Efficiency of the surface-acoustic-wave diode convolver

The diode convolver performs signal processing, for example correlation, by mixing two input waveforms in an array of diodes, each diode being connected to a tap on a surface acoustic wave delay line. This paper gives the theory for the device efficiency, for a parallel circuit arrangement of taps and diodes. The effect of stray capacity is also analyzed. An experimental 31-tap device used hybrid circuitry in order to allow close spacing of the taps, giving a tap-to-tap propagation time of 90 ns. The efficiency agrees well with theory, showing that the bilinearity factor is maximized for an intermediate value of the bias current. The maximum bilinearity factor, relating external powers, was -34 dBm.     

Processing gain of surface-acoustic-wave convolver with noise-corrupted reference waveform

An analysis is given for the output signal/noise ratio of a convolver when both input waveforms are accompanied by noise. It is shown that a close approximation to the ideal matched-filter performance can be obtained if the signal/noise ratio at the reference input is only 10 dB. Experimental measurements support the analysis.     

Correlation of long sequences by a surface-acoustic-wave convolver, with application to spread-spectrum communication

Segments of a long biphase coded waveform were correlated in a surface-acoustic-wave convolver, and the resulting correlation peaks were summed in a recirculation loop. With a 5 MHz chip rate, 250 ?s of the waveform was integrated, giving an experimental s.n.r. improvement of 36 dB. The application to fast synchronisation in spread-spectrum communication is discussed.     

Optimization of recombination levels and their capture cross section in power rectifiers and thyristors

Single level recombination statistics have been used to determine the influence of lifetime on the characteristics of power rectifiers and thyristors. It is shown that the ratings of rectifiers can be optimized by maximizing the ratio of the high level to the low level lifetime. An optimization criterion relating the recombination center location to its capture cross section ratio for holes and electrons is derived. The relationship is found to be a function of temperature but not dependent upon the resistivity of the base material. In the case of thyristors it is shown that the leakage current must also be considered in the optimization procedure. This leads to a criterion which relates the recombination center location to the resistivity and the capture cross section.In addition, presently used techniques of gold diffusion and electron irradiation are shown to produce levels which fit poorly into the optimization scheme. The work in this paper points out the need to gather more information regarding the energy levels and capture cross sections of other impurities in silicon.     

Determination of interface trap capture cross sections usingthree-level charge pumping

A modified three-voltage-level charge pumping (CP) technique is described for measuring interface trap parameters in MOSFETs. Charge pumping (CP) is a technique for studying traps at the Si-SiO₂ interface in MOS transistors. In the CP technique, a pulse is applied to the gate of the MOSFET which alternately fills the traps with electrons and holes, thereby causing a recombination current I_cp to flow in the substrate. With this technique, interface trap capture cross sections for both electrons and holes may be determined as a function of trap energy in a single device. It is demonstrated that a modified three-level charge pumping method may be used to determine not only interface trap densities but also to capture cross sections as a function of trap energy. The trap parameters are obtained for both electrons and holes using a single MOSFET     

A new technique for determining the capture cross section of theoxide traps in MOS structures

The use of an oxide voltage relaxation spectroscopy technique based on voltage-electron fluence measurements on a MOS structure under high constant current stresses for determining the trapping parameters in thin oxide is discussed. Oxide voltage relaxation spectroscopy is essentially an ultralow-speed real-fluence differential sampling technique. This technique has the benefits of accuracy, speed, and convenience, and it is useful for the study of complex oxide trap phenomena. This method has been used to determine the capture cross section of the oxide traps in thin SiO₂     

太赫兹雷达散射截面测量中定标体的确定

围绕赫兹雷达散射截面定标体选定的内容开展了一系列工作,确定了适合作为太赫兹雷达散射截面标准体的工艺要求和加工方式,并先后对6种通过不同工艺加工成的太赫兹雷达散射截面的标准体材料进行了测试,分别测出半球反射率随波长的变化关系,确定了适合作为太赫兹雷达散射截面标准体的工艺要求和加工方式,加工出符合条件的太赫兹雷达散射截面测量中用作定标金属铝球,并利用该定标体对其他目标体在低频太赫兹波段的雷达散射截面进行了初步测量。     

Radar cross section of trihedral corner reflectors using PO and MEC

Physical optics (po) and the method of equivalent currents (mec) are used for the formulation and calculation of the backscatter cross section of both the triangular and square trihedral corner reflectors. Scattering from a trihedral corner reflector is dominated by single, double, and triple reflections by the interior walls. A physical optics integration is performed on the entire surface of each plate for the evaluation of the singly reflected fields. Doubly and triply reflected fields are evaluated by first using geometrical optics (go) at initial reflections to calculate the incident plane wave on the plate where the last reflection occurs. Physical optics is then applied on the illuminated area of that plate. First-order diffractions, which are based on the fringe current expressions for the exterior edges of the trihedral, are also included in the analysis. Predictions compare very well with both experimental and fdtd data.     

