Broadband High-Integration Millimeter-Wave Complex Correlation Receiver Front-End

Abstract

This invention provides a broadband, highly integrated millimeter-wave complex correlation receiving front-end, relating to the field of microwave radiometer technology. The highly integrated broadband millimeter-wave complex correlation receiving front-end of this invention includes: an integrated housing with an internal cavity; a millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis, analog complex correlation processing, and power control integrated within the cavity. The input of the distributed frequency synthesis is connected to a system synchronization reference signal, and its output is connected to the millimeter-wave receiving front-end, providing the millimeter-wave receiving front-end with a system-coherent millimeter-wave local oscillator signal. This invention employs distributed frequency synthesis technology to realize the generation, transmission, and distribution of millimeter-wave local oscillators within each broadband millimeter-wave complex correlation receiving front-end, simplifying the system architecture and solving the drawbacks of high transmission and distribution losses and easy self-oscillation of millimeter-wave local oscillators within traditional millimeter-wave synthesized aperture radiometer arrays.

Description

Technical Field

[0001] This invention relates to the field of microwave radiometer technology, and in particular to the construction of a complex correlation receiving front-end in a millimeter-wave synthetic aperture radiometer array, specifically to a broadband, highly integrated millimeter-wave complex correlation receiving front-end. Background Technology

[0002] Millimeter-wave synthetic aperture radiometer arrays (SARs) are attracting increasing attention due to their ability to observe targets around the clock without relying on external radiation sources. The broadband millimeter-wave complex correlation receiver front-end, a fundamental component of the SAR system, is responsible for amplifying the weak microwave energy emitted by the observed target with low noise, performing phase-shifting mixing and complex correlation processing to obtain a voltage signal proportional to the target's radiation brightness temperature. Its performance directly affects the SAR array's specifications.

[0003] like Figure 1 The diagram shows a conventional millimeter-wave synthetic aperture radiometer array design containing N channels (typically N≥8) of complex correlation receiving front-ends. Due to the constraints of the operating frequency, existing millimeter-wave synthetic aperture radiometer arrays generally employ a discrete design for their complex correlation receiving front-ends, achieving the required system functions through the cascading of single functional modules.

[0004] For example, an N-channel broadband millimeter-wave low-noise receiver front-end is composed of N independent basic receiver units. The millimeter-wave low-noise amplifier, millimeter-wave preselection filter, and millimeter-wave mixer chips in each basic receiver unit channel are cascaded and packaged in a hermetically sealed metal housing using micro-assembly technology. The intermediate frequency filter amplification module is usually designed using hybrid integrated circuit technology, integrating 2N intermediate frequency amplifier chips, digitally controlled attenuator chips, and LC filters into another hermetically sealed module using hybrid integrated circuit technology. The 2N-channel analog complex correlation processing module uses reflow soldering technology to cascade broadband baluns, broadband analog multipliers, operational amplifiers, and other packaged devices on a printed circuit board, and uses a metal cavity for shielding. Then, the packaged different functional modules are fixed to the structural components and interconnected through RF / low-frequency cables to form a millimeter-wave complex correlation receiver front-end. The N coherent local oscillator signals required for phase-shifting mixing in the millimeter-wave complex correlation receiver front-end are also generated and distributed in a centralized manner. The millimeter-wave frequency synthesis also uses micro-assembly technology to cascade phase-locked loop chips, amplifier chips, power divider chips and filter chips and encapsulate them in a hermetically sealed metal box. After power division, the millimeter-wave local oscillator is sent to each functional module through radio frequency cables.

[0005] As can be seen from the above description, the phase-shifting mixing local oscillator required by the complex correlation receiving front-end inside the existing millimeter-wave synthetic aperture radiometer array adopts centralized generation, transmission and distribution, which has the drawback of high loss. It requires cascading multiple millimeter-wave amplifier circuits to compensate for the local oscillator power, which is prone to self-excitation and oscillation, thus restricting the array expansion of the millimeter-wave synthetic aperture radiometer array. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] To address the shortcomings of existing technologies, this invention provides a broadband, highly integrated millimeter-wave complex correlation receiving front-end, which solves the technical problem of high phase-shifting mixing local oscillator loss required in existing complex correlation receiving front-ends within millimeter-wave synthetic aperture radiometer arrays.

[0008] (II) Technical Solution

[0009] To achieve the above objectives, the present invention provides the following technical solution:

[0010] This invention provides a highly integrated broadband millimeter-wave complex correlation receiving front end, comprising: a dual-waveguide broadband impedance transformer, an integrated housing with an internal cavity, and a millimeter-wave receiving front end integrated in the cavity, intermediate frequency filtering and amplification, distributed frequency synthesis, analog complex correlation processing, and power control.

[0011] The dual-waveguide broadband impedance transformer is implemented by connecting a stepped impedance transformer with a radio frequency insulator.

[0012] The input of the distributed frequency synthesis is connected to the system synchronization reference signal, and the output is connected to the millimeter-wave receiving front end to provide the millimeter-wave receiving front end with a system-coordinated millimeter-wave local oscillator signal.

[0013] The millimeter-wave receiving front-end input is connected to a dual-channel interference antenna via a dual-waveguide broadband impedance transformer, and the output is connected to an intermediate frequency filter amplifier.

[0014] The intermediate frequency filtering and amplification process outputs a pair of in-phase and a pair of quadrature intermediate frequency signals to the analog complex correlation processor after filtering and amplification.

[0015] The power control provides a low-noise, highly stable power supply for the millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis, and analog complex correlation processing.

[0016] Preferably, the distributed frequency synthesis assembly includes a phase-locked crystal oscillator, a phase-locked loop chip, an active fourth frequency multiplier chip, a MEMS filter, a low phase noise amplifier chip, and a power divider chip.

[0017] The phase-locked crystal oscillator generates a reference signal that is correlated with an external reference;

[0018] The phase-locked loop chip and MEMS filter perform frequency multiplication and phase-locking processing on the reference signal to generate a high-quality, low-phase-noise X-band coherent local oscillator signal and then filter it.

