High Frequency Heterodyne Mixer

Abstract

A device and method for a detection system and heterodyne mixer having a local oscillator (LO) input, a radio frequency (RF) input, an intermediate frequency (IF) output, and a suspended waveguide structure having a quartz substrate and a patterned metal transmission line with a plurality of suppression slots.

Description

[Technical field]

[0001] This disclosure relates to high frequency electronics and detection systems, and more particularly to heterodyne mixers and methods of manufacturing the same. [Background technology]

[0002] A mixer is an electronic device that can be used to generate an output signal having a frequency different from the frequency of the received signal. For example, if two input signals are applied to a mixer, the mixer may generate an output signal having a frequency that is the sum and difference of the input signals, or a harmonic thereof. In this way, a mixer can be used to downconvert the detected signal to a lower frequency, for example to simplify subsequent processing.

[0003] The mixer shown in the '613 patent receives an input radio frequency (RF) signal, a local oscillator (LO) signal, and generates an intermediate frequency (IF) signal from a diode chip. The design uses separate RF, LO, and IF circuit paths and wire-based stub tuners for optimizing conversion efficiency and power matching.

[0004] However, there remains a need for mixer designs that are effective over a wide range of frequencies (e.g., at very high frequencies) and that are compatible with manufacturing and assembly techniques used for small components, such as those required when scaling circuit elements with decreasing signal wavelengths for a given system. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2007 / 125326 Summary of the Invention [Means for solving the problem]

[0006] According to an embodiment, a mixer device such as a heterodyne mixer is disclosed. The mixer may include a first input, such as a local oscillator (LO) input, a second input, such as a radio frequency (RF) input, an output, such as an intermediate frequency (IF) signal output, a suspended signal transmission element including a plurality of suppression slots and a plurality of filter elements, and a diode circuit mounted on the suspended signal transmission element. The suspended signal transmission element may be, for example, a waveguide. In a particular aspect, the suspended signal transmission element is a waveguide including a substrate having a first and a second surface and a transmission line on the first surface, where the substrate is a quartz substrate and the transmission line is a patterned metal microstrip (also called stripline) transmission line. Furthermore, the first input (e.g., LO) may be located between the second input (RF) and the output (e.g., IF), and the transmission element may be configured to transmit the IF signal generated in the diode circuit from the diode circuit to the output along a longitudinal axis of the transmission element.

[0007] According to an embodiment, the heterodyne mixer apparatus comprises a waveguide component, the waveguide component including filtering means, transmitting means and suppression means. One or more semiconductor devices may be mounted on a surface of the waveguide component.

[0008] According to an embodiment, a mixer is provided having one or more slotted filter elements. In certain aspects, the slots of the filter are relatively small compared to the free space wavelength. For example, the slots may be less than λ / 10.

[0009] According to an embodiment, a mixer is provided having an RF signal input at a first end, an IF signal output at a second end, and an LO signal input between (e.g., in the middle) the two ends. In a particular aspect, a waveguide transmission element extends from the first end to the second end. The transmission element may be suspended and may have a number of suppression slots and a number of filter elements. Additionally, a diode circuit may be mounted adjacent to the RF signal input at the first end of the mixer. In some embodiments, the IF signal generated in the diode circuit propagates along the transmission element to the IF signal output at the other end of the mixer. The mixer may be disposed in a detector block with the RF and LO input channels along a first axis and the IF output along a second axis perpendicular to the first axis.

[0010] According to some embodiments, a detector, such as a terahertz camera, is provided. The detector may include, for example, one or more mixers described herein, one or more feed horns coupled to an input (e.g., providing an RF signal) of at least one of the one or more mixers, a local oscillator coupled to another input of at least one of the one or more mixers, a coaxial line (or other transmission element) coupled to an output (e.g., IF) of at least one of the one or more mixers, and one or more of a low noise amplifier (LNA), a power detector, and an analog-to-digital converter (ADC) circuit element connected to the coaxial line and configured to process the output IF signal. The detector may further include additional filtering and image processing, for example, to generate an image of an object or scene that originated the received input radiation. In a particular aspect, the one or more mixers include a plurality of mixers optimized at 250 GHz and a plurality of mixers optimized at 375 GHz. The set of mixers may further include a plurality of mixers optimized at 125 GHz.

[0011] According to some embodiments, a method of operating a mixer is provided that may include, for example, receiving an RF signal at a first input of a mixer apparatus having a suspended transmission line element, a number of suppression elements, and a diode circuit, providing a local oscillator signal to the mixer, and outputting an IF signal generated by the diode circuit, where the outputting of the IF signal includes propagating the signal through a number of filters along a length of the mixer.

[0012] According to some embodiments, a method of manufacturing a mixer device, such as one or more mixers described herein, is provided. The method may begin with machining steps including: (1) machining a first housing component including a first radio frequency channel portion, a first local oscillator portion, a first intermediate frequency channel portion, a first cavity portion, a first mounting shelf portion, and a second mounting shelf portion; and (2) machining a second housing component including a second radio frequency channel portion, a second local oscillator portion, a second intermediate frequency channel portion, a second cavity portion, a third mounting shelf portion, and a fourth mounting shelf portion. A signal transmission element (e.g., a waveguide) can be suspended within at least one of the first and second cavity portions by mounting a waveguide element on at least one of the first and second mounting shelf portions and the third and fourth mounting shelf portions. Additionally, the first housing component can be attached to the second housing component to form a block, which can be a receive array block of a detector such as a terahertz camera.

[0013] According to an embodiment, a detector block is provided that includes a housing and one or more mixers mounted within the housing. The housing may include one or more feed horns coupled to an RF input of at least one of the one or more mixers, one or more local oscillator channels coupled to an LO input of at least one of the one or more mixers, and one or more output channels coupled to an IF output of at least one of the one or more mixers. The one or more mixers may include suspended signal transmission elements mounted to first and second mounting structures of the housing. In some embodiments, the one or more feed horns and the one or more local oscillator channels extend along a first axis of the housing, and the one or more output channels extend along a second axis of the housing, the first axis and the second axis being perpendicular. Additionally, the suspended signal transmission element may include a substrate having first and second surfaces and a transmission line on the first surface, the transmission line being a patterned metal microstrip transmission line including one or more suppression slots and a filter element.

[0014] According to an embodiment, a terahertz camera is provided, the terahertz camera including one or more mixers including an IF output, an LO input, and an RF input; one or more feed horns coupled to the RF input of at least one of the one or more mixers; a local oscillator coupled to the LO input of at least one of the one or more mixers; and one or more of a low noise amplifier, a power detector, and an analog-to-digital converter connected to the IF output and configured to process an output IF signal from at least one of the one or more mixers. Additionally, at least one of the one or more mixers may further include a suspended signal transmission element including a plurality of suppression slots and a filter element, and a diode circuit mounted on the suspended signal transmission element and configured to generate an IF output signal based on radiation received at the one or more feed horns and a power signal from the local oscillator. In some embodiments, the received radiation is in a band centered at about 125 GHz, 250 GHz, or 375 GHz.

