# Azimuth Full-Aperture Processing of Spaceborne Squint SAR Data with Block Varying PRF

^{1}

^{2}

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## Abstract

**:**

## 1. Introduction

## 2. Range Cell Migration Analysis for Squint SAR

## 3. PRF Design and Signal Analysis

#### 3.1. Design of the BV-PRF Scheme

#### 3.2. Properties of Echo Signal with BV-PRF

## 4. Azimuth Pre-Processing

#### 4.1. Azimuth Pre-Processing in the 1-D Domain

#### 4.2. Azimuth Pre-Processing in the 2-D Domain

## 5. Simulation Experiments

_{1}and P

_{2}; the middle block contains the echo data and spectrum of P

_{1}, P

_{2}and P

_{3}; and the third block contains the echo and spectrum of P

_{2}and P

_{3}. Consequently, the reconstructed signal of the whole scene in the 2-D time domain has uniform sampling frequency after azimuth combination, as shown in Figure 16d, and its corresponding spectrum is shown in Figure 16e. Finally, the original 2-D spectrum with sufficient sampling frequency is well-recovered by azimuth re-skewing and range-frequency-dependent filtering, as shown in Figure 16f.

_{1}and P

_{3}targets located in the edge of the scene cannot be completely obtained. Therefore, the resolution of P

_{1}and P

_{2}targets in imaging results decreases as shown in Figure 18c. The raw data of the whole scene can be successfully obtained by the CV-PRF scheme, as shown in Figure 18b, and the three targets are also well-focused in Figure 18d. However, the computational complexity of the CV-PRF scheme is approximately dozens of times greater than that of the proposed method. Therefore, the proposed approach is more effective.

## 6. Discussion

## 7. Conclusions

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Conflicts of Interest

## References

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**Figure 1.**Geometric model of spaceborne squint sliding-spotlight SAR. (

**a**) Squint-looking geometry; (

**b**) side-looking geometry.

**Figure 2.**Comparison of ${\Gamma}_{1}$ and ${\Gamma}_{2}$ with different squint angles. (

**a**) The squint angle in the middle acquisition interval is 25°; (

**b**) the squint angle in the middle acquisition interval is 30°.

**Figure 6.**Echo simulation with different pulse transmission sequences. (

**a**) Scene distribution of targets; (

**b**) the fixed PRF; (

**c**) the CV-PRF; (

**d**) the BV-PRF.

**Figure 8.**Variation curves of the instantaneous Doppler centroid varying rate ${k}_{\mathrm{rot}}$ under the side-looking and the squint. (

**a**) ${k}_{\mathrm{rot}}$ within $\pm 3.2$ under the side-looking; (

**b**) ${k}_{\mathrm{rot}}$ within $\pm 3.2$ under the squint angle 25°.

**Figure 10.**Ratios of the squint additional bandwidth to the azimuth beam bandwidth in adjacent data blocks. (

**a**) The ratio $\Phi $ in the prior data block; (

**b**) the ratio $\Phi $ in the latter data block.

**Figure 12.**One-dimensional azimuth compression results of the proposed method. (

**a**) Azimuth spectrum without azimuth resampling; (

**b**) the azimuth compression result of (

**a**); (

**c**) Doppler spectrum after azimuth resampling; (

**d**) the azimuth compression result of (

**c**).

**Figure 16.**Simulation results of the proposed method. (

**a**) The real part of echo data in three blocks; (

**b**) 2-D spectra of (

**a**); (

**c**) 2-D spectra in three blocks before azimuth combination; (

**d**) echo data of the whole imaged scene after azimuth combination; (

**e**) 2-D spectrum of (

**d**) before re-skewing; (

**f**) the recovered 2-D spectrum.

**Figure 17.**Imaging results on three point-targets handled by the proposed method. (

**a**) Imaging results with three points; (

**b**) contour plot of target P

_{1}; (

**c**) contour plot of target P

_{2}; (

**d**) contour plot of target P

_{3}.

**Figure 18.**Simulation results of the fixed PRF and CV-PRF schemes. (

**a**) The real part of echo data with the fixed PRF scheme; (

**b**) the real part of echo data with the CV-PRF scheme; (

**c**) imaging results with the fixed PRF scheme; (

**d**) imaging results with the CV-PRF scheme.

Parameter | Value |
---|---|

Relative platform velocity | 7212 m/s |

Slant range of the scene center | 750 km |

Carrier frequency | 5.6 GHz |

Azimuth antenna length | 6.3 m |

Number of PRFs | 3 |

Azimuth beam rotation rate | 2.78°/s |

Middle squint angle | 25° |

System PRF | 2462/2511/2562 Hz |

Pulse bandwidth | 150 MHz |

Range sampling frequency | 200 MHz |

Pulse duration | 8 μs |

Target | Azimuth | Range | ||||
---|---|---|---|---|---|---|

Res. (m) | PSLR (dB) | ISLR (dB) | Res. (m) | PSLR (dB) | ISLR (dB) | |

P_{1} | 2.87 | −13.27 | −10.19 | 0.94 | −13.25 | −10.10 |

P_{2} | 2.86 | −13.25 | −10.18 | 0.94 | −13.25 | −10.11 |

P_{3} | 2.76 | −13.26 | −10.18 | 0.94 | −13.28 | −10.12 |

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**MDPI and ACS Style**

Zhang, Z.; Xu, W.; Huang, P.; Tan, W.; Gao, Z.; Qi, Y.
Azimuth Full-Aperture Processing of Spaceborne Squint SAR Data with Block Varying PRF. *Sensors* **2022**, *22*, 9328.
https://doi.org/10.3390/s22239328

**AMA Style**

Zhang Z, Xu W, Huang P, Tan W, Gao Z, Qi Y.
Azimuth Full-Aperture Processing of Spaceborne Squint SAR Data with Block Varying PRF. *Sensors*. 2022; 22(23):9328.
https://doi.org/10.3390/s22239328

**Chicago/Turabian Style**

Zhang, Zhuo, Wei Xu, Pingping Huang, Weixian Tan, Zhiqi Gao, and Yaolong Qi.
2022. "Azimuth Full-Aperture Processing of Spaceborne Squint SAR Data with Block Varying PRF" *Sensors* 22, no. 23: 9328.
https://doi.org/10.3390/s22239328