[0019] The active quadruple frequency chip uses a direct synthesis method to generate the low phase noise local oscillator required for zero intermediate frequency mixing in the millimeter wave band.

[0020] Preferably, the intermediate frequency (IF) filtering and amplification includes four identical IF filtering and amplification channels. Each IF filtering and amplification channel is internally equipped with a low-noise amplifier chip, a low-pass filter chip, a digitally controlled attenuator chip, and an LC bandpass filter. The input end of the IF filtering and amplification channel is connected to the output of the millimeter-wave receiving front end, and the output end is connected to the analog complex correlation processing section. The IF signals of one pair in phase and one pair of quadrature are filtered, amplified, and then output to the analog complex correlation processing section.

[0021] Preferably, the analog complex correlation processing includes two completely identical analog correlation channels, which perform correlation operations on a pair of in-phase intermediate frequency signals with bandwidths of DC to N / 2 GHz and a pair of quadrature intermediate frequency signals with bandwidths of DC to N / 2 GHz, respectively. After active differential filtering, a pair of quadrature IQ signals are output.

[0022] Preferably, the power supply control internally includes a linear low-dropout regulator, a voltage reference, and a series-to-parallel conversion circuit;

[0023] The linear low-dropout regulator is used to convert the positive and negative switching power supply generated by the external input DC-DC converter into a high-precision, low-noise linear ±5V power supply circuit.

[0024] The voltage reference provides a high-precision and highly stable reference voltage for high-performance broadband analog multipliers and active differential filters;

[0025] The serial-to-parallel conversion circuit includes an SPI control interface.

[0026] Preferably, the cavity comprises a double-sided cavity with a front cavity and a rear cavity; the front cavity houses a millimeter-wave receiving front-end, an intermediate frequency filter amplification, a distributed frequency synthesis, and an analog complex correlation processing; the rear cavity houses a power control system.

[0027] In the front cavity, the functional components are arranged in a completely isolated manner, except for the slots necessary for interconnection.

[0028] The power control in the rear cavity and the millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis, and analog complex correlation processing in the front cavity are electrically connected by through-welding of high-temperature insulated wires.

[0029] Preferably, both the millimeter-wave receiving front-end and the distributed frequency synthesis assembly adopt microwave monolithic circuit integration design, and the chips corresponding to the millimeter-wave receiving front-end and the chips corresponding to the distributed frequency synthesis assembly are assembled using micro-assembly technology. The electrical signal transmission substrate used for assembly is a high-frequency complex dielectric board.

[0030] Preferably, the intermediate frequency filtering and amplification adopts an integrated design of MMIC microwave monolithic circuit and LC packaged filter, and is assembled using hybrid integrated circuit technology. The electrical signal transmission substrate used for assembly is a glass fiber board.

[0031] Preferably, all devices in the analog complex correlation processing are assembled into a single board using a reflow soldering process, and a multilayer PCB made of fiberglass board is used as the electrical signal transmission substrate.

[0032] Preferably, all components in the power control system are assembled on a single board using a reflow soldering process, and a multilayer PCB made of fiberglass board is used as the electrical signal transmission substrate.

[0033] (III) Beneficial Effects

[0034] This invention provides a broadband, highly integrated millimeter-wave complex correlation receiver front end. Compared with the prior art, it has the following advantages:

[0035] 1. This invention employs distributed frequency synthesis technology to realize the generation, transmission and distribution of millimeter-wave local oscillators within each broadband millimeter-wave complex correlation receiving front end, simplifying the system architecture and solving the drawbacks of high loss and easy self-excitation of millimeter-wave local oscillators in the centralized transmission and distribution of millimeter-wave local oscillators in traditional millimeter-wave integrated aperture radiometer arrays.

[0036] 2. The broadband millimeter-wave complex correlation receiving front-end of this invention integrates multiple functional units, enabling a single receiving front-end to possess complete system functions. This facilitates the expansion of the array size. The integrated design of the receiving front-end improves circuit integration and utilization, achieves cableless design, and minimizes volume, weight, and manufacturing costs. This ensures a significant reduction in the overall size, weight, and manufacturing cost of the synthetic aperture radiometer array, meeting the requirements of mass production and debugging, further promoting the engineering application of synthetic aperture radiometer arrays, and enhancing competitiveness. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 Block diagram of a broadband millimeter-wave complex correlation receiver front-end for an existing conventional synthetic aperture radiometer array;

[0039] Figure 2 This is a block diagram illustrating the structural composition of a broadband, highly integrated millimeter-wave complex correlation receiver front-end provided in an embodiment of the present invention.

[0040] Figure 3 This is a schematic diagram of an expanded N broadband millimeter-wave complex correlation receiving front-end in a synthetic aperture radiometer array provided in an embodiment of the present invention;

[0041] Figure 4 This is a schematic diagram of the overall structure of the broadband highly integrated millimeter-wave complex correlation receiving front-end provided in an embodiment of the present invention;

[0042] Figure 5 This is an exploded view of the broadband highly integrated millimeter-wave complex correlation receiving front-end provided in an embodiment of the present invention;

[0043] Figure 6 This is a schematic diagram of the front cavity of the broadband highly integrated millimeter-wave complex correlation receiving front end provided in an embodiment of the present invention;

[0044] Figure 7 This is a schematic diagram of the structure of the back cavity of the broadband highly integrated millimeter-wave complex correlation receiving front end provided in an embodiment of the present invention;

[0045] Figure 8 A circuit block diagram of a broadband, highly integrated millimeter-wave complex correlation receiver front-end provided in an embodiment of the present invention;

[0046] Figure 9 A schematic block diagram of a millimeter-wave receiving front-end provided in an embodiment of the present invention;

[0047] Figure 10 This is a block diagram illustrating the principle of distributed frequency synthesis provided in an embodiment of the present invention.

[0048] Figure 11 This is a block diagram illustrating the principle of intermediate frequency filtering and amplification provided in an embodiment of the present invention.

