Distributed receiver system for over-the-horizon radar with shelter-free receivers

Abstract

The technology disclosed herein enables a distributed OTHR receiver system for more efficient, resilient, and scalable OTHR deployments. In a particular example, a receiver system includes a plurality of input channels configured to receive analog signals from a plurality of antennas and a plurality of analog-to-digital converters (ADCs) configured to generate digitized signals from the analog signals. The receiver system also includes an output interface configured to transmit the digitized signals to an external signal processor. The external signal processor is configured to receive additional digitized signals from one or more additional receiver systems contemporaneously with the digitized signals and package the digitized signals with the additional digitized signals for transmission.

Description

DISTRIBUTED RECEIVER SYSTEM FOR OVER-THE-HORIZON RADAR WITH SHELTER-FREE RECEIVERSBACKGROUND

[0001] Over-the-horizon radar (OTHR) systems play a vital role in national defense and strategic surveillance by enabling the detection of targets at distances far beyond the line of sight. These systems operate by transmitting and receiving high-frequency signals that reflect off the ionosphere, allowing coverage of vast geographic regions. To function effectively, OTHR systems require highly sensitive receiver infrastructure capable of capturing and digitizing weak signals from large antenna arrays spread across remote and often environmentally challenging locations.

[0002] Historically, the deployment of OTHR systems has been constrained by the complexity and cost of their receiver architecture. Receivers are typically housed in environmentally controlled shelters to protect them from temperature extremes, moisture, and mechanical stress. These shelters demand significant infrastructure, including power distribution, cooling systems, and long cable runs between antennas and processing units. Likewise, site preparation tasks, such as site clearing, levelling, pouring concrete foundation pads, etc., contribute significant costs when a large number of receiver shelters are involved in a typical OTHR deployment. Such requirements not only increase the logistical burden and operational costs but also introduce potential points of failure and signal degradation. As OTHR systems scale in size and capability, these limitations have become increasingly pronounced.SUMMARY

[0003] The technology disclosed herein enables a distributed OTHR receiver system for more efficient, resilient, and scalable OTHR deployments. In a particular example, a receiver system includes a plurality of input channels configured to receive analog signals from a plurality of antennas and a plurality of analog-to-digital converters (ADCs) configured to generate digitized signals from the analog signals. The receiver system also includes an output interface configured to transmit the digitized signals to an external signal processor. The external signal processor is configured to receive additional digitized signals from one or more additional receiver systems contemporaneously with the digitized signals and package the digitized signals with the additional digitized signals for transmission.382.0001 1

[0004] In another example, a method for operating the receiver system is provided. The method includes receiving signals via a plurality of input channels from a plurality of antennas and converting the signals to digitized signals. The method further includes transmitting the digitized signals via an output channel to an external signal processor. The external signal processor receives the digitized signals, receives additional digitized signals from one or more additional receiver systems contemporaneously with the digitized signals, and packages the digitized signals with the additional digitized signals for transmission to a consumer.

[0005] In a further example, a distributed receiver system is provided having a plurality of receiver systems. Each receiver system of the plurality of receiver systems is configured to receive analog signals from antennas on a plurality of input channels, convert the analog signals to digitized signals, and transmit the digitized signals to a signal processor system. The distributed receiver system also includes the signal processor system configured to digitally down convert on the digitized signals prior to transmission and transmit the digitized signals in a data stream to a consumer.BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 illustrates an implementation for a distributed over-the-horizon radar (OTHR) receiver system.

[0007] Figure 2 illustrates an operation to capture and send signals in a receiver system of a distributed OTHR receiver system.

[0008] Figure 3 illustrates an implementation for a receiver system of a distributed OTHR receiver system.

[0009] Figure 4 illustrates an implementation for a wide open front end (WOFE) in a distributed OTHR receiver system.

[0010] Figure 5 illustrates an implementation for a distributed OTHR receiver system.

[0011] Figure 6 illustrates an implementation for signal-processing servers in a distributedOTHR receiver system.

[0012] Figure 7 illustrates an operation for software-defined processing of signals in a distributed OTHR receiver system.

[0013] Figure 8 illustrates an implementation for a distributed OTHR receiver system.382.0001 2

[0014] Figures 9-11 illustrate a receiver system housing for a distributed OTHR receiver system.

[0015] Figure 12 illustrates a computing system for processing signals in a distributed OTHR receiver system.DETAILED DESCRIPTION

[0016] The distributed receiver system for over-the-horizon radar (OTHR) herein introduces a modular and ruggedized architecture that directly addresses several limitations of conventional receiver deployments. By enabling receiver units to be installed in close proximity to antenna arrays, the system significantly reduces analog cable lengths, thereby improving signal integrity and minimizing susceptibility to electromagnetic interference. This proximity also simplifies installation logistics and reduces the need for extensive infrastructure, such as long cable runs and specialized enclosures.

