All-fiber acoustooptic filter with low-polarization sensitivity and no frequency shift

An acoustooptic tunable filter based on an all-fiber null coupler, exhibiting low polarization sensitivity and zero net frequency shift, is demonstrated. The polarization dependence has been eliminated by simultaneously applying two acoustic waves that independently satisfy the phase-matching condition for the two eigenpolarization states. A simple double-pass arrangement is employed to exactly cancel the net frequency shift and to provide an enhanced spectral sidelobe suppression of better than -17 dB.     

NOVEL BIPHASE CODE -INTEGRATED SIDELOBE SUPPRESSION CODE

A kind of novel binary phase code named sidelobe suppression code is proposed in this paper. It is defined to be the code whose corresponding optimal sidelobe suppression filter outputs the minimum sidelobes. It is shown that there do exist sidelobe suppression codes better than the conventional optimal codes-Barker codes. For example, the sidelobe suppression code     

Ultralow sidelobe-level integrated acoustooptic tunable filtersusing tapered-gap surface acoustic wave directional couplers

We propose a new weighted-coupling scheme using tapered-gap surface acoustic wave directional couplers for realization of ultralow sidelobe-level integrated acoustooptic tunable filters (IAOTF's). Appropriate design analysis has been carried out for 30-mm-long filters operating at an optical wavelength of 1.55 μm in an X-cut Y-propagating LiNbO₃ substrate. New synthesized weighting functions have been used for the improvement of sidelobe level suppression over existing single-stage filters by as much as 27 dB. The -20 dB mainlobe width of the resulting IAOTF's varies from 2.7 to 3.9 nm only for the worst sidelobe levels ranging from -30.6 to -44.7 dB, respectively. It has also been shown that further suppression of sidelobe levels by 3-9 dB is possible if the filter is underdriven at 80% mode-conversion efficiency     

NOVEL BIPHASE CODE——INTEGRATED SIDELOBE SUPPRESSION CODE

A kind of novel binary phase code named sidelobe suppression code is proposed in this paper.It is defined to be the code whose corresponding optimal sidelobe suppression filter outputs the minimum sidelobes.It is shown that there do exist sidelobe suppression codes better than the conventional optimal codes-Barker codes.For example,the sidelobe suppression code of length 11 with filter of length 39 has better sidelobe level up to 17dB than that of Barker code with the same code length and filter length.     

Lithium niobate electro-optic tunable filter with high sidelobe suppression

The first demonstration of a high sidelobe suppression, tunable, electro-optic filter fabricated in lithium niobate for 1.55 mu m is reported. Weighting of the mode convertor structure using a Taylor distribution resulted in a -3 dB passband width of 1.6 nm and nearest sidelobes of -25 dB. A continuous, linear electro-optic tuning rate of +or-30 V/nm is also reported.<>     

Reduction of filter sidelobe level by an X-crossing verticalcoupled ARROW filter

An antiresonant reflecting optical waveguide (ARROW) type vertical coupler filter exhibiting low sidelobe characteristics is demonstrated. The sidelobe level of the filter has been suppressed by using an X-crossing arrangement to provide strength apodization along the device. The main sidelobe of the fabricated filter is measured to be less than -17 dB with the central wavelength in the 1.55-μm region     

SAW 15位m序列相位编码信号的最小峰值旁瓣滤波器

本文介绍用线性规划方法求解[4,3,0]反馈连接的、起始状态为1001的15位m序列相位编码信号的最小峰值旁瓣滤波器(LP滤波器)的计算结果。长度为15的LP滤波器的峰值旁瓣电平降到－21.47dB,比匹配滤波器改善7.49dB,当滤波器的长度增加时,LP滤波器可把峰值旁瓣抑制到更低电平。并介绍用声表面波(SAW)技术制作15位m序列相位编码信号(起始状态为1001)的LP滤波器,实验结果,其峰值旁瓣电平为－19dB,与理论值相差2.47dB。     

卫星干扰信号转发天线设计

本文介绍了一种高增益卫星信号转发天线,天线阵元采用十字交叉阵子形式,通过宽带功分移相网络实现圆极化,并采用泰勒综合方法优化了阵面方向图.该阵列具备工作频带宽、高增益和低副瓣等特点.仿真结果表明,该阵列天线增益大于12 dBi,旁瓣抑制大于25 dB,轴比小于3 dB,适用于多种卫星导航干扰信号的转发.     

