Fig. 1. Schematic diagram of the photonics-assisted concurrent radar detection and spectrum-sensing prototype. LD, laser diode; OC, optical coupler; IM, intensity modulator; IF, intermediate frequency; LFM, linearly frequency-modulated; DDS, direct digital synthesizer; FBG, fiber Bragg grating; EDFA, erbium-doped fiber amplifier; PD, photodetector; EBPF, electrical bandpass filter; LNA, low-noise amplifier; PA, power amplifier; Tx, transmitting antenna; Rx, receiving antenna; DAQ, data acquisition; CIR, circulator; ISO, isolator; HNLF, highly nonlinear fiber; DP-MZM, dual-parallel Mach–Zehnder modulator; MSG, microwave signal generator; 90 deg HYB, 90 deg hybrid coupler; USB, universal serial bus; LAN, local area network.

Fig. 2. Optical spectra of the optical LFM signal under different center frequencies of the IF LFM signal. The black dotted line shows the transmission spectrum of FBG1.

Fig. 3. Electrical spectra of the generated 4-GHz bandwidth LFM radar signal ranging from 8 to 40 GHz.

Fig. 4. (a) Photograph of the ranging experimental setup. (b) A zoomed-in view of the red-dotted rectangular area in panel (a). Ranging results of the corner reflector at different distances when the center frequencies of the LFM radar signal are (c) 14 and (d) 26 GHz, respectively. (e) Ranging errors at different distances and center frequencies of the LFM radar signal.

Fig. 5. (a) Photograph of the two smaller corner reflectors placed close to each other. (b) The measured distance between two smaller corner reflectors at different center frequencies. (c)–(f) Zoomed-in views of the dechirped signal spectra at center frequencies of 12, 20, 28, and 36 GHz.

Fig. 6. (a) Schematic diagram of the radial velocity measurement. (b) Photograph of the radial velocity measurement setup. Radial velocity measurement results when the target rotates (c) clockwise and (d) counterclockwise with a rotation radius of 45 cm. (e) Radial velocity measurement results when the target rotates clockwise with a rotation radius of 60 cm.

Fig. 7. (a) Photograph of five cylinders with an outer diameter of 3 cm for ISAR imaging. (b)–(f) ISAR imaging results obtained using the prototype operating at different center frequencies.

Fig. 8. (a) Photograph of three cylinders with an outer diameter of 2.5 cm for ISAR imaging. (b)–(f) ISAR imaging results obtained using the prototype operating at different center frequencies.

Fig. 9. (a) Photograph of the spectrum sensing setup. (b) Single-frequency measurement errors at different frequencies. Single-frequency measurement results when the frequency measurement ranges are (c) 0 to 2 GHz, (d) 10 to 12 GHz, (e) 20 to 22 GHz, and (f) 30 to 32 GHz.

Fig. 10. Frequency measurement of a two-tone SUT when the frequency intervals are (a) 20, (b) 30, (c) 40, and (d) 50 MHz.

Fig. 11. Time–frequency analysis results of a frequency-sweep signal from (a) 6 to 8 GHz, (b) 10 to 12 GHz, and (c) 16 to 18 GHz. Panels (d)–(f) are the temporal waveforms corresponding to panels (a)–(c).

Fig. 12. Schematic diagram of the prototype’s application in cognitive radio scenarios.