement of the scanning mirror(s). For example, in imaging to provide successive frames of a scene, each frame will indicate the field of view. "Field of attention" in this context is intended to indicate the maximum range of the scene that can be made accessible to the system / detector by steering the scanning mirror(s) without moving the detector. With respect to the detection system 100, the field of attention indicates the angular range over which the detection system can detect an object of interest. According to an embodiment, the detector output is converted to graphical data to support a screen-based representation of the detected field of view, and may be combined, for example, to form a composite image of the field of attention. In addition, the fields of view of different bands may be combined to form a composite image of the field of view.

[0027] 2A, a cross-sectional view of a portion of the detector array 102 is shown according to some embodiments. A portion of various waveguide channels according to an embodiment is shown, including the feed horn 116 and the local oscillator (LO) channel 202. Further detail A shows a polarization rotation element 204 that may be located in one or more channels, such as the feed horn 116 or the connected waveguide channel for the RF path, according to some embodiments. The polarization element 204 may rotate the polarization of the signal along the channel (e.g., from horizontal to vertical polarization or vice versa) and may include multi-stage mode conversion. This may be, for example, to prepare the signal for further processing or to reduce propagation losses along the length of the channel. The further processing may be, for example, in a mixer stage 206. According to an embodiment, a three-step mode converter is provided, where each step rotates the electric field orientation by about 30 degrees each step by coupling one mode from the former to the latter. According to some embodiments, a two-step rotation is provided, where each step involves a 45 degree rotation. 2A also shows a signal output 208, e.g., an IF signal, from the mixer stage 206 that extends upward and / or downward and perpendicular to the plane of the feed horn 116 and the LO channel 202. That is, the output signal channel may be orthogonal to the input signal channels (e.g., the feed horn and the LO channel). According to an embodiment, the IF output channel 208 may include a coaxial cable for transporting the signal.

[0028] In some embodiments, as shown in Figures 2B and 2C, a waveguide, such as a channel of the detector array 102, 104, may be machined as two halves and then connected. Figure 2B shows a low-loss waveguide using a mirror half waveguide split along the top wide wall (i.e., along a wider cross section) to reduce loss in some cases. In this example, the first half 210 is combined with the second half 212 to form a waveguide with a split 214, where the split is along the wider top and bottom surfaces of the waveguide channel. In other cases, as shown in Figure 2C, a waveguide may be formed by the first half 222 and the second half 224, where the split 226 is through the shorter sidewall of the resulting waveguide. In some arrangements, having the split 214 may result in less loss than having the split 226. Thus, according to some embodiments, the rotating element 204 may be used to rotate the signal from a high-loss split waveguide (e.g., 226) to a low-loss split waveguide (e.g., 214). Depending on the input signal, the arrangement may be reversed.

[0029] Waveguides are most easily formed by machining a slot of suitable dimensions into either face of a metal block. As shown in FIG. 2B, at higher frequencies, e.g., frequencies above 30 GHz, it is often necessary to split the waveguide at the midpoint of its wide wall to minimize resistive losses. This is because at higher frequencies, resistive losses become dominant as the current flows, which is limited by the skin effect, making the surface finish very important. In addition, the current in a rectangular waveguide travels along the wide wall and down the narrow wall. Thus, while the propagating signal is relatively immune to small gaps in the wide wall, gaps in the narrow wall cause signal loss, since the gap effectively creates an open circuit for the current.

[0030] In certain embodiments, the problem of increased loss when a waveguide is split across a narrow wall versus a wide wall is frequency dependent. As frequency increases, loss increases because any small gap between surfaces effectively represents a larger fraction of a wavelength. It becomes increasingly difficult to clamp the waveguides together, and therefore more difficult to close the gap, because less space is required for the clamping screws. An embodiment of the present disclosure mitigates this problem by using a polarization rotator at a relatively low frequency (e.g., 125 GHz) and keeping the polarization rotator as short as possible.

[0031] 3, a schematic diagram of a detection system 300 according to some embodiments is provided. Radiation may be received at inputs 302, 304, and 306, which may be feed horns of blocks 308, 310, and 312, respectively. In some embodiments, block 308 may correspond to detector array 102, and each of blocks 310 and 312 may form part of detector array 104. Each of the radiation signals received at inputs 302, 304, 306 is sent to a mixer element, shown as elements 314a, 314b, and 314c. In some embodiments, one or more of the received signals may be rotated, such as by an optional polarization rotation element 316, before being processed by the mixer. The processed signals from the mixers, e.g., one or more intermediate frequency (IF) signals, are sent to the output of each block (318a, 318b, 318c) before undergoing further processing by low noise amplifiers (LNAs) (320a, 320b, 320c), power detectors (321a, 321b, 321c), and analog to digital converters (ADCs) (322a, 322b, 322c). The further processing may include filtering. The digital signals may then be sent to an image generator 324 to form an image based on the detected radiation, e.g., a composite image of an object or scene may be formed using the radiation received at 302, 304, and 306. The image processing 324 may be coupled to or part of a display system 336, e.g., a computer or monitor. In some embodiments, the IF signals are output using a coaxial cable in each block.