[0049] Figure 12 This is a block diagram illustrating the principle of simulated complex correlation processing provided in an embodiment of the present invention.

[0050] Figure 13 A principle block diagram of power control provided for an embodiment of the present invention;

[0051] Among them, 1 is the front laser sealing cover; 2 is the back laser sealing cover; 3 is the shielding cover; 4 is the front screw-on cover; 5 is the back screw-on cover; 6 is the integrated metal housing; 7 is the dual waveguide broadband impedance converter; 8 is the millimeter wave receiving front end; 9 is the intermediate frequency filtering and amplification; 10 is the distributed frequency synthesis; 11 is the analog complex correlation processing; 12 is the power control, with the left power control unit 1201 and the right power control unit 1202. Detailed Implementation

[0052] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0053] This application provides a broadband, highly integrated millimeter-wave complex correlation receiver front-end that employs distributed phase-coordinated frequency synthesis technology. This addresses the shortcomings of traditional millimeter-wave synthesized aperture radiometer arrays, which suffer from high losses and susceptibility to self-oscillation due to centralized millimeter-wave local oscillator generation, transmission, and distribution. By adopting an integrated design, multiple functional components are integrated into the broadband millimeter-wave complex correlation receiver front-end, enabling a single front-end to possess complete system functionality. This fully utilizes available system resources and mass production technology, improving circuit integration and utilization. It also solves the technical problems of low integration and difficulty in array expansion in existing millimeter-wave complex correlation receiver front-ends for synthesized aperture radiometer arrays.

[0054] The technical solution in this application is to solve the above-mentioned technical problems, and the general idea is as follows:

[0055] Existing integrated aperture radiometer arrays use broadband millimeter-wave complex correlation receiver front-ends as follows: Figure 1 It consists of N wideband millimeter-wave low-noise receiver front-ends, 2N intermediate frequency filter amplification modules, and 2N analog correlation processing modules. The main problem with this architecture in engineering is that:

[0056] I. The coherent local oscillator signal required for phase-shift mixing is generated using an independently packaged frequency synthesizer module. This millimeter-wave local oscillator is then amplified via a power divider and sent to various broadband millimeter-wave receiver front-ends through RF cables. In the millimeter-wave band, local oscillator transmission loss is high, requiring multi-stage cascaded circuitry for compensation. This process is prone to oscillation and self-excitation. Furthermore, the limited isolation of RF cables in the millimeter-wave band results in significant local oscillator leakage, leading to poor electromagnetic compatibility and limiting the array expansion of millimeter-wave synthetic aperture radiometer arrays.

[0057] II. In existing technologies, millimeter-wave complex correlation receiver front-ends for integrated aperture radiometer arrays are basically designed separately, and the required functions of the system are achieved by cascading single functional modules. For example, the broadband millimeter-wave low-noise receiver front-end uses a multi-chip micro-assembly process to cascade and package millimeter-wave low-noise amplifiers, millimeter-wave pre-selection filters, and millimeter-wave mixers within a single basic receiver unit channel into a hermetically sealed metal housing. The intermediate frequency (IF) filter amplification module typically integrates IF amplifiers, digitally controlled attenuators, and filters using hybrid integrated circuit technology into another hermetically sealed module. The analog complex correlation processing module uses reflow soldering to cascade broadband baluns, broadband analog multipliers, operational amplifiers, and other packaged devices on a printed circuit board, and uses a metal cavity for shielding. Then, the packaged different functional modules are fixed onto structural components to form the millimeter-wave complex correlation receiver front-end. Due to the large number of components, large packaging volume, limited circuit density, low integration, and large area occupied by the microstrip board, the size and weight of the existing millimeter-wave complex correlation receiver front-end cannot be effectively controlled. Consequently, the millimeter-wave integrated aperture radiometer array contains many connectors, a huge number of connecting cables, and has a large overall size, weight, and high manufacturing cost.

[0058] As can be seen from the above description, the existing millimeter-wave complex correlation receiving front-ends used in synthetic aperture radiometer arrays have high local oscillator losses in the millimeter-wave band, requiring multi-stage circuit cascades for compensation. This can easily lead to oscillations and self-excitation, limiting the increase in the number of millimeter-wave complex correlation receiving front-ends and restricting the further expansion of the synthetic aperture radiometer array.

[0059] Furthermore, existing millimeter-wave complex correlation receiver front-ends are constructed using discrete components. Due to the large number of components, large packaging volume, limited circuit density, low integration, and large microstrip board area occupied, the size and weight of existing millimeter-wave complex correlation receiver front-ends cannot be effectively controlled. Consequently, the integrated aperture radiometer array contains numerous connectors and a huge number of connecting cables, resulting in a large overall size, heavy weight, and high manufacturing cost. As the basic unit of the integrated aperture radiometer array, the size, weight, and manufacturing cost of the millimeter-wave complex correlation receiver front-end determine the overall size, weight, manufacturing cost, and reliability of the integrated aperture radiometer array. Obviously, constructing millimeter-wave complex correlation receiver front-ends by cascading different functional modules is difficult to apply in practical engineering, thus limiting the application of integrated aperture radiometer arrays.

[0060] In summary, the key issues that need to be addressed in the design of broadband millimeter-wave complex correlation receiver front-ends for integrated aperture radiometer arrays are solving the problem of millimeter-wave local oscillator transmission, achieving high-frequency cableless interconnection, reducing system size and weight, lowering manufacturing costs, and meeting the requirements of mass production and debugging. These issues also represent the bottlenecks restricting their application in practical engineering.

[0061] To address the aforementioned issues, this invention proposes a highly integrated broadband millimeter-wave complex correlation receiving front-end for synthetic aperture radiometer arrays. Utilizing distributed frequency synthesis technology, the previously externally transmitted millimeter-wave local oscillator is simplified into an externally transmitted reference signal. Distributed millimeter-wave local oscillator frequency synthesis is achieved through a low-phase-noise phase-locked loop combined with direct frequency doubling processing within the broadband millimeter-wave complex correlation receiving front-end. This significantly reduces the difficulty of local oscillator transmission allocation and facilitates the expansion of the synthetic aperture radiometer array.

