Wideband chaotic microwave signal generation in a ring system with a nonlinear delay line on coupled ferromagnetic films

Various regimes of chaotic signal generation have been studied in an self-oscillating ring system with a wideband nonlinear delay line based on coupled ferromagnetic films, in which magnetostatic backward volume waves (MSBVWs) are excited. It is shown for the first time that the simultaneous excitation of two waves in the coupled films leads to the appearance of a falling part in the dynamic characteristic of the MSBVW delay line and the generation of a broadband chaotic signal with a continuous spectrum. Under certain conditions, the ring exhibits a regime of intermittency, in which broadband chaotic signals with both continuous and discrete spectra are generated.     

Generation of chaotic microwave pulses in a ring system based on a klystron power amplifier and a nonlinear delay line on magnetostatic waves

The autonomous generation of stationary chaotic microwave pulse trains in a self-oscillating ring system with a multicavity klystron power amplifier operating in a small-signal regime and a wideband non-linear delay line on surface magnetostatic waves has been experimentally studied. It is established that the characteristics of generated chaotic microwave pulses can be controlled by varying the electron beam current and accelerating voltage in the klystron.     

Optimum filtration of microwave signals by a multiband spin-wave ring resonator

The optimum filtration of pulsed microwave signals by a multiband active spin-wave ring resonator has been studied for the first time. The ring resonator, which comprises a spin-wave delay line based on a ferromagnetic single crystal film of yttrium iron garnet with a microwave amplifier in the feedback chain, possesses a comblike amplitude-frequency characteristic with a large number of pass bands. It is established that the best filtration of a periodic train of rectangular microwave pulses is achieved provided that harmonics of the signal coincide with the positions of the resonator pass bands. Thus, an active spin-wave ring resonator can be used as the optimum filter for periodic pulsed microwave signals.     

Synchronous amplitude and time control for an optimum dynamic range variable photonic delay line

A synchronous-amplitude-controlled and time-delay-controlled photonic controller for phased-array antenna applications is proposed and demonstrated. Amplitude control is based on a variable optical attenuator system that operates in synchronism with the photonic delay line (PDL). This amplitude control system can provide both the signal calibration for the different PDL channels and settings required for driving the antenna elements of a phased-array radar and the optimum optical power levels that impinge on the photodetector for optimum fiber-optic-link performance. Various variable amplitude control modules based on ferroelectric liquid crystals, polymer-dispersed liquid crystals, and photoconductive devices are proposed. We show that the dynamic range loss due to a switched-PDL inherent structure loss can be compensated when we control the optical power from the laser, using the synchronous optical attenuation system. For the first time to our knowledge, full dynamic range loss compensation is demonstrated for an external-modulation-fed 3-bit switched PDL with a structure optical insertion loss of 5.5 dB. A compression dynamic range of 158 dB.Hz was measured at 6 GHz, and a spurious free dynamic range of 111 dB.Hz(2/3) was estimated. Feasibility of the dynamic range compensation technique for multichannel, higher-insertion-loss PDL systems is discussed.     

Influence of nonlinear amplitude dynamics on estimated delay time of coupling between self-oscillatory systems

The well-known method of estimating the delay time of coupling between self-oscillatory systems on the basis of their time series is based on empirical modeling of the observed phase dynamics by a system of first-order phase oscillators under the assumption that amplitude fluctuations can be ignored. We have studied the applicability of this method in the presence of significant amplitude fluctuations caused by an external noise or the chaotic dynamics of oscillators. Numerical experiments with systems of standard coupled oscillators show that the method under consideration gives incorrect estimations in some situations. A diagnostics of these situations is proposed, and modification of the estimator that eliminates errors is described and justified.     

Controlled chaotic microwave generation under conditions of four-wave parametric interaction of surface spin waves

Controlled chaotic microwave generation under the conditions of four-wave parametric interaction of the surface spin waves has been experimentally studied in active resonance rings based on tangentially magnetized ferromagnetic films. It is shown that the chaotic microwave signal parameters can be effectively controlled.     

Generator of chaotic microwave oscillations based on a high-power bipolar transistor

A chaotic microwave autooscillatory system has been designed, implemented on a high-power bipolar transistor (2T 982 A-2), and studied. The experiments showed stable generation of chaotic oscillations in a 5.26?C5.44 GHz range with a spectral power density of 1.3 × 10^?3 W/MHz.     

Chaotic millimeter-wave generation on the basis of wideband gyro-amplifiers with a helical corrugated waveguide

The possibility of generating random noiselike radiation in gyro-amplifiers with a helical corrugated waveguide when introducing delayed feedback has been shown. The cyclotron resonance detuning corresponding to the maximum slope of the amplitude characteristic of an amplifier after saturation is optimal for implementing the mode of developed dynamic chaos. Assessments are carried out for the parameters of a noise generator based on an experimentally implemented gyro-travelling-wave tube of 35-GHz band, according to which the generation of multifrequency radiation is possible with a spectrum width of 3—4 GHz, an average power up to 70 kW, and an efficiency of order of 10%.     

