# X-Band Photonic-Based Pulsed Radar Architecture with a High Range Resolution
## 3 Experimental Setup and Results  
Figure 4 shows the prototype of the proposed photonic-based pulsed radar architecture for conducting the indoor experiment. Considering the blind region and indoor testing circumstances, different from Figure 1, the transmitting and receiving antennas are separated without a circulator to possibly detect nearby targets. In addition, regarding the input frequency range of an ADC, the optical delay (OD) line is employed to increase the beat frequency between the reference signals and the received signals. In Figure 4a, the output power of the CW laser source (TeraXion Inc.: Quebec city, QC, Canada, PS-NLL-1550) is set 18 dBm at a wavelength of 1550 nm for the indoor test. The prototype of the proposed \(X\)-band photonic-based pulsed radar is designed operating at a center frequency of 10 GHz and a bandwidth of 640 MHz. For operating the prototype, the IF-band signal with a bandwidth of  
Figure 4: The prototype of the proposed photonic-based pulsed radar architecture for conducting the indoor experiment. (**a**) Configuration of the proposed radar architecture for indoor experiment. (**b**) Prototype implementation of the proposed radar architecture. HC: Hybrid coupler, TxPD: Transmit photodetector, HPA: High power amplifier, OD: Optical delay. 160 MHz, the center frequency of 2.5 GHz, and a PRF of 10 kHz is generated by the AWG (Keysight: Santa Rosa, CA, USA, N5182B). The electrical characteristics of the DPMZM (Fujitsu: Tokyo, Japan, FTM796 EP), which is used for IF-band signal modulation, are a half-wave voltage(\(V_{\pi}\)) of 3.5 V and a 3-dB bandwidth of 22 GHz. The OC with 10:90 coupling ratio is applied to split the output signal of the DPMZM and 10% optical power is used for the transmission considering the limited indoor testing circumstance. The upper lane of the OC in Figure 4a is connected to the MZM (SDL Inc.: Los Angeles, CA, USA, IOAP-MOD9140-F-F-0), which has an insertion loss of 3.5 dB and a half-wave voltage is 4.9 V at 10 GHz, for generating the gated LFM signal, which has a pulse repetition frequency of 1 kHz with a 10% duty cycle. The output signal of the MZM is sent to a transmitted PD (New Focus Inc.: San Jose, CA, USA, 1544-B), which has 3-dB bandwidth up to 12 GHz. The generated gated LFM signal is passed along the optical delay line of 33 m to increase the beat frequency considering the input range of the ADC and sent to a transmitting horn-type antenna (MTG Inc.: Chungnam, Korea, SGH-90) with a gain of 22 dB and 13\({}^{\circ}\) of beamwidth for target detection. Describing the receiver of the proposed architecture, the signal reflected by a target is acquired by the receiving antenna, and it is amplified by a solid state amplifier (Narda West Inc.: Folsom, CA, USA, DBS-0618N727) with a gain of 43 dB, and sent to the PM (EO Space, PM-055-PFA-PFA), which has a bandwidth of 40 GHz. The 50:50 optical coupler is located after the PM as shown in Figure 4a. Each of the two branches is connected to the DOBPF (Fiberpro Inc.: Daejeon, Korea, LE2000) to filter the required frequency components in Equation (10), and the selected optical signals are sent to the BPD (Thorlabs: Newton, NJ, USA, PDB450C) to convert the signal from optical domain to the electrical domain. The domain-converted signal is sent to the ADC to convert for the digital signal, and the signal processing occurs at the DSP stage in real-time. Figure 5 shows the characteristics of the transmitted signals. Figure 5a,b are the max-hold spectra, which were measured by a spectrum analyzer, of the generated IF-band signal and the output signal of the DPMZM, respectively. As shown in Figure 5a,b, both of the center frequency and bandwidth of IF-band signal were quadrupled through the DPMZM. Figure 5c shows the spectrogram of the quadrupled LFM signal. According to Figure 5c, the output signal of the DPMZM had a center frequency of 10 GHz and a bandwidth of 640 MHz with a repetition interval of 100 us. It is confirmed that the IF-band signal quadrupling by the DPMZM was successful.