[0017] Each receiver unit may be housed in a weather- sealed enclosure designed for outdoor deployment in harsh environments. The enclosure may incorporate passive thermal management features, including extended surfaces for heat dissipation, and mechanical protections against shock, vibration, and moisture ingress. These design elements eliminate the need for environmentally controlled shelters, reducing both capital and operational expenditures while maintaining reliable performance across a wide range of field conditions.

[0018] The receiver architecture is modular, with each unit comprising a limited number of input channels, analog-to-digital converters (ADCs), and digital signal processing components. This modularity enables scalable deployment across large antenna fields and supports distributed receiver configurations by deploying as many receiver units as are needed to service the number of antennas in the deployment. Multiple receiver units can operate synchronously, transmitting digitized signals to a centralized signal processor for aggregation, calibration, and analysis.

[0019] To ensure high-fidelity signal acquisition, each receiver unit may include analog front-end filtering and amplification stages optimized for low noise figure and high linearity. These stages may be followed by high-resolution ADCs and digital equalization components that perform amplitude and group delay compensation. The receiver system also supports coordinated operation across multiple units, enabling distributed receiver arrays to function as a unified system. Timing and synchronization signals are distributed via optical links, allowing precise coordination of382.0001 3sampling and calibration across geographically dispersed units. For instance, clock synchronization circuitry may be included to enable coherent sampling across channels and across multiple receiver units, supporting phase-aligned data acquisition for advanced radar processing. This distributed architecture enhances scalability and fault tolerance, while simplifying system expansion and maintenance.

[0020] The output interface of each receiver unit is configured for high-speed, preferably fiber-optic, transmission, allowing real-time delivery of digitized signals to remote processing shelters. This separation of acquisition and processing functions reduces power consumption at the receiver site and enables centralized management of signal processing resources. The system supports integration with commercial off-the-shelf (COTS) servers and software-defined digital down conversion (DDC) or other processing features, allowing flexible and future-proof signal channelization.

[0021] The receiver system provides a distributed architecture that enables scalable deployment of over-the-horizon radar (OTHR) capabilities with reduced infrastructure requirements. By integrating ruggedized enclosures, modular signal acquisition components, and high-speed optical data interfaces, the system supports reliable operation in remote environments while facilitating centralized signal processing. This configuration addresses several limitations of prior OTHR systems, including the need for environmentally controlled shelters, long analog cable runs, and complex installation procedures, thereby enabling more efficient and adaptable radar system deployments.

[0022] Figure 1 illustrates implementation 100 for a distributed OTHR receiver system. Implementation 100 includes receiver system 101, receiver systems 102, and signal processor 103. The distributed OTHR system of implementation 100 may include any number of receiver systems 102 in addition to receiver system 101 to implement a desired antenna array. For example, 25 receiver systems with four antenna channels each would be used for a 100 antenna array. Receiver system 101 includes any number of antenna inputs 111-1 IN connected to respective antennas 141-14N. Receiver system 101, likewise, includes respective analog to digital converters (ADCs) 121-12N. Receiver system 101, therefore, includes a number of antenna inputs and ADCs corresponding to a number of antennas that will be connected to receiver system 101. For example, a four channel version of receiver system 101 would include four antenna inputs 111-1 IN, each with a corresponding one of ADCs 121-12N, and an eight channel version of receiver system 101382.0001 4would include eight antenna inputs 111-1 IN, each with a corresponding one of ADCs 121-12N. The antennas may be physically positioned in accordance with desired characteristics of the distributed OTHR receiver system. While not shown, OTHR systems include at least one transmitter configured to transmit a radar signal in the frequency range to which the distributed OTHR receiver system’s antennas are tuned such that reflections of those signals can be identified from received signals in the same band.

[0023] An analog-to-digital converter (ADC) is an electronic component that samples an analog signal and converts it into a digital representation, typically by measuring the signal’s amplitude at discrete intervals and encoding the values into binary format. Each of ADCs 121-12N may be configured to sample at rates of 100 to 200 million samples per second (MSPS) with 16- bit resolution, suitable for digitizing high-frequency signals in the 3-35 MHz range commonly referenced as being high-frequency. Other sampling rates and / or resolutions may be used in other examples. In some implementations, the ADCs may be preceded by analog front-end modules including filters and amplifiers to condition the incoming signals for optimal noise figure and linearity. Alternatives to the ADCs may include higher-resolution converters or converters with integrated digital down conversion (DDC) capabilities, depending on system requirements.

