| Microwave photonics is an interdisciplinary area that studies the interaction between microwave and optical signals,which has found applications such as wireless communication,satellite communication,sensor network,radar,electronic warfare,biology,medicine,and astronomy,due to its intrinsic advantages including small size,light weight,broad instantaneous bandwidth,low loss,and immunity to electromagnetic interference.With the continuous development of broadband,array,and miniaturized electronic information system,microwave photonics has been considered one of the key solutions to overcome speed and bandwidth bottlenecks,since it has advantages of the flexibility of microwave technology and broadband and high speed of photonic technology.The thesis studys on manipulation and transmission of broadband microwave signals based on external electro-optic modulation including photonic generation of broadband microwave signals,photonic measurement of microwave signals,and radio over fiber transmission.In terms of photonic generation of microwave signals,two schemes are proposed and experimentally demonstrated to generate phase-coded microwave signals and reconfigurable linear frequency-modulated signals based on dual-polarization and dual parallel Mach-Zehnder modulater（DP-DPMZM）.In the area of photonic measurement of microwave signals,the parameters of Doppler frequency shift and angle of arrival of microwave signals received by antennas can be obtained by down-converting a microwave signal at high-frequency to a lower one based on optic-electrical conversion,hybrid,filter,and electro-optic conversion.In the area of radio over fiber,we build a coherent radio fiber link to transmit multiple microwave vector signals.A digital phase noise cancellation algorithm is developed and applied to eliminate the joint phase noise introduced by the transmitter laser source and local oscillator source.The main contributions of this dissertation are listed as follows:（1）To improve the Doppler tolerance,we propose and experimentally demonstrate a photonic method to generate quaternary phase-coded microwave signals using a DP-DPMZM.The upper DPMZM driven by a radio frequency signal acts as an optical wavelength shifter,while the lower DPMZM driven by two independent electrical signals is used to generate a quadrature phase shift key signal.By combining the wavelength-shifted optical sideband and phase-modulated optical carrier,center frequency tunable,quaternary phase-coded microwave signals can be generated.In the proof-of-concept experiment,a5-Gb/s phase-coded signal with the carrier frequency of 10 GHz and a 7.5-Gb/s phase-coded signal with the carrier frequency of 15 GHz are obtained.（Chapter 3）（2）Aiming at the diverse needs of radar for emission waveforms,we propose and experimentally demonstrate a photonic approach to generating switchable down-,up-,and dual-chirped linear frequency-modulated（LFM）microwave signals utilizing a DP-DPMZM.By precisely controlling the bias voltages of the DP-DPMZM and phase shifts of two microwave signals and baseband LFM microwave signals,different formats（down-,up-,and dual-chirped）LFM microwave signals can be obtained.Experimental results show that switchable down-,up-,and dual-chirped LFM signals with a center frequency of 5 GHz and chirp rate of 1 GHz/4μs,a center frequency of 15 GHz and chirp rate of 2 GHz/4μs are generated.（Chapter 3）（3）A photonic method to estimate the angle-of-arrival（AOA）of microwave signals based on optical phase scanning is proposed and experimentally demonstrated.To reduce the bandwidth and sampling rate required of an analog-to-digital（ADC）converter and cut the system’s cost,microwave signals at high frequency are converted to lower ones based on optical hybrid,optical phase scanning filter,and beating.Experimental results show that the AOA measurement error is less than 2.27° for a single-tone signal at 10GHz.（Chapter 4）（4）Aiming at the multi-function processing requirements for radar,we propose and experimentally demonstrate a photonic method to measure the AOA and Doppler-frequency-shift（DFS）of microwave signals simultaneously.Microwave signals received by antennas at high frequency are converted to lower ones based on optical signal processing and divided into two paths.The DFS and AOA can be calculated by measuring the frequency and phase difference of the signals from two paths.Experimental results show that the DFS between±100-k Hz with<±5×10-3Hz error and the AOA from 1.82° to 90°with<0.85° error at 10 GHz are obtained.（Chapter 4）（5）To increase the spectral efficiency and receiver sensitivity,we propose and experimentally demonstrate three radio over fiber links to transmit multiple microwave vector signals based on coherent detection and digital signal processing.In the first link,an approach to transmitting two microwave vector signals on a single optical carrier with one polarization state utilizing a dual-drive Mach-Zehnder modulator（DDMZM）is proposed and experimentally demonstrated.In the second link,an approach to transmitting four independent microwave vector signals on a single optical carrier based on polarization-division multiplexing（PDM）is proposed and experimentally demonstrated,where the spectral efficiency is doubled.In the third link,an approach to transmitting four independent microwave vector signals on a single optical carrier with one polarization state utilizing a DPMZM is proposed and experimentally demonstrated,where the spectral efficiency can be further improved.Experimental results show that when the received optical power is-18 d Bm,the BERs for the two recovered microwave signals are 1.9×10-5,3.1×10-4,1.6×10-3,and 1.3×10-3,which enable error-free transmission under 6.7%FEC limit.（Chapter 5）In conclusion,with the aid of microwave photonics,broadband pulse compression signal generation,AOA and DFS measurements of microwave signals,coherent radio over fiber with high spectral efficiency are achieved,which can find applications,such as radar,communication,and electronic warfare. |