[0032] Although the system is shown with three mixer elements or inputs, the system may be implemented with more or fewer elements. For example, system 300 may be expanded to include a fourth set of input feed horns, each of which may have a corresponding set of mixers and processing circuitry.

[0033] In some embodiments, local oscillator (LO) signals are provided to the mixers of system 300 using fewer LO sources than mixers. For example, in the example shown in FIG. 3, a single LO source 326 provides an LO signal to each of mixers 314a-c. According to an embodiment, this is accomplished using one or more power dividers 328a, 328b and possibly one or more frequency multipliers 330a-c, such as, for example, doublers or triplers. For example, the original LO signal from source 326 may be provided to divider 328a, which then provides a signal to divider 328b and to optional multiplier 330a. Multiplier 330 may be used to provide a higher frequency LO signal to mixer 314a than that provided by source 326. Similarly, divider 328b may provide a signal to optional multipliers 330b and 330c for mixers 314b and 314c. In this regard, each of blocks 308, 310, and 312 may be configured for operation at different frequencies / wavelengths. Such configuration may include, for example, the design of the mixers and the shape and dimensions of the input feed horns (e.g., 116, 118, and 120), etc. Thus, radiation signals of different wavelengths may be detected, processed, and used by processing circuitry 324 to form a composite image using data at multiple wavelengths. One or more amplifiers, such as amplifier 332, may be used to enhance the signal between at least one of the source, splitter, multiplier, and mixer. Other amplifiers are not shown in the example of FIG. 3.

[0034] The size of the feed horns should be selected to provide optimum coupling to the selected optical components, and the spacing should be selected to provide optimum coverage for the application.

[0035] In certain aspects, the components are optimized to minimize the amount of LO power reflected from the RF coupling circuit over as wide a range of circuit operating conditions as possible. This limits the reflected LO signal from propagating back to one or more LO power splitters, thus limiting interference between channels. To further reduce the reflection problem, a 90 degree 3 dB hybrid power splitter, such as a Magic-T or 3 dB hybrid branch guide coupler, may be implemented.

[0036] According to some embodiments, one or more of the distributors 328a and 328b are unequal distributors as described with respect to Figures 5A-5C. According to some embodiments, the multipliers 330a and 330b are doublers, while the multiplier 330c is a tripler. In some embodiments, one or more of the multipliers are not required. For example, the multiplier 330a may be omitted in some embodiments.

[0037] According to some embodiments, a common local oscillator source 326 is provided and the frequencies are multiplied using different order frequency multipliers (e.g. doublers and triplers) to realize a sub-harmonic mixer. For example, the mixers 314a-c may operate in bands centered on frequencies 125 GHz, 250 GHz, and 375 GHz, respectively, which may use local oscillator frequencies of 62.5 GHz, 125 GHz, and 187.5 GHz. In this example, the base local oscillator source 326 may be a Gunn oscillator operating at 62.5 GHz providing approximately 100 mW. This is split into two equal signals using a splitter, e.g., distributor 328a. This splitter may be an equal power splitter, e.g., a standard magic tee, or an unequal splitter as described with respect to Figs. 5A-5C. One half of the splitter output pumps the 125 GHz array (block 308 in this example) and the second half is input to a power amplifier (e.g., amplifier 332 in this example) to provide a signal of about 400 mW, which is then used to pump the frequency multipliers 330b and 330c. As a sub-harmonic mixer is used in this frequency example, multiplier 330a is not needed in this case. In some embodiments, the system is optimized by using a configurable unequal power divider to provide optimal power to the 125 GHz array and the power amplifiers. Each frequency mixer array requires similar local oscillator power, which is 30-40 mW in this example. However, the typical efficiency of a doubler is 40% compared to 15% for a tripler. This means that the use of a uniform power splitter, such as a Magic Tee, can result in excess power (80 mW) being generated for the 250 GHz array (e.g., block 310 in this example) and marginal power being generated for the 375 GHz array (e.g., block 312 in this example).Conventional power splitters such as magic tees rely on input power being split evenly in half, but if such an approach were used in this embodiment, it would result in excess power being provided to the 125 GHz doubler (e.g., multiplier 330b) and insufficient power being provided to the 187.5 GHz tripler (e.g., multiplier 330c). Thus, to provide sufficient power to the tripler, which is typically less efficient than the doubler, the power amplifier would need to be over-specified, and the power to the doubler would be unnecessarily attenuated (which could otherwise be damaged). Not only is this costly and wasteful of LO signals, but it could be difficult to achieve with existing technology, resulting in higher electrical bias power and heat removal requirements. Thus, according to an embodiment, a configurable power splitter is used that can split the local oscillator pump power arbitrarily into two or more paths, so that the power to the multipliers of each local oscillator arm is distributed according to their respective power requirements. According to an embodiment, at least one of the splitters 328a and 328b is configurable. Thus, by matching the power division with each frequency arm so that the delivered power meets the peak efficiency input power requirement for each respective multiplier, a system can be provided which minimizes overall system LO power requirements (and costs).