[0062] It should be noted that in the embodiments of the present invention, phase-shift mixing is used. By utilizing the orthogonality of the detection of complex correlation, the influence of phase inconsistency within the radiometer system can be eliminated. Therefore, the low-frequency synchronous clock of the system can be used as the reference signal of the frequency synthesizer. The required millimeter-wave mixing local oscillator is generated in each broadband millimeter-wave complex correlation receiving front end using distributed frequency synthesis technology, realizing distributed coherent design. This solves the drawbacks of large transmission and distribution losses and easy self-excitation of millimeter-wave local oscillators in the traditional millimeter-wave integrated aperture radiometer array.

[0063] Furthermore, the original architecture was improved by adopting an integrated approach. By combining multi-chip micro-assembly, hybrid integrated circuit technology, and reflow soldering technology, multiple functional components were integrated into the broadband millimeter-wave complex correlation receiver front-end module. This allows each broadband millimeter-wave complex correlation receiver front-end to independently possess complete system functions, making full use of the system's available resources and mass production technology, improving circuit integration and utilization, minimizing the size and weight of the broadband millimeter-wave complex correlation receiver front-end, and reducing manufacturing costs. This ensures that the overall size, weight, and manufacturing cost of the integrated aperture radiometer array can be greatly reduced, meeting the requirements of mass production and commissioning, further promoting the engineering application of integrated aperture radiometer arrays, and enhancing competitiveness.

[0064] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0065] This invention provides a highly integrated broadband millimeter-wave complex correlation receiving front end, such as... Figure 2As shown, it includes: a housing (in this embodiment of the invention, the housing is preferably an integrated metal housing), a dual-waveguide broadband impedance converter, a millimeter-wave receiving front end, an intermediate frequency filter and amplification, a distributed frequency synthesis, analog complex correlation processing, and power control;

[0066] The housing has an internal cavity for integrating millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis, analog complex correlation processing and power control.

[0067] The dual-waveguide broadband impedance transformer is implemented by connecting a stepped impedance transformer with a radio frequency insulator. The radio frequency insulator is welded to the input end face of the integrated housing to achieve the airtight design of the millimeter-wave complex correlation receiver front end.

[0068] The input of the distributed frequency synthesis is connected to the reference signal, and the output is connected to the millimeter-wave receiving front end to provide the millimeter-wave local oscillator signal to the millimeter-wave receiving front end.

[0069] The millimeter-wave receiving front-end input is connected to a dual-channel interference antenna via a dual-waveguide broadband impedance transformer, and the output is connected to an intermediate frequency filter amplifier.

[0070] The intermediate frequency filtering and amplification process outputs a pair of in-phase and a pair of quadrature intermediate frequency signals to the analog complex correlation processor after filtering and amplification.

[0071] The power control provides a highly stable power supply for the millimeter-wave receiving front-end, intermediate frequency filtering and amplification, millimeter-wave distributed frequency synthesis, and analog complex correlation processing.

[0072] The highly integrated broadband millimeter-wave complex correlation receiving front-end provided in this invention integrates various functional components such as millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis, analog complex correlation processing, and power control into a single design, forming a basic unit of a synthetic aperture radiometer array. This basic unit possesses complete system functionality. By increasing the number of highly integrated broadband millimeter-wave complex correlation receiving front-ends, the scale of the synthetic aperture radiometer array can be easily expanded, such as... Figure 3 As shown.

[0073] The following is a detailed description of the overall architecture and various functional components of the highly integrated broadband millimeter-wave complex correlation receiver front-end:

[0074] At the architectural level:

[0075] The embodiments of the present invention provide an overall structure for a broadband, highly integrated millimeter-wave complex correlation receiver front-end as follows: Figure 4 As shown, its exploded view is as follows Figure 5 As shown, the internal cavity of the integrated metal casing is a double-sided cavity comprising a front cavity and a back cavity, the structures of which are as follows: Figure 6 , Figure 7 As shown.

[0076] The millimeter-wave receiving front-end (8), intermediate frequency filtering and amplification (9), distributed frequency synthesis (10), and analog complex correlation processing (11) are arranged in the front cavity, while the power control (12) is arranged in the rear cavity. Physical shielding and isolation are achieved through insulating metal ribs. Except for gaps at interconnection points, each functional part is completely isolated, allowing multiple modules to be installed in a single cavity. This reduces component size and the complexity of interconnection while ensuring isolation between modules and preventing stray interference from components in the link.

[0077] refer to Figures 4-7 This invention provides a broadband, highly integrated millimeter-wave complex correlation receiver front-end, structurally composed of an integrated metal housing 6, a dual-waveguide broadband impedance transformer 7, a front laser-sealed cover plate 1, a rear laser-sealed cover plate 2, a shielding cover plate 3, a front screw-on cover plate 4, and a rear screw-on cover plate 5. The RF input is electrically connected to the dual-waveguide broadband impedance transformer 7 via a stepped impedance transformer and a hermetically sealed RF insulator welded to the integrated housing. The hermetically sealed low-frequency input and output are connected via a J30JMI hermetically sealed connector, while the non-hermetically sealed input and output are connected via a J30JY rainproof connector. The shielding cover plate 3 and the internal partition of the integrated metal housing 6 form a connected front cavity, isolating different module circuits, reducing crosstalk between circuits, and improving the stability and reliability of the components. The addition of the front laser-sealed cover plate 1 and the rear laser-sealed cover plate 2 ensures the hermetically sealed requirements of the cavity containing the chip, guaranteeing the stable and reliable operation of the internal MMIC chip.