Surface Elastic Wave Bandpass Filters for Frequency Synthesis (Short Papers)

Surface elastic wave bandpass filter techniques have been applied to the development of a minaturized frequency synthesizer for satellite communications systems. A bandpass filter centered at 247 MHz has been developed exhibiting less than 7-dB insertion loss over a 6-MHz 1-dB band, with sidelobe rejection greater than 45 dB.     

Saw minimum peak sidelobe filter for 15-bitM-sequence phase code signals

This paper presents computation results of the minimum peak sidelobe filter (LP filter) for the 15-bitM-sequence phase coded signal with feedback connection [4,3,0] and initial condition 1001. The design of the filter resorts to the linear programming method. The peak sidelobe level is reduced to −21.47 dB by the LP filter of length 15, and is 7.49 dB lower than that by the matched filter. The LP filter can suppress the peak sidelobe even more by increasing its length. The minimum peak sidelobe filter for the 15-bitM-sequence phase coded signal (initial condition 1001) has been implemented with a surface acoustic wave (SAW) device. Experiments show that the peak sidelobe level of the manufactured filter is −19 dB and, thus, only differs from the theoretical value of −21.47 dB by 2.47 dB.     

极化滤波器的性能比较

基于极化滤波器的最优解,分析了最优极化滤波器的性能,并与固定极化、干扰抑制滤波器ISPF、信号匹配滤波器SMPF进行了比较.最优滤波器的性能比ISPF和SMPF平均要好1～3dB,比固定极化平均要好6～15 dB,最高可达30 dB以上.因此,最优极化滤波器的得益还是很可观的,这对研究最优极化理论的应用具有重要的理论指导意义和使用价值.     

ARROW-type vertical coupler filter: design and fabrication

Vertical coupler filters (VCF) exhibiting narrow bandwidth and low sidelobe levels have been designed and demonstrated. Narrow bandwidth filter response is achieved due to the strong asymmetry between the waveguides of the filter and the nondispersive characteristics of the anitresonant reflecting optical waveguide (ARROW) structure. An ARROW-type VCF with a conventional parallel coupled directional coupler configuration with a full width at half-maximum (FWHM) of 1.36 nm and a maximum sidelobe level of -8.5 dB was fabricated using a compound glass consisting of SiO₂ and SiO₂-Ta₂O₅ . The filter sidelobe levels were then further suppressed by using an X-crossing arrangement to provide coupling strength apodization along the device. The sidelobe levels of this modified X-crossing filter were suppressed to below -23 dB and the measured FWHM was 3.9 nm. The central wavelength of the reported filters are in the 1.55 μm region. The measured results are in good agreement with theoretical results from an analysis procedure that combines the coupled mode theory with the finite difference complex mode solver     

Fine tuning of surface-acoustic-wave resonator filters with metallisation thickness

Two-port surface-acoustic-wave resonator filters with Q factors in excess of 3000 and a sidelobe suppression of 30 dB have been fabricated from yz LiNbO3 with aluminium metallisation. The dispersion of the centre frequency with aluminium thickness has been found to be 70?10 kHz/?m at 35 MHz. The ability to fine tune with metal thickness has been used to compensate inherent substrate inhomogeneities and to fabricate a high-Q factor flat-top filter.     