[0038] According to some embodiments, one or more blocks may be provided that are configured to receive and process radiation at a fourth frequency. For example, one or more blocks may be configured at 500 GHz. The mixers for such blocks may operate similarly using the same LO source, such as with additional splitters and / or doublers in one or more of the LO paths shown in FIG. 3. In some embodiments, this block may be a sub-block or array 102, 104.

[0039] According to some embodiments, the LO source 326 may have multiple outputs at one or more frequencies and the initial splitter 328a and / or multiplier 330a may not be required. In some embodiments, one or more of the splitter 328a and multiplier 330a are integrated into the local oscillator source 326 such that the source 326 provides multiple frequency signals of configurable power. Although two outputs are used as an example, this implementation may be expanded by using additional unequal power splitters and / or multipliers.

[0040] 4A and 4B, one or more detector array blocks are shown according to some embodiments. These may correspond to, for example, arrays 102, 104 and blocks 308, 310, 312. An array, such as arrays 102, 104, may be formed as a single block (e.g., as shown in FIG. 4A). In addition, an array, such as arrays 102, 104, may be formed from multiple blocks (e.g., by two blocks as shown in FIG. 4B) to form a composite detector block having multiple rows and columns of feed horns. In addition, according to an embodiment, each sub-block may be formed from two parts as shown with respect to FIG. 12A, which shows a half block part 1202 attached to another half block part 1204.

[0041] Now referring to FIG. 4A, a block 400 according to some embodiments is provided. In some cases, one or more of the detector arrays 102, 104 may include the block 400. The block 400 includes one or more signal inputs 402, one or more secondary inputs 404, and one or more outputs 406. For example, the signal input 402 may correspond to the detector feed horns 116, 118, or 120 shown in FIG. 1A, FIG. 1B, FIG. 2, and FIG. 3. Similarly, the secondary input(s) 404 may be an LO signal input, such as, for example, those described with respect to FIG. 2A and FIG. 3. The output(s) 406 may be a detected signal output, such as, for example, one or more IF signals from a mixer as described with respect to FIG. 3. According to an embodiment, the inputs are provided in the same plane, while the outputs are provided in orthogonal planes. In the example of FIG. 4A, the inputs 402, 404 are provided along the z-axis, while the output 406 is provided along the x-axis. Each input 402, 404 extends along the z-axis through the block 400, while each output 406 extends along the x-axis through the block 400 in an orthogonal manner. According to an embodiment, processing circuitry may be connected to the output 406. For example, there may be multiple processing circuitry units in the y-axis direction to process the signal output from the block 400. Similarly, additional blocks (e.g., 400) may be stacked in the y-axis direction to extend the detector. A similar arrangement with circuit elements 460a-n is shown in FIG. 4B. As shown with respect to FIG. 3, such circuits may include, for example, one or more LNAs, wideband power detectors, and / or ADCs. In some embodiments, a power detector is used to convert the wideband microwave power to a baseband signal by thermal means (e.g., a bolometer) or by using an amplitude modulation (AM) detector. In addition, the processing circuitry may include one or more filters, for example, on either side of the LNA or ADC. According to an embodiment, power detectors, such as 321a, 321b, 321c, detect power across a band and output a voltage related to that power.

[0042] 4B, according to an embodiment, a first block (e.g., block 400) can be combined with a second block (e.g., 450) to form a single detector array block, such as array 102, 104. In this example, inputs 452 and 454 of block 450 extend along the z-axis, and output 456 extends along the vertical x-axis. Given this arrangement of inputs and outputs, processing circuits 460a-n can be stacked in the y-axis direction on the outer surface of blocks 400, 450 without interfering with signal capture from the source by input 452 or impeding the transmission of LO to input 454. Although circuits 460a-n are shown on the block 400 side of the array, this stacking may also be provided on the other side of the array (e.g., the block 450 side). In this regard, a first stack of processing circuits 460a-n may be provided on one side of the array, a second stack of processing circuits 4670a-n may be provided on a second side of the array, an input signal (e.g., an RF input) may be provided on a third side of the array, and in some embodiments, another input signal (e.g., an LO) may be provided on a fourth side of the array. The circuits 460a-n may include, for example, at least one of one or more LNAs, an AM (envelope) power detector, and an ADC, and possibly a filter. As shown in FIG. 4B, according to some embodiments, there may be no inputs or outputs at the top or bottom of the blocks 400, 450.

[0043] Although the array in FIG. 4B is shown with two connected blocks, embodiments are not so limited. For example, according to embodiments, a detector array, such as arrays 102, 104, may be formed of blocks that are not directly connected, or may be formed of more than two blocks. For example, processing circuitry 460a-n may be placed between two sub-blocks of the array (e.g., between blocks 400 and 450). In some cases, three sub-blocks may be used with circuitry placed between the first and second blocks and between the second and third blocks. In such an arrangement, the circuitry between the first and second blocks may process signals from either or both of the first or second blocks, while the circuitry between the second and third blocks may process signals from either or both of the second and third blocks. In addition, another stack of circuits may be provided on one or more of the outer portions of the array, for example to process signals from the first or third blocks. Although described with three blocks, according to embodiments, this arrangement may be repeated to extend the width of the array beyond three blocks. The detection array can also be expanded in the y-direction, for example by stacking additional blocks 400, 450. According to embodiments, the top and bottom surfaces of the array blocks 400, 450 are free of inputs and outputs, allowing another block to be stacked without obstruction. Some embodiments include blocks 400, 450 with six primary sides, with at least one of the inputs and outputs exposed on the outside (e.g., at least one of the inputs and outputs in the x-direction and z-direction), but not on the top or bottom (e.g., in the y-direction). As shown in Figures 12A and 12B, stacking can be further improved by notches 1206.