[0078] Within the front cavity, both the millimeter-wave receiving front-end 8 and the millimeter-wave distributed frequency synthesis assembly 10 employ a micro-MIC microwave monolithic circuit integrated design, assembled using micro-assembly technology. To reduce transmission loss in the millimeter-wave band, a high-frequency complex dielectric substrate, ROGERS5880, is used as the electrical signal transmission substrate. Simultaneously, at the location where the microstrip board is mounted, the integrated housing is slotted and cavityd according to the microstrip board's shape, with partial gold plating at the bottom of the cavity. Since it operates at millimeter-wave frequencies, the microstrip board is made of ROGERS5880 material with a dielectric constant of 2.2. To reduce the height difference between the microstrip board and the MMIC chip, the microstrip board thickness is set to 0.254 mm, and a gold-plated copper ground is applied to the back of the microstrip board, which is then directly soldered to the gold-plated integrated housing at the bottom of the cavity, providing good grounding performance. The cavity depth at the location where the millimeter-wave receiving front-end 8 and the millimeter-wave distributed frequency synthesis assembly 10 are partially soldered to the microstrip board is preferably 3 mm, and the width is preferably 3.6 mm.

[0079] The intermediate frequency (IF) filter amplifier 9 adopts an integrated design of MMIC microwave monolithic circuit and LC packaged filter. Internally, it is assembled using hybrid integrated circuit technology, using inexpensive FR4 as the substrate to avoid excessive transmission loss and reduce costs. The bottom of the integrated housing where the substrate is mounted is partially gold-plated. To reduce the height difference between the substrate and the MMIC chip, the substrate thickness is set to 0.2mm, and a gold-plated ground copper layer is laid on the back of the substrate, which is directly soldered to the gold-plated integrated housing at the bottom of the cavity, providing good grounding performance. At the LC packaged filter mounting location, the integrated housing is slotted and cavity-cut according to the filter's shape. The cavity depth allows for bonding with the substrate using the filter's input and output RF insulators. The bottom of the filter is padded with indium foil to provide good grounding, and it is secured from the back of the integrated housing using screws, spring washers, and flat washers. The cavity depth and width at the IF filter amplifier section where the substrate is soldered can both be set to 5mm, reducing the difficulty of the assembly process.

[0080] All components within the Analog Complex Correlation Processor 11 are assembled on a single board using a reflow soldering process, and a low-cost FR4 (fiberglass) multilayer PCB is used as the electrical signal transmission substrate, improving the design's integration. Furthermore, the multilayer circuit board of the Analog Complex Correlation Processor 11 is implemented using single-function packaged devices, directly mounted within the module's front cavity using screws.

[0081] Within the rear cavity, a metal partition divides the space into two chambers, housing the left and right sections of the power control 12. The left power control 1201 provides the millimeter-wave receiver front-end 8, the intermediate frequency filter and amplification module 9, and the millimeter-wave distributed frequency synthesis module 10 with a high-precision ±5V power supply processed by a linear regulator, along with phase-shifting and attenuation code control after serial-to-parallel conversion. It is electrically connected to the front cavity using a sealed low-frequency insulator. A laser-sealed cover 2 is used on the rear cavity corresponding to the left power control unit 1201 to achieve localized airtightness, further improving the reliability of the module containing the chip components. The linear low-dropout regulator, extremely low-noise, high-stability voltage reference, and serial-to-parallel conversion circuit in the power control 12 are all implemented on a single FR-4 printed circuit board using surface-mount devices manufactured using reflow soldering.

[0082] The right power control unit 1202 provides the analog complex correlation processor 11 with a high-precision +5V power supply processed by a linear regulator and a high-precision, highly stable reference voltage. The front and back cavities are electrically connected by through-welding high-temperature insulated wires. The back cavity corresponding to the right power control unit 1202 is sealed with a back screw-on cover plate 2 to further reduce costs.

[0083] The left power control unit 1201 and the right power control unit 1202 are connected via a J30JMI airtight connector. The right power control unit 1202 is connected to the outside via a J30JY rainproof connector mounted on the side wall of the integrated housing.

[0084] Meanwhile, it should be noted that the cavity containing the MMIC microwave monolithic circuit adopts an hermetically sealed design. The RF insulators, low-frequency insulators, and low-frequency connectors are all welded. The low-frequency electrical connections on the front and back of the cavity adopt a vertical transition method using low-frequency insulators. The low-frequency insulator end face of the cavity containing the chip adopts a flat-head gold-plated design, which can easily achieve gold wire bonding with the MMIC chip and microstrip board. The other end can be bonded to the corresponding functional pads on the power control printed circuit board in the back cavity after molding. Combined with the cover plate with partial laser sealing on the front, it can achieve a local hermetically sealed design for the module containing the chip, improving reliability and reducing costs.

[0085] The microstrip board / substrate where the chip is placed inside the cavity needs to be grooved, and a 0.2mm thick gold-plated molybdenum copper substrate needs to be inserted into the groove as a stress buffer. The molybdenum copper substrate is cut to size according to the chip and soldered to the bottom of the integrated housing. The chip and the molybdenum copper substrate are bonded using conductive adhesive, preferably H20E two-component conductive adhesive. The electrical interconnection of the MMIC microwave integrated monolithic circuit is achieved using gold wire bonding. The interconnection between MMIC chips and between MMIC chips and the microstrip board uses gold wire bonding technology to improve integration and reduce module size.

[0086] like Figure 4 The main structural dimensions of the broadband highly integrated millimeter-wave complex correlation receiver front-end shown in the table below are as follows.

[0087] Table 1. Main structural dimensions of the broadband highly integrated millimeter-wave complex correlation receiver front end

[0088]

[0089] In the implementation of this application, distributed frequency synthesis, microwave monolithic integration, integrated structural design and process integration are used to integrate millimeter-wave radiometer circuits with different functions into a whole module. This enables the broadband millimeter-wave complex correlation receiving front-end to independently possess complete system functions, simplifies the connection relationship with the system, eliminates the design of separate modules and internal connecting cables, thereby achieving the purpose of reducing the overall weight and volume. While ensuring the electrical performance of the broadband highly integrated millimeter-wave complex correlation receiving front-end, it also achieves miniaturization and has the advantages of simple structure and low cost, which can easily realize the expansion of the integrated aperture radiometer array.

