【作者】 谢小军；

【导师】 李蔚；

【作者基本信息】 北京邮电大学 ， 电磁场与微波技术， 2013， 硕士

【摘要】 在现代战争中,攻击对方的信息系统和保障己方信息系统的现代电子战技术已经被各个国家广泛应用。在电子战中,电子侦察接收机是电子侦察系统和电子情报保障体系中的重要组成部分,主要用于接收雷达信号和通信信号。现代战争环境中,信号频率的覆盖范围广(0-18GHz),信号参数多变,信号形式也日益复杂,有频率捷变,脉冲压缩,跳频扩频等多种信号形式。同时信号密集交织,每秒钟可高达几十万个甚至上百万个信号脉冲。因此要求电子侦察接收机能在很宽的带宽范围内,对多个信号进行实时、高精度探测。但是传统接收机只能瞬时截获单个信号,同时测频精度不高,高频插损大,因此传统的电子侦察接收机难以应对高密集度和高复杂度的信号环境。由于光具有极大带宽这一优势,基于光子技术的电子侦察接收机可以从根本上突破传统微波器件的带宽限制,极大地增加频率侦察范围,减小了设备SWaP (Size, Weight and Power),但是该类型接收机仍然只能实现瞬时单频信号测量。为了能在大的侦察带宽内,对多频点信号进行侦察接收,基于光子技术的信道化接收机应运而生。本文主要工作围绕着基于光频率梳的宽带光子信道化接收机的关键技术以及其实现展开了研究,论文主要创新工作如下：一、分析光频率梳的不同的产生方式,并着重分析基于循环频移器的超宽带光频率梳产生方式,分析了光频率梳平坦度和信噪比。研究了调制器偏置点,调制器加载的射频功率以及偏振态对光频率梳平坦度以及稳定性的影响。最终通过实验产生了基于循环频移器的光频梳。该光频率梳的自由光谱范围为20GHz,光信噪比为15.5dB,在2.5dB平坦度条件下频率梳数量超过80根的,频率覆盖范围高达1.6THz。二、提出了基于光频率梳的信道化滤波接收机,充分利用光频率梳频率周期特性和法布里珀罗滤波器的频响周期特性以及游标卡尺效应,实现了高载波(0-18GHz)、超宽带(4GHz)内任意多频点信号的测量。其射频感知精度为正负500MHz,达到了目前国内外光子信道化射频感知系统的同等精度。同时我们在理论上进一步分析了法布里珀罗滤波器透射谱型对信道化接收机性能的影响,并提出了改善基于光频率梳的信道化滤波接收机性能的途径。三、尽管上述方案可以实现对超宽带多频点信号的探测接收,然而该方案仍无法克服传统光子信道化接收机方案普遍存在的探测精度不高的问题,同时该方案也缺乏对接收信号的进行进一步处理和分析的能力。因此,论文进一步提出基于高相干性光频率梳和I／Q解调技术的光子信道化接收机方案。该方案是利用自由光谱范围略微不同的两个高相干性的光频率梳之间的相干下变频,实现对射频信号的信道划分。同时由于该方案使用了I／Q解调技术,因此可以实现射频信号的高精度接收和处理。实验中我们实现了高载波(0-20GHz以内)、超宽带(3.5GHz)内任意多频点信号的精细测量,实现的射频感知精度达到125kHz；而目前国内外光子信道化射频感知系统的精度远低于此指标(均在百MHz量级甚至更低)。四、信道化接收机可以实现对大带宽范围内的多信号侦察接收,但是信道化接收机也面临着系统非线性带来的限制。对于宽带信道化接收机,非线性不仅仅局限于三阶交调失真,还存在信道间的交调失真。而传统的抑制三阶交调的方案并不适用于宽带信道化接收机。因此我们提出的基于前向失真信号提取和后向数字信号处理相结合的方式来实现对信道内三阶交调和信道间交调失真的同时抑制。我们通过实验实现了27dB的信道间交调失真抑制以及24dB的信道内三阶交调失真抑制,因此通过该方案可保证信道化接收机实现对宽带多信号高保真的处理和接收。更多还原

【Abstract】 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.更多还原