Research On Key Technologies Of Reconfigurable Photonic-assisted Transmitting And Receiving Broadband Microwave Signal

Radio frequency(RF)front-end is one of the key components in the microwave systems such as modern mobile communications,radar,and electronic warfare.The increasing demands of civilian and military applications put forward higher requirements on operating frequency,bandwidth and flexibility of the RF front-end.It is urgent to have a broadband RF front-end with software definition function.However,due to the limited carrier mobility of the semiconductors,signals in a frequency range of only a few GHz can be directly processed by the digital signal synthesizer(DDS)and the analog-to-digital converter(ADC).In order to process broadband signals with a high frequency,cascaded up/down conversion and frequency multiplication technology must be employed,which makes the system complicated and inflexible.Therefore,traditional electronic RF frontend system cannot meet the requirements of RF front-end integration.Photonics-assisted RF transceiver technology,which takes full advantage of the photonics technology,such as ultra-broadband,wide-band tunable,reconfigurable,and anti-electromagnetic interference,is a potential method to realize RF front-end integration with software definition function.In this dissertation,photonics-assisted reconfigurable and broadband RF front-end is researched,where special attentions are paid to the key technologies such as photonics-assisted broadband microwave signal down-conversion,optical analog-todigital conversion,and photonics-assisted broadband radio frequency transceiver.The main contents of the dissertation are listed as follows:(1)In order to overcome the operating frequency range limitation of the traditional electronic mixer and avoid using a broadband tunable microwave source,an approach to achieve flexibly tunable microwave frequency conversion is proposed based on a widely tunable optoelectronic oscillator(OEO).In this scheme,a microwave photonic filter is constructed by a phase modulator,a phase-shifted fiber Bragg grating and a tunable laser source.The frequency of the local oscillator signal is tuned by changing the frequency difference between the optical carrier and the reflection notch of the phase-shifted fiber Bragg grating.Therefore,flexibly tunable microwave frequency conversion can be achieved within a frequency range of multi-tens of GHz.The proposed scheme is experimentally evaluated,where optically tunable local oscillator signals in the frequency range of 6 GHz to 15 GHz are generated,and RF signals in the frequency range of 7 GHz to 16 GHz are successfully down-converted to the intermediate frequency band around 1 GHz.(2)In order to meet the demand of microwave frequency measurement with high resolution and broad bandwidth,a microwave frequency measurement scheme with highresolution and broad bandwidth is proposed by employing three low-speed photonic sampling ADCs.In the simulation,single-tone and multi-tone microwave frequency measurements within a frequency range of 0-100 GHz are realized by utilizing three photonic ADCs with sampling rates of 1.005 GS/s,1.010 GS/s and 1.015 GS/s,where the frequency measurement error is ±0.5 MHz.In the proof-of-concept experiment,three photonic ADCs with sampling rates of 27.69 MS/s,27.71 MS/s,and 27.73 MS/s are employed,which correspond to an unambiguous frequency measurement range of 0-38 GHz.Microwave frequency measurement in the frequency range of 0-20 GHz is experimentally demonstrated with an error of ±8 kHz.(3)As one of the key components in the photonics-assisted broadband RF transceiver,the microwave characteristic of the electro-optic intensity modulator is critical to the system performance.A self-calibrating approach to finely characterizing the microwave performance of the electro-optic intensity modulator is proposed based on low-speed photonic sampling and low-frequency detection.This method is theoretically analyzed.In addition,numerical simulation and experiment are implemented to demonstrate the feasibility of the proposed scheme.Magnitude-frequency response,together with half-wave voltage versus frequency,of a commercial Mach-Zehnder modulator is accurately measured in the frequency range of 0-40 GHz by analyzing the frequency components under 100 MHz after photodetection.In addition,the measurement range of the system can be easily expanded to hundreds of GHz by just increasing the output frequency range of the microwave signal source.(4)In order to meet the urgent requirement of broadband operation and software definition in an RF front-end,a reconfigurable broadband microwave transceiver scheme is proposed based on cyclic four-wave mixing.In the proposed scheme,an OFC with a flexibly tunable repetition frequency is generated through cyclic four-wave mixing.In the transmitter,microwave signal in a broad frequency range is generated through optical filtering and electro-optic frequency shift of the OFC.In the receiver,the OFC is also employed to complete broadband photonic sampling ADC in a broad frequency range.The feasibility of the proposed scheme is numerically demonstrated,and the influence of the component parameters on the system performance is also analyzed.In addition,the proposed scheme is experimentally demonstrated,where an OFC with a flexibly tunable repetition frequency is realized.By employing an OFC with a repetition frequency of 15 GHz,microwave signals in the frequency range of 8-37 GHz are generated,and photonic analog-to-digital conversion of a 32 GHz microwave signal is achieved with an effective number of bits of 5.42 bits.