[0015] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate various embodiments. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 illustrates a mixer apparatus according to some embodiments. [Diagram 2] 2A and 2B are diagrams illustrating a mixer device according to some embodiments. [Diagram 3] 3A and 3B are diagrams illustrating details of a mixer device according to some embodiments. [Figure 4] 1 is a flow diagram illustrating a process according to some embodiments. [Diagram 5] FIG. 1 is a schematic diagram illustrating a detection system according to some embodiments. [Figure 6] 6A to 6C are diagrams illustrating a detector block according to an embodiment. [Figure 7] 1 is a flow diagram illustrating a process according to some embodiments. [Figure 8] 8A and 8B are diagrams illustrating microstrip fields and currents according to some embodiments. [Figure 9] FIG. 1 illustrates a detection system, such as a terahertz camera, according to an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Detecting microwave, millimeter wave, and / or sub-millimeter wave signals from an object or scene can require extremely sensitive detectors, for example, power levels of received signals can be in the femtowatt range.

[0018] In some cases, e.g., certain microwave frequencies, a low noise amplifier can be used to increase the power level of the signal by several orders of magnitude (e.g., 100-1000 times), which can then be processed to generate a DC voltage. This DC voltage can then be further amplified until it is powerful enough to be converted to a digital value, which can then be used to create image data. Other detection schemes, e.g., bolometers, can also be used. Bolometers are effective sensitive thermometers that generate a voltage that is directly proportional to the power level of the scene. When the power levels are fairly low, it may be necessary to cool the bolometer to very low temperatures, typically below 20 Kelvin, so that the weak received signal is strengthened against the inherent noise of the bolometer itself (caused by random motion of electrons due to thermal vibrations of atoms / molecules in the material used in the bolometer). This cooling requirement may require complex cryogenic technology, which may significantly increase cost, volume, and mass, as well as requiring large power levels. Thus, the application for bolometer-based imaging may be limited. For example, many security and material inspection applications require a high degree of portability from the system, which in turn requires low mass, volume, and power.

[0019] At higher frequencies, such as millimeter and sub-millimeter wavelengths, it can be difficult to operate high-gain, low-noise amplifiers at room temperature with high enough performance to obtain passive imaging in real time. In addition, as frequency increases, the path length of the amplifier gate also increases, requiring smaller devices. This leads to higher resistance, increased signal loss and noise, and reduced gain. When the operating frequency increases by a factor of two, the area of ​​the circuit typically decreases by a factor of four and its volume by a factor of eight. Thus, even a small increase in frequency can create manufacturing and assembly challenges that can increase costs due to reduced repeatability and yield. Such an increase in frequency can also reduce the utility of conventional assembly tools for machining high-frequency components.

[0020] As an example, quartz filters used to separate the RF, LO, and IF signals can become extremely small and difficult to handle at frequencies above 250 GHz. In addition, if bond wires are required to "tune" the above three signals of the heterodyne mixer, it becomes difficult to realize those wires and connections in a stylized manner that requires precise dimensioning of the bond wires to optimize all three signals. In addition, if a filter, such as an IF filter, is formed by high and low quarter-wave impedance sections realized on the IF output pin, it can complicate the assembly, increasing the cost and assembly time.

[0021] According to embodiments, certain problems with existing systems are solved by using a mixer so that the detection signal can be downconverted to a lower (e.g., lower microwave) frequency for amplification and processing. According to embodiments, the mixer can achieve high downconversion efficiency from RF to IF signals while using a minimal amount of LO signal power. In certain aspects, the disclosed designs can minimize the amount of signal reflected at the IF output (i.e., good IF matching). In certain aspects, good IF matching can mean that the mixer circuit under LO pump conditions (i.e., during operation) is about 50 ohms. In some cases, this may be the same impedance as one or more IF amplifiers.

[0022] According to embodiments, designs at higher frequencies can be formulated, manufactured and assembled with circuits that simultaneously provide improved performance by isolating the effects of circuit elements on each other while providing increased scope for circuit optimization. By increasing the available size on the filter substrate, the ohmic resistance of the filter metallization can be reduced, which in turn reduces the amount of signal that would be lost in a smaller circuit.

[0023] In some embodiments, wideband transverse waveguides are used at both the LO and RF microstrip junctions to provide a simplified circuit layout and topology. Odd-mode and transverse mode suppression slots may be used along with an air-suspended microstrip filter topology with low impedance sections of one or more filter circuits. In certain aspects, this allows the use of wide filter channels, relaxing matching tolerances, improving manufacturing yields, and reducing assembly complexity.

[0024] A microstrip circuit configuration can be used to realize the quartz filter circuit. According to an embodiment, the signal propagates longitudinally in the fundamental order Transverse Electromagnetic Mode (TEM-00), where there is no component of the electromagnetic field in the longitudinal direction, even though all power transfer is longitudinal. To propagate the TEM-00 mode, in some embodiments, the microstrip configuration consists of two conductors that are small enough to prevent the propagation of higher order modes. These conductors can include the outer walls of the filter channel and the internal filter metallization. In this geometry, the fields can be calculated using finite element analysis for each cross section and combinations thereof. When the size of the outer conductor increases relative to the signal wavelength, which may be desirable for reasons emphasized herein, it can generate higher order TEM-nn modes, such as odd modes (e.g., TEM-01 and TEM-10). As the signal propagates through the filter channel, these higher order odd modes can create blocking resonances between the filter cross sections that degrade wideband performance. Transverse wave propagation may also result in loss of power transfer between mixer circuit elements. Furthermore, using the widest possible cross section may increase the probability of odd modes and transverse wave propagation. However, to cause odd TEM modes and transverse wave propagation, lateral surface currents across the geometry (e.g., filter conductor geometry) are necessary. Thus, for example, by incorporating longitudinal slots in the first filter element, unwanted modes and propagation can be suppressed.

[0025] According to some embodiments, the use of a common centerline feed of wide longitudinal filters can minimize resistive losses for all three signals (LO, RF, IF). Additionally, the use of capacitively inductively tuned shorting pads used in conjunction with a physical DC ground can lock all three signal paths to ground at the shortest possible length, thereby increasing the inherent bandwidth of the entire circuit. This eliminates the need for separate tuning bonds / wires for each frequency, for example, further minimizing resistive losses.

