Multi-function Systems Inching Closer
Combining the functional resources of EW and radar systems in smaller form factors and possibly in a single system along with speeding new technology into fielded systems are key
goals within DoD. Nevertheless, after championing the idea more than a decade ago it has little to show for it. The technology to make this happen appears to be available now or soon will be although major challenges will obviously have to be surmounted. The other key factor as outlined in the next article is DoD’s deeply-entrenched process in which the Army, Navy, and Air Force develop systems for their own use with little or no regard for their potential application by other services. The result has been a large number of systems developed by different prime contractors that share nothing more than their intended function. As the need to provide greater functionality and performance in smaller spaces, using less power, with lighter, smaller hardware is essential, and since the DoD budget will be under the knife in the next decade or more, now is the time for change.
Human nature notwithstanding, orchestrating the functions of radar and EW systems with the same hardware poses fundamental problems, as these systems are vastly different in many respects. For example, radars operate at defined frequencies such as L-band, S-band, and X-band, while EW systems operate over multiple octaves of bandwidth, potentially from HF well into the millimeter-wave region. They have different performance requirements as well, from dynamic range to sensitivity, latency, RF output power, beamwidth, and many others. So achieving optimum radar and EW performance with a single system seems at the least conflicting and at worst impossible.
Both systems do however process massive quantities of data, act on them at incredible speeds, use the same type of components from active and passive RF and microwave components to analog-to-digital and digital-to-analog converters, FPGAs, general purpose and graphics processors, data storage, and communications buses. Radar systems employ an AESA architecture and EW systems are likely to follow suit, and it is likely to make its first appearance in the Next Generation Jammer program if not sooner.
Unfortunately, this is where the similarity ends, and the first outlier is the antenna, which in both cases will be a phased array (i.e. AESA). But radar and EW will have difficulty sharing a single aperture, as their frequencies will be different so their elements will be of widely varying sizes and spacings. In addition, antennas forced to cover very broad bandwidths sacrifice gain and sensitivity, and the antenna will need to have both very wide and very narrow beamwidths.
In addition to these and other technical challenges is the question of which system gets priority. That is, it is certainly possible that both systems will need to operate simultaneously, so software-delivered “what-if” scenarios must be orchestrated, which might prove unacceptable in certain circumstances.
When all possibilities have been explored, the end result may be that there is in fact no Holy Grail: systems will share components and software to the greatest extent possible, but a “one-box” solution may result in more problems than solutions. Multiple apertures and other seemingly redundant components will be required. This still would be a giant step forward, especially if these systems were designed by a team that could (and would be willing to) work together so that their end results could be used across multiple platforms and services without wholesale redesign.
Fortunately, there is now an architecture available that at least from a digital perspective provides a way to build systems using a common, COTS-based form factor: VPX. The VPX form factor (also an ANSI standard) that in its developmental form was called VITA 46 and was defined under the auspices of the VME International Trade Association (VITA), is a VME-based architecture that provides support for switched fabrics and uses a unique high-speed connector. It has broad industry support and was created for defense applications. It is compatible with VME’s 6U and 3U form factors and supports PCI mezzanine card (PMC), XMC mezzanines (PMC with high-speed serial fabric interconnect), and FMC mezzanine cards.
It is designed to be integrated with PCI Express and 10-Gigabit Ethernet and is forward-looking as it can be integrated with very-high-speed switched fabrics like Infiniband that embrace multiprocessing and local communications between multiple digital signal processors. It also embodies the ruggedness required of defense systems, various cooling schemes, general-purpose and graphics processors, DSP, FPGAs, and various attributes specific to defense applications. The OpenVPX system specification ratified by ANSI in 2010 improves on interoperability issues that resulted from the way in which VPX was created (that is, by different manufacturers instrumental in creating the standard). In short, VPX is the form factor that will drive “COTS-based systems” in the future, and will benefit any movement toward multi-function systems.
DARPA Calls for Change
DARPA has long been hammered for spending taxpayer dollars on research that is either somewhat other-worldly or produces nothing of substance. However, such is the nature of basic research, without which consumers would not have smartphones or the transistors that power them. DARPA has also had some huge successes, two of which are directly related to defense. Its MIMIC program in the 1980s drove the development GaAs MMICs and ultimately created a multi-billion-dollar industry. Its multiple gallium nitride development programs have driven this technology into the market far faster than would have been possible if industry alone was championing it.
The results of its Arrays at Commercial Timescales (ACT) program announced in the spring may not deliver the same level of results but may help pave the way to overcoming the stasis in DoD procurement that in turn may make possible multi-function systems, speed new technology into the field, and allow systems to be built with greater cross-platform utility. The goal of this multi-faceted R&D program is to create antenna arrays using COTS components that can be deployed in a “time-scale” more like that of commercial or consumer products so that technological developments can be implemented rapidly within fielded systems.
DARPA doesn’t mince words on the subject of how current systems are deployed, frankly stating that antenna arrays have “come at a severe cost in terms of system development time and the ability to upgrade capabilities in the field. Research must push past the traditional barriers that lead to 10-year array development cycles, 20- to 30-year static life cycles, and costly service life extension programs”. It also acknowledges that the gap in performance is widening between RF capabilities of fielded systems and the rapidly-evolving digital electronics that surround it. DARPA specifically calls out the need to abandon “heavily compartmentalized and ‘siloed’ array system development, procurement, and sustainment.
Participants in the ACT program will develop a digitally-interconnected building block from which larger systems can be formed, called the “Common Module”, and a reconfigurable RF interface that will be scalable and customizable for each application without a full redesign. This DARPA hopes, will end the era of “one-off” antenna array programs that do not consider reuse, because from 70% to 80% of the array’s development cycle cost will be built into the Common Module. DARPA assumes that greater digital content in RF systems can achieve an “unprecedented level of commonality between systems and across application requirements”.
ACT will demonstrate how developments in RF and digital electronics can enhance commonality of an underlying component base, and personalization of the Common Module for a specific use will include frequency, bandwidth, polarization, RF power level, scan angle, geometry, beam characteristics, and number of elements. The last facet of the program will create scalable arrays not just within one platform but across multiple platforms by stitching together array panels to generate coherent, spatially-distributed radiation and transferring data between them digitally via fiber to achieve coherent power aggregation.
The digital and RF components are ready, a form factor, signal buses and fabrics, signal processing algorithms, AESA architecture, and more or less everything else required to take a stab at creating multifunction systems are either ready now or soon could be. So the “only” missing link is the willingness on the part of DoD to change the way it does business. And that may be the greatest challenge of them all.