[0044] According to an embodiment, the detection system may be optimized for up to four detection frequency bands. For example, each of the arrays 102, 104 may include two blocks such as blocks 400, 450 combined as shown in FIG. 4B. In this case, each input feed horn 452 and subsequent processing can accommodate a different frequency band, allowing multi-frequency detection of up to four frequency bands. According to an embodiment, the bandwidth may be set by a combination of at least one of a mixer, an IF amplifier, and an envelope detector. In some embodiments, the bandwidth is + / - 20% of the center frequency for the waveguide.

[0045] 5A-5C, the geometry of one or more unequal power splitters and / or polarization rotators according to some embodiments are shown. As shown in FIG. 5A, unequal power splitter 500 may include an input 502 and outputs 504 and 506. The power at output 504 may be different than the output at 506. Additionally, as shown in the detailed view of FIG. 5B, one or more channels (i.e., the input, the first output, or the second output) may include a polarization rotation element 508. Such a rotation element is further shown as 514a-c in FIG. 5C. As further shown in FIG. 5C, the unequal power split may be achieved by two waveguide openings at the split. That is, the first waveguide opening 510 may be smaller than the second waveguide opening 512, thereby directing more power to output 506 than to output 504. In this example, the rotating elements 514a-c cause the waveguide power split with a different polarization than the signal at the input 502 or output 504, 506. In certain embodiments, the ratio of the power split may be approximately linearly dependent on the relative height of the waveguide at the point where the waveguide splits. If the split is half the height (narrow dimension) of the waveguide, the power is split evenly. If the split is, for example, 20% of the height, the power is split 80:20, and so on.

[0046] According to an embodiment, and with further reference to FIGS. 5A-5C, a non-uniform configurable power splitter can be achieved by integration of a polarizer rotator at each port. The bulk of the component can then be machined in a first orientation, for example, to position the waveguide split in the center of the wide wall. Furthermore, this approach can be utilized to provide a means to fully integrate the LO power network into a single, easy to CNC machine combination manifold that can be used between the power amplifier and the multiplier. In certain aspects, this approach provides the ability to arbitrarily rotate the waveguide orientation by 90 degrees depending on the overall system layout requirements. Such an LO network manifold can at least one of reduce cost, eliminate the need for flanges between components, and enable the realization of a significantly more compact system.

[0047] According to an embodiment, the detection system provides temporally and spatially aligned multi-frequency data from outdoor (or indoor) scenes optimized to take advantage of optimal characteristics of the Earth's atmosphere. In doing so, aspects of the present disclosure provide data that allows for a degree of material specificity that can greatly aid the decision-making process in determining the exact nature of a threat item. Because human tissue has specific properties, it can also be used to show human signatures in cluttered outdoor scenes in real time.

[0048] The Earth's atmosphere provides unique illumination characteristics due to the atmospheric transmittance at the observed frequencies, which is determined by the amount of water vapor present above the scene and the wavelengths used for detection. Two phenomena govern this effect. First, water molecules have rotational resonances in the millimeter to terahertz domain, so that they absorb photons at certain frequencies. At frequencies away from these lines, water molecules pass photons, which may be understood as the water window. In addition, shorter wavelengths increase the effective path length through the atmosphere, increasing attenuation. At frequencies where the transmittance is highest, the Earth's atmosphere is transparent, so that the cold background of space provides very high contrast during millimeter wave detection. That is, the outdoor scene being observed is dominated by the "cold" sky illumination. At frequencies where the Earth's atmospheric transmittance is low, the scene is dominated by the "warm" illumination from the air column above the scene. According to an embodiment, a mix of high, medium and low transmittance wavelengths is required to provide color scenes where different contrast types are achieved. Experimental investigations have determined that these wavelengths are approximately 35 GHz wide bands centered at approximately 125 GHz, 250 GHz, and 375 GHz.

[0049] According to an embodiment, to maximize usefulness, an image is generated in the shortest time, with the highest thermal sensitivity, and with the highest possible spatial resolution. The first two of these requirements are usually in conflict. The following equation applies to the thermal sensitivity of a scene: ΔT=T sys / (tx B) 1 / 2 , where ΔT is the minimum resolvable temperature difference between spatially resolved regions. The variable T sys is the system noise temperature of the detector electronics, t is the time taken to collect a sample, and B is the bandwidth of the detector.

