Correlation receiver of below-noise pulsed signals based on parametric interactions of spin waves in magnetic films

A correlation receiver capable of receiving pulsed microwave signals having amplitudes substantially below the noise level is proposed and experimentally realized. The device is based on the parametric interaction of two contra-propagating spin waves excited by the received microwave signal and the reference pulsed signal, containing information about the received signal shape, in a ferrite film waveguide. The output nonlinear correlation signal having the doubled carrier frequency and the signal-to-noise ratio enhanced by several orders of magnitude is received by a dielectric resonator coupled to an output microwave transmission line.     

Effects of collisions on linear and non-linear spectroscopic line shapes

A fundamental physical problem is the determination of atom-atom, atom-molecule and molecule-molecule differential and total scattering cross sections. In this work, a technique for studying atomic and molecular collisions using spectroscopic line shape analysis is discussed. Collisions occuring within an atomic or molecular sample influence the sample's absorptive or emissive properties. Consequently the line shapes associated with the linear or non-linear absorption of external fields by an atomic system reflect the collisional processes occuring in the gas. Explicit line shape expressions are derived characterizing linear or saturated absorption by two- or three-level “active” atoms which are undergoing collisions with perturber atoms. The line shapes may be broadened, shifted, narrowed, or distorted as a result of collisions which may be “phase-interrupting” or “velocity-changing” in nature. Systematic line shape studies can be used to obtain information on both the differential and total active atom-perturber scattering cross sections.     

Subwavelength grating waveguide devices in siliconon-insulators for integrated microwave photonics

We provide an overview of our recent work on developing subwavelength grating(SWG) waveguide devices as an enabling technology for integrated microwave photonics. First, we describe wavelength-selective SWG waveguide filters, including ring resonators, Bragg gratings, and contradirectional couplers. Second, we discuss the development of an index variable optical true time delay line that exploits spatial diversity in an equal-length waveguide array. These SWG waveguide components are fundamental building blocks for realizing more complex structures for advanced microwave photonic signal processing.     

Hybrid Transmission Line for ECRH in the Helically Symmetric Experiment

The HSX oversized, mode-converting ECRH transmission line has been upgraded to a hybrid system to increase launched microwave power and reduce electrical arcing. Filtering of high-order, spurious modes ensures efficient coupling to a Gaussian beam for optimal electron heating. A Vlasov mode converter and two phase-correcting ellipsoidal mirrors convert the TE₀₂ gyrotron output mode to a symmetric, linearly polarized, microwave beam. A swappable twist reflector plate rotates beam polarization for 2nd-harmonic X-mode or fundamental O-mode ECRH. Long distances are traversed by coupling the beam to a dual-mode (TE₁₁ + TM₁₁), smooth, circular cross-section waveguide. This system has been successfully tested without arcing for 50 ms pulses and over 100 kW of launched power. Analysis of the microwave beam for 50 kW, 2 ms microwave pulses reveals agreement with predicted beam shapes at two beam locations. The new system has also demonstrated increased plasma stored energy for ECRH plasmas with equal launched power.     

同轴线-矩形波导结散射特性的数值分析

 提出了一种数值分析同轴线-矩形波导结散射特性的模式匹配方法。采用同轴线和矩形波导的本征模函数表示电磁场分量,通过同轴线-矩形波导结截面横向场分量匹配获得波导结的散射参数,引入电场模式匹配矩阵的解析形式提高了计算效率。给出了基于模式匹配法数值仿真的各种同轴线-矩形波导结散射特性及仿真结果分析,并与3维全电磁波分析软件HFSS的仿真结果进行了比较,二者非常吻合。模式匹配法计算效率高,能广泛应用于微波毫米波元器件及系统结构的设计与优化。     

The line shapes of a tumbling triplet

The line shapes of a triplet spin system which interacts simultaneously with the molecular environment and with an externally applied field depend on the relative strengths of these interactions and on the motion of the molecule relative to the laboratory. In this paper line shapes are reported for zero, low, intermediate and strong applied fields, assuming that the molecular motion is due to strong collisions and that the tumbling rate is slow or intermediate.     

