SPAR: Signal Processing at RF

The electromagnetic (EM) spectrum is a scarce resource, in which a variety of friendly, unfriendly and neutral entities contend for available spectrum at any given time, location and frequency. DoD radio frequency (RF) systems, such as communication networks and radar, must operate within the context of an increasingly congested and contested electromagnetic spectrum. What’s more, in typical DoD applications, mission-compromising RF interference, from both self- and externally-generated signals, can be strong and the EM environment is unpredictable. This is in contrast to commercial wireless applications, where the potential interference within pre-allocated spectral bands is carefully controlled through regulation, standardization and pre-planned, pre-deployed infrastructure, such as the base stations that make thousands of cell phones work so well all at once even within small geographic areas.

The Signal Processing at RF (SPAR) program aims to mitigate both externally generated interfering signals (from adversaries seeking to jam signals, for example) and self-generated interfering signals (from transmitters within a shared network or RF systems on a common platform, for example) of known and unknown characteristics. SPAR’s engineering challenges center on designing, building and demonstrating RF signal-processing components, which can remove in-band interferers from the desired receive signal at the RF front end—that is, before the signals reach the receiver electronics. With the interference mitigated sufficiently, RF signals of interest can reach in-receiver digital components, which then can perform roles akin to cell towers and other spectrum-management systems commonly integrated into the civilian communications infrastructure.

The technologies developed under the SPAR program must achieve not only the desired levels of signal isolation but also the low noise and high linearity required of components operating directly at the RF front end. Furthermore, these components must be reconfigurable so they can work with the many waveforms, frequencies and filter codes associated with a high number of friendly spectrum users.

If successful, the SPAR program will lead to technologies that significantly reduce critical interference issues. Furthermore, SPAR-catalyzed technologies should enable RF systems to simultaneously transmit and receive at the same frequency, doubling spectrum efficiency. All told, SPAR aims to enhance radio and radar operation in increasingly congested and contested RF environments.