High-Performance X-Band Receiver Demo
GMR received funding from the Air Force Research Lab to build a prototype X-Band receiver incorporating NLEQ and iNLEQ technologies in a real-time system. This two-year SBIR Phase II effort was completed in May 2011. The GMR system exceeded the program goals, achieving 30 dB in improved linearity over a 70% larger band.
The system comprised an X-band receiver, a wideband digitizer, and an NLEQ digital processor.
The receiver was designed to work in the 9.24-9.675 GHz band, and was operated with a 9.7 GHz local oscillator. The digitizer system captured data at 485 Msps using two 12-bit, 250 MSPS, time-interleaved wideband digitizers (Linear LT2242-12 ADCs). The NLEQ processor was implemented on an Altera Stratix III FPGA. The digitized, NLEQ-compensated data exited the system at the full data rate with a very low latency.
To demonstrate the performance of the NLEQ-compensated receiver, a viewer program was written in C++ to communicate with the system FPGA and display received signals. The FPGA was used to capture parts of the digitized signal and transfer it serially to the support computer. The software then displayed a frequency plot of the received signal.
The images below were captured by the software, showing a narrow-band signal before and after NLEQ and iNLEQ processing. The before image has clear distortion artifacts, which are eliminated by the NLEQ processor as indicated in the after image. The strongest distortions are pushed from -57 dBFS to below the noise floor, which begins at about -85 dBFS. The system was improved by 28 dB in this region of signals.
X-band receiver FFT before and after NLEQ and iNLEQ processing