Increase in the average radiation power of a plasma relativistic microwave generator

The operation of a pulse-periodic plasma relativistic microwave generator with a pulsed power of 50 MW was experimentally studied. A change in the shapes of the electron collector and output unit allowed a significant increase in the average emission power. The microwave pulse duration was increased from 30 to 70 ns, and the repetition rate of microwave pulses was increased from 5 to 50 Hz.     

Ionization by a pulsed plasma surface wave

The ionization mechanism is studied of a pulsed surface wave generating a microwave discharge. When the plasma is dominated by collisions, it is found that the velocity of the ionization front depends on the ponderomotive force due to the field gradient in the front.     

Pulsed microwave-driven argon plasma jet with distinctive plume patterns resonantly excited by surface plasmon polaritons

Atmospheric lower-power pulsed microwave argon cold plasma jets are obtained by using coaxial transmission line resonators in ambient air.The plasma jet plumes are generated at the end of a metal wire placed in the middle of the dielectric tubes.The electromagnetic model analyses and simulation results suggest that the discharges are excited resonantly by the enhanced electric field of surface plasmon polaritons.Moreover,for conquering the defect of atmospheric argon filamentation discharges excited by 2.45-GHz of continued microwave,the distinctive patterns of the plasma jet plumes can be maintained by applying different gas flow rates of argon gas,frequencies of pulsed modulator,duty cycles of pulsed microwave,peak values of input microwave power,and even by using different materials of dielectric tubes.In addition,the emission spectrum,the plume temperature,and other plasma parameters are measured,which shows that the proposed pulsed microwave plasma jets can be adjusted for plasma biomedical applications.     

Investigation of plasma electron collisions in flames by means of the Luxemburg-effect of microwaves

Using a novel microwave double bridge, acetylene-oxygen and acetylene-air flames burning through an X-band waveguide at atmospheric pressure have been investigated. In order to obtain information about the collision behaviour of the plasma electrons, they are heated by microwave pulses of variable intensity, and the modulation transfer to a probing wave (Luxemburg-effect) is studied. It is shown, how the nonlinearity of the complex conductivity depends upon certain assumed collision models: via the velocity dependence of the collision frequency and via the shift and the deformation of the electron velocity distribution function. At low and medium heating power, Luxemburg-effect can not be seen. This means that the collisions can be described as those between electrons and induced dipoles. However, when the field strength of the heating pulse becomes much stronger than the plasma field strength, we observe cross modulation: the transferred pulse indicates that the collisions become harder.     

单次短脉冲微波频率分析系统环流波导色散线

 提出环流波导色散线微波频率分析方法,介绍了环流波导色散线系统设计思想、电路工作原理、主要性能及应用结果。实验应用表明,该系统测频分辨力比相同长度普通色散线提高6倍以上,克服了微波脉宽引起的测频误差,测量误差小于2％,同时能 够测量不同频率成份在微波脉冲中的时间分布,为单次短脉冲微波频率分析提供了一种有效的手段。     

Research technique of metamaterials with the controlled effective negative refractive index and their characteristics

A design of the two-beam hybrid microwave interferometer for measuring refractive indices of metamaterials is described. It is based on the branching of radiation using a waveguide directional coupler. Radiations of the interferometer waveguide arms are summed and the phase disbalance of the interferometer arms is counted on the waveguide measuring line. The frequency dispersion of the negative refractive indices of the metamaterial samples with a variable distance between its constituent plates is experimentally investigated. A possibility of controlling the refractive index of a metamaterial is demonstrated.     

A continuous-wave and pulsed electron spin resonance spectrometer operating at 275 GHz

An electron paramagnetic resonance (EPR) spectrometer is described which allows for continuous-wave and pulsed EPR experiments at 275 GHz (wavelength 1.1 mm). The related magnetic field of 9.9 T for g approximately 2 is supplied by a superconducting solenoid. The microwave bridge employs quasi-optical as well as conventional waveguide components. A cylindrical, single-mode cavity provides a high filling factor and a high sensitivity for EPR detection. Even with the available microwave power of 1 mW incident at the cavity a high microwave magnetic field B1 is obtained of about 0.1 mT which permits pi/2-pulses as short as 100 ns. The performance of the spectrometer is illustrated with the help of spectra taken with several samples.     

