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RF Technology for Defense

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by Per Vices

Radio frequency (RF) transceiver technology has played a prominent role in defense applications since its inception, supporting signals intelligence (SIGINT), electronic warfare (EW), radar, and communications functions. With adversary technological threats and capabilities becoming more sophisticated, funding for advanced defense RF technologies is increasing to counteract and protect from malicious attacks and surveillance as well as improve defense related RF technologies.

In terms of signal intelligence, radar and spectrum monitoring and recording are widely employed for the detection of objects, while also related to, and enabling, electronic warfare and electronic countermeasures. More modern aspects of using RF communications on the battlefield include drones/unmanned aerial vehicles (UAVs), signal jammers, and sensors worn by soldiers, to name a few, which require the integration of transceiver technology of various sizes, using unique frequencies and bandwidths. Therefore, the RF technology in defense is switching towards software-defined radio (SDR) due to its extensive, reconfigurable, and flexible capabilities to adapt to many defense RF requirements in radar, and spectrum monitoring and recording applications.

SDR Architecture

Whereas traditional radios relied on analog hardware for operation, SDR uses a combination of analog hardware and software and/or firmware in order to carry out signal processing tasks.  Figure 1 shows the basic block diagram of an SDR. It includes an analog radio front-end (RFE) that allows for transmitting (Tx) and receiving (Rx) the RF signals using various amplifiers, mixers, and filters. The analog-to-digital converter (ADC) and digital-to-analog converter (DAC) convert the signal from one domain to another, while the digital back-end handles the signal in the digital domain and transfers data to/from a host computer or other interfacing equipment.

Figure 1: Basic Block Diagram of a SDR

Figure 2 shows a high-level overview of a high-end SDR architecture. Larger frequency tuning ranges and channel counts are ideal when needing to tune and monitor a variety of frequencies on one platform, as they can be analyzed independently using specific parameters. The range varies depending on the product and application, but can go from near DC to over 18 GHz for high-end stock SDR models. Similarly, SDRs like Per Vices Cyan, can offer a very high instantaneous bandwidth of up to 3 GHz. In the digital back-end, a field-programmable gate array (FPGA) is implemented for various digital signal processing (DSP) functions by utilizing the FPGA’s reconfigurable logic gates. The FPGA can perform various onboard DSP functions like modulation, demodulation, digital up-conversion (DUC), and digital down-conversion (DDC) as well as application specific computation. The main advantage of using an FPGA in the digital back-end is its reconfigurability, which allows new protocols and algorithms to be carried out efficiently and without changing the existing hardware. 

Figure 2: High-level overview of Per Vices Crimson TNG SDR architecture

A Brief History of SDRs in Defense

SDR is a deep-rooted concept in defense which the military has been focusing on for years. It began as an optimal solution for the design of more flexible radios that traditionally relied on single-channel communication technology, which had underperformed in various situations. The design of the first large-scale defense SDR project, the SpeakEasy I, enabled the military to communicate effectively using multi-frequency bands, multi-waveforms, and the associated radio protocols. The SpeakEasy I system was designed to support interoperability between different branches of the U.S. military which had their own unique radio communication standards. Similar projects still exist today, as defense programs such as the European Secure Software Defined Radio Program (ESSOR) and the US DoD Joint Tactical Radio System (JTRS) are tasked with maximizing interoperability between coalition forces’ tactical radios.

The flexibility of SDR provides promising opportunities in defense as it enables the performance of various ultra-fast, parallel signal processing and communication tasks using upgradable and reconfigurable software and IP cores on FPGAs. SDR provides numerous benefits, including size, weight, and power (SWaP) reductions, jamming or interception resistance, multi-channel Tx and/or Rx radio functionality, and improvements of other capabilities important for the most demanding communications networks in defense. After more than 30 years of SDR technology being deployed in countless applications, it can be genuinely said that SDR is no longer used exclusively for tactical radios, but has expanded to radar, spectrum monitoring & recording, as well as several other RF defense communications systems.

SDR in Radar

One of the most prominent applications of SDR in defense is its integration into radar systems. Radar is a system that uses radio waves for detecting the presence, direction, distance, and speed of aircraft, ships, projectiles, and other objects. Radar works on the principle of radiating electromagnetic energy into space and monitoring the reflected signals from the object. Radars are used in land, air, and sea, including on large surface ships, submarines, military vehicles, fighter jets, and drones. They operate in many frequency bands, including Ka, K, Ku, X, C, S, L, UHF bands.

