High-power microwave pulses generated by a resonance relativistic backward wave oscillator with a power supply system based on explosive magnetocumulative generators

High-power microwave radiation has been generated using a relativistic backward wave oscillator (BWO) powered by a high voltage source comprising an inductive energy storage and an electric-explosion current switch. The high voltage source and the BWO magnetic system are energy pumped by explosive magnetocumulative generators. In experiments, the proposed setup generated 30-ns single-mode radiation pulses with a carrier frequency of 3.6 GHz at an output power of 0.75 GW.     

Exchange coupling controlled ferrite with dual magnetic resonance and broad frequency bandwidth in microwave absorption

Ti-doped barium ferrite powders BaFe_12−xTi_xO₁₉ (x = 0, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were synthesized by the sol–gel method. The phase structure and morphology were analyzed by x-ray diffraction (XRD) and scanning electron microscopy, respectively. The powders were also studied for their magnetic properties and microwave absorption. Results show that the Ti-doped barium ferrites (BFTO) exist in single phase and exhibit hexagonal plate-like structure. The anisotropy field H_a of the BFTO decreases almost linearly with the increase in Ti concentration, which leads to a shift of the natural resonance peak toward low frequency. Two natural resonance peaks appear, which can be assigned to the double values of the Landé factor g that are found to be ∼2.0 and ∼2.3 in the system and can be essentially attributed to the existence of Fe³⁺ ions and the exchange coupling effect between Fe³⁺ and Fe²⁺ ions, respectively. Such a dual resonance effect contributes a broad magnetic loss peak and thus a high attenuation constant, and leads to a dual reflection loss (RL) peak over the frequency range between 26.5 and 40 GHz. The high attenuation constants are between 350 and 500 at peak position. The optimal RL reaches around −45 dB and the practicable frequency bandwidth is beyond 11 GHz. This suggests that the BFTO powders could be used as microwave absorbing materials with extraordinary properties.     

Formation of a diamond-like phase under conditions of preferential deposition of nondiamond carbon in a microwave gas discharge plasma with electron cyclotron resonance

Films with crystallite sizes up to approximately 0.5 μm were obtained. Results of complex investigations of these films are presented. Pis’ma Zh. Tekh. Fiz. 24, 25–31 (February 26, 1998)     

Tunable microwave filters with controlled ferroelectric capacitors

Microwave microstrip resonators and filters controlled by ferroelectric capacitors have been simulated and experimentally studied. Control at room temperature and under cryogenic conditions has been ensured by capacitors based on BSTO and STO films, respectively. Cooled devices based on YBa₂Cu₃O_7-δ high-temperature superconducting films have been fabricated. The developed filters are efficiently tuned by applying a control voltage, are small, and have a low level of introduced losses.     

Characterization of chirped pulses with the fractional-order Fourier transformation.

We show that the fractional-order Fourier transformation (FRT) is a suitable method to describe chirped pulses submitted to group-velocity dispersion in a linear dispersive medium. Amplitudes exhibiting different chirp coefficients are easily separated with the FRT, although they are temporally superposed.     

Active microwave pulse compressor utilizing an axisymmetric mode of a circular waveguide

A novel active microwave pulse compressor in the form of an axisymmetric cavity is implemented and investigated. The cavity is formed by: a) a Bragg reflector, b) a cylindrical section, and c) an output resonance reflector in the form of an electrically controlled gas-filled spark gap. The compressor is excited by the TE₀₁ mode of a circular waveguide at a frequency of 9.4 GHz. Working at atmospheric pressure, the compressor produces output pulses with a power of 1.8 MW and duration 25 ns at a compression coefficient of around 20. Pis’ma Zh. Tekh. Fiz. 24, 6–11 (October 26, 1998)     

Choice of operating conditions and plasma parameters of a magnetoplasma compressor

B. I. Stepanov Institute of Physics, Academy of Sciences of Belorussia, Minsk. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 3, pp. 386–390, March, 1992.     

Analysis of inductive multiport microwave devices employing a novel double parallel plate approach

The authors present a novel surface integral equation approach to analyse inductive microwave devices with several parallel input-output ports containing inductive metallic and dielectric obstacles. The technique decomposes the main problem into three subproblems, employing different kinds of Green's functions. One of the subproblems uses the classical Green's functions of an infinite unbounded medium with the constitutive parameters of the dielectric obstacles. A novel point of the technique is the formulation of the two other subproblems with two different, 90deg rotated parallel plate regions. In these regions the parallel plate waveguide Green's functions are used to simplify the modelling of the excitation problem. The second novel aspect of the work is in the treatment of these Green's functions, to smooth their behaviour, and to improve their convergence. Several numerical results are presented to demonstrate the usefulness of the algorithms proposed. Also, several results for inductive microwave devices are presented to show the practical value of the approach.     