同轴虚阴极振荡器数值模拟

 给出了同轴型虚阴极振荡器的数值模拟和部分理论分析结果, 指出许多几何结构参数包括阴极宽度、二极管间隙等都对输出微波的频率、带宽和能量转换效率有较大的影响。给出了这些参量之间关系的数值模拟结果，在一定程度上为同轴虚阴极振荡器的实验研究提供了理论基础。     

X波段极化可重构高功率微波辐射器仿真设计

为了提高高频段高功率微波反射面天线的馈电效率,同时使波束波导馈线更加紧凑,提出一种新型的X波段极化可重构高功率微波辐射器结构。通过波纹喇叭辐射器产生准高斯的HE11模辐射,采用双相位修正镜组成的波束变换系统实现将准高斯波束转换为电场分布更为均匀的平顶波束或其余期望分布的波束,平顶分布的输出波束可使得馈源在相同介质窗尺寸下获得更高的功率容量,同时实现了波束传播方向的90°转弯;此外采用双圆极化栅网的级联组合,实现了对输出波束极化特性的调变。通过全电磁波仿真分析验证了该辐射器的设计思路。     

A monolithic microwave delay line

A microwave acoustic delay line ordinarily has three parts. These are electromagnetic coupling circuit, transducer, and delay medium. In the device considered here, these three parts are coalesced into a single, simple, unstructured block of material, which has been termed an integral delay line. This type of delay line is suitable for use in both waveguide and coax systems, and both cases are described.     

Comments on the use of Schmidt orthogonalization in quantum chemistry

The electron resonance spectra of ³P₂ oxygen atoms have been studied over a wide range of pressure and microwave power. The shapes of the spectra, in particular those showing various multiple quantum transitions, are well matched by those calculated using a theory involving a single relaxation parameter. Identification of this parameter with the time between collisions yields cross sections in excellent agreement with those determined by other workers.     

扇形波导谐振宽边纵缝的归一化电导

扇形波导可作为高功率微波圆柱共形波导缝隙阵天线的基本单元。分析了扇形波导中主模场分量,根据实际情况对主模场进行了合理近似。采用互易定理推导由波导主模横向场分量和缝隙场分量表示的波导场分量的前向或后向散射系数。根据波导传输线理论,将波导宽边纵缝等效为并联导纳,再根据波导边界条件得到扇形波导宽边谐振纵缝的归一化电导与波导散射系数之间的关系式。根据缝隙天线与振子天线的互补关系得到扇形波导谐振缝隙的辐射阻抗,结合波导功率平衡关系得到由波导横向场散射系数表示的缝隙辐射功率表达式,得到归一化电导的与谐振宽边纵缝的偏移位置、缝隙宽度、波导波长以及扇形波导尺寸参数之间的解析表达式。给出了算例,在波导中间区域,通过商用软件计算得到的电导与理论公式结果基本吻合。     

利用波导截止特性测量微波源辐射功率

 对波导的截止特性作了理论分析,并分析了利用该特性进行高功率微波功率测量的可行性及准确性。在远场条件下,利用该特性对工作频率为1.75 GHz的磁绝缘线振荡器进行了微波功率测量。测量结果表明：微波源辐射功率2.3 GW,辐射模式为TM01主模,实测辐射模式方向图与模拟计算结果一致,微波脉宽大于40 ns,未发现明显的功率击穿现象;使用波导截止特性测量微波功率是可行的,有利于防止接收喇叭的功率击穿,测量精度较高。     

Radio frequency excited waveguide CO2 lasers on sequence-band transitions

2 lasers based on either a quartz or an alumina waveguide were studied on the 00°2 - [10°1,02°1]_I,II sequence bands. A compact multisegment RF excitation with capacitive coupling was used for pumping the gain section of the laser waveguide. The use of a separate intracavity hot CO₂ waveguide suppresses the regular-band transitions. The quartz waveguide laser has a total of 62 lines lasing on both the 9.4 and 10.4 μm sequence bands. The alumina waveguide laser has 40 lines lasing on the 10.4 μm sequence band. These lasers can be either pulsed or continuous-wave (CW) operated on the selected line without a line jumping problem. Received: 29 September 1997/Revised version: 2 December 1997