## 5 Experimental Data
### Through-Wall Detection  
The photo and the top view of the experimental scenario for through-wall detection is shown in Figure 12. A concrete wall separates the radar from the targets. The concrete wall is made of solid bricks cast in cement. The thickness and relative permittivity of the concrete wall used are 0.37 m and 4, respectively. The radar is placed against the outside of the wall, and a human body is standing stationary facing the radar at the distance of 1.6 m from the inside of the wall. A square metal plate is placed to the left of the radar and its direct distance from the inside of the wall is 0.8 m. The metal plate is used to simulate the echo from a strongly reflected stationary target. In this case, the components of the beat signal include the directly coupled wave from the transceiver antenna, the reflected wave from the inner wall, the reflected wave from the metal plate, and the reflection from the stationary human target. The reflected wave from the inner wall is the strongest. Because of the presence of phase-locked loop spuriousness, clutter is generated on both sides of the first three echoes.  
The reflection from the inner wall is the strongest, so the position of the main lobe of the echo from the inner wall is taken as the coordinate origin. The beat signal is processed according to the steps in Section 3. The main lobe of each echo that does not vary with  
Figure 12: The experimental scenario of through-wall detection. (**a**) The photo of the experimental scenario; (**b**) The top view of the experimental scenario.  
time is eliminated, while the vital signal of the human target and clutter that vary with time are left. After accumulating along the slow time, the clutter is highlighted, as shown in Figure 13a. As can be seen from the figure, in addition to the vital signal from the human target, clutter is present at three other locations. They seriously interfere with the detection of the vital signal, causing false alarms. After accessing long delay lines which have an equal length of 4.6 m, the symmetrical parts of these clutters are revealed, as shown in Figure 13b. The clutter from the reflected wave from the inner side of the wall is the largest, as shown in the red dashed box. They are symmetric about the red dashed line which corresponds to 4.6 m. The other two pairs of clutter are generated by the directly coupled wave of the transceiver antenna and the echo of the metal plate, respectively. The range-slow time matrix is divided into upper and lower parts according to the dividing line with a range equal to 4.6 m.  
Using the calculation of the proposed correlation coefficient, the results are obtained as shown in Figure 13c. The horizontal and vertical axes represent the difference in range between the rows of the two matrices and the dividing line, respectively. A strong correlation between the before and after of paired clutter signals is evident from the main diagonal. Other highlights show that there is also some correlation between unpaired clutter. However, there is no correlation between the clutter and the vital signal. Using the proposed method, the location of the clutter is recognized and then eliminated. Figure 13d shows that the clutter is eliminated clearly and only the vital signal is left.