| Radar is an extremely important weaponry in modern military.It is mainly responsible for the detection,imaging,recognition,tracking,and guidance of targets.Its excellent performance is the key factor to win modern warfare.Microwave photonic radar is a new system radar that uses microwave photonic technology.Compared with the existing electronic radar,it has the advantages of high frequency,large bandwidth,low loss,small size,light weight,easy reconfiguration,anti-jamming,multi-function and so on.It can break the electronic bottleneck of the existing radar,improve the key performance index of radar,such as the detection range,resolution accuracy,response speed,reconfiguration ability,deployment ability and survivability,and realize the integration of radar target detection,electronic countermeasures and information communication.Microwave photonic radar is the trend and solution of future radar.Microwave photonic radar uses microwave photonic technology to replace traditional electronic technology to realize the key modules of the radar.It gives full play to the advantages of photonic technology and equipment to achieve a breakthrough in radar performance.Microwave photonic radar is composed of various key microwave photonic modules.These modules are the basis and core of microwave photonic radar.From the perspective of the engineering application of microwave photonic radar,this paper has carried out in-depth research on the principle and structure of key microwave photonic modules that realize the radar pulse compression function:waveform generation module and pulse compression module.New module schemes are proposed and verified.The specific work and innovations of this paper are as follows:1.In the microwave photonic waveform generation module,aiming at the problem of baseband component in the existing binary phase coded microwave waveform(BPCMW)pulse generation scheme,a baseband-free BPCMW pulse waveform generation scheme based on optical carrier phase modulation is proposed.This scheme uses dual-parallel dual-drive Mach-Zehnder modulator(DP-DMZM)to realize optical carrier equivalent phase modulation and double-sideband with carrier suppressed(DSB-SC)modulation.By controlling the phase of the optical carrier relative to the double-sideband(DSB)through the polarity of the baseband coding signal,the two-phase coding and pulsing of the microwave waveform are realized.Using phase modulation,the power of light wave is constant,the baseband component is avoided directly.This scheme has the advantages of compact structure,simple operation,large tuning range,high phase accuracy,and background baseband elimination.The experiment realized the waveform generation of 2 GBuad 14 GHz and 4 GBuad 16 GHz baseband-free BPCMW pulse.2.In the microwave photonic waveform generation module,aiming at the problem of baseband component in the existing BPCMW pulse generation schemes,a baseband-free BPCMW pulse waveform generation scheme based on baseband complementary superposition is proposed.This scheme uses polarization division multiplexing dual-parallel Mach-Zehnder modulator(PDM-DPMZM)to construct two parallel BPCMW pulse generation links.The two link adopts intensity polarity switching to realize the two-phase coding and pulsing of microwave wave.By using modulator and baseband coding signal configuration,the baseband components of the two generated waveforms are complementary and the coding microwaves are the same.Through the incoherent superposition of the polarization multiplexing photodetection,the baseband component is eliminated.This scheme has the advantages of compact structure,simple operation,high phase accuracy,and background baseband elimination.The experiment realized the waveform generation of 0.6 GBuad 1.2 GHz and 0.6 GBuad 2.4 GHz baseband-free BPCMW pulse.3.In the microwave photonic waveform generation module,aiming at the problem of background signal(Non pulsization of generated waveform)in the existing arbitrary phase coded microwave waveform(APCMW)generation scheme,a APCMW pulse waveform generation scheme based on the conversion between intensity modulation and phase modulation of optical carrier is proposed.This scheme uses DP-DMZM combined with two baseband coding signals to realize optical carrier equivalent intensity-phase modulation and DSB-SC modulation.The single-sideband(SSB)modulated optical signal with the conversion capability between intensity modulation and phase modulation is obtained by utilizing an optical bandpass filter(OBPF).After photoelectric detection,the microwave waveform with adjustable intensity and phase is realized,and the arbitrary phase coding and pulsing of microwave waveform are realized.This scheme has the advantages of large tuning range,compact structure,simple operation,and background elimination.The experiment realized the waveform generation of 2 GBuad 14 GHz and 1 GBuad 16 GHz APCMW pulse.4.In the microwave photonic waveform generation module,aiming at the problem of baseband component in the above-mentioned APCMW pulse generation scheme,a baseband-free APCMW pulse waveforn generation scheme combining optical carrier intensity phase modulation conversion and polarization multiplexing balance detection is proposed.This scheme uses the polarization division multiplexing dual-drive Mach-Zehnder modulator(PDM-DMZM)to replace the above scheme DP-DMZM.On the basis of the above scheme,an orthogonal polarization multiplexed SSB modulated optical signal with intensity and phase modulation conversion capability is obtained.After the SSB modulated optical signal is controlled by the polarization device,a specific balanced detection is performed,the baseband components are subtracted and eliminated.This scheme further eliminates the baseband component and improves the waveform performance.The experiment realized the waveform generation of 1.2 GBuad 9.6 GHz and 2 GBuad 12 GHz baseband-free APCMW pulse.5.In the microwave photonic pulse compression module,aiming at the problem of broadband waveform pulse compression processing,a pulse compression scheme suitable for multi-octave linear chirped microwave waveforms(LCMW)is proposed.This scheme uses dual-parallel Mach-Zehnder modulator(DPMZM)and dispersion loop based on linearly chirped fiber Bragg grating(LCFBG)to realize chirped phase filter.By configuring DPMZM to suppress the overlapping harmonic interference of multi-octave LCMW.Using the band-pass characteristics and dispersion accumulation characteristics of LCFBG,the system chirp direction is adjusted by controlling the optical carrier,and the system chirp rate is adjusted by controlling the dispersion loop.The scheme has the advantages of harmonic interference suppression,chirp direction adjustable,chirp rate adjustable,and structure operation simple.The experiment realized the phase filter with chirp rates of 22.568 GHz/ns,11.355 GHz/ns,-23.229 GHz/ns,-12.051 GHz/ns,which are suitable for pulse compression of multi-octave LCMW.6.In the microwave photonic waveform generation and pulse compression module,an integrated scheme of LCMW waveform generation and pulse compression based on spectral symmetry shaping is explored.The scheme is based on spectrum-shaping and wavelength-to-time mapping(SS-WTM)technology.A pair of interference spectrum shaping structures composed of a waveform shaper and two adjustable delay lines are used to realize symmetrical spectrum shaping.After the same dispersion mapping,a pair of matched response filters are realized.One filter is used to realize the waveform generation of the LCMW,and another filter is used to realize the pulse compression of the LCMW.This scheme has strong reconfiguration and high matching,and has the potentiality to realize the integration of LCMW transceiver module. |
