Real-time assessment of the electromagnetic environment can provide a key tactical advantage. The rapid development and proliferation of advanced radios, however, has made this a challenging task. Radio frequency (RF) sensor systems on the modern battlefield must cover many RF and microwave bands through noise and powerful interferers. Ultra-wideband analog-to-digital conversion (ADC) has emerged as an essential technology to interface between propagating analog RF signals and digital processing for reactive decision-making. Such an ADC allows for high-speed and reconfigurable digital processing in a complex electromagnetic environment.
Despite the significant military need, progress in high-resolution, high-speed ADC systems has slowed. This can be attributed to fundamental limits of the timing jitter of the ADC clock and sample-and-hold circuits in conventional ADCs. Optical mode locked lasers have demonstrated timing jitter that is orders of magnitude better than electronic approaches. An architecture employing optical sampling could overcome jitter limitations of all-electronic ADCs.
DARPA’s RADER program seeks to dramatically enhance direct ADC conversion of remote signal inputs, over a broad instantaneous bandwidth, for enhanced signal collection with high dynamic range for target detection in cluttered electromagnetic environments.
The RADER program seeks to achieve ADC conversion over a 10 GHz bandwidth with 10 effective bits of resolution and 63 dB of spur free dynamic range through the incorporation of a photonic front-end. RADER aims to develop low-jitter sampling sources, novel photonic ADC architectures, and backend signal processing algorithms necessary for such a high performance ADC system. The final system may be capable of remoting signals over 50 meters and operating under 50 Watts.
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