Digital meets RF
In the not too distant past, computers and RF were not to be in the same room, let alone the same piece of computing equipment. Then over the years the two became friendlier as microprocessors were used to control radios and eventually led to the creation of soft radios and today’s highly popular smart phone.
Countless critical defense applications depend on radio spectrum technology as part of their architecture. As Electronic Warfare (EW) and Electronic Attack (EA) missions, Signal Intelligence (SIGINT), and associated programs have grown in sophistication, the level of radio spectrum (sub 3kHz to 30+ GHz) technology integrated into platforms continues to grow.
The many piece parts within radio spectrum technology in support of EW, EA, and SIGINT continue to play an important role. Mixers, filters, capacitors, limiters, oscillators, digital receivers, and more have all been part of the lexicon for decades. Advanced Digital Radio Frequency Memory (DRFM) jammers, and Integrated Microwave Assemblies (IMAs) utilize this “kit of parts” in ways that before hadn’t been imagined. An IMA, for example, often offers customized designs for mission-specific applications. They can combine the integration of switches and switch matrices, amplifiers, attenuators, filters, oscillators, as well as other RF and microwave functions.
Several technology advancements have led to an overwhelming acceptance of RF into the world of digital technologies. These advancements enable products that we have come to depend on in our everyday lives. These advancements are also finding their way into the latest defense systems. Four areas in particular have benefited most.
Good electromagnetic interference (EMI) practices have been integrated into design tools, making it easier to address critical issues early when something can be done to correct potential problems. Printed circuit board (PCB) designers are keenly aware of impedance discontinuities so low amplitude signals are a must. PCB materials and manufacturing techniques make it possible to laminate digital and RF circuits together in ways that minimize the interference. Improvements to multi-layer board technology make it possible to isolate interfering circuits. Hybrid circuits can now be built that significantly reduce the size of a digital/RF module. Advances in Phase-Lock-Loop (PLL) circuits, frequency resolution, quality, and digital PLLs, have made them an important building block in circuits.
Cabling and interconnects
Shrinking circuits make it possible to reduce trace and cable lengths, leading causes of EMI. Shielding techniques enable better protection between critical circuits, reducing or eliminating interference. Connector shielding advances have made it possible to connect to boards without causing undue RF interference. Mechanical enhancements in connectors have reduced extraneous emissions. Shielding has improved across the board as board designers have learned new techniques for designs. Active cables bring yet another level of protection, enabling lower amplitude signals to extend further at higher quality and frequencies.
Input output filters
Filters are much more accurate and tunable. Laser-trimmed filters allow the circuitry to shrink in ways that make it possible to build even smaller devices. Many new chip-level devices have built-in filters.
Mechanical enhancements have made it possible to cool components while not compromising on shielding. ANSI/VITA 48.7 Air Flow-By cooling, for instance, has made it possible to provide critical cooling capability while not compromising on shielding. New materials for shielding and gaskets push the resistance to EMI higher. Packaging and circuit isolation techniques have emerged that make it possible to build even smaller devices without sacrificing RF interference.
Consumer electronics have led the charge in many of these developments. Advancements in cell phone technology where many different RF transmitters and receivers can be found in a single phone have blazed a path that many other applications can leverage.
“RF and microwave technologies have been part of the underlying fabrics of critical defense applications for generations, yet little progress has been made to date in standardizing these technologies in order to meet the DoD’s directives around affordability and open system architectures,” explained Dr. Ian Dunn, vice president of Mercury’s Embedded Products group. Most RF and microwave systems are custom designed and built, foregoing the trends in other areas of electronics technology that leverage standards and open architectures. Each system depends on unique architectures, integration schemes, testing, and manufacturing, with little regard to design and intellectual property re-use.
“Mercury Systems saw a need for standardization in RF and microwave systems for EW and SIGINT,” continued Dr. Dunn. “As a result, we are launching OpenRFM, an initiative created specifically to address the RF and microwave integration challenges our customers have told us they face.”
What is OpenRFM?
OpenRFM is a modular, open architecture that combines hardware, firmware, and software that can be applied to EW and SIGINT challenges (see Figure 1).
Its benefits are that it allows:
- Affordability driven by high channel density, modular design, advanced connector technology, and the integration of digital signal processing and RF technologies
- Sustainability with a solution that provides maximum re-use of standardized technology that will protect investments for the long haul, making it “future proof”
- Versatility by providing many systems designs with multiple building blocks
- Interoperability driven by modular architecture, standardized control plane, and advanced software interface
OpenRFM, with its modular, standardized, scalable approach allows prime contractors and the DoD to develop or augment existing applications to counteract evolving threats in EW and EA. It also allows for the faster deployment of applications and classified techniques that are the lifeblood of rapidly evolving EW-related programs. Programs that are growing in importance as the complexion of our defense base and the missions it serves continues to change. OpenRFM will allow already existing EW, EA, and SIGINT applications to be deployed more effectively and affordably. These include areas such as deceptive jamming, pulse jamming, and spot jamming. In the realm of electronic countermeasures OpenRFM can speed up deployment of techniques such as “cloaking” the outgoing signal with random noise. Rolling out EW applications can and will be made more predictable and affordable with the standardized OpenRFM solutions already being built.
The specification that will eventually emerge is expected to provide a definition for the physical volume of modules; electrical characteristics; how-to slot profiles for various blades, such as VPX or AdvancedTCA; and the software/hardware abstraction layers to connect to Ethernet and PCI Express.
Mercury Systems is still iterating a strategy to make OpenRFM an industry standard with a supporting ecosystem. You can expect announcements on a standards strategy in the near future.
OpenRFM is intended to make it more affordable and faster to deploy RF technologies. Its goal is to allow digital and RF to seamlessly merge together.
Mercury is currently developing OpenRFM-based standardized subsystems that can meet the open system architecture requirements required for affordable, standardized, interoperable solutions for EW and SIGINT applications. Technical briefings on these standardized solutions are underway with select customers, and a technical white paper will be published soon.