Research On Microwave Photonic Radio-Frequency Signal Receiving And Measurement

With the rapid growth in the volume of information and communication technology services,modern wireless systems are evolving towards higher frequency bands and larger bandwidths.However,traditional microwave and radio frequency(RF)technologies face electronic bottlenecks such as large size and weight,limited bandwidth,and susceptibility to electromagnetic interference,making it difficult to meet the demands of the next-generation wireless systems.With the emergence of microwave photonics as an interdisciplinary field,RF signal processing methods based on microwave photonics technology have many advantages over traditional RF signal processing technologies,such as large bandwidth,low transmission loss,and immunity to electromagnetic interference.Based on this research background,this paper aims to study RF signal receiving and measurement technology based on microwave photonics by combining the advantages of microwave photonics with the bottlenecks faced by traditional RF signal processing technologies.What follows are the detailed works:We proposed a microwave photonic frequency down-conversion scheme with the functions of self-interference cancellation and signal–signal beat interference(SSBI)mitigation,targeting the development of KK receivers and the application scenarios of in-band fullduplex communication.The structure utilizes a dual-polarization quadrature phase shift keying modulator to achieve self-interference cancellation and down-conversion of the useful signal.The amplitude and delay of the reference signal are controlled by adjusting the electrical delay line and the modulator bias,and the subtraction of the reference signal and the self-interference signal is completed in the optical domain.After direct detection,the useful signal is down-converted to an intermediate frequency signal with self-interference cancellation.In addition,the KK algorithm is used in the digital domain to restore the fullfield information of the useful signal and mitigate SSBI.Experimental results show that the proposed scheme can effectively eliminate single-tone and broadband self-interference signals,with a suppression depth of 50 d B for single-tone self-interference and 29 d B for100 MHz broadband self-interference.Moreover,using the KK algorithm can also effectively suppress SSBI,reducing the error vector magnitude(EVM)of the useful signal from 14.97% to 8.77%.To address the problems of complex structure,single functionality,and limited bandwidth in traditional signal parameter measurement schemes,a scheme for measuring signal parameters based on a dual optical comb structure in large instantaneous bandwidth is proposed.This scheme can simultaneously measure the frequency and angle of arrival of RF signals.The structure utilizes two mode-locked lasers(MLL)to construct a dual optical comb structure to achieve frequency measurement of large instantaneous bandwidth.Through phase shift analysis of intermediate frequency signals,the scheme achieves unambiguous identification of the signal interval,solving the problem of ambiguous intervals in traditional dual optical comb frequency measurement schemes.At the same time,a single baseline interferometer structure is used to achieve angle of arrival measurement of the signal.Experimental results show that the scheme has the ability to measure multi-tone signals,broadband signals,and pulse signals.For single-tone signals,the frequency measurement range can reach 60 GHz with a measurement error less than 60 k Hz.In addition,the scheme can achieve phase shift measurement with an error less than 2° within a range of0 to 360 degrees.Aiming at the problem of intermediate frequency overlap in the dual-comb signal parameter measurement structure,a signal parameter measurement method based on phase analysis is proposed.This structure only uses one MLL to generate an optical pulse sequence and builds two optical sampling links with different delays through optical couplers and cascaded optical delay lines to achieve undersampling of RF signals.Since the two sampling links have different delays,the mapping of the signal’s Nyquist band order to the phase shift between the intermediate frequency signal channels is achieved.Finally,the original signal frequency is calculated by the frequency of the intermediate frequency signal and the Nyquist band order mapped by the phase shift.This method also uses a multi-baseline interferometer structure to measure the angle of arrival of signal.Compared with the singlebaseline interferometer structure,the multi-baseline interferometer has higher accuracy in measuring angle of arrival.The experimental results show that the unambiguous frequency measurement range of this method reaches 31 GHz,and it has the detection capability of multi-tone signals and broadband signals.For angle of arrival measurement,the measurement error can be less than 1°.Considering the limitations of system sensitivity and frequency measurement range,a signal parameter measurement scheme with multiple delay structures is proposed.This scheme adds an optical undersampling link with a different delay to achieve the mapping of the signal’s Nyquist band to multiple intermediate frequency phase shifts,further improving the sensitivity and frequency measurement range of the system.