# Airborne Radar Staggered PRF Coherent Processing Method for Down-Looking Target Detection
## 4 Simulation Results
### Target Detection Clutter Avoidance and Track Integrity Analysis  
The previous experiments verified Doppler ambiguity resolution and coherent accumulation for targets and clutter. To further analyze target occlusion by clutter, the track integrity detection method is employed for comparison. Simulated targets can be obstructed by ground clutter. Radar parameters are consistent with previous experiments, with an antenna beam pointing of 50 in azimuth and 50 in elevation. Based on radar height, radar speed, and beam pointing angle, the clutter Doppler center is determined to be 2589.2 Hz, with a clutter Doppler bandwidth of 1093.7 Hz, and ground clutter distribution ranging from 14.1 Km to 17.4 Km. The genetic algorithm optimizes the PRF based on the clutter Doppler spectrum, resulting in five optimized PRF groups: [5758 Hz, 4827 Hz, 4262 Hz, 5243 Hz, 4022 Hz]. For comparison, LPRF, HPRF, and traditional multi-MPRF working modes are used. LPRF is set at 1.5 KHz, HPRF at 100 KHz, and traditional Multi-MPRF as [17 kHz, 19 kHz, 17.3 kHz, 19.2 kHz, 19.8 kHz]. Under LPRF, distance ambiguity is absent, but Doppler ambiguity is more severe, with clutter Doppler widely distributed on the RD map. When the target's distance and ambiguity-resolved Doppler coincide with the clutter Doppler distribution, accurate target detection becomes challenging. Extracting the target's velocity information is also problematic due to Doppler ambiguity. With HPRF, distance ambiguity in the RD result is more severe, and clutter is widely distributed in the distance cell corresponding to the target's Doppler spectrum. Consequently, when the target's Doppler coincides with clutter Doppler, the target is submerged in clutter and remains undetected. Even if the target is not obscured by clutter, accurate extraction of the target's distance information is impossible due to significant distance ambiguity. The multi-group MPRF method minimizes clutter Doppler spectrum obscuring the target, but separate detections within a dwell time prevent full utilization of transmitted signal energy, resulting in missed target detection under low SNR conditions and reduced radar power range. In the simulation, a target within the radar field of view starts moving away from the radar at a distance of 2 km, accelerates, decelerates, and hovers over the ground. The target's trajectory within 200 s is simulated, and target detection is performed in clutter. The speed and distance of the target during the simulation time period are shown in Figure 19.  
Figure 18: Comparison of Doppler resolution. (**a**) Doppler resolution of the traditional method. (**b**) Doppler resolution of our method. Assuming the radar transmission power is 10 kW and the target's RCS is 0.1 m\({}^{2}\). According to the target distance and radar equation, after multi-pulse coherent processing, the power of the target throughout its trajectory can be obtained, and the result is shown in Figure 20.  
To ensure an equivalent comparison, the radar is configured with the same transmission energy during each dwell time, resulting in a fixed average transmission power. Under LPRF, the pulse signal exhibits high instantaneous power, while HPRF demonstrates low instantaneous power. After coherent processing, the echo power is calculated for each PRF. LPRF and HPRF maintain full coherence throughout the dwell time, resulting in equal echo power for the target. In the case of traditional multi-group MPRF, five groups of MPRF signals are used, and each group is separately detected, resulting in coherent performance of only 1/5 of the total energy. The method proposed in this paper uses three groups of signals in five groups for coherent accumulation detection, resulting in coherent processing performance equivalent to 3/5 of the total energy. During the simulation process, the received echo's noise power is set to \(-64\) dBw. The detection results of the target at different PRFs throughout the entire track are depicted in Figure 21.  
Figure 19: Target’s velocity and distance set in simulation experiment.