Methods of hardware analysis of non-stationary processes active spectrum

The purpose of this paper is to expose an active spectrum real time analysis main point. We use the meaning about adjusted time. As a result we propose a method of non-stationary processes active spectrum hardware analysis, and we show a possibility of creation of such parallel type analyzer, whose analyzing narrowband filters are adequate to such processes. These filters are band-pass filters or following one-band modulators, which are similar to known systems of automatic frequency following. Proposed method allows to improve essentially the main engineering factors of known analogous random processes spectrum analyzers.     

影响频谱分析仪频率分辨率的因素

频率分辨率是频谱分析仪的一项重要技术指标,在介绍频谱分析仪原理的基础上,对频谱分析仪的分辨率带宽、频率选择性、本振残余调频和本振相位噪声参数进行了解析,从而使读者掌握各参数与频谱分析仪频率分辨率之间的关系,在选购频谱仪和实际测量时合理地考虑以上参数。     

Measurement of Dielectric Properties for Low-Loss Materials at Millimeter Wavelengths

We describe here a system for accurate measurement of the dielectric properties of very low-loss materials in the 130 to 170 GHz frequency range. This system utilizes an open resonator with a quality factor ∼ 1 × 10⁶. Resonance curves for this resonator are acquired with a commercial spectrum analyzer equipped with an external millimeter-wave harmonic mixer. The excitation source is a backward-wave oscillator locked to the spectrum analyzer local oscillator via a digital phase-locked loop. This system permits rapid and accurate measurement of resonance curve line widths, permitting determination of loss tangents down to the 10^-6 range. Results are reported for silicon carbide (SiC), CVD diamond, sapphire, and quartz.     

A technique for measuring FM noise in microwave oscillators

Previous methods of analyzing the low-frequency noise spectrum of microwave oscillators have employed the usual scanning-type spectrum analyzer or an arrangement of fixed-tuned filters. The visual presentation of the spectrum analyzer makes high accuracy difficult, while a series of filters does not provide the necessary frequency discrimination. The present system makes use of a chart recorder to present noise level versus frequency as a continuous plot from 0 to 16,000 cycles.     

Optical frequency comb generation based on dual-parallel Mach–Zehnder modulator and intensity modulator with RF frequency multiplication circuit

A new method of generating optical frequency comb by cascading a single dual-parallel Mach–Zehnder modulator and two intensity modulators is proposed. The intensity modulators are modulated by a frequency multiplication circuit of radio frequency. Theoretical model of the system is derived, and optical frequency comb with ultra-flatness and high side-mode suppression ratio can be obtained. The study results show that 72-line optical frequency comb with spectrum power variation of 0.26 dB, SMSR of 21 dB and frequency space of 4 GHz is gotten easily by adjusting the amplitude of radio frequency signal and the direct current bias of the modulators. The simulation result is in good agreement with the theoretical analysis model.     

基于OMAP-L138平台多通道手持频谱分析仪研究

针对部分特殊场合对频谱分析仪使用需要多通道、便携等需求,设计了一种通道数最多支持64通道的手持多通道频谱分析仪。该频谱分析仪以美国德州仪器公司推出的DSP＋ARM双核CPU芯片OMAP—L138为平台,采用多通道A／D转换器进行数据采集,使用QT开发GUI界面对系统进行控制和数据显示,能实现频谱分析、失真测量、信号采集、多通道数据对比分析等功能。测试结果表明：本设计能完成信号采集及频谱分析功能,并拥有较小的采集频率误差,误差值≤1％。     

Near-ideal RF upconverters

This paper presents experimental results on the application of a new quadrature modulator compensator, which allows existing quadrature modulators to achieve near-ideal RF upconversion over a wide bandwidth. A test setup using an arbitrary waveform generator and a spectrum analyzer shows that over 70 dB of spurious-free dynamic range may be obtained over a bandwidth of 1.2 MHz using an off-the-shelf Mini Circuits in-phase/quadrature modulator operating at 895 MHz. A conventional compensator provides only 45 dB of sideband suppression in the same experimental setup.     

A New Optical Phase Modulator Dynamic Response Measurement Technique

A new technique for measuring the dynamic response of optical phase modulators is presented. It is based on a photonic signal processor principle, in which the phase modulator is inserted in a Sagnac loop, and coherent summation of the counter-propagating phase modulated signals converts the off-loop-center phase modulation into intensity modulation, so that modulator response can be measured on a network analyzer from the envelope of the resulting microwave photonic filter response. Experimental results demonstrate that this technique is applicable for both polarizing and nonpolarizing waveguide optical phase modulators, and that it has wideband measurement capabilities with swept frequency response characterization features.      