[0026] 1, a cross-sectional view of a mixer 100 according to some embodiments is provided. The mixer 100 may be, for example, a heterodyne mixer including at least one of a superheterodyne, harmonic, and subharmonic mixer. In some embodiments, a balanced mixer design may be used.

[0027] The mixer 100 may include a first input 102, e.g., an LO input, a second input 104, e.g., an RF input, and a signal output 106, e.g., an output for an IF signal. According to an embodiment, the first input 102 may be a portion of the mixer 100 configured to couple a signal from a local oscillator via an LO waveguide 114 that delivers the LO signal to the mixer 100. In some embodiments, a waveguide height reduction and matching elements may be used to impedance match the LO signal to the mixer. Additionally, the second input 104 may be a portion of the mixer 100 configured to couple a signal from a radio frequency source via an RF waveguide 116. In certain embodiments, the RF waveguide 116 delivers an RF signal as part of a detection system, e.g., via one or more feed horns of a high frequency camera. In certain embodiments, the inputs 102, 104 may be antennas. An example of a machined signal path coupled to the inputs and outputs of the mixer is provided in FIG. 6A. Although shown with a waveguide input and antenna, one or more of the LO and RF signals may be delivered to the mixer 100 using other transmission elements, such as, for example, coaxial or coplanar lines. As shown in the example of Figure 1, the mixer has an RF input at one end and an IF output at the opposite end, with an LO input in between (e.g., in the center of the mixer).

[0028] The signal output 106 provides an output signal from a mixer circuit, such as a diode circuit 110. In some embodiments, the diode circuit 110 includes two Schottky diodes in an anti-parallel configuration. However, other circuits may be used. In some embodiments, the IF signal from the diode circuit 110 is output from the mixer 100 via a coaxial connection, such as a connection element 118 in the output channel. Alternatively, the IF signal may be output using one or more of a waveguide or other wired connection depending on the frequency. As indicated by the directional arrow 134, the IF signal may be transmitted from the diode circuit 110 to the output 106 along the length of the suspended transmission line element 108. In this arrangement, the LO input 102 is placed between the RF input 104 and the IF signal output 106. According to an embodiment, the RF input section 104 is located at a first end of the mixer 100 and the waveguide element 108, the IF output section 106 is located at a second end of the mixer 100 and the waveguide element 108, and the LO input section 102 is located in a central region of the mixer 100 and the waveguide element 102.

[0029] According to an embodiment, the mixer 100 includes a suspended element 108, which is a waveguide, mounted within a cavity of a mixer housing 132 via substrate mounts 120a and 120b. Thus, at least two sides (e.g., top and bottom) of the suspended waveguide element 108 are provided with an air gap 130. As another example, the suspended waveguide element 108 may have an air gap 130 on all four sides, as shown in FIG. 2A. One or more substrate mounts may be flat, as in mount 120a, or stepped, as in mount 120b. The waveguide element 108 may include a substrate portion and a patterned metal surface portion. For example, the substrate may be quartz (or another suitable dielectric, such as aluminum nitride) with a patterned gold layer forming a microstrip transmission line. Other suitable transmission line materials may include other metallic or otherwise conductive materials. The diode circuit 110 may be disposed, for example, on a patterned metal surface of the waveguide element 108 that is at least partially within the RF input 104. In some embodiments, the suspended waveguide element 108 includes suppression slots configured to suppress unwanted transmission and resonant modes. In some embodiments, the housing 132 may include a block or a portion of a block, such as, for example, a detector array block. For example, blocks 514, 600, 620, and 650 may include the housings shown in FIGS. 1-3.

[0030] According to an embodiment, a signal may propagate on the surface of the suspended waveguide element 108 along a transmission line through one or more filters. For example, the suspended waveguide element 108 may include an LO filtering / suppression section 124, an RF filtering / suppression section 126, and an RF receiving element (e.g., an antenna) 128, which may be part of the RF input section 104. The LO filtering / suppression section 124 may filter the LO signal from reaching the IF output section 106. In some embodiments, this may eliminate the need for separately machined LO and / or IF coaxial filter pins. The RF filtering / suppression section 126 may filter the RF signal from reaching the IF output section 106 and / or filter spurious signals from reaching the diode circuit 110. Additionally, the RF receiving element 128 may be configured with a number of slots (e.g., suppression slots). In some embodiments, suppression slots used along the surface of the suspended waveguide element 108 extend longitudinally and suppress odd-mode propagation. For example, a slot feature in the stripline can prevent unwanted odd modes from propagating along the stripline towards the IF output section 106 by preventing current from flowing across the width of the suspended waveguide element 108. According to an embodiment, the desired even mode propagation of the IF signal is not affected by the suppression slot.

[0031] In some embodiments, the slot has a width less than λ / 10 and a length of at least ¼λ.

[0032] According to an embodiment, a slot feature in a microstrip circuit prevents current from flowing across the width of the microstrip metal, preventing unwanted odd modes from propagating along the microstrip circuit, but allowing desirable even mode propagation to remain unaffected by the slot.

[0033] As shown in Figure 1, the mixer 100 includes one or more mounting structures 120a, 120b for the suspended waveguide element 108. Thus, in embodiments, the mixer's filters are suspended at the ends of the striplines rather than at the sides. This allows for less dielectric substrate in the cavity, which moves higher modes above the mixer's operating frequency. Also, in some embodiments, the sides of the channel cavity are flat and less likely to perturb the filter's characteristics.

[0034] According to an embodiment, one or more filters of the mixer 100 couple to at least one of the top and bottom of the housing cavity in which the mixer is mounted. For example, a suspended stripline filter can be designed such that the filter sections couple primarily to the top or bottom of the cavity, rather than to the sides of the cavity. This improves the manufacturability of the mixer, since the characteristics of the filter depend more on the size of the filter features than the size of the machined channel (or assembly location within the channel). The filter features can be more easily controlled precisely, for example, as they are defined by photolithography. In some embodiments, the width of the suspended waveguide comprises 90% or more of the width of the cavity of the housing 132. In certain aspects, the presence of a dielectric below the edges of the metallization can cause the filter sections to couple primarily to the sides of the cavity. According to an embodiment, by suspending the substrate, the walls of the cavity are moved further away from the filtering element. However, the dielectric attracts the field lines at the edges of the metallization to the sidewalls. Thus, the associated current density is higher at the edges where there are no slots, minimizing resistive losses that might otherwise be induced. For example, as shown in the example of FIG. 2A, the filter section 124 has a wide central strip 204 with slots spaced from each edge of the suspended transmission line 108.