[0050] For the heterodyne detector used in some embodiments, the system bandwidth is fixed, so the options for improving thermal sensitivity are T sysand increasing the integration time t. However, T sys There may be little room to improve t other than by cooling the entire array, which may be infeasible. It is possible to increase the integration time t, but at the expense of frame update rate. Thus, according to embodiments, an improvement to maintain the fastest frame rate is provided by increasing the number of detectors, which allows each detector to observe the scene for more time. According to embodiments, the number of detectors can be increased both vertically and horizontally, and in addition, detector arrays can be paired with intervening plates. Furthermore, stackable multi-frequency detector configurations are described, which can be scaled to incorporate any number of detectors with combinations of up to three or more frequency bands.

[0051] According to embodiments, a polarizer element and a power splitter are integrated into the detection system. These two components work in combination to enable a compact multiplexed optical delivery system that provides near perfect spatial and temporal alignment for multi-frequency data retrieval. The embodiments also provide a means for scaling the detector count by stacking detectors in a vertical plane in a repetitive manner.

[0052] According to an embodiment, a virtual array is formed using a linear polarization grid placed in close proximity to the feed horns of the detector array to overlap the field of view of each detector. For example, a schematic diagram is shown in FIG. 6, which shows incident radiation passing through the linear polarization grid toward a first set of feed horns at 602, reflected toward a second set of feed horns at 604, and the combined detected data at 606. In this example, the polarization grid is completely transparent to vertically linearly polarized radiation, but completely reflects horizontally polarized radiation. When placed at 45 degrees between orthogonal arrays (e.g., arrays 102, 104, etc.), the horizontally polarized radiation appears as a vertical array that overlaps with the vertically polarized array at 606. In this particular example, the terms "vertical" and "horizontal" are intended to distinguish between orthogonal axes.

[0053] In practice, a small amount of signal, typically 2-5%, is lost due to scattering and resistive losses in the wire grid beam combiner. By accepting this loss, a stacked arrangement of feed horns can be realized that is very compact and configurable. By overlapping or spacing the feed horns at each polarization output from the polarization beam combiner, a completely versatile and configurable "virtual" 2D array is possible. This can be made with multiple frequencies, multiple overlapping polarizations, or any array layout, such as a sparse array. For example, one array (e.g., 102) may be configured for a first frequency or set of frequencies, while a second array (e.g., 104) may be configured for a second frequency or set of frequencies. In this regard, multi-frequency detection can be achieved by capture in two dimensions. Alternatively, by configuring both arrays (e.g., 102, 104) at the same frequency, vertically polarized radiation at that frequency can be captured (e.g., 602) and horizontally polarized radiation at that frequency can be captured (e.g., 604) to form a composite 606 for single frequency detection. According to embodiments, the layout of this quasi-2D array can be designed for adaptive scanning. For example, the sparse array can be "filled" by dithering the scanning mirror with small, fast increments. Additional phenomenological information can be gathered by combining the two polarizations.

[0054] According to an embodiment, a polarizing grid beam combiner is used with overlapping beams to double the signal collection for each position in the field of view.

[0055] 7, a detection system 700 for polarization of received radiation is shown generally according to some embodiments. In this example, radiation from the field of view having vertical polarization passes through element 710 towards feed horns 702 and 704. At the same time, horizontally polarized radiation from the field of view is reflected off element 710 towards feed horns 706 and 708. As shown in FIG. 7, the detection data received at feed horns 702, 704, 706, and 708 can be combined to form a composite representation of the field of view. According to an embodiment, feed horns 702 and 704 are spaced apart from one another, as are feed horns 706 and 708. Thus, as shown in FIG. 7, the horizontal and vertical signal information may partially overlap at the output.

[0056] According to an embodiment, the detector layout of the system forms a sparse array.

[0057] According to some embodiments, feed horns 702, 704, 706, and 708 are all configured for the same wavelength of radiation. Using polarizing elements 710 in conjunction with two sets of arrays effectively doubles the amount of usable received and processed radiation.

[0058] According to an embodiment, the spacing arrangement shown in Figures 7 and 8 can be applied to a multi-frequency detection system, i.e., feed horns 702, 704, 706, and 708 may be optimized for different frequencies.

[0059] Referring now to FIG. 8, the system 700 is further illustrated by an embodiment with LO sources 802, 806 and IF processing circuits 804, 808. According to an embodiment, the feed horns are spaced far enough apart that the IF processing circuits 804, 808 may be physically located between the feed horns. Such circuits may include, for example, one or more LNAs, power detectors, and / or ADCs. This may be done using, for example, an orthogonal channel arrangement such as that shown with respect to FIG. 4A and FIG. 4B. This setup allows the field of view width Xn to be extended as far as necessary for both the vertical and / or horizontal arrays. The height can also be set to the desired height, for example, by stacking blocks or varying the height of the blocks. This allows for a wider capture (increasing the number of feed horns) without loss of temporal and spatial correspondence of the field of view. The resulting image display 900 with a pair of detector arrays having multiple feed horns spaced apart with a width of 2 and a height of 4 is shown in FIG. 9. As illustrated in Figure 9, the width and height of the array (i.e., image capture) can be extended by Xn in either dimension as needed. In some embodiments, the feed horns are spaced apart by a distance determined by the size of the circuitry placed between them. For example, the feed horns may be spaced at a distance equal to the size of the circuitry, 1.5 times its size, or twice its size.