Designing of Acousto—optic Spectrum Analyzer

The structure of the acousto- optic spectrum analyzer was investigated including the RF amplifying circuit, the optical structures and the postprocessing circuit, and the design idea of the module was applied to design the spectrum analyzer. The modularization spectrum analyzer takes on the performance stabilization and higher reliability, and according to different demands, the different modules can be used. The spectrum analyzer had such performances as the detecting frequency precision of 1 MHz, the detecting frequency error of 0.58 MHz, detecting responsivity of 90 dBm and bandwidth of 50 MHz.     

Traveling-Wave Tube Nanosecond Pulse Generator In 24-Gc Region

A 24-Gc traveling-wave tube of the type ECL-1180 /24W80 was used for generating nanosecond carrier pulses. The helix of the traveling-wave tube was modulated by a 40-Mc high voltage sine wave. Duration, power and carrier frequency shift of the output RF pulse were examined quantitatively with respect to the modulating voltage. It was found that the delay time of a traveling-wave tube has a large effect on the characteristics of the output pulse. The theory of transmission line modulators was developed to explain the pulse shaping mechanism in the traveling-wave tube. Observations of output pulses were made with three measuring devices, i.e., video-sampling oscilloscope with crystal detector, interferometer, and spectrum analyzer. The interferometer was found to be useful for measuring half-amplitude duration of carrier pulse. Output pulses with half-amplitude duration of as short as 1 nsec were observed.     

Filter Bank Spectrum Sensing for Cognitive Radios

The primary task in any cognitive radio (CR) network is to dynamically explore the radio spectrum and reliably determine portion(s) of the frequency band that may be used for the communication link(s). Accordingly, each CR node in the network has to be equipped with a spectrum analyzer. In this paper, we propose filter banks as a tool for spectrum sensing in CR systems. Various choices of filter banks are suggested and their performance are evaluated theoretically and through numerical examples. Moreover, the proposed spectrum analyzer is contrasted with the Thomson's multitaper (MT) method - a method that in the recent literature has been recognized as the best choice for spectrum sensing in CR systems. A novel derivation of the MT method that facilitates our comparisons as well as reveals an important aspect of the MT method that has been less emphasized in the recent literature is also presented.     

Unbroadened-spectrum chirped Modulation: effects of the chirp-inducing mechanism on the spectral broadening in LiNbO/sub 3/ Modulators

The spectrum of a chirped optical nonreturn-to-zero data stream obtained by an external Mach-Zehnder modulator (MZM) is analyzed. We demonstrate that it is possible to induce chirp without broadening the optical spectrum by employing an MZM with optical power unbalancing in the two waveguides. For standard chirped MZMs (different electric fields on the two arms), such as z-cut LiNbO/sub 3/ modulators, the broadening as a function of chirp factor is measured for comparison.     

An integrated optic RE spectrum analyzer in a ZnO-GaAs-AlGaAswaveguides

A report is presented on the realization of an integrated optic RF spectrum analyzer (IOSA) that combines a wideband acoustooptic Bragg cell and a pair of waveguide lenses in ZnO/GaAs/Al_0.15Ga_0.85As composite waveguide 7×23 mm² in size. A total of 10 and 40 channels at the center frequencies of 167 MHz and 500 MHz, respectively, and a frequency resolution of 5.5 MHz were realized. The diffraction efficiencies of 11.5%/W and 4.0%/W of RF drive power at the center frequencies of 167 MHz and 500 MHz, respectively, and a dynamic range larger than 16 dB were measured. Further integration of this IOSA (integrated optic spectrum analyzer) with a laser source, a photodetector array, and electronic driving circuits could produce a monolithically integrated optic RF spectrum analyzer     