三次泛音单片式、高频及高阻带晶体滤波器

研究了三次泛音模式下单片式晶体滤波器的设计方法、制作工艺。通过优化滤波器结构、合理控制晶片镀回频率等方法,实现了晶体滤波器的高阻带和高杂波抑制。制作出一种工作频率为41.4 MHz,响应模式为三次泛音的单片式晶体滤波器。结果表明,该晶体滤波器的-1 dB带宽为2.9 kHz,带内波动为0.3 dB,阻带抑制为82 dB。     

Polarization-independent integrated optical, acoustically tunabledouble-stage wavelength filter in LiNbO3

We report a polarization-independent integrated acousto-optical double-stage wavelength filter in X-cut, Y-propagating LiNbO₃. The device consists of a combination of four acousto-optical mode converters, a TE- and a TM-pass polarizer, and two polarization splitters; their specific design and properties are discussed. The filter has a bandwidth of 1.4 nm and a tuning range of 76 nm around λ1.55 μm. Maximum filter transmission is achieved with a RF drive power of only 80 mW; it excites via a single unidirectional transducer a guided surface acoustic wave driving the four polarization converters of both stages. Fiber-to-fiber insertion loss is 4.6 dB for TM- and 4.8 dB for TE-polarized waves. Multiwavelength filtering has been demonstrated     

Adaptive Deconvolution Using a SAW Storage Correlator

A new analog adaptive filter for deconvolving distorted signals is described in this paper. The filter uses a storage correlator which implements a clipped version of the least mean squared (LMS) algorithm and uses a special iterative technique to achieve fast convergence. The new filter has a potential bandwidth of 100 MHz and would eventually handle pulsed signals of 10-µs width. For signals with time-bandwidth products of less than 100, the adaptation time is less than 1 ms, which allows operation in real time for most applications, including resolution of radar signals in a cluttered environment, removal of echoes from television signals, deconvolution of distorted signals in nondestructive evaluation, and also in telephony. The filter is particularly suited for radar and communications, as it processes signals directly in the VHF range. Two experiments related to ghost suppression of a pulse and to the field of NDE are described in this paper. The results are in good agreement with computer simulations and show a ghost suppression of 15 dB for the first example and a sidelobe suppression of 8 dB for a transducer signal. The adaptation time is less than 450 µs.     

W波段45°线极化天线阵设计

提出了一种带反射相消单元的W波段45度线极化微带贴片天线阵列.单列串馈天线阵采用泰勒加权结合反射相消单元实现了25dB的旁瓣抑制,通过添加贴边矩形槽改善了主瓣内的交叉极化.一阶十路功分器通过T型结取代一般的四分之一波长匹配段实现4.5倍的不等功分比.仿真与实测结果表明：组阵后的天线工作在75.7GHz~77.6GHz,水平和垂直方位3dB波束宽度可覆盖正负45度,该宽度内交叉极化比均高于18dB.天线增益达24dB,旁瓣抑制度达20dB.该天线形式可用于汽车防撞雷达并提高其抗干扰能力.     

线性调频信号主瓣不展宽旁瓣抑制方法

以汉明窗为代表的加权方法在抑制线性调频信号的匹配滤波输出峰值旁瓣的同时展宽主瓣,致使距离分辨力下降。为兼顾旁瓣抑制和高距离分辨力的需求,该文提出一种新的主瓣不展宽旁瓣抑制方法。该方法首先将匹配滤波和加权处理的输出幅度进行归一化处理,然后逐点进行比较,再取各点对应的最小值作为最终的输出数据。该方法兼取了匹配滤波和加权处理的优点,其-3 dB主瓣展宽系数与匹配滤波相比仅为1,而旁瓣抑制性能和对应的加权处理相当。仿真结果和湖上试验验证了该方法的有效性。     

线性伸缩波形的雷达距离模糊特性及旁瓣抑制

该文提出了任意信号的时域线性伸缩表达式,给出了一类新的雷达波形,并对这类波形的压缩形式(匹配滤波输出)在时域进行旁瓣抑制数字滤波。仿真结果表明,这类波形的距离模糊函数的峰值旁瓣电平可达-18~-20 dB,而4dB主瓣宽度仅为相同参数的线性调频(LFM)压缩信号主瓣宽度的54%~70%;对这类波形的匹配滤波输出用该文改进的数字旁瓣抑制滤波器滤波后,其峰值旁瓣电平可低达-50dB,且主瓣宽度仅为单位采样符号长度。