[0035] According to embodiments, higher order transverse electromagnetic (TEM) modes that may propagate longitudinally through the microstrip circuit are suppressed by using one or more slot features near the transition between the microstrip quartz circuit and the waveguide (e.g., where the diode is located across the gap). According to embodiments, this is accomplished by interrupting the transverse surface current path across the central conductor by introducing a gap. However, longitudinal propagation of the desired fundamental mode is not affected because there is no transverse current for the fundamental mode. An aspect of this feature is shown in Figures 8A and 8B. In some implementations without these features, the higher order modes may introduce resonances in the low impedance sections of the passband of the filter, which may limit the bandwidth of the overall mixer by limiting the bandwidth and thus the operating bandwidth of the filter.

[0036] In some embodiments, the mixer 100 further includes ground connections 112a and 112b, which may be by way of a wired connection, for example. The mixer 100 may further include a regulated shorting pad 122. In some embodiments, the ground connection 112b is made from the pad 122 to the housing 132. Additionally, one side of the diode circuit 110 may be attached to the pad 122.

[0037] With regard to the tuned shorting pad 122, in some embodiments, one end of the stripline circuit is capacitively coupled to ground through a rectangular metal pad, through the stripline substrate, to the metal shelf on which it rests. This connects the circuit to ground as an effective short at the detection signal (RF) and LO mmWave frequencies through capacitive coupling. This capacitive coupling can reduce the effect of bond wire assembly variations at the ground point on the LO and RF signals. A bond wire from this pad to a metal step connects the circuit to ground at lower frequencies (low microwave) and DC. This allows the length of the lines to be significantly shorter, providing a wider bandwidth that can be achieved with a minimum bond length and number.

[0038] According to an embodiment, separately machined LO and / or IF coaxial filter pins are not required.

[0039] In certain aspects, to achieve the widest possible bandwidth, a ground connection with a minimum length close to the ground side of the diode circuit 110 is provided for all signals. Conventionally, such a connection has been achieved using a "virtual" reaction including tuning stubs with bond wires of multiples of 1 / 4λ at the LO and signal frequencies. However, according to an embodiment, the IF signal also has a short ground length to achieve wideband matching, which may not be compatible with conventional techniques. To achieve an ideal ground at all frequencies, including sufficiently high LO and signal frequencies, in some embodiments, a virtual wideband short circuit at both frequencies is achieved using a combination of the capacitance of the bond wire pad and the inductance of the short bond wire. In this embodiment, a wideband physical short circuit is achieved because the frequency of the IF signal is too low to be affected by the capacitance of the bond pad or the inductance of the bond wire, and the physical length is very short (e.g., less than λ / 10) compared to the IF wavelength.

[0040] 2A and 2B show the upper surface of the suspended waveguide 108 within the housing 132 of the mixer 100. For example, these figures show the patterned metal layers on the substrate to form the waveguide path for the signal within the mixer. In FIG. 2B, the diode circuit 110 is omitted to show the pad structure.

[0041] As shown in FIG. 2A, the upper surface of the suspended waveguide 108 may include a microstrip transmission line 202 with a wide central strip 204. In this example, an air gap 130 in a housing 132 is provided on four sides around the suspended waveguide 108 to form a cavity. The sides of the cavity are shown, for example, as cavity sidewalls 206a-d. In the top view image of the mixer 100 shown in FIG. 2B, the coupling of the waveguides 114 and 116 and the coaxial connection 118 are further shown. Although a coaxial connection is shown by way of example, other output channels may be used. According to an embodiment, the input channels may extend along a first direction while the output sections extend vertically, as shown, for example, in FIG. 6A. The waveguides 114 and 116 may be in a first plane while the output channel (e.g., with the coaxial connection 118) is in a second orthogonal plane. 2A and 2B may correspond to an LO filtering / suppression section 124, an RF filtering / suppression section 126, and an RF receiving element (e.g., an antenna) 128, in some embodiments.

[0042] 3A and 3B show further details of the surface of a waveguide element 108 according to an embodiment.

[0043] FIG. 3A illustrates an example of the LO filtering section 124 and the RF filtering section 126 on either side of the LO waveguide input 114, according to some embodiments. As illustrated in the example of FIG. 3A, the patterned transmission line on the surface of the suspended waveguide 108 includes a number of slots, which may provide one or more of unwanted mode suppression, filtering, and matching. For example, the suppression slots may provide suppression and filtering simultaneously. In some embodiments, a hammerhead filter 302 may be used and extended longitudinally to filter the LO signal from reaching the IF output 106. Similarly, the half hammerhead structure 304 provides filtering of spurious RF. In certain aspects, the hammerhead (or half hammerhead) structure may be a combination of inductive capacitances acting as an effective virtual short, spaced λ / 2 apart, that provide filtering by blocking the passage of the signal.

[0044] In an embodiment, the inclusion of the slotted suppression feature allows for a wide central path through the transmission line, thus reducing resistive losses along the length of the suspended waveguide element as the IF signal passes from the diode circuit 110 to the IF signal output 106. In an embodiment, the thickness of the metallization layer is at least three times the skin depth.

[0045] FIG. 3B illustrates a close-up view of an RF receiving element (e.g., antenna) 128 that may be part of the RF input section 104, according to some embodiments. In this example, the receiving element 128 includes a first set and a second set of slots, where the first set 306 is provided for filtering spurious RF and the second set 308 helps suppress unwanted transmission modes by providing a current block for higher order signals. According to an embodiment, the first slot 306 is wider than the second slot 308. Furthermore, in some embodiments, both the first and second sets 306, 308 are narrow enough to allow the receiving element 128 to provide broadband coupling to the RF input waveguide 116. In the drawing of FIG. 3B, the diode circuit 110 is not shown to allow various metallization layers (e.g., pads), such as pad 122, to be visible.

[0046] According to an embodiment, the mixer 100 may be optimized for a particular frequency range. For example, the width of the patterned metal features (e.g., filter width) on the surface of the waveguide element 108 may be set to about 0.3-0.4λ, where λ is the free space wavelength. For example, the filter channel width for operation at 375 GHz may be about 0.3 mm. In some embodiments, the mixer is optimized at one of 125 GHz, 250 GHz, and 375 GHz. Although specific frequencies / wavelengths are provided in this example, the design and manufacture of the disclosed mixer may be optimized over a wide range of frequencies / wavelengths. For example, the mixer 100 may be applicable as a mixer in the microwave, millimeter wave, and sub-millimeter wave ranges.

[0047] According to embodiments, the center of the LO and RF filter arrangement is designed to be as wide as possible to minimize resistive losses. In some embodiments, the width of the centerline is 30%-50% of the width of the cavity in which the mixer is mounted. In some embodiments, the width of the centerline is 50% or more of the width of the waveguide substrate. In some embodiments, the width of the line is 0.1-0.2λ at the operating frequency. For example, for optimization at 375 GHz, the width of the centerline extending from the signal end to the IF output end may be approximately 100 microns wide.