[0060] According to an embodiment, the disclosed system can create a “virtual” 2D imaging array that can be extended to n elements with alternating polarizations, as shown in the beam footprints of the compound split polarizing elements shown in Figures 7-9.

[0061] 10, a detection method 1000 according to some embodiments is provided. The process may be performed using a detection system such as those described with respect to one or more of Figures 1A-1B, 3, and 13A-13B according to embodiments. For example, the process may be performed by a terahertz camera.

[0062] Method 1000 may begin with step s1010, which includes receiving a first radiation signal having a first polarization at a first detector block of the camera, where the first radiation signal is received from a radiation source through a polarizing plate. In step s1020, process 1000 includes receiving a second radiation signal having a second polarization at a second detector block of the camera, where the second radiation signal is received from the radiation source as a reflected signal from the polarizing plate. In steps s1040 and s1050, the signal is processed, which includes processing the first radiation signal to form first detection information and processing the second radiation signal to form second detection information, for example, as described with respect to Figures 3 and 4. This processing may include, for example, sending the signal to a mixer to generate an intermediate frequency signal, and further processing the signal by one or more of an LNA, a PD, and an ADC. According to some embodiments, the detected information is image data that can be used to construct a two-dimensional image of at least a portion of the field of view to which the detected radiation signals correspond, for example as described with respect to Figures 6-9. In some cases, the detected information is a digital magnitude indicative of the intensity of the radiation received by a given channel.

[0063] In some embodiments, process 1000 includes an optional step s1030, in which at least one of the first and second received radiation signals is passed through a polarization rotation element before further processing.

[0064] In optional step s1060, according to some embodiments, method 1000 further includes combining the first and second detected information to form an image indicative of one or more characteristics of the radiation source. Combining the detected information to form the image may be performed by at least one of image processing 324 and display system 336, for example, as shown in relation to Figure 3. In some embodiments, combining is performed as described in relation to Figures 6-9.

[0065] According to an embodiment, a portion of an image corresponding to the first detection information (e.g., information generated from a signal detected by a first feed horn) and a portion of an image corresponding to the second detection information (e.g., information generated from a signal detected by a second feed horn) completely overlap in the image, or a portion of an image corresponding to the first detection information and a portion of an image corresponding to the second detection information partially overlap in the image, or a portion of an image corresponding to the first detection information and a portion of an image corresponding to the second detection information do not overlap at all in the image.

[0066] According to an embodiment, the portion of the image corresponding to the first detection information and the portion of the image corresponding to the second detection information partially overlap in the image or do not overlap at all (i.e., do not completely overlap). In this example, the first detector includes a first plurality of feed horns having a first width and spaced apart by at least the first width, and the second detector includes a second plurality of feed horns having a second width and spaced apart by at least the second width. In this example, processing the first radiation signal may be at least partially performed in a first processing circuit located between two feed horns of the first plurality of feed horns, and processing the second radiation signal may be at least partially performed in a second processing circuit located between two feed horns of the first plurality of feed horns. In addition, according to an embodiment, the first plurality of feed horns are arranged in an array of feed horns having a height and a width both greater than two, and the second plurality of feed horns are arranged in an array of feed horns having a height and a width both greater than two.

[0067] According to an embodiment, the processing element is adapted to color-code the image data generated at the different frequencies (and / or the different detector arrays) such that the composite image data includes a composite color-code from the image data generated at the different frequencies. This composite color-code can be used to characterize a surface. For example, a reflective metal would be indicated to be the temperature of the environment at both low and high frequencies, whereas skin would be indicated to be the temperature of the environment only at lower frequencies. At higher frequencies, skin would be indicated to be body temperature. Thus, the composite color-code from the different frequencies would indicate skin as a different color than metal. The data can be assigned to pixels in the image to identify areas having a specified characteristic.

[0068] According to an embodiment, the detector array sends its analog IF signal to one or more LNAs, AM detectors, and digitizers, which ultimately convert and filter the IF signal to a digital signal. This may be, for example, part of steps s1040 and s1050. In this example, the processing element (e.g., 324 and / or 326) receives the filtered digital signals from the respective selected set of detectors, assigns an image color to each detector in the set, and then adds the signals for each pixel of the image signal 335 so that the pixels will be displayed in a color that is a combination of the colors received at different frequencies for the selected set of detector channels. According to an embodiment, the arrays may not be aligned, so some adjustment may be necessary to ensure that the data they generate corresponds at least over a common range of interest in the field of view.