[0024] Output interface 131 is a communication interface including components for transmitting digitized signals output by ADCs 121-12N to signal processor 103. The physical link between output interface 131 and signal processor 103 may be wired or wireless. Although, an optical fiber link may be preferable based on high bandwidth (e.g., to handle multiple streams of wideband digitized signals) and long distance (e.g., tens of kilometers) capabilities of optical fiber. Wired links, like the preferred optical fiber link, typically also allow higher throughput than wireless links while having more predicable latency. A single unbroken link may span from output interface 131 to signal processor 103 or some communication component(s) may be installed in the path. For instance, depending on the distance being covered and the type of medium for the link, a signal booster may be installed to ensure the digital signal from output interface 131 reaches signal processor 103. In some examples, a multiplexing component may receive signals from multiple of receiver system 101 and receiver systems 102 and combine the signals onto a communication link to signal processor 103. The output interface may include a fiber-optic transceiver, such as a 10GBASE-LR module, and may support packetized data formats with metadata headers for downstream processing. In some embodiments, the output interface may also382.0001 5include timing synchronization inputs, such as pulse-per-second (PPS) and reference clock signals, to maintain coherence across distributed receiver systems.

[0025] Each of receiver systems 102 includes similar components to those described for receiver system 101. As such, signal processor 103 receives digitized versions of analog signals captured by antennas at each of receiver system 101 and receiver systems 102. Signal processor 103 processes the digitized signals prior to streaming the processed signals to a consumer of the signal streams. The signal processing may include channelizing each wideband signal into multiple narrow band signals, performing digital down conversion, performing pulse compression, beamforming, or some other type of digital signal processing - including combinations thereof. Signal processor 103 may include one or more commercial off-the-shelf (COTS) servers equipped with multi-core processors and RAID storage systems. Digital down conversion may be implemented in software using floating-point arithmetic, with numerically controlled oscillators (NCOs) operating at 64-bit precision and interpolation filters at 32-bit precision. The system may, for example, support up to 10 narrowband channels per antenna input, with bandwidths ranging from 2 kHz to 500 kHz and wideband channels with bandwidths ranging from 500 kHz to 30 MHz.

[0026] Figure 2 illustrates operation 200 to capture and send signals in a receiver system of a distributed OTHR receiver system. In operation 200, analog radio signals from antennas 141— 14N enter receiver system 101 via antenna inputs 111-1 IN (step 201). Each analog signal is passed to a respective one of ADCs 121-12N, which samples the signals for digitization (step 202). Output interface 131 receives all the digitized signals and transmits the digitized signals to signal processor 103 (step 203). Signal processor 103 processes the digitized signals for distribution to consumers (step 204). In some implementations, the digitized signals may be pre-processed by a field-programmable gate array (FPGA) within the receiver system prior to transmission, including optional digital equalization to correct for amplitude and group delay mismatches. The digitized signals may be transmitted over single-mode optical fiber using subscriber connectors (SCs) and may be aggregated at the signal processor using a data handler or channelizer module before further processing. Steps 201-204 occur continuously in real time such that consumers can be provided with real time digitized signals from signal processor 103. A consumer, such as a radar system operated by a government, may further process the signals to determine whether the signals indicate objects, such as aircraft, as is the primary purpose of OTHR systems.382.0001 6

[0027] Figure 3 illustrates implementation 300 for a receiver system of a distributed OTHR receiver system. Implementation 300 includes receiver system 301, which is a four-channel example of receiver system 101. Being a four channel receiver system, receiver system 301 connects to four high-frequency (HF) antennas 341-344. HF wide open front ends (WOFEs) 311— 314 receive analog HF signals from antenna 341 and pass the signals to ADCs 321-324. Field- programmable gate array (FPGA) 330 is programmed to implement digital equalizer 332 and fiber optic interface 331. The programmable nature of an FPGA enables components implemented using FPGA 330 to be updated. Each WOFE 311-314 includes analog signal conditioning components such as filters and amplifiers, which prepare the incoming HF signals for digitization by removing unwanted frequency components and boosting signal strength. The ADCs 321-324 may operate at sampling rates of 100 to 200 MSPS with 16-bit resolution, enabling accurate digitization of signals in the 3-35 MHz range. FPGA 330 is a reconfigurable integrated circuit that can be programmed to perform custom digital signal processing tasks. In implementation 300, FPGA 330 performs digital equalization via digital equalizer 332 and manages high-speed data transmission via fiber optic interface 331. Digital equalization compensates for amplitude and phase distortions introduced by analog components or cable mismatches (e.g., different cable impedances), helping to preserve signal integrity across channels. The fiber optic interface 331 transmits the digitized and equalized signals to a remote signal processor using high-bandwidth antenna 341, which may span tens of kilometers.