[0048] In some embodiments, the patterned metal microstrip transmission line includes a centerline that extends from the diode circuit through one or more filter elements to an output, the centerline having a width of between 0.1λ and 0.2λ, the suspended waveguide element having a width of about 0.2λ, and the substrate having a thickness of 0.04λ. The housing cavity may have a width (e.g., lateral) of about 0.35λ (e.g., 0.3-0.4λ), and the patterned microstrip transmission line is disposed within the cavity to couple the even transmission mode to the sidewalls of the housing 132 cavity.

[0049] According to an embodiment, mixer 100 may be realized without separate tuning stubs (e.g., wires) or machined LO filter pins, as contrasted with designs such as that of U.S. Pat. No. 6,399,433, which require one or more stub tuners in the form of additional wires and a quadrature coaxial filter at the IF output to handle LO signal filtering.

[0050] According to an embodiment, an open circuit waveguide probe is also used to achieve the highest bandwidth in the RF and LO input circuits, which may provide an improvement over the open circuit waveguide probe since a shorted waveguide is inherently narrowband and often results in poor power coupling over the desired band.

[0051] 4, a method 400 of operating a mixer according to some embodiments is provided. The mixer may be, for example, mixer 100 or any other mixer having the features shown with respect to Figures 1, 2A, 2B, 3A, 3B, and 6A.

[0052] Method 400 may begin at step s410, which includes receiving an RF signal at a first input of a mixer apparatus having a suspended waveguide element, a number of suppression elements, and a diode circuit. At step s420, a local oscillator signal is provided to the mixer. At step s430, an intermediate frequency (IF) signal generated by the diode circuit is output. According to an embodiment, outputting the IF signal includes propagating the signal through a number of filters along a length of the mixer (e.g., mixer 100). The filters may be, for example, part of the number of suppression elements. According to some embodiments, the RF and LO signals are received and provided along a first axis relative to the mixer, while the IF is output along a different, perpendicular axis.

[0053] 5, a detection system 500 according to some embodiments is provided. In this example, an array of feed horns 502 provides RF signals to one or more mixers 504, such as the mixer(s) 100 described above. The RF signals may be mixed with an LO signal 512 from a source 508, such as one or more Gunn oscillator sources. The resulting IF may then be provided to processing circuitry 506 for further processing, including one or more of amplification, filtering, analog-to-digital conversion, and image generation. In some embodiments, the output IF is provided from the mixers to the one or more processing circuits 506 via a coaxial line. In some embodiments, the feed horns 502, mixers 504, and signal paths (e.g., 512) may be housed within block 514. Blocks for use with one or more mixers described herein are shown, for example, with respect to FIGS. 6A-6C.

[0054] According to an embodiment, the set of mixers 504 includes at least three types of mixers, where a first mixer is optimized at a first frequency, a second mixer is optimized at a second frequency, and a third mixer is optimized at a third frequency. In this example, all types of mixers follow the design and configuration of mixer 100 shown in Figures 1-3. In some embodiments, the frequencies are 125 GHz, 250 GHz, and 375 GHz. In some embodiments, a fourth type of mixer using the design and configuration of mixer 100 is included, where the fourth type of mixer is optimized at 500 GHz.

[0055] 6A, two machined halves of a detector block 600 are shown according to some embodiments. In this example, a first machined portion 602 can be combined with a second machined portion 604 to form a detector block. The block may include, for example, the housing 132 and block 514 of the mixer 100. As shown in FIG. 6A, each of the halves may include one or more feed horn portions 606, which may act as channels for sending RF signals to the mixer 100. In addition, each of the halves may include an input signal (e.g., LO) transmission portion 608 and a mixer cavity, shown in detail 610. Additionally, in some embodiments, the mixer may couple its output to a signal output 612 (e.g., including a coaxial line or other transmission line), which may be formed within each block half such that the coaxial cable may extend through the mixer housing 132. The output 612 may carry, for example, an IF signal generated by the mixer. According to an embodiment, the feed horn 606 and the LO input section 608 may be machined along the same axis (e.g., the x-axis) or in the same plane (e.g., the plane formed by the x-axis and the z-axis). Additionally, in some embodiments, the mixer output section 612 may be machined in a perpendicular / orthogonal manner (e.g., along the y-axis). In this regard, the output signal from the mixer may be sent in a direction different from the direction in which the input signal is received. For example, the signal may be output in a direction perpendicular to the plane in which the signal is received.

[0056] 6B and 6C, one or more detector array blocks are shown according to some embodiments. These may correspond to, for example, array 502 and block 514. A detector element, such as block 514 having an array of feed horns 502, may be formed as a single block (e.g., as shown in FIGS. 6A and 6B). A detector element may also be formed from multiple blocks (e.g., by two sub-blocks as shown in FIG. 6C) to form a composite detector block having multiple rows and columns of feed horns. Additionally, according to an embodiment, each sub-block may be formed from two parts as shown with respect to FIG. 6A, which shows a half block portion 602 attached to another half block portion 604 to form block 600.

[0057] Referring now to FIG. 6B, a block 620 according to some embodiments is provided. In some cases, one or more detector arrays 502 and block 514 may include block 620. Block 620 includes one or more signal inputs 622, one or more secondary inputs 624, and one or more outputs 626. For example, signal inputs 622 may correspond to the detector feed horns shown in FIG. 2, FIG. 5, FIG. 6A, and FIG. 9. Similarly, secondary input(s) 624 may be LO signal inputs, for example as described with respect to FIG. 2, FIG. 5, FIG. 6A, and FIG. 9. Output(s) 626 may be detector signal outputs, such as one or more IF signals from mixer 100, for example as described with respect to FIG. 9. According to an embodiment, the inputs are provided in the same plane, while the outputs are provided in a lateral plane. In the example of FIG. 6B, inputs 622, 624 are provided along the x-axis, while output 626 is provided along the y-axis. According to an embodiment, a processing circuit may be connected to the output 626. For example, multiple processing circuit units may be stacked in the z-axis direction to process the signal output from the block 620. Similarly, additional blocks may be stacked in the z-axis direction to expand the detector. FIG. 6C shows a similar arrangement with elements 660a-n. Such circuitry may include, for example, one or more LNAs, wideband power detectors, and / or ADCs, as shown with respect to FIG. 9. 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 circuit may include one or more filters, for example, on either side of the LNA or ADC. According to an embodiment, the power detectors, such as 921a, 921b, 921c, detect the power over the entire band and output a voltage related to the power.