Photoconductivity study of semiconductors using the surface acoustic wave convolver

Photoconductivity study of a semiconductor using the SAW convolver is presented. The semiconductor is placed either on or a small distance above the SAW delay line. A fast rise time pulse of light is applied to the semiconductor surface through the piezoelectric substrate, and the resulting change in the semiconductor conductance is observed by the relaxation of the SAW propagation loss. This technique has the important advantage that no ohmic contact to the semiconductor is needed.     

Radar cross section of curved plates using geometrical and physical diffraction techniques

Geometrical and physical optics techniques, supplemented by their respective extensions, i.e., geometrical and physical diffraction, are applied to the problem of finite cylindrically curved plates. Numerical calculations of the radar backscattering cross sections were made, and a graphical comparison of these methods with experimental results is made. Keller's and Ufimtsev's theories axe discussed and compared as they apply to this problem.     

应用切比雪夫逼近快速求解目标宽带雷达散射截面

将切比雪夫逼近理论应用于目标宽带电磁散射特性分析中,通过求解给定频带内的切比雪夫节点和节点处的目标表面电流,实现了频带内任意频率点表面电流的快速预测,从而实现目标宽带雷达散射截面的快速计算.组合场积分方程的使用消除了内谐振问题.将计算结果与传统矩量法逐点计算的结果进行了比较,结果表明在不影响精度的前提下,该方法的计算效率大大提高.     

Radar cross section of insects

X-band measurements of radar cross section as a function of the angle between insect body axis and the plane of polarization are presented. A finding of particular interest is that in larger insects, maximum cross section occurs when the E-vector is perpendicular to the body axis. A new range of measurements on small insects (aphids and planthoppers) is also described, and a comprehensive summary of insect cross-section data at X-band is given.     

利用140 GHz雷达实现目标缩比模型的RCS测量与成像

构建了140 GHz频段的单基雷达用于缩比模型的高分辨力成像和雷达散射截面积(RCS)测量。雷达的相干收发机用全固态的方式实现,其发射信道采用一个Ka波段频率源驱动的倍频链作为本振,在5 GHz的带宽内实现了0.5 mW的输出功率,接收机采用基于肖特基二极管的次谐波混频器实现相干接收。该雷达RCS测试系统显示出高信噪比的特点,获得了大于100 dB的动态范围和3 cm的成像分辨力。除了可实现对目标的逆合成孔径成像,该系统还可完成对旋转目标全方位角的RCS测量。利用该系统对某航空母舰1/720th模型进行了成像实验和RCS测量,模拟了全尺寸目标在P波段的结果。所获得的数据根据缩比定律可为P-波段雷达设计提供参考。     

双反射面天线的雷达散射截面

近年来,降低天线的雷达散射截面已是电子对抗领域中的重要课题。该文针对已广泛应用的双反射面天线讨论降低其雷达散射截面的方法。结果表明,在保持增益不变的情况下合理选择主反射面的焦距是能够达到降低雷达散射截面的需要的。     

Radar cross section of long wires

Using a continuous wave (CW) Doppler radar at 60 GHz, the radar cross sections of long metallic rods were measured. The results show linear increase with growing distance between radar and rods. A new expression for the radar cross section, which was also derived, demonstrates good agreement with the measured data.     

Radar cross section of axisymmetric objects

A method for computing the resonant region scattering by slender axisymmetric objects with arbitrary surface impedance is outlined. This method employs matching of the electric and magnetic fields on axis. Results obtained by this method have been used to generate contour maps of radar cross section (RCS) as a function of frequency and aspect. Maps for three conducting cones and a cone-spheroid covering the diameter-to-wavelength range of 0.05 to 0.70 are shown. The relationship of the high and low frequency asymptotic behavior to the mapped results is discussed. Computed and measured RCS patterns are compared.     

On the radar cross section of a dipole

Literature references dealing with the radar cross section of a dipole target contain a possible source of confusion in that two definitions of cross section have been used. To clarify this situation, the radar cross section of a randomly oriented half-wave dipole is considered using both definitions.