Optically controlled semiconductor microwave modulator with nanosecond response

A microwave modulator optically controlled by laser pulses has been theoretically studied, constructed, and tested. Results of numerical simulations performed by the finite-difference method are presented, design parameters are reported, and coincidence between the calculated and experimentally measured characteristics is demonstrated. The switching time of the modulator is about 1 ns, the characteristic energy of control laser pulses sufficient for the optimum switching is 10 mJ, and the range of mechanical tuning of the microwave frequency is about 10% (66–72 GHz). It is experimentally demonstrated that the modulator reliably operates when the control laser radiation parameters vary within broad limits.     

Measurement of high-power microwave pulses by resistive hot-electron sensors

Use of hot-electron semiconductor detectors for the measurement of high-power microwave pulses may lead to anomalously large errors. Methods of separation of the error signal and determination of the measurement error are considered.     

Generation of chaotic microwave pulses in broadband self-oscillating ring system with ferromagnetic film under the action of external pulse-modulated microwave signal

We have experimentally studied specific features of the generation of chaotic microwave pulse trains in a self-oscillating ring system with nonlinear delay line on surface magnetostatic waves, bandpass filter, and power amplifier on GaAs field-effect transistors under the action of an external pulse-modulated microwave signal occurring outside the band of the generated chaotic signal. It is established that a decrease in the off/duty ratio in the external pulse-modulated microwave signal leads to an increase in this ratio for the chaotic microwave pulses. The integral power of the chaotic microwave signal generated under the pulsed external signal action is increased as compared to the power of signal generated in the autonomous regime.     

Spectral transformation of femtosecond Cr:forsterite laser pulses in a flint-glass photonic-crystal fiber

Nonlinear-optical performance of photonic-crystal fibers (PCFs) made of highly nonlinear TF10 glass is studied and compared with the general tendencies of nonlinear-optical interactions in fused-silica PCFs. The loss of TF10 glass PCFs prevents the generation of supercontinuum emission with a broad and flat spectrum, which typically requires propagation lengths comparable with or exceeding the attenuation length of the fiber. However, dispersive-wave emission of solitons, induced by high-order dispersion, phase-matched four-wave-mixing processes, and self-phase-modulation-induced spectral broadening are substantially enhanced in TF10 glass PCFs due to the high material nonlinearity, providing a high efficiency of frequency conversion of Cr:forsterite laser pulses.     

基于谐振法测试微波介质材料的介电参数

介电常数是介质材料的主要性能参数之一,该文讨论了微波介质的介电参数的理论计算,分析了谐振法的模型,研制了基于谐振法测量微波介质材料介电参数的测量系统.通过对多个样品进行实测,结果表明与参考值比较吻合,评价了该测量系统测量结果不确定度,从而建立了微波频段内微波介质材料介电常数测量平台.     

Generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external noise

The generation of single chaotic microwave pulses in a self-oscillating ring system with ferromagnetic film under the action of external narrow-band noise microwave signal occurring outside the band of frequencies of the chaotic microwave signal was observed. Chaotic generation emerged due to the parametric instability of the magnetostatic surface wave in the ferromagnetic film, whereas formation of single chaotic microwave pulses was caused by the absence of complete suppression of chaos under the action of narrowband noise.     

Measurement of time-frequency parameters of picosecond optical pulses

A method is proposed that permits accurate and reliable measurement of the train-average pulse duration as well as the value and sign of the frequency chirp of picosecond optical pulses in high-repetition-rate trains.     

Formation of acoustooptical bound states by optical pulses

An interesting aspect of the acoustooptical interaction is studied in this paper — the formation of acoustooptical bound states by optical pulses. An analysis is made of the solution of a system of three nonlinear partial differential equations describing the case of collinear acoustooptical interaction. A specific example of this solution is examined for the case of the interaction of a sequence of acoustic pulses with a digital sequence of optical pulses. It is shown that the values of the recorded sequences of scattered light correspond to the logical operation “ AND” operating on the sequence of acoustic and optical pulses, that is, a programmable switching of the input optical digital signal by a sequence of acoustic pulses occurs. The experiment reported in this paper corresponds to the case of detuning of the wave vectors, but on the whole it supports the calculations In summary, this work demonstrates (experimentally and theoretically) the possibility of realizing an optoelectronic programmable switching of optical signals. Pis’ma Zh. Tekh. Fiz. 23, 88–95 (January 26, 1997)     

The parameters of nonequilibrium microwave discharge in nitrogen in a tube in a rectangular waveguide

Computer codes are developed for the processing of emission spectra of nonequilibrium plasma in nitrogen for the purpose of obtaining information about the translational T _g and rotational T _rot temperatures, the populations of vibrational levels in the ground electron and electron-excited states, the electron energy distribution function, the electron concentration N _e , and the electric field intensity E. The computer codes are used to determine the parameters of microwave-discharge plasma in nitrogen in discharge systems of two types, namely, in a discharge tube (with a radius of 1 cm), which crosses a rectangular waveguide (plasmatron on the H ₁₀ wavelength, at a pressure of 1.7 torr and absorbed power density of 1.5 W/cm³), and in a discharge section of similar structure on the basis of prismatic resonator (at a pressure of 1.0 torr and absorbed power density of 0.4 W/cm³). The mechanisms of population of the N₂(C ³Π_u) state are treated.