A microwave photonic (MWP) pulse radar system for high-resolution target detection is proposed and experimentally demonstrated in this article. In the transmitter, a pulsed linearly-frequency-modulated (LFM) wave is generated based on optical frequency operation module (OFOM), which can generate LFM waves with ultra-flexibly tunable center frequency. In the receiver, optical-domain down-conversion is employed to convert the incoming echo to an intermediate frequency signal by a microwave photonic frequency mixer, which can free the receiver from high-speed ADC and provide an excellent wideband processing. Experimentally, a Ku-band pulsed LFM wave with a bandwidth of 840 MHz is generated and received through self-closed-loop and target detection test by the constructed system. The performance verifies that the proposed pulsed MWP radar has the potential of supporting high-resolution detection and recognition of distant targets.
A method of dual-broadband signal generation based on the same optoelectronic oscillator with different tuning mechanisms is proposed in this paper. The structure includes a compatible dual-passband microwave photonic filter based on stimulated Brillouin Scattering effect (SBS) and phase-shifted Bragg fiber (PS-FBG). By implementing the Fourier-domain mode-locked mechanism, the proposed optoelectronic oscillator can simultaneously generate signals in different frequency bands with adjustable center frequency and bandwidth. The effectiveness of the proposed method is verified by experiments. Oscillating signals with bandwidth of 600 MHz and center frequencies at 5 GHz and 6 GHz are generated.
A single sideband (SSB) phase-modulated link with an improved spurious-free dynamic range (SFDR) is proposed and experimentally demonstrated. By generating a single-sideband phase-modulated signal containing a specific spectrum for demodulation, the third-order intermodulation distortion (IMD3) is effectively suppressed. The theoretical analysis is presented, and the experimental results show that a carrier-to-interference ratio of 62.45 dB is achieved. The improved SFDR is 120.25 dB · Hz4/5, which is 14.47 dB higher than that of a conventional SSB phase-modulated link.
An ultra-wideband random OEO using both stimulated Brillouin effect and Rayleigh scattering effect is proposed, which can generate random oscillating microwave signals covering all frequency bands. By using stimulated Brillouin scattering effect to amplify weak reverse Rayleigh scattering, the microwave signals with random characteristics which is independent of fixed cavity length can be generated. Experimentally, the work realized the generation of ultra-wideband (DC up to 32 GHz) random microwave signals. Compared with previous methods,the proposed random OEO mechanism is realized in an easier way, which can avoid using 1450 nm laser and promote its application in electronic interference.
KEYWORDS: Radar, Microwave photonics, Signal generators, Receivers, Digital signal processing, X band, Modulation, Transmitters, Optical filters, Ku band
A coherent dual-band microwave photonic (MWP) radar system is proposed and experimentally demonstrated in this paper. In the transmitter, coherent dual band linear frequency modulation (LFM) waves with the characteristics of tunable central frequency and the same large bandwidth are generated based on an improved optical frequency operation module (OFOM). In the receiver, the information of targets is obtained after the echoes at two bands are received and de-chirp processed simultaneously. Experimentally, the presented coherent dual-band MWP radar system operating in X band and Ku band with an instantaneous bandwidth of 3GHz is constructed. A target-detection experiment verifies that centimeter level resolution can be achieved by the system.
Complex electromagnetic environment in the future battlefield requires spectrum sensing equipment to have broadband and high-resolution measurement capabilities. This paper proposes a microwave photonic frequency measurement method based on optical spectrum operation and stimulated Brillouin scattering. The use of optical spectrum operation is to realize generating pump light in a large range, so as to realize the excitation of stimulated Brillouin scattering in a wide spectrum range, and further the stimulated Brillouin scattering is employed to realize high-resolution frequency sensing. The principle of this method is given and the feasibility of the method is verified experimentally. Experiment results show the measurement capability of the proposed method covers a frequency range of 0.03–40 GHz with a resolution of 25 MHz. The proposed method can effectively support high-resolution frequency sensing in complex electromagnetic environments.
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