[0058] 6C, in accordance with an embodiment, a first block (e.g., block 620) may be combined with a second block (e.g., 650) to form a single detector array block, such as block 514 with array 502. In this example, inputs 652 and 654 of block 650 are disposed in a single plane along the x-axis, and outputs 656 are disposed vertically along the y-axis. With the inputs and outputs disposed in this manner, processing circuits 660a-n may be stacked in the z-axis direction on the outer surface of blocks 620, 650 without interfering with the capture of a signal from a source by input 652 or blocking the transmission of an LO to input 654. Although circuits 660a-n are shown on the block 620 side of the array, the stack may also be disposed on the other side of the array (e.g., block 650 side). In this regard, a first stack of processing circuits 660a-n may be provided on one side of the array, a second stack of processing circuits 660a-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 660a-n may include, for example, at least one of one or more LNAs, an AM (envelope) power detector, and an ADC, as well as possibly filters, etc.

[0059] Although the array in FIG. 6C is shown with two connected blocks, embodiments are not so limited. For example, according to embodiments, the detector array may be formed of blocks that are not directly connected, or may be formed of more than two blocks. For example, processing circuitry 660a-n may be placed between two sub-blocks of the array (e.g., between blocks 620 and 650). 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 to more than three blocks. The detector array can also be expanded in the z-direction, for example by stacking additional blocks 620, 650. According to embodiments, the upper and lower surfaces of the array blocks 620, 650 are free of inputs and outputs, allowing another block to be stacked on top of them without obstruction. Some embodiments include a block 620, 650 having six major sides and having inputs and / or outputs exposed to the outside (e.g., inputs and / or outputs in the x- and y-directions through the block) but not exposed on the top or bottom (e.g., in the z-direction).

[0060] According to embodiments, the detection system may be optimized for up to four detection frequency bands. According to embodiments, 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 band is + / - 20% of the center frequency for the waveguide.

[0061] 7, according to some embodiments, a method 700 of manufacturing a mixer device is provided. The method may be used to manufacture the mixer 100, for example, as shown with respect to Figures 1-3, and to form the machined portions 602, 604 shown in Figure 6A.

[0062] Method 700 may begin at step s710, which includes machining a first housing component (e.g., 602) including a first radio frequency channel portion, a first local oscillator portion, a first intermediate frequency channel portion, a first cavity portion, a first mounting shelf portion, and a second mounting shelf portion. In step s720, a second housing component (e.g., 604) is machined, the second housing component including a second radio frequency channel portion, a second local oscillator portion, a second intermediate frequency channel portion, a second cavity portion, a third mounting shelf portion, and a fourth mounting shelf portion. The method may further include suspending a waveguide element within at least one of the first and second cavity portions by mounting the waveguide element on at least one of the first and second mounting shelf portions and the third and fourth mounting shelf portions (s730). This may be, for example, waveguide element 108. The method 700 may further include attaching the first housing component to the second housing component to form a block (s740). For example, the method may be used to form a block (or multiple blocks) as shown in Figures 6B and 6C.

[0063] According to an embodiment, two halves of a complete feed horn are machined into each half of the block using a bullnose cutter and a 5-axis machine. This allows flexibility in horn shape, such as an elliptical cross-section horn. This allows the beam pattern of the feed horn to be adjusted to achieve optimal optical coupling. For example, a circular horn provides an elliptical beam that must be corrected by the optics or the image may have inadequate stigmatism. However, an elliptical feed horn can achieve a circular beam that does not require correction. Thus, according to some embodiments, a feed horn (e.g., for delivering received RF to mixer 100) may have an elliptical shape.

[0064] Now referring to Figures 8A and 8B, electric and magnetic fields are shown. For example, Figure 8A shows a transverse electromagnetic mode 802. When the microstrip outer channel is less than half the guided wavelength, typically only the fundamental transverse electromagnetic mode (TEM-00) can exist. In this case, the electric and magnetic field lines are transverse and propagate in the same direction from the inner conductor to the outside of the metal channel, or loop in the same direction around the filter metallization (a conductor in air in this example), as shown, for example, in 804, which shows the transmission passband. The arrangement is further shown by 808 with circuit lines (e.g., gold) 810 on a quartz substrate 812.

[0065] The dimensions of the effective microstrip filter metallization width and the external channel width scale inversely as a function of frequency, so that at higher frequencies, the width of the filter metallization pattern and the channel in which it is located becomes very small, both of which make manufacturing difficult and costly, and the dimensional requirement that the external width of the channel remain less than half the guided wavelength increases. When this condition cannot be met (e.g., either is greater than half the guided wavelength), higher order transverse and longitudinal modes can be excited (e.g., by discontinuities in the channel or the filter) and propagate. This situation is shown at 814. The electric and magnetic field lines are no longer uniform and resonant conditions may occur, resulting in non-uniform behavior as a function of frequency and reflected power as shown at 806, where resonances appear in the passband. These resonances can reduce the smooth wideband operation of the mixer.

[0066] Microstrip filters will often cascade quarter-wavelength low and high impedance sections. The filter is most sophisticated when the ratio of high to low impedance sections is greatest, which is achieved with the narrowest and widest lines. This is shown in FIG. 8B by 822 and 824, respectively. Thus, the performance of such filters is fundamentally limited when the generation of higher order modes is considered, since there is a finite width before the higher order modes are excited and introduce resonant reflections into the filter frequency response. Aspects of the present disclosure can provide the benefits of wider lines (e.g., lower impedance and improved filtering) without the adverse effects of higher order mode propagation. This can be achieved, for example, by the inclusion of current interruptions or slots along the length of the filter sections, as shown at 830 in FIG. 8B. This is in contrast to 826, as shown at 828, where the current flows uninterrupted, resulting in non-ideal passband performance. When higher modes are generated, current no longer flows only along the longitudinal direction as in the case of the fundamental mode, but also laterally through the filter metallization. By introducing a current block, these transverse currents are blocked and the excitation of higher modes is suppressed even if it would otherwise be possible due to the width of both the filter section and the channel. A significantly lower impedance filter section is achieved, as shown at 832, along with a smooth filter frequency behavior.

[0067] 9, a schematic diagram of a detection system 900 according to some embodiments is provided. In some embodiments, the system 500 can be implemented using the arrangement of FIG.