[0069] According to an embodiment, the detection system described herein may use a heterodyne mixer. For example, an array of feed horns routes the incoming radiation through a waveguide to a diode-based mixer and an intermediate frequency (IF) output to a processing circuit. The feed horns are scaled in size to give the same coupling coefficient to the waveguide according to frequency. In the mixer, the incoming signal is combined with a reference signal provided, for example, from a local oscillator (LO), which may incorporate frequency control. The mixer may include a nonlinear element, for example, a Schottky diode, which combines the radiation with an integer multiple of the reference signal to generate sum and difference signals that include the IF. According to an embodiment, a subharmonic mixer may be used. The IF signal is typically at a lower frequency compared to the received terahertz radiation and the reference signal, typically 0.1-40 GHz, whereas the input radiation and the reference LO signal are at 100-500 GHz. Here, because the IF signal is at a relatively low frequency, it can be easily filtered, amplified, and envelope (AM) detected to produce a voltage whose intensity is directly proportional to the intensity of the received terahertz radiation, which can then be used to form an image of the field of view. According to embodiments, envelope detection can be omitted. In certain aspects, the one or more digitizers operate at clock speeds in the GHz (or tens of GHz).

[0070] 11, a manufacturing process 1100 according to some embodiments is provided. For example, the process 1100 may be used to manufacture one or more detector arrays 102, 104 according to embodiments, and / or one or more blocks shown in FIGs. 4A and 4B. Similarly, the process 1100 may be used to manufacture one or more elements (e.g., elements 1302 and 1304) of the system 1300 shown in FIG. 13A. FIG. 12A illustrates the combination of a first machined housing component 1202 and a second machined housing component 1204 according to some embodiments and the process 1100.

[0071] The process 1100 may begin with step s1110, which includes machining a first housing component including a first radio frequency (RF) channel portion, a first local oscillator (LO) channel portion, a first intermediate frequency (IF) channel portion, a polarization rotation portion, and a first mixer mounting cavity. Similarly, step s1120 includes machining a second housing component including a second radio frequency (RF) channel portion, a second local oscillator (LO) channel portion, a second intermediate frequency (IF) channel portion, a polarization rotation portion, and a second mixer mounting cavity. In some embodiments, the process 1100 includes optional steps s1130-s1150. In step s1130, a heterodyne mixer is mounted in at least one of the first and second mounting cavities. In step s1140, the first and second housing components are attached to form a first detector block. In step s1150, a second detector block is attached to the first detector block to form an integrated block, such as array 102, 104 or block 400, 450. Attaching the first and second detector blocks may include attaching an outer surface of the first detector block to an outer surface of the second detector block, where the outer surface of the first detector block is formed in the same plane as the RF and LO channel portions and in a plane orthogonal to the IF channel portion.

[0072] In some embodiments, the first and second blocks are not directly attached, but instead have processing circuitry located between them. Thus, process 1100 may include providing processing circuitry between the first and second blocks.

[0073] According to an embodiment, process 1100 may be repeated to form one or more blocks on a first side of the polarizing plate, and then to form one or more blocks on a second side of the polarizing plate. Thus, process 1100 may include placing the polarizing plate between the detector blocks (e.g., at a 45 degree angle).

[0074] 12A, a block 1200 can be formed by attaching components 1202 and 1204. Block 1200 can be one or more of array blocks 102, 104, 400, and 450, or sub-blocks of array blocks 102, 104, 400, and 450. As shown in FIG. 12A, block 1200 can include notches 1206. For example, a first notch 1206a can be provided on a first surface 1208 (e.g., a lower surface) of block 1200, while a second notch 1206b is provided on an opposing surface (e.g., an upper surface). In some embodiments, the notches are angled. However, in other embodiments, the notches can be perpendicular to block surface 1208. As further shown in FIG. 12A, the first and second notches 1206a, 1206b can be aligned with each other. For example, these notches may be used to stack multiple blocks 1200 to extend the array size vertically, for example, for arrays 102, 104, and system 100. This is shown by way of example in FIG. 12B with blocks 1200 in a stacked arrangement. In this example, block 1210 is stacked on top of block 1212, which may be identical stacking modules in some embodiments. Although identical blocks with the same feed horn size are shown, blocks 1200 for different frequencies (i.e., feed horn sizes) may have the same overall shape and size, including one or more notches 1206, and thus may be stacked. In the example of FIGS. 12A-12C, there is no RF input, LO input, or IF output on the surface that includes stacking notches 1206. As shown in FIG. 12C, blocks 1200 may be arranged to extend the array size both vertically (by n1 blocks) and horizontally (by n2 blocks), as discussed in connection with, for example, FIGS. 6-9. The block 1200 may include a signal input or feed horn 1214 , a power input or LO channel 1216 , and a signal output or IF channel 1218 .As shown in FIG. 12A, the inputs 1214, 1216 extend along a first axis, while the output 1218 extends along a second, perpendicular axis.

[0075] 13A and 13B, images of a detection system 1300 are provided according to some embodiments. As shown in FIG. 13A, the system 1300 includes first and second detector arrays 1302 and 1304 with a polarizing plate 1306 disposed therebetween. Processing circuitry 1308 is provided in a stacked configuration and has an output for image processing 1310. The LO signal is provided by a source 1312 with splitters 1314a and 1314b. FIG. 13B shows another angle of the system 1300, detailing the polarizing plate 1306 and the wire grid 1320 portion of the plate.