Figure 3: Radar display (PPI) screen

Radar consists of 6 essential elements: transmitter, waveguide, antenna, duplexer, receiver, indicator/display. As the name suggests, the transmitter generates a required RF signal with a specific power and radiates that generated signal by utilizing the antenna. An antenna is a transducer that converts the electric signal to RF signals and vice versa. Waveguides are used for the transmission of RF signal from one point to another. In radar, a waveguide transfers signal energy to and from the antenna, where the impedance needs to be matched for efficient power transmission. In radar, one antenna is used to transmit and receive RF signals, so the duplexer enables the antenna to switch between the transmit and receive radio chains. The reflected radio waves picked up by the antenna and directed towards the receiver are a low-power noisy signal. The received signal is passed through a filter and then amplified using an amplifier. After that, the signal is converted into the digital domain, processed, and displayed on a screen in a meaningful way, such as a plan position indicator (PPI) as shown in Figure 3

The military uses a variety of air, land, and sea-based radar for both offensive and defensive purposes. For air-based radar, the Enhanced Traffic Alert Collision Avoidance System is designed to reduce the incidence of collision between aircraft. Another, air-based reconnaissance radar, is used to obtain information on enemy activity and determine the nature of a suspected adversary’s terrain. Radar also has many applications on land, such as weather monitoring and navigational radar employed for landing aircraft on bases. Moreover, gunfire control radar such as STIR (Signal Tracking and Illumination radar), can be used to guide projectiles and is used for artillery control. Similarly, radar has many uses in the sea, for instance, coastal surveillance radar, Antisubmarine Warfare (ASW) radar, and Surface Search radar are prominent examples. In short, the military depends on radar for many purposes and surveillance is incomplete without utilizing radar in defense. 

Figure 4: Block diagram of Radar/SDR

SDR has a flexible hardware architecture that can be easily integrated into modern defense radar systems. One of an SDR’s hardware traits is its multi-input multi-output (MIMO) channels, suitable for modern radar systems. High-performance SDR platforms offer up to 16 channels, thus allowing the implementation of radars utilizing a multi-channel phased array system through a single device. A MIMO SDR is also ideal for implementing a complex radar system with multiple radar antennas with different range capabilities. 

Figure 4 represents a radar system architecture with an SDR integrated to function as various components, thus reducing the amount of stand-alone equipment that is found in a traditional system. The SDRs digital backend uses a reconfigurable FPGA that performs DSP functions such as storing and triggering waveforms/pulses, automatic gain control, and controlling radar antenna arrays. Such a reduction in complexity of a radar system by using an SDR is significant to modern systems requiring immense capability but limited by SWaP requirements. 

High-performance SDR systems also have a wide frequency tuning range, making them suited for the most demanding radar applications. In addition to permitting appropriate channel spacing, this feature allows a single SDR to cover all of the frequency bands utilized in radar applications. Furthermore, these platforms have excellent frequency and phase stability, making them appropriate for modern radar systems.

SDR in Spectrum Monitoring

Another RF technology used for defense is spectrum monitoring and recording. Spectrum monitoring systems continually monitor the range of frequencies used by defense RF devices and remove the unwanted or offending interference signal. Spectrum monitoring and recording is needed everywhere in defense where there is wireless communication in order to prevent eavesdropping and/or signal jamming, and other forms of electronic warfare. For instance, military bases and test ranges are essential facilities to a nation’s armed forces at home and abroad. These restricted military areas use a multitude of electronic hardware that produce various RF signals, on the ground, in the air, and at sea. Important information is contained in these signals, which sometimes encounter breaching by unwanted or enemy UAVs/drones, or other RF reconnaissance and/or surveillance. Due to the classified and restricted nature of operations on these bases, any spectrum interference, whether malicious or accidental, has to be monitored, identified, and eliminated. Other areas in defense where spectrum monitoring and recording are needed include protecting national borders, spectrum sharing, and situational awareness. 

As RF technologies have improved significantly in terms of frequencies used and anti-detection capabilities (for instance, using frequency hopping), a large amount of instantaneous bandwidth must be captured for detecting offending signals. This causes a problem for modern spectrum monitoring systems; inspecting a broad spectrum in real-time is computationally intensive. To meet this requirement, a SDR combined with a storage solution has become ideal for spectrum monitoring. A large RF spectrum coverage and user-adjustable bandwidth, combined with the technology for seamless data capture, make detecting RF signals quick and accurate. Multiple channels allow for capturing a large amount of data and allow for tuning into specific parts of the spectrum for further analysis and higher data fidelity. 

Conclusion

This article discusses the significance and application of RF technology in defense and the advantages of using SDR transceivers to carry out communication and signal processing tasks. SDR continues to be a promising technology that replaces radio equipment that has been traditionally implemented in analog hardware. Due to its flexibility and reconfigurability, as well as immense computational abilities, SDR has a preeminent role in defense applications like interoperability of tactical radios, radar, and spectrum monitoring and recording, as well as many other defense applications not discussed here. 

Per Vices has extensive experience in designing, developing, building, and integrating SDRs for military applications including radar and spectrum monitoring & recording. We have a range of stock SDR products as well as customization abilities, depending on your needs. Contact solutions@pervices.com today to see how we can help you with your SDR needs.

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