Photonic RF Channelizer Based On Optical Frequency Comb

In modern warfare, electronic warfare techniques have been widely used to attack enemies’ information systems and to protect one’s own information systems by various countries. In electronic warfare, electronic reconnaissance receiver is an important part of the electronic reconnaissance system and electronic intelligence security system and mainly used to receive radar signals and communication signals. In modern warfare environment, the signal frequency coverage becomes wider (from2GHz to18GHz) and the signal parameters and forms change more complex (frequency agility, pulse compression, frequency hopping and spread spectrum). Meanwhile thousands of different signal pulses appear at one second, which demands the electronic surveillance receiver to process a plurality of wide-band signals with real-time and high-precision. However, traditional receiver can only intercept a single signal instantaneously with the low frequency accuracy and high frequency insertion loss, which sets a limitation on its application in complex signal environment. Due to the great bandwidth, the electronic reconnaissance receiver based on the photonic technology has fundamentally broken the bandwidth limitations of conventional microwave devices and greatly increased the reconnaissance frequency range, reduced equipment SWaP (Size, Weight and Power). In order to detect multiple signals in a broad bandwidth, the photonic RF channelizer is proposed. In this dissertation, several schemes to achieve the broadband photonic RF channelizer are intensively investigated. The main works of this dissertation are summarized as follows:First we analyzed the different generation mechanisms of the optical frequency comb, and focused on the ultra-wideband optical frequency comb generation mechanism based on the recirculating frequency shifter (RFS). We researched the effect of the bias point of the modulator, RF power loaded on the modulator and polarization on the flatness and stability of the optical frequency comb. Then we experimentally generated an ultra-wideband optical frequency comb based on recirculating frequency shifter. The free spectral range of the optical frequency comb was20GHz, the OSNR was15.5dB. With2.5dB flatness, the number of the optical frequency comb was more than80, which covered the frequency range of up to1.6THz.Second we proposed a photonic RF channelizer based on optical frequency comb and Fabry-Perot filter. We took advantage of the periodicity of optical frequency comb and Fabry-Perot filter frequency and Vernier Caliper effect to achieve a high-frequency (2-18GHz) and ultra-wideband (4GHz) multi-frequency measurement. The accuracy of the scheme was±500MHz and achieved the same accuracy of other RF channelization schemes. In theory, we further analyzed the effect of the transmission spectrum of Fabry-Perot filter on the channelizer performance and proposed the methods to improve the channelizer performance.Third although the proposed scheme could achieve ultra-wideband multiple RF signals receiving. However, the scheme still couldn’t overcome poor accuracy of the traditional photonic channelization. Meanwhile the scheme couldn’t process and analyze the received signal further. Therefore, we proposed a photonic RF channelizer based on highly coherent OFC and I/Q demodulator. The channelization scheme was achieved by coherent down-conversion between two highly coherent optical frequency combs with different free spectrum ranges. Since the1/Q demodulation was applied, high detection accuracy could be achieved. Experimentally, we achieved a high carrier frequency and ultra-wideband channelization. The accuracy is200kHz, which went beyond the performance of other schemes.Fourth channelizer could detect and process multiple broadband RF signals, but the channelizer also had to face the system nonlinearity. A wideband channelizer suffered from third order intermodulation distortion (IMD3) and cross modulation distortion (XMD). The proposed distortion compensation schemes couldn’t work on the wideband channelization scheme. Therefore, we proposed a compensation scheme based on forward distortion information acquisition and post digital signal processing to suppress IMD3and XMD simultaneously. We experimentally achieved24dB IMD3suppression and27dB XMD suppression. Our compensation scheme could make it possible that a photonic RF channelizer received and processed broadband multiple RF signals with high fidelity.