[0028] Figure 4 illustrates implementation 400 for a wide open front end (WOFE) in a distributed OTHR receiver system. Implementation 400 includes WOFE 401, which is an example of any one of HF WOFEs 311-314. WOFE 401 includes HF input 411, filter 412, and amplifier 413. As signal processing beyond the analog functions of elements 411-413 is performed by FPGA 330 and signal processor 103, WOFE 401 uses significantly less power than had such processing been included. The analog electrical HF signal representing radio waves captured by HF antenna 441 is received at HF input 411. The analog signal is filtered by filter 412, which may be multiple filters, to remove unwanted frequencies (e.g., filter 412 may be a bandpass filter to remove frequencies outside of the 3-35 MHz range). Amplifier 413 amplifies the filtered signal prior to outputting the signal on output channel 442 to an ADC (e.g., one of ADCs 321-324). Signal filtering is typically performed using bandpass filters that allow only a desired frequency range to pass through while attenuating out-of-band noise and interference. Multiple filter stages may be382.0001 7used to achieve sharper roll-off and better selectivity. Amplifier 413 boosts the filtered signal to a level suitable for digitization, ensuring that the ADC operates within its optimal dynamic range. The amplifier may also be designed to maintain high linearity and low noise figure, which are critical for preserving signal quality in congested electromagnetic environments. The output signal on channel 442 is then routed to the ADC, where it is sampled and converted into a digital format for further processing.

[0029] Figure 5 illustrates implementation 500 for a distributed OTHR receiver system. Implementation 500 includes shelter 501 having servers 551 therein, receiver systems 502, consumer 503, and communication network 504. Receiver system 301 or receiver system 101 may be an example of the systems in receiver systems 502. For example, if the distributed OTHR system includes 100 antenna channels, then receiver systems 502 may include 25 of receiver system 301. Servers 551 is an example implementation of signal processor 103. Servers 551 may include common off the shelf server components and implement signal processing functions using software-defined processing. This approach allows for flexible and scalable deployment, as software-defined processing can be updated or reconfigured without modifying hardware. Unlike custom-designed signal processing circuitry, which may be optimized for specific tasks but lacks adaptability, COTS servers offer general-purpose computing resources that can support a wide range of digital signal processing functions, including digital down conversion, channelization, pulse compression, and beamforming. Additionally, servers 551 may include multi-core processors and high-speed memory subsystems, enabling parallel processing of multiple data streams from receiver systems 502.

[0030] Shelter 501 is an enclosure protecting servers 551 from the outside elements, providing power to servers 551, or otherwise providing a suitable environment for servers 551 to operate as described herein. Shelter 501 may also include environmental controls such as cooling systems, uninterruptible power supplies, and electromagnetic shielding to ensure reliable operation of the servers in remote or harsh environments. Servers 551 are connected to communication network 504. Communication network 504 includes one or more networks, such as local area network (LANs) or wide area networks (WANs) like the Internet. Servers 551 packages and transmits processed signals over communication network 504 to one or more computing systems of consumer 503. In some cases, there may be multiple consumers. The processed signals may be formatted as packetized data streams with embedded metadata, allowing consumers 503 to access382.0001 8specific channels or time segments as needed. Consumers may include command centers, data archives, or automated analysis systems that use the processed radar data for situational awareness, surveillance, or scientific research.

[0031] Figure 6 illustrates implementation 600 for signal-processing servers in a distributed OTHR receiver system. Implementation 600 includes an example of servers 551 collectively. The tasks may be distributed amongst servers 551 depending on hardware configurations, processing capacity, or some other factor. Servers 551 include fiber interfaces 601. Each of servers 551 may receive a single one of optical fibers 541 (e.g., from a single one of receiver systems 502) or may receive multiple of optical fibers 541 (e.g., the server may have the processing capability to handle signals from multiple of receiver systems 502). The fiber interfaces 601 may include multiple lOGbE optical transceivers, each capable of receiving high-throughput digitized data streams from wideband ADCs. Each of servers 551 also include at least one of network interfaces 602 for communicating over communication network 504. Network interfaces 602 may be Ethernet interfaces, may be optical network interfaces, or may be some other type of network interface. These interfaces allow servers 551 to transmit processed data to downstream consumers or storage systems, and may support protocols such as TCP / IP, UDP, or DDS (Data Distribution Service) depending on the application.

