FPGA-Based Linear Frequency Modulated Waveform Generation and Baseband Validation for SAR-Oriented Prototyping

Introduction: Linear frequency-modulated (LFM) chirp waveforms are widely used in synthetic aperture radar (SAR) systems because they provide large time-bandwidth products and enable pulse compression. This work presents a configurable FPGA-based LFM waveform generator for SAR-oriented waveform prototyping on commercial off-the-shelf FPGA/SDR hardware.

Methods: The generator was implemented on a Xilinx Zynq-7000 system-on-chip platform paired with an AD9361-based SDR front end. A Xilinx DDS Compiler IP core was controlled by a custom three-state finite-state machine and configured through AXI4-Lite registers from the ARM Cortex-A9 processing system. The design generated a 14 MHz down-chirp from 16 MHz to 2 MHz over a 45 microsecond sweep interval at a 40 MS/s complex baseband sample rate. Baseband I/Q samples at the programmable-logic output were captured using a Xilinx Integrated Logic Analyzer and analyzed offline using instantaneous-frequency estimation and FFT-based matched-filter pulse compression.

Results: The measured frequency trajectory followed the ideal linear 16 to 2 MHz sweep. The generated waveform had a time-bandwidth product of 630 and a theoretical range resolution of approximately 10.7 m. Matched-filter processing produced a compressed pulse width of 0.07 microseconds, corresponding to a 600-fold compression ratio, with a peak sidelobe ratio of -39.0 dB. FPGA resource utilization on the XC7Z020 device remained low for LUT and flip-flop resources.

Conclusions: The results confirm that the programmable-logic baseband output is suitable for pulse-compression processing. The implementation can therefore be used as a configurable baseband waveform source for SAR waveform and range-processing prototyping.