[0090] At the functional circuit level:

[0091] The circuit principle of the broadband highly integrated millimeter-wave complex correlation receiver front-end provided in this embodiment of the invention is as follows: Figure 8 As shown in the figure. The principle block diagram of the millimeter-wave receiving front end is as follows: Figure 9 As shown in the diagram, channel A and channel B are completely identical; only channel A is described here. The following components are connected in sequence: low-noise amplifier N1, preselector filter Z1, low-noise amplifier N2, and power divider N3. Power divider N3 splits the in-phase signal into two paths. One path connects sequentially to attenuator N4, mixer N5, attenuator N6, and low-pass filter Z3; the other path connects sequentially to attenuator N7, mixer N8, attenuator N9, and low-pass filter Z4. N1 and N2 provide low-noise amplification of the weak target temperature radiation signal, exhibiting low noise and high gain. Z1 is a high rectangular coefficient bandpass filter providing frequency selectivity. Z3 and Z4 are low-pass filters suppressing leaked local oscillator signals. N4 and N7 are fixed attenuators that improve inter-stage VSWR and optimize in-band ripple. The input local oscillator signal is sequentially connected to power divider N34. Power divider N34 splits the local oscillator signal in phase into two paths. One path is sent to local oscillator power divider N33 on echo channel 2, and the other path is sequentially connected to local oscillator amplifier N25 and local oscillator power divider N24. Power divider N24 again splits the local oscillator signal in phase into two paths. One path is sequentially connected to local oscillator amplifier N20, phase shifter N19, local oscillator amplifier N19 and the local oscillator port of mixer N5. The other path is sequentially connected to local oscillator amplifier N21, phase shifter N22, local oscillator amplifier N23 and the local oscillator port of mixer N8. N20, N21, and N25 are local oscillator drivers. Together with power divider N24, they realize active power division amplification of the local oscillator after frequency doubling and filtering. N20 and N21 also provide reverse isolation for the local oscillator to prevent the standing wave pull during phase shifting of the phase shifter from affecting the phase shifting accuracy of the local oscillator. N19 and N22 are numerically controlled phase shifters that can achieve phase shift traversal from 0° to 360° in the smallest step.

[0092] The active power division amplification function of the millimeter-wave local oscillator is integrated into the millimeter-wave receiving front end. It uses low phase noise amplifier chips N25 and N33, power divider chips N34, N24, and N32, combined with low-loss microstrip circuits to complete the active amplification and power division of the millimeter-wave low phase noise local oscillator.

[0093] N1 and N2 serve as the first-stage low-noise amplifiers in the broadband, highly integrated millimeter-wave complex correlation receiver front-end. Their noise figure directly affects the system's minimum sensitivity. The first-stage amplifier is set to the low-noise amplifier NC10229C-2640, which has a noise figure of 2.3dB and a gain of 22dB in the millimeter-wave band. Its low noise figure and high gain contribute to the overall reduction of the noise figure. N19 and N22 are digitally controlled phase shifters on the local oscillator branch, model WYD330370-6, whose phase shift accuracy can reach within 3°, exhibiting high accuracy.

[0094] Figure 10 A principle block diagram of a millimeter-wave distributed frequency synthesis module is given, based on the above. Figure 8 From the perspective of the circuit structure, the orthogonality of phase-shift mixing and complex correlation detection can be used to eliminate the inconsistency in the millimeter-wave complex correlation receiving front-end channel. Therefore, a simple distributed frequency synthesis method can be used to replace the centralized local oscillator generation and distribution.

[0095] Figure 10 The phase-locked crystal oscillator N101 generates a reference signal coherent with an external reference (different frequencies of reference signals are selected based on the external reference, such as generating a coherent 100MHz reference signal based on a 10MHz external reference). This signal is then passed through a low-phase-noise phase-locked loop chip N102 to generate a high-quality, low-phase-noise X-band coherent local oscillator signal. This signal is then passed through a MEMS filter chip Z101, which suppresses spurious and harmonic noise generated by the PLL, improving the purity of the spectral output. The silicon-based bandpass filter using MEMS technology simplifies the frequency synthesizer circuit structure, provides excellent filtering performance, and is small in size and low in cost. The filtered signal is further amplified by a driver amplifier N103 and then input to an active fourth frequency multiplier chip N104. Through direct frequency multiplication and synthesis, a low-phase-noise local oscillator is generated for zero-IF phase-shift mixing in the millimeter-wave band. Apart from the phase-locked crystal oscillator, the entire frequency synthesis generation section is implemented in an integrated housing using four functional chips through micro-assembly technology. It adopts a combination of active frequency multiplication and locking, and works in conjunction with a power divider network integrated in the millimeter-wave receiver front end using the same technology. This achieves highly integrated, low-cost distributed frequency synthesis, which greatly reduces transmission loss, reduces the number of cascaded amplifiers, and solves the problems of high transmission loss of millimeter-wave local oscillator signals and easy oscillation caused by multi-stage cascading.

[0096] In the specific implementation, the N104 active frequency multiplier chip was configured as a low-power, high-harmonic-suppression, high-power-output active frequency multiplier WBD350400-B4, capable of outputting 12dBm of power within the millimeter-wave operating frequency range. The phase-locked loop (PLL) was configured as a wideband, low-phase-noise integrated PLL SIPL219.

[0097] The intermediate frequency filtering and amplification module contains four completely identical amplification and filtering channels. After removing DC from the signal output from the phase-shifted mixing of the millimeter-wave receiving front end, it is further filtered and amplified to meet the requirements of the subsequent analog complex correlation processing for the frequency and power range of the input signal. Figure 11This is a block diagram illustrating the principle of intermediate frequency (IF) filtering and amplification. The IF channels 1, 2, 3, and 4 described in the diagram are identical; only IF channel 1 is described here. Taking IF channel 1 as an example, the IF amplifier N111, bandpass filter Z111, digitally controlled attenuator N112, and IF amplifier N113 are connected sequentially. The inputs and outputs of N111 and N113 are AC-coupled to avoid interference from the DC components generated near zero-IF mixing, which would otherwise interfere with the subsequent analog complex correlation unit operations.

