An adaptive delay calibration method for optical beamforming networks (OBFN) based on wideband sweep and windowed FFT spectrum analysis is proposed and demonstrated by simulation. With the FFT spectrum analysis of the wideband sweep signal, the delay difference between different channels in OBFN can be obtained continuously, and can be canceled adaptively by controlling variable optical delay lines(VODL), resulting in fast and high precision calibration for an OBFN. Furthermore, assisted by pilot carriers with multiple frequencies, the phase unwrapping can be achieved, and phase difference beyond 2π can be compensated. In order to demonstrate such method, a 16-arrayoptical beamforming simulation system is presented in this paper. Simulation results show that delay calibration range reaches467.1ps with the frequency range of 6-18 GHz. The delay calibration accuracy is increased by 50 times from5ps to 0.1ps. In addition, the number of simultaneous beamformer achieves to be 3, which covers the airspace from-30° to +30°.
In this paper, a photonic dual-band radar receiving and processing technique based on a Stepped Linear Frequency Modulation (SLFM) signal has been proposed, achieving high-resolution radar detection driven by a low-rate signal source. The generation of dual-band radar signal with GHz-level bandwidth from SLFM sub-pulse signals with MHz-level bandwidth is utilized, significantly conserving the bandwidth resources of the radar driving signal source. Subsequently, a photonics-assisted dual-channel radar de-chirper cascaded with two electro-optic modulators is employed to realize wideband radar pulse compression processing covering both the X-band and Ku-band. Finally, the coherent fusion processing algorithm for dual-band radar is utilized, not only accomplishing an equivalent high-resolution radar ranging and Inverse Synthetic Aperture Radar (ISAR) imaging but also facilitating an anti-jamming radar detection. In simulation experiments, this paper has achieved the reception of dual-band SLFM radar signals with a sub-pulse number of 100 and a frequency coverage range of 8GHz-16GHz. Due to the coherent fusion processing algorithm, the radar target ranging and ISAR imaging with a resolution of ~2cm (equivalent bandwidth of 8GHz) successfully have been achieved.
KEYWORDS: Extremely high frequency, Photonics, Radar, Signal generators, Signal detection, Radar signal processing, Signal processing, Wireless communications
Multifunctional integration of electronic equipment is a main development trend in the future, wherein the integrated signal generation enables a key part. Therefore, it is of great significance to develop the generation of anti-jamming joint radar-communication (JRC) signal. Here, a photonics-assisted generation scheme of millimeter-wave (MMW) anti-jamming JRC signal is proposed. A large-bandwidth MMW dual-band agile JRC signal is generated based on a photonic MMW up-conversion and frequency permutation techniques. Meanwhile, thanks to the dual-band photonic radar de-chirping combined with coherent fusion method and low-cost communication self-coherent reception, the high resolution radar detection and communication with large amount of information are realized simultaneously. In the photonics-assisted JRC simulation system in W-band, a dual-band agile stepped-linear frequency modulation JRC signal covering 81-93 GHz is generated. Moreover, through a dual-band coherent fusion processing, the dual-band signals occupying with only a bandwidth of 2 GHz are successfully fused into an equivalent ultra-wideband signal with a bandwidth of 12 GHz, enabling a radar ranging with a resolution of 1.26 cm. Using a low-cost self-coherent reception, an anti-jamming wireless communication with factorial 10 is demonstrated, which can achieve up to 21.8 bits quantity of information.
A temporal convolution system for the short-time Fourier transformation (STFT) of an electrical signal based on a bidirectional chirped fiber Bragg grating (CFBG) is proposed and experimentally demonstrated. In this system, the electrical signal to be analyzed is applied to an electro-optical modulator to simultaneously modulate the temporal waveform and the spectrum of a time-stretched optical pulse, which is generated by a mode-locked laser and dispersed by a CFBG. The modulated optical signal is filtered to be several parts, added with separate time delays and sent to the other port of the same CFBG. Thus the optical signal is temporally recompressed and the spectrum of the electrical signal is able to be mapped into the time domain. The bidirectional CFBG realizes exactly complementary dispersion value for the optical pulse propagating in two opposite directions, which guarantees an optimal frequency resolution of the STFT system. An STFT experiment for a microwave signal with four different frequencies at 5 GHz, 10 GHz, 15 GHz and 20 GHz has been demonstrated.
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