[0032] Servers 551 include data handler / NB (narrowband) channelizers 611-612, each of which corresponds to a digitized wideband signal received over optical fibers 541. If receiver systems 502 are four-channel receivers, an optical fiber from one of receiver systems 502 will carry four digitized wideband (WB) signals from that receiver system. The digitized signals are passed to memory in servers 551 for processing using software-defined signal processing elements. Data handler / NB channelizers 611-612, NB DCC 621, WB DCC 631, DCCs 641, pulse compressor / beamformer 651, and data packager 661 are all implemented by program instruction executing on servers 551, enabling such components to be updated as needed / desired. Software- defined signal processing allows for dynamic reconfiguration of processing parameters, such as filter bandwidths, decimation rates, and beamforming weights, without requiring hardware changes. This flexibility enables the system to adapt to changing mission requirements, electromagnetic environments, or antenna configurations. It also simplifies maintenance and upgrades, as new algorithms or performance enhancements can be deployed via software updates. Moreover, because servers 551 utilize general-purpose processors with floating-point arithmetic382.0001 9capabilities, they can perform high-precision calculations — such as 64-bit NCO phase generation and 32-bit filtering — that would be impractical or cost-prohibitive to implement in the lower-cost, simpler receiver systems 502. This separation of acquisition and processing enables the receiver systems to remain lightweight and power-efficient, while offloading computationally intensive tasks to centralized, scalable processing resources.

[0033] A channel through data handler / NB channelizer 611 and NB DCCs 621-62N / WB DCC 631 is detailed in implementation 600 but data handler / NB channelizers 612 and DCCs 641 will operate similarly on additional channels received via optical fibers 541. Data handler / NB channelizer 611 handles retrieval of data containing the digitized signal for the present channel and channelizes the wideband signal into multiple narrowband signals. For example, a 5-35 MHz wideband signal may be channelized (e.g., using digital bandpass filtering) into six 5 MHz wide narrowband signals (e.g., 5-10 MHz, 10-15 MHz, 15-20 MHz, etc.). In this example, data handler / NB channelizer 611 also outputs the original wideband signal but that may not be true in other examples. NB DCCs 621-62N down convert each narrowband signal to baseband (or at least a lower frequency band) and WB DCC 631 similarly down converts the wideband signal. Digital down conversion (DCC) involves mixing the signal with a numerically controlled oscillator (NCO) and applying decimation filters to reduce the sample rate while preserving the signal content. In software-defined implementations, the NCOs may use 64-bit floating-point arithmetic to minimize phase jitter and spurious tones, while the filters may use 32-bit floating-point arithmetic for high dynamic range and precision. This approach enables the system to achieve spurious-free dynamic ranges (SFDR) exceeding 140 dBc, which is critical for detecting weak signals in the presence of strong interferes. Despite data handler / NB channelizer 611 being software executing on servers 551, data handler / NB channelizer 611 still able to process the signals quickly enough to satisfy expectations that consumer 503 receives the processed data streams in what can still be referred to as real time.

[0034] Pulse compressor / beamformer 651 is fed the down-converted signals and performs pulse compression and beamforming on the signals before the signals are packaged for transmission over communication network 504 via network interfaces 602. Pulse compression improves range resolution by correlating received signals with known transmitted waveforms, allowing detection of targets with high timing accuracy. Beamforming combines signals from multiple antennas or channels to enhance spatial resolution and suppress interference from382.0001 10undesired directions. These operations may be implemented using matrix-based algorithms and executed in parallel across multiple CPU cores or GPU accelerators within servers 551. Network interfaces 602 may be network interface cards or some other circuitry installed in servers 551 to communicate over communication network 504. A consumer, like consumer 503, receives the processed signals over communication network 504 and performs any additional processing on the signals that the customer sees fit. Consumers may include radar operators, automated detection systems, or archival storage platforms, and may access the data in real time or on demand depending on system configuration.

[0035] Figure 7 illustrates operation 700 for software-defined processing of signals in a distributed OTHR receiver system. Servers 551 receive digitized wideband signals from receiver systems 502 (step 701). The wideband signals are each channelized into two or more narrowband signals (step 702). This channelization may be performed using digital filter banks that isolate specific frequency bands of interest, enabling parallel analysis of different portions of the spectrum. The narrowband signals, and the wideband signal in some cases, are down converted to baseband (step 703) before being streamed to consumer 503 (step 704). Streaming may be performed using high-throughput protocols over fiber or Ethernet, and may include metadata such as timestamp, frequency band, and signal quality indicators. The software-defined nature of the processing allows for real-time adaptation to changing signal environments, such as dynamic frequency hopping or interference mitigation. In some implementations, the system may also support recording and playback of digitized signals for post-processing or simulation purposes.

