Addressing the needs for wide instantaneous bandwidth, parallel reception, and down-conversion processing in fields such as wireless communications and spectrum sensing, Radio Frequency (RF) channelization technology is receiving widespread attention. To achieve instantaneous ultra-wideband signal reception in the C, X, and Ku bands, research on 4- channel optical channelization has been conducted, with each channel having a bandwidth of 4 GHz and a 1 GHz overlap between adjacent channels. Due to the optoelectronic/electro-optic conversion losses and active optical noise present in microwave photonic links, the broadband frequency conversion link introduces significant noise figures and in-band gain fluctuations. By incorporating balanced detection technology in the coherent detection link, the relative intensity noise introduced by the laser is reduced, ensuring the signal-to-noise ratio (SNR) of the module output signal. Additionally, antialiasing filtering is performed using intermediate frequency (IF) band-pass filtering in the electrical domain, achieving high flatness, high suppression ratio, high isolation, and steep edge channel division. This effectively overcomes the poor filtering characteristics of a single optical filter, with the full IF band gain fluctuation being ±3 dB. To verify the accuracy of signal detection, the module was integrated into the system for experimental testing, achieving effective detection of signals in four channels, with a frequency measurement accuracy better than 1 MHz.
In order to avoid an unacceptable in-band S21 flatness in the multi-channel broadband microwave photonic system design, this paper established a relationship between the S21 flatness of a muti-channel broadband link and amplitude and delay errors. According to the deduction, the effect of amplitude error on S21 flatness is much less than that of delay error. And the maximum in-band S21 difference is expressed into a function of the muti-channel delay inconsistency. According to the derivation, for ensuring the in-band S21 flatness of a multi-channel microwave photonic system is less than 3dB, the delay error must be less than 13.89ps. Experimental results and simulation results demonstrate the reliability of the derivation relationship between the in-band S21 flatness and amplitude and delay errors.
In order to better utilize the broadband advantage of microwave photonic radar, a signal transmission model is proposed to analyze the transmission of electric signal and optical signal on microwave photonic link. In this model, signal transmission is divided into three processes: electro-optical conversion, optical signal process, and optical-electrical conversion. For each process, the connection of devices is established by the radar design, and the input output relationship of each device is modeled by the parameters. And for each device, its effect on the performance of the microwave photonic link can be calculated by its parameters. Therefore, this signal transmission model is able to help researchers to design and analyze the microwave photonic radar. Proven by the experimental results, this signal transmission model can explain the important phenomena of the microwave photonic link, and can effectively analyze the influence of each device on performance of microwave photonic link.
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