## 6 Experiment
### Experimental Data Analysis  
The 24 GHz detector was tested both without rain and with torrential rain, and the test results of the beat signal spectrum are shown in Figure 10a. For comparison with the test results, a simulation of the beat signal spectrum at 6 m of the 24 GHz detector under torrential rain conditions was conducted, and the result is presented in Figure 10b. Similarly, there is rain backscatter noise at the low end of the simulated beat signal spectrum of the 24 GHz detector. In Figure 10a, the target echo signal and the rain backscatter noise signal are marked with dashed boxes and solid boxes, respectively. A low peak bulge exists at the low end of the four signal spectra, which is the rain backscatter noise. However, no such peak is observed in the low-frequency part of the signal spectrum without rain. This is consistent with the simulation conclusion that there is rain backscatter noise at the low end of the MMW fuze beat signal spectrum under rainy conditions. The 35 and 60 GHz MMW fuzes were tested both without rain and with torrential rain, and the test results of the beat signal spectra are shown in Figure 11a,b. Three sets of test results with torrential rain and two sets without rain are presented. The target echo signals are marked with dashed boxes. Other high-peak signals in the spectrum correspond to the leakage noise of the hardware system. Figure 10: 24 GHz detector: (**a**) test results; (**b**) simulation result. Figure 9: Detection scenarios: (**a**) 35 GHz and 60 GHz; (**b**) 24 GHz. The arrows in the figure connect the actual detection scene and the virtual schematic scene. In the test results shown in Figure 11, the highest peak in the spectrum within the range of 10-15 m corresponds to the target at 13.5 m. By identifying this peak, the target distance can be accurately determined. This finding aligns with the simulation results, which indicate that the MMW fuze can reliably measure the distance to nearby strong reflection targets even under heavy and torrential rain conditions. Furthermore, no significant difference exist between the echo signals recorded during torrential rain and those observed in dry conditions. To quantify the similarity of target signals in the echo spectra under rainy and rainless conditions, the Pearson correlation coefficient was calculated [30]. The correlation coefficient between spectra obtained without rain and with torrential rain at 10-15 m for the 35 and 60 GHz fuzes ranges from 0.58 to 0.84 and from 0.72 to 0.78, respectively. This wide variation is influenced by factors such as temperature differences between the rainy and dry environments, changes in the wet state of the target object, and increased background noise due to rainfall. Despite this variability, correlation coefficients remain 0.5-0.8, indicating that the frequency spectra of the echo signals under both conditions exhibit a moderate correlation level of overall similarity [31]. As the power of the bottom noise caused by rainfall is very low, it fails to meet the detection sensitivity requirements of the three fuzes; thus, the test results mentioned above cannot describe the changes in the power of the bottom noise. Therefore, the test data reported in [8] are used for comparison, with the bottom noise test result shown in Figure 12a. Additionally, the noise signals within the spectrum range of 2-4 MHz in the simulation results are extracted to calculate the noise power, where the noise power without rain is set as 0 dB. Based on this, the noise power values under different frequencies and rainfall conditions in the Monte Carlo simulation are presented in Figure 12b. Figure 11: Test results without rain and with torrential rain: (**a**) 35 GHz; (**b**) 60 GHz. Figure 12: Bottom noise test result (**a**) in [8]; (**b**) simulation.