# X-Band Photonic-Based Pulsed Radar Architecture with a High Range Resolution
## 3 Experimental Setup and Results
If the IF signal with a higher center frequency and wider bandwidth can be applied to the DPMZM using a state-of-the-art AWG, the center frequency and the bandwidth of the quadrupled signal can be higher and wider, similar to previous studies in References [11; 12; 21; 22; 23]. To evaluate the performance of the range and cross-range resolution of the proposed prototype, two metal plates with the height and width of 0.2 m each were placed at a distance of at least 2.5 m to a maximum of 3.5 m apart from the antennas. The spacing between two plates was set as 0.25 m, and the initial positions were located at both ends of the rails with each other as shown in the sub-figure in Figure 6a. The graph in the Figure 6a is the power spectral density of the beat frequency, which is caused by two metal plates and there are two clearly distinguishable peaks at 1.681 MHz and 1.723 MHz, respectively. According to Equation (11), the calculated distance between the two targets is 0.984 m, which is quite similar to the real value and corresponds to the frequency differences between the two peaks. As seen in Figure 6b, the de-chirped signal is converted to a digital signal in the time domain with a sampling rate of 60 MSa/s. Each of the de-chirped signal has the same repetition frequency as the PRF of the IF signal. It should be noted that one of the pulse train, which is enlarged and emphasized in red box in Figure 6b, has the different from the others because it is produced by the beating between the transmitted pulse signal and the base signal in the PM. Furthermore, as seen in Figure 3, the gated LFM signal, which is generated by the MZM, is effectively produced and it is confirmed that the proposed photonic-based radar architecture operates as a pulsed radar. Since radars should be able to detect a moving target as well as a fixed target, the additional indoor experiments were conducted using two moving targets to examine the performance the tracking the movements of two targets in real-time. Figure 7 shows the target history and the high-resolution range profiles (HRRP) of two moving targets. The initial position of two targets and the variation of positions of two targets are shown in Figure 7a,b, respectively. In Figure 7b, the motion of two target is described  
Figure 5: Cahracteristics of the transmitted signals. (**a**) Max-hold spectrum of the IF-band signal. (**b**) Max-hold spectrum of the quadrupled signal. (**c**) Spectrogram of the quadrupled signal with a 640-MHz bandwidth and 100-\(\upmu\)s period. Figure 6: Characteristics of de-chirped signal. (**a**) Power spectral density of the de-chirped signal and picture of targets. (**b**) De-chirped signal representation in time domain. as follows: two targets moved at the same speed in opposite directions and remained stationary for a while at the end of rails for resuming the movement to the opposite directions. The HRRP at the initial positions of the two targets 2.5 m and 3.5 m from the receiving antenna is shown by the red line in Figure 7c. The blue line in Figure 7c shows the HRRP when the positions of the two targets were at the same position from the receiving antenna. It is noted that if two targets existed at the same distance from the receiving antenna, as in case of the blue line, the signal reflected by the targets had a larger amplitude, as reflected in the only one larger target. If two metal targets were located at the minimum detectable distance to be separated, the HRRP is represented in green line in Figure 7c. As shown in the green line in Figure 7c, when two targets are located at 2.87 m and 3.13 m from the receiving antenna, respectively, which is 0.26 m apart from each other, the two targets can be distinguished. According to Equation (11), the theoretical range resolution for detecting two targets separately is 0.23 m. Therefore, it is confirmed that the actual range resolution was quite close to the theoretical range resolution. In order to examine the cross-range resolution, two targets have to be in the same distance from the receiving antenna.