[0068] Radiation may be received at inputs 902, 904, and 906, which may be feed horns of blocks 908, 910, and 912, respectively. In some embodiments, each of blocks 908, 910, and 912 may form part of at least one of detector arrays 502, 514, 600, 620, and 650. Each of the radiation signals received at inputs 902, 904, 906 is sent to a mixer element, shown as elements 914a, 914b, and 914c, which may be, for example, mixer 100. In some embodiments, one or more of the received signals may be rotated prior to processing by the mixer, such as by optional polarization rotation element 916. The processed signals from the mixers, such as one or more intermediate frequency (IF) signals, are sent to the output of each block (918a, 918b, 918c) for further processing by low noise amplifiers (LNAs) (920a, 920b, 920c), power detectors (921a, 921b, 921c), and analog-to-digital converters (ADCs) (922a, 922b, 922c). Additional processing may include filtering. The digital signals are then sent to an image generator 924 to form an image based on the detected radiation, such as a composite image of an object or scene using the radiation received at 902, 904, and 906. The image processing 924 may be coupled to or part of a display system 936, such as a computer or monitor. In some embodiments, the IF signals are output using coaxial cables within each block.

[0069] Although the system is shown with three mixer elements or inputs, the system may be implemented with more or fewer elements. For example, system 900 may be expanded to include a fourth set of input feed horns, each with a corresponding set of mixers and processing circuitry. In addition, blocks 908, 910, and 912 may each include an array of inputs and multiple mixers 100. Information may be processed by a stack of circuits as shown in FIG. 6C.

[0070] In some embodiments, local oscillator (LO) signals are provided to the mixers of system 900 using fewer LO sources than mixers. For example, in the example shown in FIG. 9, a single LO source 926 provides an LO signal to each of mixers 914a-c. According to an embodiment, this is accomplished using one or more power splitters 928a, 928b and possibly one or more frequency multipliers 930a-c, such as doublers or triplers. For example, the original LO signal from source 926 may be provided to splitter 928a, which then provides a signal to splitter 928b and optional multiplier 990a. Multiplier 930 may be used to provide a higher frequency LO signal to mixer 914a than that provided by source 926. Similarly, splitter 928b may provide a signal to optional multipliers 930b and 930c for mixers 914b and 914c. In this regard, each of blocks 908, 910, and 912 may be configured for operation at different frequencies / wavelengths. Such configurations may include, for example, mixer design and input feed horn shape and dimensions. Thus, to form a composite image using data from multiple wavelengths, processing circuitry 924 may detect, process, and use radiation signals at different wavelengths. One or more amplifiers, such as amplifier 992, may be used to boost the signal between at least one of the source, splitter, multiplier, and mixer. Other amplifiers are not shown in the example of FIG. 9.

[0071] The size of the feed horns should be selected to provide optimum coupling for the selected optical system, and the spacing should be selected to provide optimum coverage for the application.

[0072] 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 reflection issues, a 90 degree 3 dB hybrid power splitter, such as a Magic-T or 3 dB hybrid branch guide coupler, may be implemented. Although a single LO 926 is shown, multiple LOs may be used depending on the embodiment.

[0073] In some embodiments, one or more of the dividers 928a and 928b are unequal dividers. In some embodiments, the multipliers 930a and 930b are doublers, while the multiplier 930c is a tripler. In some embodiments, one or more of the multipliers are not required. For example, in some embodiments, the multiplier 930a may be omitted.

[0074] According to some embodiments, a common local oscillator source 926 is provided and the frequency is multiplied using frequency multipliers of different orders (e.g., doublers and triplers) to realize a sub-harmonic mixer. For example, the mixers 914a-c may operate in bands centered on frequencies 125 GHz, 250 GHz, and 375 GHz, respectively, and they may use local oscillator frequencies of 62.5 GHz, 125 GHz, and 187.5 GHz. In this example, the base local oscillator source 926 may be a Gunn oscillator providing approximately 100 mW operating at 62.5 GHz. This is split into two equal signals using a splitter, such as divider 928a. This splitter may be an equal power splitter, such as a standard magic tee, or an unequal splitter. One half of the splitter output pumps the 125 GHz array (block 908 in this example) and the second half is input to a power amplifier (e.g., amplifier 992 in this example) to provide a signal of about 400 mW, which is then used to pump the frequency multipliers 930b and 930c. As a sub-harmonic mixer is used in this frequency example, multiplier 930a 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 may result in excess power (80 mW) being produced for the 250 GHz array (e.g., block 910 in this example) and marginal power being produced for the 375 GHz array (e.g., block 912 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 could result in excessive power being provided to the 125 GHz doubler (e.g., multiplier 930b) and insufficient power being provided to the 187.5 GHz tripler (e.g., multiplier 930c). Thus, to provide sufficient power to the tripler, which is typically less efficient than the doubler, the power amplifier would need to be overspecified, and the power to the doubler would be unnecessarily attenuated (or the doubler could be damaged). Therefore, and 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 split according to their respective power requirements. According to an embodiment, at least one of the splitters 928a and 928b 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 therefore costs).

[0075] 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. 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. 9. In some embodiments, this block may be a sub-block or at least one of arrays 514, 620, and 650.

[0076] According to some embodiments, the LO source 926 may have multiple outputs at one or more frequencies, and the initial splitter 928a and / or multiplier 930a may not be required. In some embodiments, one or more of the splitter 928a and multiplier 930a are integrated into the local oscillator source 926, such that the source 926 provides a multiple frequency signal 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.

[0077] The Earth's atmosphere provides a unique illumination signature through the observed atmospheric frequency transmission, 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 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 transmission is highest, the Earth's atmosphere is transparent, so 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 atmosphere has low transmission, the scene is dominated by the "warm" illumination from the air column above the scene. According to embodiments, a mixture of high, medium, and low transmission wavelengths may be used to provide color scenes in which different contrast types are realized. Experimental investigations have determined that these wavelengths are bands centered at approximately 125 GHz, 250 GHz, and 375 GHz, up to approximately 35 GHz wide.

[0078] 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.

[0079] 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 example 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.

[0080] 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. Thus, it is contemplated 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, except where a step is expressly described as following or preceding another step and / or where it is implicit that a step must follow or precede another step, the steps of any method disclosed herein need not be performed in the exact order disclosed.

Claims

1. A heterodyne mixer apparatus (100), comprising: A first input unit (102); A second input unit (104); An output unit (106); a suspended signal transmission element (108) including a plurality of suppression slots and a plurality of filter elements for suppressing unwanted transmission and resonant modes; a diode circuit (110) mounted on a first end side of the suspended signal transmission element and electrically coupled to the suspended signal transmission element; Including, the first input is a local oscillator (LO) input; the second input is a radio frequency (RF) input; the output is an intermediate frequency (IF) signal output; the suspended signal transmission element is a waveguide element; the radio frequency (RF) input is located at the first end; the intermediate frequency (IF) signal output section is located on a second end side of the suspended signal transmission element; the local oscillator (LO) input is located between the radio frequency (RF) input and the intermediate frequency (IF) signal output; Device.

