| Microwave technology has been widely used in many fields such as defense science and technology,scientific research,industry and agriculture,and daily life.It is deeply involved in wireless communications,satellite communications,radar,electronic warfare,remote sensing,and other fields.Among these fields,microwave signal measurement plays a crucial role.With the rapid development of microwave technology and communication technology,traditional microwave measurement technologies are facing a series of challenges,such as large instantaneous bandwidth,high transmission loss,and strong immunity to electromagnetic interference?EMI?.Thus it is much more difficult to meet the requirements on broadband microwave signal parameter detection.As an emerging field,microwave photonic technology brings new ideas to facilitate microwave signals detection and anslysis.Compared with the electronic methods,it has unparalleled advantages in large bandwidth,immunity to EMI,low loss,and light weight.Therefore,this thesis focuses on photonic microwave measurement technology,and it aims to explore new photonic methods for multi-dimensional parameters measurement of microwave signals,and to improve the performance of microwave signal measurement systems.The following three aspects have been extensively studied:instantaneous frequency measurement?IFM?,intra-pulse parameters measurement and modulation format recognition,Doppler frequency shift?DFS?measurement of microwave signals,respectively.?1?.A novel photonic approach to simultaneously implement frequency measurement and signal discrimination is proposed for pulsed and continuous-wave?CW?microwave signals.Firstly,based on the birefringence effect of a polarization maintaining fiber,a complementary optical comb filter is designed.Secondly,based on the frequency-optical power mapping method,the frequency information of CW and pulsed microwave signals are converted to the amplitudes of direct current?DC?and low-frequency alternating current?AC?signals,respectively.Here,the CW signal is converted to a DC signal,and the pulsed microwave signal is converted into an AC signal.The DC and the AC signal are separated by the simple logic circuit?e.g.,capacitance and inductance?.Finally,the carrier frequencies of CW and pulsed microwave signals are identified by monitoring their amplitudes?e.g.,DC and the first harmonic?,respectively.Within the frequency range from 5 to 20 GHz,measurement errors less than±0.1,±0.11,and±0.13 GHz are achieved for a pulsed signal with pulse repetition frequency of 0.25,0.5,and 1 MHz,whereas the errors less than±0.08GHz are derived for a CW microwave signal.Meanwhile,the discrimination of them is realized.?2?.Based on optical comb filter,three digitalized IFM schemes based on parallel quantization coding are designed,wherein digital frequency measurement results with different binary encoding rules are obtained.?1?Based on an optical filter array with multiplied free spectral ranges?FSRs?,an approach is proposed to perform IFM,with natural binary coded digital outputs being achieved.The measurement range is FSR,and an efficient bit is N.?2?A digitalized frequency measurement scheme is designed using a plurality of phase-shifted optical comb filters and a single doubled FSR optical comb filter.In the scheme,only a high refractive medium is employed to realize multiple phase-shifted optical comb filters and doubled FSR optical comb filter.In the experiments,the measurement range can reach to 2?FSR,and the efficient bit is2?10?log2?N-1?.?3?A simplified photonic approach to implement digitalized IFM using complementary optical filters is proposed.The binary code is obtained by directly comparing the two outputs powers of the complementary filters.Based on the above structure,through photonic integrated chip designed software?i.e.,ASPIC?,the complementary optical comb filters using the MZI structure are designed,and the phase shifted and multiplied FSRs optical comb filters can be easily obtained by simply adjusting the arm length difference of MZI.?3?.A photonic approach to measure intra-pulse parameters of the complex microwave signals is proposed.Firstly,the time-frequency characteritics of the microwave signals with different modulation formats are analyzed,wherein they reflects the modulation type of the microwave signal.Secondly,based on the time domain analysis method,the feasibility of the photonic scheme for measuring simple pulse microwave signal,and intra pulse with BPSK,QPSK,LFM,BFSK,3FSK,4FSK modulation is analyzed theoretically.Meanwhile,multi-dimensional intra-pulse parameters measurement and modulation formats recognition of the above microwave signal are realized.Finally,the performance of photonics-based IFM systems using commercial optical devices,in terms of the signal to noise of the received microwave signal and the weak microwave signal is analyzed theoretically.Furthermore,the improved method is given.?4?.Based on the optical mixing,two novel photonic schemes to the microwave DFS measurement are proposed.?1?A photonic approach for wideband DFS measurement using cascaded electro-optic modulators?EOMs?and optical frequency shift module is proposed.In the proposed approach,a light wave from a laser diode is split into two paths.In one path,the DFS information is converted into an optical sideband close to the optical carrier by using the two EOMs,while in the other path,the optical carrier is up-shifted by a specific value.Then the optical signals from the two paths are combined and detected by a low-speed photodetector?PD?,generating a low-frequency electronic signal.The value as well as the direction of DFS can be obtained just by comparing the measured frequency of the low-frequency signal with the specified optical frequency shift.?2?A photonic approach for wideband DFS based on parallel EOMs and coherent quadrature demodulation is proposed.The DFS between the transmitted microwave signal and the echo signal is converted to the frequency difference between the two specified optical sidebands using two parallel EOMs.After low-speed photoelectric detection,the in-phase?I?and orthogonal?Q?DFS signals are obtained.By analyzing their spectra and the phase difference between them,the value and the direction of DFS are identified.In conclusion,with the aid of microwave photonics,the IFM,intra-pulse parameter measurement and modulation format recognition,and wideband DFS measurement with no direction ambiguity of the microwave signal are realized,which have important applications in radar,communication,electronic warfare and other fields. |
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