Technology Today

2010 Issue 2

Multifunction RF
Next Generation RF Systems:
Multifunction Designs to Meet Future Warfighter Needs

To control the evolving battlespace, our customers increasingly require systems that sense more phenomena; transfer the results of the sensing to the decision maker more quickly; provide electronic protection; and do all this without adding cost, weight or power. These factors are driving future system designs that must incorporate multiple functions.

Raytheon has a long tradition of providing the absolute best in sensor and communication systems. These systems, however, were optimized for one or two functions, and their host platforms were optimized for a limited set of missions. The changing nature of defense acquisition in the 21st century is placing different demands on weapons systems, requiring that they support a broad set of missions. To meet this requirement, platforms must have a broader range of sensors and greater communications connectivity. Because weight, power, cooling and cost constraints prohibit carrying a full suite of optimized, federated systems, an urgent need has emerged for a new generation of radio frequency (RF) systems that can support multiple functions.

Raytheon is already meeting customers' needs for multi-functionality with systems like the AN/APG-79 airborne Active Electronically Scanned Array (AESA) radar for the Navy's F/A-18 aircraft, and the SPY-3 shipboard AESA for the Navy's Zumwalt-class destroyer. We are therefore well positioned to meet this challenge.

AN/APG-79

SPY-3

One needs to look no further than the United States National Table of Frequency Allocations to appreciate the diversity of RF functions that exist within a limited frequency range.1 These functions can be classified into groups as passive sensing, active sensing and communications. Each group places similar but different requirements on RF performance. Key performance characteristics common to all three groups include tunable frequency range, instantaneous bandwidth, dynamic range, effective radiated power, modulation diversity and linear transmit operation. Raytheon's next generation of systems must provide a balanced combination of these capabilities to enable multifunction operation.

Figure 1. Communications, surveillance and radar functions are present within the tunable range of a Strawman 7-17 GHz multifunction radio

Passive sensing functions include radar warning, electronic support measures and signals intelligence, plus others. These systems require sensitivity over a wide tunable frequency range to detect signals of interest, wide instantaneous bandwidth to capture wide-band signals, and large dynamic range to detect weak and strong signals.

Active sensing functions include radar and jamming, plus others. Radar systems require a wide tunable frequency range to operate without interference (and comply with international frequency allocation standards), wide instantaneous bandwidth to provide high-resolution target identification, large dynamic range to detect targets in the presence of clutter (and interference), effective radiated power to meet the range requirement, and programmable waveform modulations tailored to the target characteristics being sensed to maximize target detection. Jamming systems are also designed for a wide tunable frequency range, but to interfere with targeted systems. Jamming also requires adjustable instantaneous bandwidth and waveform modulations to optimize the effect on threat systems, and sufficient effective radiated power to neutralize the threat system.

Communications systems include a variety of one- and two-way links for networking and sharing information. These systems require frequency agility for spread-spectrum waveforms to operate in authorized communications bands, instantaneous bandwidth and programmable modulations to satisfy waveform requirements, sufficient dynamic range to receive signals in the presence of strong interference, and sufficient power to complete the link and achieve the required availability. In addition, communications systems have two unique requirements that are more stringent than those of other radio frequency capabilities. The first mandates isolation between transmit and receive during simultaneous transmit-receive (full duplex) operation. This is facilitated by having orthogonally polarized transmit and receive antennas or having separate transmit and receive frequency band allocations. The second requirement is for high-efficiency, linear transmit operation, which is used to support the communications waveform modulations.

Raytheon is already delivering many multi-function RF systems. Although limitations of today's technologies often require compromises in the functionality and performance of secondary RF functions, Raytheon is working on technologies to eliminate those compromises. Two breakthrough technologies include Ultra-Wideband (UWB) Samplers and Ultra-Short Pulse Laser-Based Frequency Sources. The UWB sampler enables the instantaneous bandwidth and dynamic range to be tuned to the function via software. The Laser-Based frequency source provides an ultra-pure, ultra-stable reference for waveform synthesis and coordination. Raytheon's future systems are being designed with the architecture and technologies to give the best in multifunction capability.

Our customers need the next generation of radio frequency systems to support passive sensing, active sensing and communications; with the minimum number of apertures and back-end electronics units; and at an affordable price. By considering the customer's needs up front, Raytheon will provide RF systems that meet all of the performance needs of the warfighter, and do so affordably.

1 Image is from the United States Frequency Allocations: The Radio Spectrum, October 2003, National Telecommunications and Information Administration, Department of Commerce, Office of Spectrum Management.

Eric Boe

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