32通道光纤阵列式高灵敏飞秒激光光谱分析仪

针对飞秒激光光谱学研究中对微弱光信号的多通 道光谱分析的需求,提出了一种32通道光纤阵列- 锁相放大光谱分析仪(OSA)设计方案。32通道光纤阵列用于传输线型分布光谱信号,经光电 探测器(PD)转换的电信号 由32通道同步数字锁相放大器进行处理。基于现场可编程门阵列(FPGA)设计的32通道同步 数字锁相放 大器,实现了各路独立的微弱光谱信号同时检测功能。针对飞秒激光光谱测量中重复频率为 1kHz的强干 扰,设计1kHz陷波器,提高信号测量的动态范围。设计的OSA的测量光谱范围 为400～1100nm,通 道光谱间隔为4nm。实验结果表明:32通道光纤阵列OSA的通道隔离度大于80dB,输入光噪声密 度为37.9fW/Hz,各通道极限检测灵敏度可达 18.9fW,动态储备达到120dB。应用于飞秒时间分辨荧光 光谱测量,对超荧光干扰抑制效果明显,同时极大地提高了测量灵敏度并缩短动力学测量时 间至6min。 本文实现的OSA具有灵敏度高、体积小和性价比高等优点,适用于对微弱光谱 信号的高灵敏与快速检测分析。     

A folded-type integrated-optic spectrum analyzer using butt-coupled chirped grating lenses

A folded-type integrated-optic spectrum analyzer (IOSA) using reflection-type chirped grating lenses butt-coupled to a LiNbO3waveguide Bragg cell is presented. The lenses can be easily fabricated by the well-established planar process, and the IOSA has good performance as well as a reduced device length. The spectrum analyzer function of 4.0 MHz resolution in 95-345 MHz RF frequency range is demonstrated.     

高效微带线聚合物电光调制器的研制

设计、制作并测试了1.55 m 光波长的微带线行波电极电光调制器。如果聚合物材料的电光系数33=30 pm/V,中心电极L 为20 mm,设计的调制器性能参数半波电压为6.70 V。用自主合成的发色团分子组成二阶非线性光学聚合物材料做为芯层制作的聚合物调制器,对调制器的各项性能参数进行了直流、低频和微波性能的测试,采用不同极化方法,在1.55 m 波长上测得低频半波电压分别为10.5 V(电晕极化)和4.9 V(接触极化),折算得芯层材料的电光系数分别为21 pm/V 和45 pm/V。测得消光比为24 dB。用矢量网络分析仪测试电极系统的微波性能,S 参数反映了此电极系统具有低的微波传输损耗和反射损耗。     

Investigation of distortion of signal shape and spectrum at the combined method of frequency keying

For the first time, analysis of distortion of signal shape and spectrum has been performed depending on frequency deviation values in the channels of the frequency and phase modulators relaizing the combined FM method.     

Analysis of circular-polarization electrooptic amplitude modulators

An analysis of electrooptic (EO) amplitude/IM modulators of light having the form of circular polarizer-sample-circular analyzer (CPSA) systems is presented. On the assumption of nonideal components, with the sample being a linear EO crystal, principal characteristics and performance parameters of the above modulators are derived and investigated as to the effect of azimuthal misalignments &thetas; in the crystal birefringence axes. The so obtained results are compared with those drawn from the study of linear-polarization EO amplitude modulators structured as linear polarizer-sample-linear analyzer (LPSA) systems in their optimized variety (45°-CLPSA modulators). From this comparison, it is found that a CPSA modulator in its optimized configuration (ACPSA modulator) is superior in EO-modulation sensitivity and considerably more stable against misalignments &thetas; than its 45°-CLPSA counterpart. On the other hand, both kinds of modulator exhibit identical behavior as regards harmonic distortion and maximum-nonlinearity parameters     

射电天文台站准实时电波环境测量方法

随着频率使用率的提高,瞬态信号对射电天文观测影响越来越大,有效的电波环境测量及频谱分析可为现有射电天文台址干扰缓解策略提供依据.基于现有射电望远镜台站电波环境特征,结合信号分析仪原理,深入分析了仪器设备关键参数配置方法及测量时间计算方法;结合实际测量需求,确定了测试时间规划策略,提出一种准实时电波环境测量方法.运用此方法对新疆天文台南山台站电波环境进行测量,分析了频谱、频率占用度随时间变化特点,结果表明,该方法能够有效分析电磁干扰随时间的变化趋势.     

基于RFSoC的4 GHz频谱仪设计

介绍了一种基于RFSoC的4 GHz频谱仪的设计。该频谱仪采用扫频工作原理,包括扫频本振LO1、固定本振LO2、混频、滤波等射频电路,以及DDC,CPU,FLASH,RAM等数字电路。利用CPU实现对LO1的扫频控制、功率电平计算以及数据通讯。RFSoC加上少量外围器件,即可完成整个扫频和信号处理流程。得益于SoC和DDC的成功运用,该频谱仪具有硬件简单、功能灵活、功耗低的特点。