From 8 Seconds to 370ms: Kernel-Fused SAR Imaging on Apple Silicon via Single-Dispatch FFT Pipelines

We present the first kernel-fused SAR Range Doppler pipeline on any GPU platform. By fusing FFT, matched-filter multiply, and IFFT into a single Metal compute dispatch – keeping all intermediate data in 32,KiB on-chip memory – we process a $4096\text{\hspace{0.17em}⁣}\times \text{\hspace{0.17em}⁣}4096$ complex SAR scene in $\mathbf{\text{370}}\mathbf{\text{ms}}$ on an Apple M1 GPU, a $\mathbf{\text{22}}\times$ speedup over the multi-dispatch baseline (8.16,s). We further report the first FFT to exploit Apple’s $\mathtt{\text{simdgroup\_matrix}}$ 8$\times$8 hardware MMA, enabled by an in-place Cooley–Tukey decimation-in-frequency formulation that halves the memory footprint versus Stockham. Radar image quality is preserved: all five point targets show 0.0,dB SNR deviation from the unfused FP32 reference.