## 4 Discussion
The target positions shown on this range angle map is not the actual position of the targets because this map is a mapping of the actual target positions to a map where the vertical axis is the distance from the radar to each target and the horizontal axis is the angle of the position of each target to the radar. The chest displacement, heartbeat, and breathing waveform graphs in Figures 8-12 are obtained from the chest wall displacement detection. The vertical axis unit of these figures is mm, and the horizontal axis of these figures is Frame Index. The A-frame consists of a sequence of chirps [30], as shown in Figure 15.  
Figure 14: Beat frequency spectrum in FMCW radar [29]. Figure 15: FMCW chirp and frame structure [30]. We can see that the chest displacement signals are more complex than the heartbeat and breathing signals graphs. The reason for this is that the chest displacement signal is still a summation of heartbeat and breathing signals. On the other hand, heartbeat and breathing signals look simpler. Likewise, we see that the heartbeat signal is of a higher frequency than the breathing signal. This corresponds to the fact that the heart rate is faster than the breathing rate. In these figures we can also indicate the intervals between respiratory and cardiac activities. In the numerical display, we can see the heartbeat rate of each target, the breathing rate of each target, the distance and angle of position of each target from the measurement site. The target distances of 1 to 4 successively from the radar are as follows: 0.82 m, 1.11 m, 0.62 m, and 1.11 m. The angles of the target positions 1 to 4 from the radar are shown in degree: \(-\)18, 18, 22, and 37. A minus angle means that the target is to the left of the radar, while a positive angle implies that the target is to the right of the radar. We can also attain the results of the spectral estimation method reported as pk, FT, and CM. The pk stands for peak interval. What is meant by FT is FFT (Fast Fourier Transform). CM stands for confidence metric. These entities are explained in Section 2. The peak interval is the distance between peak values in the spectral information. These peak values are the harmonics of the fundamental frequency. The process of FFT is needed to obtain the spectral information of the heartbeat waveforms and breathing waveforms [31], while the confidence metric is the last step to decide the values of the recorded heartbeat rates and breathing rates. The results of heartbeat rate measurements are shown by the numbers at the upper parts of vitalSigns_1 to vitalSigns_4. These are between 52 and 82 beats per minute. These heartbeat rate measurement results correspond to normal heartbeat rates, as shown in Section 2. This proves that the method used in our experiments for heartbeat rate measurements is correct because the results are in accordance with the normal heartbeat rates of healthy people. The results of breathing rate measurements are shown by the numbers at the lower parts of vitalSigns_1 to vitalSigns_4. They are between 10 and 35 breaths per minute. These breathing rate measurement results correspond to normal breathing rates, as shown in Section 2; therefore, this proves that the method used in our experiment for breathing rate measurement is also correct. It can be seen that there are data match between the measurement data from the range angle map image and the numerical measurement results. The results of vital sign measurements by this radar were also compared with the results of vital sign measurements by oximeter. From the measurement of vital signs using an oximeter, the obtained heartbeat rate results were between 69 and 80 beats per minute, and breathing rates were between 10 and 21 breaths per minute. We can see here that the measurement of vital signs using these two different measuring instruments produce similar data.