[0036] Figure 8 illustrates implementation 800 for a distributed OTHR receiver system. Implementation 800 includes servers 810 and receiver systems 861-86N. Servers 810 are an example of servers 551 and receiver systems 861-86N are an example of receiver systems 502. Implementation 800 shows additional information that may be transmitted between receiver systems 861-86N and servers 810. Clock transmitter 801 transmits a clock signal to respective clock interfaces 811-81N of receiver systems 861-86N. The clock signal provides a reference timing source used to synchronize the sampling operations of ADCs across receiver systems 861- 86N, ensuring phase coherence and time alignment of digitized signals. Receiver systems 861- 86N include internal clock circuitry that use the clock signal to synchronize the ADCs therein. This synchronization is critical for applications such as beamforming and interferometry, where precise timing relationships between signals from different antennas must be preserved.382.0001 11

[0037] Pulse per second (PPS) transmitter 802 transmits a PPS signal to respective PPS interfaces 821-82N interfaces of receiver systems 861-86N. The PPS signal serves as a timing marker that aligns data acquisition events to a common time base, often derived from GPS or another high-precision timing source. This allows for accurate timestamping of received signals and coordination across geographically distributed receiver systems. Calibration transmitter 803 transmits a calibration signal to calibration interfaces 831-83N of receiver systems 861-86N. The calibration signal may be used to inject known reference tones or waveforms into the receiver signal path, allowing the system to measure and correct for gain, phase, and delay mismatches between channels. Calibration routines may be performed periodically or on demand to maintain system performance and compensate for environmental changes or hardware drift.

[0038] Control interface 804 and control interfaces 841-84N of receiver systems 861-86N exchange control information (e.g., commands, status information, feedback, etc.) between servers 810 and receiver systems 861-86N. This control channel enables remote configuration and monitoring of receiver systems, including setting gain levels, selecting filter bands, initiating calibration sequences, and reporting health status. It may also support firmware updates and fault diagnostics. ADC signal interfaces 851-85N of receiver systems 861-86N are interfaces like fiber optic interface 331 of receiver system 301 that transmit digitized signals to ADC signal interface 805, which itself is an example of fiber interfaces 601. These interfaces typically use high-speed optical links to transmit wideband digitized data from each receiver system to servers 810, preserving signal fidelity over long distances.

[0039] While shown as separate links, some of the signals in implementation 800 may be transmitted over a common link (e.g., wire, optical fiber, etc.). For example, clock and PPS signals may be multiplexed onto a single fiber using wavelength division multiplexing (WDM), or embedded within a control protocol over Ethernet. Each of servers 810 may have a clock transmitter 801, PPS transmitter 802, calibration transmitter 803, control interface 804, and ADC signal interface 805 for connecting to one or more of receiver systems 861-86N or the signals may be transmitted via some other distribution of servers 810. For instance, a subset of servers 810 may be responsible for sending out the clock signal to clock interfaces 811-8 IN. This modular distribution allows for scalable system architectures, where timing and control responsibilities can be assigned based on server roles, processing capacity, or physical layout.382.0001 12

[0040] While not shown, receiver systems 861-86N require power to operate. Each of receiver systems 861-86N may include a power supply connect to grid power, a battery, a generator, a power connection to the processing shelter (e.g., shelter 501), or may receive power from some other source - including combinations thereof. Power sources may be selected based on deployment environment, with remote or austere locations relying on solar panels, wind turbines, or fuel-based generators. Receiver systems may also include power conditioning and backup systems to ensure continuous operation during outages or fluctuations.

[0041] Figures 9-11 illustrate different angles of receiver system housing 900 for a distributed OTHR receiver system. Receiver system housing 900 is an example four-channel receiver housing for a receiver system like receiver system 301. Receiver system housing 900 is a clamshell-style housing but other styles of housings can be used instead that still provide protection to the receiver system inside from the elements outside without having to build expensive receiver shelters infrastructure. Additionally, limiting receiver system 301 to a low number of antenna channels (e.g., 4 in this example or 8 in others) relative to sheltered receivers in existing OTHR installations, analog cable lengths may be shortened, which improves the quality of the analog signals input into the receiver system. Receiver system housing 900 includes upper casing 901, lower casing 902, hinge 903, heat dissipation surfaces 904, fasteners 905, antenna cable connectors 911, optical connector 931, and status LEDs 941. Weather seal 951 creates a seal between upper casing 901 and lower casing 902 to isolate the inside of receiver system housing 900 from water, dust, or other elements outside of receiver system housing 900. The clamshell design allows for easy access to internal components for maintenance or upgrades, while maintaining a compact and rugged form factor suitable for outdoor deployment. Weatherproofing features such as seal 951 help ensure long-term reliability by preventing ingress of moisture, dust, and corrosive particles, which could otherwise degrade signal integrity or damage sensitive electronics. This design enables receiver systems to be deployed directly in the field near antenna arrays, eliminating the need for environmentally controlled shelters and significantly reducing installation costs and logistical complexity. Heat dissipation surfaces 904 provide passive thermal management, allowing the system to operate within safe temperature ranges without requiring active cooling systems.