[0098] In this embodiment of the invention, the bandpass filter Z111 is constructed using a high-pass and low-pass LC filter, with a signal bandwidth set to 0.1 GHz to N / 2 GHz. A high-pass filter with a cutoff frequency of 0.1 GHz is used because after zero-IF mixing, the additional phase noise from the local oscillator at 0.1 GHz is already far lower than the channel's thermal noise; therefore, the additional local oscillator noise introduced by mixing in the in-band IF signal can be ignored. N111 and N113 are broadband amplifiers on the IF branch, model NC11236C-106, with ripple less than 0.8 dB within the operating frequency band, exhibiting good flatness. N112 is a digitally controlled attenuator, model BW163, with an integrated driver, eliminating the need for an external driver, thus improving circuit integration and reducing component costs.

[0099] Figure 12 A block diagram of the analog complex correlation processing principle is presented, comprising two identical analog correlation channels. These channels perform correlation operations on a pair of in-phase intermediate frequency (IF) signals with bandwidths ranging from DC to N / 2 GHz and a pair of quadrature IF signals with bandwidths ranging from DC to N / 2 GHz, respectively. After active differential filtering, a pair of orthogonal IQ signals are output. Since the signal energy is distributed across the DC to N / 2 GHz frequency range after passing through a broadband analog multiplier, a low-pass filter with the lowest possible cutoff frequency is needed to filter out channel noise to the maximum extent, retaining only the bandwidth matching the signal variation. The dual-channel complex correlation unit employs differential design for its input, output, and internal processing to minimize potential common-mode interference. Under the same power supply voltage, it can provide twice the amplitude of a single-ended signal and better linearity, solving the problems of DC drift and common-mode interference suppression.

[0100] Figure 12 The in-phase and quadrature paths described in the text are completely identical in hardware configuration; only the in-phase path is described here. The following components are connected in sequence: broadband baluns N121 and N125, broadband high-performance multiplier N122, matching network 1, passive differential filter Z121, matching network 2, operational amplifier N123, matching network 3, operational amplifier N124, and feedback network.

[0101] N121 and N125 are broadband baluns, which convert two intermediate frequency broadband signals into differential signals and output them to the subsequent broadband high-performance multiplier N122. N122 performs multiplication on the input signals and features broadband operation and high consistency. Matching network 1 matches the output impedance of N122 with the input impedance of the differential passive low-pass filter Z121. N123 and N124 are operational amplifiers. Matching network 2 matches the output impedance of the differential passive low-pass filter Z121 with the input impedance of N123. Matching network 3 matches the stages of operational amplifiers N123 and N124. The feedback network provides negative feedback and filtering for the operational amplifiers, and together with N123 and N124, forms an active differential low-pass filter.

[0102] In this embodiment of the invention, N121 and N125 are configured as a broadband unbalanced-to-balanced conversion circuit TC-1-13M+, N2 is configured as a wideband, high-performance, supersymmetric analog multiplier ADL5391, N123 is configured as a precision instrumentation amplifier AD8139 with extremely high linearity and temperature stability, and N124 is configured as a differential drive amplifier LTC1992 with low offset and high stability.

[0103] Figure 13 A block diagram of the power supply control principle is presented, including linear low-dropout regulators N131, N132, and N133, an ultra-low noise and high-stability voltage reference N134, and a serial-to-parallel conversion circuit N135. N131, N132, and N133 are linear low-dropout regulators. N131 and N133 provide highly stable, low-noise +5V and -5V power supplies, respectively, processed by the linear regulators, to the millimeter-wave receiving front-end, intermediate frequency filter, and distributed frequency synthesis. N132 provides a highly stable, low-noise +5V power supply, processed by the linear regulator, to the analog complex correlation processing. N134 provides a high-precision, highly stable reference voltage for the analog complex correlation processing, effectively ensuring the stability of the correlation processing output voltage. Furthermore, the power supply control also includes the serial-to-parallel conversion circuit N135, allowing an external host to operate the phase shifter in the millimeter-wave receiving front-end and the digitally controlled attenuator in the intermediate frequency filter amplification via an SPI interface. In addition, the serial-to-parallel conversion circuit is implemented using a dedicated integrated circuit, simplifying the interface design. In this embodiment of the invention, N131, N132, and N133 are configured as low-noise, low-dropout output XC5322BMACs, capable of providing a maximum output current of 3A. N134 is configured as a high-precision, highly stable reference voltage reference ADR431. N135 is preferably NC20415F, capable of providing a maximum of 24 bits of parallel code output.

[0104] In summary, compared with existing technologies, it has the following beneficial effects:

[0105] 1. In this embodiment of the invention, distributed frequency synthesis is achieved by integrating low phase noise phase-locked generation with direct synthesis frequency doubling processing inside the broadband millimeter-wave complex correlation receiving front end, which greatly reduces the difficulty of local oscillator transmission allocation and enables convenient expansion of the integrated aperture radiometer array.

[0106] 2. The embodiments of the present invention ensure the required electrical performance indicators of the system while integrating multiple functional components into a broadband millimeter-wave complex correlation receiving front-end module. This allows the individual millimeter-wave complex correlation receiving front-end to possess complete system functions, fully utilize the resources available to the system and mass production technology, improve circuit integration and utilization, minimize the size and weight of the broadband millimeter-wave complex correlation receiving front-end, and reduce manufacturing costs. This ensures that the overall size, weight, and manufacturing cost of the integrated aperture radiometer array can be greatly reduced, meeting the requirements of mass production and debugging, further promoting the engineering application of integrated aperture radiometer arrays, and enhancing competitiveness.