2. 2. The apparatus of claim 1, The suspended signal transmission element includes: a substrate having a first and a second surface; a transmission line (202) on the first surface; the transmission line is a patterned metal microstrip transmission line including one or more of the plurality of suppression slots and the plurality of filter elements; Device.

3. 3. The apparatus of claim 2, The substrate is a quartz substrate. Device.

4. The device according to any one of claims 2 to 3, the first input is located between the second input and the output; the waveguide element is configured to transmit a signal generated in the diode circuit from the diode circuit to the output along a longitudinal axis of the waveguide element. Device.

5. 5. The apparatus of claim 4, the signal generated in the diode circuit is an IF signal; Device.

6. The device according to any one of claims 2 to 5, a housing (132) having a first mounting shelf (120a), a second mounting shelf (120b), and a cavity; The suspended signal transmission element is mounted on the first and second mounting shelves within the cavity to form an air gap between the suspended signal transmission element and the housing on at least two sides of the suspended signal transmission element.

7. 7. The apparatus of claim 6, the housing is made of machined metal and the cavity is formed on four sides of the suspended signal transmission element; Device.

8. 8. An apparatus according to claim 6 or 7, comprising: the suspended signal transmission element extends along a length of the heterodyne mixer apparatus between the first and second mounting shelves; Device.

9. An apparatus according to any one of claims 6 to 8, The housing includes: a first channel coupled to the first input; a second channel coupled to the second input; and a third channel coupled to the output; the second channel includes one or more feed horns of a radiation detector; the first and second channels are disposed along a same plane of the housing, and the third channel is disposed along a direction perpendicular to the plane; Device.

10. 10. The apparatus of claim 9, The radiation detector is a terahertz camera. Device.

11. An apparatus according to any one of claims 6 to 10, the diode circuit includes two Schottky diodes in an anti-parallel configuration; Device.

12. An apparatus according to any one of claims 6 to 11, the suspended signal transmission element includes a first filter element for an LO signal, a second filter element for an RF signal, and an RF receiving antenna; each of the first filter element, the second filter element, and the RF receive antenna includes one or more of the plurality of suppression slots; Device.

13. 13. The apparatus of claim 12, each of the first filter element and the second filter element includes one or more hammerhead or half-hammerhead filter components; the plurality of suppression slots of the RF receive antenna include at least one slot of a first width and a second slot of a second, different width. Device.

14. An apparatus according to any one of claims 6 to 13, comprising: the patterned metal microstrip transmission line includes a centerline extending from the diode circuit through one or more filter elements to the output; Let λ be the wavelength of the signal received at the second input, the width of the centerline is 0.1λ or more, the width of the suspended signal transmission element is about 0.3λ, and the thickness of the substrate is 0.1λ or less; Device.

15. 15. The apparatus of claim 14, the signal received at the second input is a detected RF signal; Device.

16. An apparatus according to any one of claims 6 to 15, the cavity in the housing has a lateral width of 0.3 to 0.4 λ, where λ is the wavelength of a signal received at the second input; the patterned microstrip transmission line is disposed within the cavity to couple an even transmission mode to a sidewall of the cavity of the housing. Device.

17. An apparatus according to any one of claims 6 to 16, comprising: the signal received at the second input is one of a 125 GHz signal, a 250 GHz signal, a 375 GHz signal, and a 500 GHz signal; Device.

18. An apparatus according to any one of claims 6 to 17, a first wire connected to the output; a second wire connected to the inductively tuned capacitive pad and to a surface of the housing; The apparatus further comprising:

19. 20. The apparatus of claim 18, the diode circuit is attached to the second input and to the inductively tuned capacitive pad; Device.

20. An apparatus according to any one of claims 6 to 19, the cavity is bisected at the first input by a local oscillator waveguide path; Device.

21. An apparatus according to any one of claims 1 to 20, the second input is a broadband input including a broadband RF antenna; Device.

22. An apparatus according to any one of claims 1 to 21, the plurality of restraining slots include a plurality of gaps on a surface of the suspended signal transmission element; Each of the gaps extends along a longitudinal direction of the suspended signal transmission element. Device.

23. A detector (500, 900), One or more heterodyne mixer devices according to any one of claims 1 to 22; one or more feed horns (502) coupled to the second input of at least one of the one or more heterodyne mixer devices (504); and a local oscillator (508) coupled to the first input of at least one of the one or more heterodyne mixer units; an output channel coupled to the output of at least one of the one or more heterodyne mixer devices; one or more of a low noise amplifier, a power detector, and an analog-to-digital converter connected to the output channel and configured to process (506) an output IF signal from at least one of the one or more heterodyne mixer units; a detector.

24. 24. A detector as claimed in claim 23, comprising: the detector is a terahertz camera; the output channel includes a coaxial line (118); Detector.

25. 25. A detector according to claim 23 or 24, comprising: the one or more heterodyne mixer devices A plurality of heterodyne mixer devices optimized at 250 GHz; A plurality of heterodyne mixer devices optimized at 375 GHz; a detector.

26. A detector according to any one of claims 23 to 25, the one or more heterodyne mixer devices include a plurality of heterodyne mixer devices optimized at 125 GHz or 250 GHz; Detector.

27. A terahertz camera (500, 900), one or more mixers (100, 504, 914) including an IF output, an LO input, and an RF input; one or more feed horns (502, 902, 904, 906) coupled to an RF input of at least one of the one or more mixers; a local oscillator (508, 926) coupled to an LO input of at least one of the one or more mixers; one or more of a low noise amplifier (920), a power detector (921), and an analog-to-digital converter (922) connected to the IF output (918) and configured to process an output IF signal from at least one of the one or more mixers; Including, At least one mixer of the one or more mixers is a suspended signal transmission element (108) including a plurality of suppression slots and a plurality of filter elements for suppressing unwanted transmission and resonant modes; a diode circuit (110) mounted to a first end of the suspended signal transmission element and electrically coupled to the suspended signal transmission element and configured to generate the output IF signal based on radiation received at one or more of the feed horns and a power signal from the local oscillator; Further comprising: the suspended signal transmission element is a waveguide element; the RF input portion is located on the first end side, the IF output unit is located on a second end side of the suspended signal transmission element, the LO input is located between the RF input and the IF output; camera.

28. 28. The camera of claim 27, the suspended signal transmission element is arranged to transmit the output IF signal generated in the diode circuit from the diode circuit to the IF output along a longitudinal axis of the suspended signal transmission element. camera.

29. 29. A camera according to claim 27 or 28, the IF output section includes a coaxial line; camera.

30. The camera according to any one of claims 27 to 29, the received radiation includes radiation located within a frequency band centered at about 125 GHz, 250 GHz, or 375 GHz; camera.

Images