This paper investigates a real-time process generator of wideband signals, which calculates waveforms in a field-programmable gate array (FPGA) using the high-level synthesis (HLS) method. To obtain high-resolution and wide-swath images, the generator must produce multiple modes of large time-bandwidth product (TBP) linear frequency modulation (LFM) signals. However, the conventional storage method is unrealistic as it requires huge storage resources to save pre-computed waveforms. Therefore, this paper proposes a novel processing approach that calculates waveforms in real-time based simply on parameters such as the sampling frequency, bandwidth, and time width. Additionally, this paper implements predistortion through the polynomial curve to approximate phase errors of the system. The parallelizing process in the FPGA is necessary to satisfy the high-speed requirement of a digital-to-analog converter (DAC); however, repeatedly multiplexing real-time calculation consumes extensive logic and DSP resources, potentially exceeding FPGA limitations. To address this, this paper proposes a piecewise linear algorithm to conserve resources, which processes the polynomial only once, acquires the difference in two adjacent values through the register and pipeline, and then adds this increment to facilitate parallel computations. The performance of this proposed generator is validated through simulation and implemented in experiments with an X-band airborne SAR system.

Synthetic aperture radar (SAR) typically transmits a linear frequency modulation (LFM) waveform. It utilizes weighted windowing to depress the peak-to-sidelobe ratio (PSLR), which results in a decrease in signal-to-noise ratio (SNR). In contrast, a nonlinear frequency modulation (NLFM) signal can reconstruct the power spectral density (PSD) to achieve lower sidelobes without compromising the SNR. Considering the substantial challenges posed by hardware constraints in the real-time generation of complex NLFM waveforms, this letter proposes a piecewise linear (PWL) algorithm to optimize resource utilization while realizing parallel processing via pipeline execution and the Horner method. Meanwhile, an improved predistortion approach integrated with the PWL algorithm is utilized to compensate for the phase errors in the SAR system. The high-level synthesis (HLS) technique is applied in the waveform generator based on the radio frequency system-on-chip (RFSoC). The performance of the proposed method is validated through simulations, and practical experiments are conducted on an X-band airborne SAR system.

Generally, synthetic aperture radar(SAR)generates linear frequency modulation (LFM) signals by method of look‐up table (LUT), which requires calculating different LFM signals and storing these waveforms in advance. With the demand for multi‐mode, high‐resolution and wide swath of airborne SAR systems, the method of LUT is not available, because that requires huge storage resources. In order to solve these drawbacks in limited hardware resources, this letter proposes a novel LFM signal generator in real‐time processing. By taking advantage of high level synthesis (HLS) on FPGA, the proposed generator calculates the LFM signal simply using parameters of pulse width, bandwidth, and sampling frequency. Meanwhile, in order to compensate for the SAR system phase error, the proposed generator calculates phase error using a linear polynomial algorithm, which can compensate for the phase error in real time. The simulation results prove that this approximation can achieve a good effect. The performance of this method is implemented by experiments with an X‐band airborne SAR system.