A note on the amplitude modulation of symmetric regularized long-wave equation with quartic nonlinearity

We study the amplitude modulation of a symmetric regularized long-wave equation with quartic nonlinearity through the use of the reductive perturbation method by introducing a new set of slow variables. The nonlinear Schr?dinger (NLS) equation with seventh order nonlinearity is obtained as the evolution equation for the lowest order term in the perturbation expansion. It is also shown that the NLS equation with seventh order nonlinearity assumes an envelope type of solitary wave solution.     

Power delay profile modelling of the ultra wideband off-body propagation channel

This study presents a statistical power delay profile (PDP) model for the evaluation and design of ultra wideband (UWB) off-body communication systems. The analysis is based on extensive real-body measurements carried out in the frequency range between 3.5 and 6.5 GHz. Due to the dependence of the radio propagation channel on the body region (i.e. front, side and back), we gradually develop separate stochastic tapped-delay-line models for each body region. Based on the newly estimated parameters, channel simulation methods are provided for each of the proposed models. Finally, several comparisons between the empirical data and the simulations results are presented, by means of key properties of the recorded PDP profiles.     

The influence of vacuum conditions on the microwave generation in a vircator

The effect of residual gases on the lifetime of a virtual cathode (VC) was studied. Dependence of the output pulse energy of a high-power vircator on the vacuum conditions was studied. It is demonstrated that a rough vacuum of 5×10^?4 Torr achieved with a mechanical pump is sufficient for a vircator operation without significant loss of the output radiation energy. The experimental data agree with a model of the mechanism of VC degradation as a result of the gas ionization.     

Effect of positive ions on the microwave generation in a low-voltage vircator

The effect of vacuum conditions on the characteristics of microwave generation in a nonrelativistic electron beam with a virtual cathode (VC) formed in a retarding field (low-voltage vircator) has been experimentally studied. The ionization of residual gases in the working chamber of a low-voltage vircator leads to displacement of the VC out of the interaction space, which results in breakdown of the microwave generation. The experimental data agree with the results of numerical simulations.     

Localization of an object in tissue with phase modulation spectroscopy: Reduction of the effects of the relative amplitude and phase on amplitude cancellation

Abstract

In this paper, we discuss the effects of various factors on the localization of an object with amplitude cancellation phase modulation spectroscopy (PMS) by an analytical method. The factors include the relative modulation phase and the amplitude between two sources, the absorption coefficient and the size of the localized absorber. A localization method that can reduce the effects of the relative modulation amplitude and phase between two sources on measurement is presented. In the new method, two measurements are carried out, where modulation signals of two sources in the second measurement are exchanged relative to those in the first measurement. The principle and the feasibility of the method are shown theoretically. Primary experimental results are presented.     

Ultralow-voltage generator of chaotic microwave oscillations on counterpropagating electron beams

Technical Physics Letters - The new scheme of an ultralow-voltage generator of broadband chaotic microwave oscillations is considered, which operates on counterpropagating turbulent electron beams....     

A microwave photonic generator of chaotic and noise signals

The transition to chaos in a microwave photonic generator has been experimentally studied for the first time, and the generated broadband chaotic microwave signal has been analyzed. The generator represented a ring circuit with the microwave tract containing a low-pass filter and a microwave amplifier. The optical tract comprised a fiber delay line. The possibility of generating chaotic oscillations with uniform spectral power density in a 3–8 GHz range is demonstrated.     

Group delay equalised monolithic microwave integrated circuit amplifier for ultra-wideband based on right/left-handed transmission line design approach

A group delay equalised InGaP/GaAs HBT monolithic microwave integrated circuit (MMIC) amplifier with an active balun for ultra-wideband (UWB) application has been developed. The MMIC consists of a broadband amplifier with an active balun and a group delay equaliser. The group delay equaliser was designed based on a theory using a composite right/left-handed (CRLH) transmission line. Adding a right-handed (RH) transmission line to a CRLH transmission line in parallel, a convex group delay characteristic is realised. Since various UWB components have concave group delay characteristics, the group delay equaliser can compensate a concave group delay characteristic of the amplifier in an operation frequency band. In this paper, dispersion, group delay and impedance characteristics for the proposed CRLH/RH circuit have been theoretically analysed. Moreover, a minimised group delay equaliser circuit on an MMIC has been designed and fabricated based on the proposed CRLH/RH circuit. A fabricated group delay equalised InGaP/GaAs HBT MMIC amplifier with an active balun exhibited an improved group delay characteristic compared with the MMIC amplifier without the group delay equaliser. The standard deviations of group delays for a frequency variation in a gain band were decreased from 12.8 to 5.5 ps at S₂₁ and decreased from 10.3 to 7.3 ps at S₃₁.     

Effects of Fourier-plane amplitude and phase errors on image reconstruction. I. Small amplitude errors

The effects of Fourier-plane, or spectral, amplitude and phase errors on reconstructed images are studied in terms of the expected mean square error in the image. The relationship between the variance of amplitude and phase errors and the expected mean square error is derived for small amplitude errors and arbitrarily large phase errors. This allows "equivalent" amplitude and phase errors to be defined. The effects of large amplitude errors are discussed in general terms. Simulations are used to verify these relationships, and the effects of spectral amplitude and phase errors on reconstructed images are compared.