[0076] Although the embodiment uses 125 GHz, 250 GHz, 375 GHz, and 500 GHz as examples, other frequency sets may be used, for example 60, 120, 240, 360, and 480 GHz, which are related to the absorption characteristics of atmospheric oxygen.

[0077] Aspects of the present disclosure relate to scanning methods and apparatus for electromagnetic detection using the electromagnetic spectrum in the centimeter to sub-millimeter wavelength range. Certain embodiments may be applied to the radio frequency or terahertz regions of the electromagnetic spectrum, which have particular benefits for many applications and provide high resolution in small systems. The terms radio frequency and terahertz in this context may refer to the electromagnetic spectrum in wavelengths near the millimeter, millimeter, and sub-millimeter ranges (e.g., 30 GHz to 1 THz).

[0078] Although various embodiments of the present disclosure are described herein, it should be understood that they are provided as examples only and are not limiting. Thus, the breadth and scope of the present disclosure should not be limited by any of the exemplary embodiments described above. In general, all terms used herein should be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and / or the context in which the term is used indicates. All references to a / an / the element, device, component, means, step, etc. should be openly interpreted as indicating at least one instance of that element, device, component, means, step, etc., unless expressly stated otherwise. Any combination of all possible variations of the above-mentioned elements is encompassed in the present disclosure, unless otherwise indicated herein or clearly denied by the context.

[0079] In addition, while the processes described above and illustrated in the figures are shown as a sequence of steps, this has been done for illustrative purposes only. It is therefore anticipated that some steps may be added, some steps may be omitted, the order of steps may be rearranged, and some steps may be performed in parallel. That is, the steps of any method disclosed herein need not be performed in the exact order disclosed, except when a step is expressly described as following or preceding another step and / or when it is absolutely necessary that a step follow or precede another step.

Claims

1. A detection system (300), comprising: A first detector block (308, 310, 312, 400); a local oscillator (LO) source (326); and one or more intermediate frequency (IF) processing circuits (320, 321, 322, 460); The first detector block includes: one or more heterodyne mixer elements (314); one or more LO input waveguide channels (202, 404) configured to provide an LO signal from the LO source to the one or more heterodyne mixer elements; one or more waveguide feed horns (116, 402) configured to provide a detected radio frequency (RF) signal to the one or more heterodyne mixer elements; one or more IF output channels (208, 406) configured to provide IF signals from the one or more heterodyne mixer elements to the one or more IF processing circuits; The one or more waveguide feed horns and the one or more LO input waveguide channels extend along a first axis of the first detector block, and the one or more IF output channels extend along a second axis of the first detector block, the first axis and the second axis being perpendicular. the one or more waveguide feed horns are exposed to a first surface of the first detector block; an input of the one or more LO input waveguide channels is exposed to a second face of the first detector block; the second surface is opposite the first surface of the first detector block. system.

2. 2. The system of claim 1, the first detector block includes a plurality of the heterodyne mixer elements, a plurality of the waveguide feed horns arranged in an array on a surface of the first detector block, and a plurality of the IF processing circuits; The system, wherein the plurality of IF processing circuits are arranged in a stacked configuration.

3. 3. The system according to claim 1 or 2, The system further includes a second detector block (450) adjacent to the first detector block, the second detector block including a second plurality of heterodyne mixer elements and a second plurality of waveguide feed horns arranged in an array on a surface of the second detector block.

4. 4. The system of claim 3, The system further comprising a second plurality of IF processing circuits, said second plurality of IF processing circuits also arranged in a stacked configuration.

5. 5. A system according to claim 3 or 4, comprising: the plurality of waveguide feed horns of the first detector block are sized for a first frequency and the second plurality of waveguide feed horns of the second detector block are sized for a second, different frequency.

6. A system according to any one of claims 3 to 5, At least one of the first and second detector blocks includes a polarization rotation element.

7. A system according to any one of claims 3 to 6, The system, wherein the LO source is coupled to the first or second detector block by an unequal power splitter.

8. A system according to any one of claims 3 to 7, The system further includes a polarizing plate positioned to pass or reflect radiation relative to the first and second detector blocks.

9. A system according to any one of claims 3 to 8, a third detector block and a fourth detector block; the third and fourth detector blocks are stacked on top of the first and second detector blocks; the third and fourth detector blocks are mounted on the first and second detector blocks using one or more stacking notches. system.

10. A system according to any one of claims 3 to 9, at least one of the first and second detector blocks is provided with one or more angled stacking notches; system.

11. A system according to any one of claims 3 to 10, the plurality of waveguide feed horns of the first detector block are sized for radiation having a first center frequency and the plurality of waveguide feed horns of the second detector block are sized for radiation having a second center frequency; The system, wherein the first central frequency is 250 GHz and the second central frequency is 375 GHz.

12. A system according to any one of claims 3 to 9, The system, wherein the plurality of waveguide feed horns of the first and second detector blocks are sized for radiation having a same center frequency.

13. 13. The system of claim 12, The system, wherein the central frequency is 125 GHz or 250 GHz.

14. A system according to any one of claims 3 to 13, At least one of the IF processing circuits is located between two RF feed horns of the first or second detector block.

Images