[0107] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0108] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly integrated broadband millimeter-wave complex correlation receiver front end, characterized in that, The highly integrated broadband millimeter-wave complex correlation receiving front-end is used for millimeter-wave synthetic aperture radiometer arrays, including: a dual-waveguide broadband impedance transformer, an integrated housing with an internal cavity, and a millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis, analog complex correlation processing and power control integrated in the cavity. The dual-waveguide broadband impedance transformer is implemented by connecting a stepped impedance transformer with a radio frequency insulator welded to an integrated housing. The input of the distributed frequency synthesis is connected to the synchronization reference signal of the millimeter-wave integrated aperture radiometer array, and the output is connected to the millimeter-wave receiving front end to provide the millimeter-wave receiving front end with a system-coordinated millimeter-wave local oscillator signal. The distributed frequency synthesis independently generates a millimeter-wave local oscillator within the highly integrated broadband millimeter-wave complex correlation receiving front end, eliminating the need for external centralized local oscillator transmission; The millimeter-wave receiving front end includes a digitally controlled phase shifter and a mixer; the input of the millimeter-wave receiving front end is connected to a dual-channel interferometric antenna through a dual-waveguide broadband impedance transformer, and the output is connected to an intermediate frequency filter and amplifier. The intermediate frequency filtering and amplification process outputs a pair of in-phase and a pair of quadrature intermediate frequency signals to the analog complex correlation processor after filtering and amplification. The power control provides a low-noise, highly stable power supply for the millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis and analog complex correlation processing; Phase-shift mixing is adopted, and the orthogonality of complex correlation detection is utilized to eliminate phase errors within the receiving channel. A simple distributed frequency synthesis method is used to replace the centralized local oscillator generation and distribution. Through the distributed millimeter-wave frequency synthesis technology, the distributed coherent design of the millimeter-wave synthetic aperture radiometer array is realized. The cavity comprises a double-sided cavity with a front cavity and a back cavity; the front cavity houses a millimeter-wave receiving front-end, intermediate frequency filtering and amplification, distributed frequency synthesis, and analog complex correlation processing; the back cavity houses a power control system. In the front cavity, the functional components are arranged in a completely isolated manner, except for the slots necessary for interconnection. The power control in the rear cavity and the millimeter-wave receiving front end, intermediate frequency filtering and amplification, distributed frequency synthesis, and analog complex correlation processing in the front cavity are electrically connected by through-welding of high-temperature insulated wires. The distributed frequency synthesis includes a phase-locked crystal oscillator, a phase-locked loop chip, an active quadruple frequency chip, a MEMS filter, a low phase noise amplifier chip, and a power divider chip. The phase-locked crystal oscillator generates a reference signal that is correlated with an external reference; The phase-locked loop chip and MEMS filter perform frequency multiplication and phase-locked filtering of the reference signal to generate a high-quality, low-phase-noise X-band coherent local oscillator signal and then filter it. The active quadruple frequency chip uses a direct synthesis method to generate the low phase noise local oscillator required for zero intermediate frequency mixing in the millimeter wave band.

2. The highly integrated broadband millimeter-wave complex correlation receiving front end as described in claim 1, characterized in that, The intermediate frequency filtering and amplification includes four identical intermediate frequency filtering and amplification channels. Each intermediate frequency filtering and amplification channel is equipped with a low-noise amplifier chip, a low-pass filter chip, a digitally controlled attenuator chip, and an LC bandpass filter. The input end of the intermediate frequency filtering and amplification channel is connected to the output of the millimeter wave receiving front end, and the output end is connected to the analog complex correlation processing. The intermediate frequency signals of a pair of in-phase and a pair of quadrature signals are filtered, amplified, and then output to the analog complex correlation processing section.

3. The highly integrated broadband millimeter-wave complex correlation receiving front end as described in claim 1, characterized in that, The analog complex correlation processing includes two completely identical analog correlation channels, which perform correlation operations on a pair of in-phase intermediate frequency signals with bandwidths of DC to N / 2 GHz and a pair of quadrature intermediate frequency signals with bandwidths of DC to N / 2 GHz, respectively. After active differential filtering, a pair of quadrature IQ signals are output.

4. The highly integrated broadband millimeter-wave complex correlation receiving front end as described in claim 1, characterized in that, The power control unit is equipped with a linear low-dropout regulator, a voltage reference, and a series-to-parallel conversion circuit. The linear low-dropout regulator is used to convert the positive and negative switching power supply generated by the external input DC-DC converter into a high-precision, low-noise linear ±5V power supply circuit. The voltage reference provides a high-precision and highly stable reference voltage for high-performance broadband analog multipliers and active differential filters; The serial-to-parallel conversion circuit includes an SPI control interface.

5. The highly integrated broadband millimeter-wave complex correlation receiving front end as described in any one of claims 1 to 4, characterized in that, Both the millimeter-wave receiving front-end and the distributed frequency synthesis assembly adopt microwave monolithic circuit integration design. The chips corresponding to the millimeter-wave receiving front-end and the chips corresponding to the distributed frequency synthesis assembly are assembled using micro-assembly technology. The electrical signal transmission substrate used for assembly is a high-frequency complex dielectric board.

6. The highly integrated broadband millimeter-wave complex correlation receiving front end as described in any one of claims 1 to 4, characterized in that, The intermediate frequency filtering and amplification adopts an integrated design of MMIC microwave monolithic circuit and LC packaged filter, and is assembled using hybrid integrated circuit technology. The electrical signal transmission substrate used for assembly is a glass fiber board.

7. The highly integrated broadband millimeter-wave complex correlation receiving front end as described in any one of claims 1 to 4, characterized in that, All components in the analog complex correlation processing are assembled on a single board using a reflow soldering process, and a multilayer PCB made of fiberglass board is used as the substrate for electrical signal transmission.

8. The highly integrated broadband millimeter-wave complex correlation receiving front end as described in any one of claims 1 to 4, characterized in that, All components within the power control system are assembled on a single board using a reflow soldering process, and a multilayer PCB made of fiberglass board is used as the substrate for electrical signal transmission.

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