[0042] Using receiver system 301 as an example, antenna cable connectors 911 are connectors that enable cables of HF antennas 341-344 to connect through receiver system housing382.0001 13900 to HF WOFEs 311-314. Optical connector 931 enables antenna 341 to connect to fiber optic interface 331 through receiver system housing 900. Power connector 921 provides a receptacle for power to pass to HF WOFEs 311-314, ADCs 321-324, FPGA 330, or any other component of receiver system 301 located in receiver system housing 900. These external connectors are designed to maintain the weatherproof integrity of the housing while supporting high-performance signal and power transmission. Status LEDs 941 provide visual indicators of operational status, such as power, link activity, or fault conditions, allowing for quick diagnostics in the field. Fasteners 905 secure the casing and may be tool-free or tamper-resistant depending on deployment requirements. The hinge 903 allows the upper casing 901 to be opened for service while keeping the lower casing 902 and internal components protected and stable.

[0043] Figure 12 illustrates a computing system 1200 for processing signals in a distributed OTHR receiver system. Computing system 1200 is representative of any computing system or systems with which the various operational architectures, processes, scenarios, and sequences disclosed herein can be implemented. Computing system 1200 is an example architecture for a server of servers 551, although other examples may exist. Computing system 1200 includes storage system 1245, processing system 1250, and communication interface 1260. Processing system 1250 is operatively linked to communication interface 1260 and storage system 1245. Communication interface 1260 may be communicatively linked to storage system 1245 in some implementations. Computing system 1200 may further include other components such as a battery and enclosure that are not shown for clarity.

[0044] Communication interface 1260 comprises components that communicate over communication links, such as network cards, ports, radio frequency (RF), processing circuitry and software, or some other communication devices. Communication interface 1260 may be configured to communicate over metallic, wireless, or optical links - including combinations thereof. Communication interface 1260 may be configured to use Time Division Multiplex (TDM), Internet Protocol (IP), Ethernet, optical networking, wireless protocols, communication signaling, or some other communication format - including combinations thereof. Communication interface 1260 may be configured to communicate with other computing systems via one or more networks.

[0045] Processing system 1250 comprises microprocessor and other circuitry that retrieves and executes operating software from storage system 1245. Storage system 1245 may include382.0001 14volatile and nonvolatile, removable, and non-removable media implemented in any method or technology for storage of information, such as computer readable instructions, data structures, program modules, or other data. Storage system 1245 may be implemented as a single storage device but may also be implemented across multiple storage devices or sub-systems. Storage system 1245 may comprise additional elements, such as a controller to read operating software from the storage systems. Examples of storage media include random access memory, read only memory, magnetic disks, optical disks, and flash memory, as well as any combination or variation thereof, or any other type of storage media. In some implementations, the storage media may be a non-transitory storage media. In some instances, at least a portion of the storage media may be transitory. In no interpretations would storage media of storage system 1245, or any other computer-readable storage medium herein, be considered a transitory form of signal transmission (often referred to as "signals per se"), such as a propagating electrical or electromagnetic signal or carrier wave.

[0046] Processing system 1250 is typically mounted on a circuit board that may also hold the storage system. The operating software of storage system 1245 comprises computer programs, firmware, or some other form of machine-readable program instructions. The operating software of storage system 1245 comprises digital signal processing module 1230. The operating software on storage system 1245 may further include an operating system, utilities, drivers, network interfaces, applications, or some other type of software. When read and executed by processing system 1250 the operating software on storage system 1245 directs computing system 1200 to process digitized OTHR signals as described herein. Digital signal processing module 1230 may execute natively on processing system 1250 or the operating software may include virtualization software, such as a hypervisor, to virtualize computing hardware on which digital signal processing module 1230 executes.

[0047] In at least one example, digital signal processing module 1230 executes on processing system 1250 and directs processing system 1250 to implement at least a portion of data handler / NB channelizers 611-612, NB DCC 621, WB DCC 631, DCCs 641, pulse compressor / beamformer 651, and data packager 661.

[0048] The included descriptions and figures depict specific implementations to teach those skilled in the art how to make and use the best mode. For teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate382.0001 15variations from these implementations that fall within the scope of the invention. Those skilled in the art will also appreciate that the features described above can be combined in various ways to form multiple implementations. As a result, the invention is not limited to the specific implementations described above, but only by the claims and their equivalents.382.0001 16

Claims

CLAIMSWhat is claimed is:

1. A receiver system for over-the-horizon radar (OTHR), the receiver system comprising: a plurality of input channels configured to receive analog signals from a plurality of antennas; a plurality of analog-to-digital converters (ADCs) configured to generate digitized signals from the analog signals; and an output interface configured to transmit the digitized signals to an external signal processor configured to receive additional digitized signals from one or more additional receiver systems contemporaneously with the digitized signals and package the digitized signals with the additional digitized signals for transmission.

2. The receiver system of claim 1, comprising: a clamshell housing configured to enclose the plurality of input channels, the plurality of ADCs, and the output interface; and weather sealing where joining edges of the clamshell housing meet.

3. The receiver system of claim 2, wherein the external signal processor is configured to channelize the digitized signals into multiple narrowband signals.

4. The receiver system of claim 1, comprising: a plurality of filters configured to filter unwanted portions of the analog signals prior to reaching a plurality of amplifiers; and the plurality of amplifiers configured to amplify the analog signals prior to reaching the plurality of ADCs.

5. The receiver system of claim 1, comprising: a digital equalizer configured to perform amplitude and group delay compensation.382.0001 176. The receiver system of claim 5, comprising: a Field-Programmable Gate Array (FPGA) including the digital equalizer and the output interface.

7. The receiver system of claim 1, wherein the output interface is a fiber-optic interface.

8. The receiver system of claim 1, comprising: clock circuitry configured to synchronize operation of the plurality of ADCs.

9. The receiver system of claim 8, comprising: a clock input configured to receive a clock signal synchronizing the clock circuitry with the one or more additional receiver systems.

10. A method for operating a receiver system for over-the-horizon radar (OTHR), the method comprising: receiving signals via a plurality of input channels from a plurality of antennas; converting the signals to digitized signals; and transmitting the digitized signals via an output channel to an external signal processor, wherein the external signal processor receives the digitized signals, receives additional digitized signals from one or more additional receiver systems contemporaneously with the digitized signals, and packages the digitized signals with the additional digitized signals for transmission to a consumer.

11. The method of claim 10, comprising: filtering unwanted components from the signals; and after filtering the unwanted components, amplifying the signals prior to converting the signals to the digitized signals.

12. The method of claim 10, comprising: performing amplitude and delay compensation on the digitized signals prior to transmission.382.0001 1813. The method of claim 10, wherein the output channel is a fiber optic channel.

14. The method of claim 10, wherein converting the signals to the digitized signals comprises: synchronizing sampling of the signals across the plurality of input channels.

15. The method of claim 14, wherein synchronizing the sampling comprises: receiving an external clock signal coordinating the sampling with the one or more additional receiver systems.

16. The method of claim 14, wherein synchronizing the sampling comprises: delaying the sampling on one or more of the plurality of input channels to account for different cables to the plurality of antennas.

17. A distributed receiver system for over-the-horizon radar (OTHR), the distributed receiver system comprising: a plurality of receiver systems wherein each receiver system of the plurality of receiver systems is configured to: receive analog signals from antennas on a plurality of input channels; convert the analog signals to digitized signals; and transmit the digitized signals to a signal processor system; and the signal processor system configured to: channelize the digitized signals from individual wideband signals into multiple narrowband signals prior to transmission; and transmit the digitized signals in a data stream to a consumer.

18. The distributed receiver system of claim 17, wherein the signal processor system comprises: a reference clock configured to generate a reference clock signal for analog-to-digital converters (ADCs) in the plurality of receiver systems; and a clock interface configured to transmit the reference clock signal to the plurality of receiver systems.382.0001 1919. The distributed receiver system of claim 18, wherein each receiver system of the plurality of receiver systems comprises: a plurality of ADCs configured to convert the analog signals to the digitized signals; and clock circuitry configured to receive the reference clock signal and synchronize operation of the plurality of ADCs.

20. The distributed receiver system of claim 17, wherein the signal processor system comprises: a fiber optic interface configured to receive the digitized signals; and a communication network interface configured to transmit the data stream over a communication network.382.0001 20

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