Using the modified algorithm for calculating the ambiguity function, we consider the method of estimation of the mutual time delay of wideband signals, which are recorded by multiposition systems for determining the radiation-source location with the help of the space segment. It is based on the extraction of narrowband channels from the received signals and their further optimal quasi-coherent processing

We consider the model of a mixture of probability distributions for background and target samples in the problem of extracting a signal from radiophysical sounding under conditions of a priori nonparametric uncertainty. Based on the study of this model, approaches relying on the risk function and selection of anomalous readouts in the sample are proposed for detection and extraction of a continuous

We discuss the relationship between the electron temperature and the potential of the body of an artificial Earth satellite in the upper ionosphere. The formula for the spacecraft potential is analyzed, and the limitations of the theoretical representation are shown. The experimental results obtained within the framework of the Sura—DEMETER and Sura—SWARM programs are considered and serve as the basis

We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar (Tromsø, Norway) during modification of the high-latitude ionosphere in the magnetic zenith direction by high-frequency radio waves of the EISCAT/Heating facility (Tromsø, Norway). The measurements were performed during two experiment campaigns in

We perform mathematical modeling of diffraction of plane electromagnetic waves by multilayer metasurfaces comprised by elements of graphene nanoribbons. The modeling is based on solving the three-dimensional boundary value diffraction problem by three methods, specifically, those of self-contained units with Floquet channels, the volume integro-differential equation, and approximate boundary conditions

We consider the characteristics of radio-signal detection using the nonlinear decision function of a threshold device. This work is aimed at estimating the influence of the difference between the nonlinear decision function of the receiver threshold device and the step function on the characteristics of detecting radio signals with a random initial phase and random initial phase and amplitude. New

The efficiency of the previously developed algorithm for predicting extreme solar flares from their geomagnetic precursors has been tested on the example of a series of class X flares recorded on September 6, 2017. Over the past few years, these events of the solar flare activity are seen as the most intense. The algorithm consists in comparing the total histograms of the normalized number of synchronization

We report on the results of studying the radio emission of the Rydberg states of atoms and molecules in the Earth’s upper atmosphere at ionospheric altitudes when the ionosphere is modified by high-power HF radio waves radiated by the Sura heating facility. Radio emission from the upper atmosphere, caused by the emission of highly excited Rydberg atoms and molecules with the principal quantum number

We propose a method for reconstruction of dynamical systems with delayed feedback, which have several hidden variables including a hidden variable with a time delay. The method is based on the original approach allowing one to significantly reduce the number of the starting guesses for a hidden variable with a delay. The method is used for reconstructing the model system of the Lang–Kobayashi equations

In this work, we study the problems of processing complex-nature signals subject to noise, which arise because of the insufficient dynamic range of these signals in the case of their digital representation. The information criteria of quantization of the complex-signal amplitude are considered. The information-analytical approach to solving the problem of coding the signal amplitudes, which is aimed

We describe the mathematical tools of the optimal estimation method for retrieval of tropospheric temperature profiles (0–10 km) from radiometric data with the desired profiles parameterized in the form of expansion over empirical orthogonal functions obtained by a singular analysis of the covariance matrix of the radiosonde measurement data. It is shown that within the framework of such an approach

We present the results of numerical simulation and comparison of characteristics of optimal spatial selection of a signal and two correlated interferences in a linear equidistant antenna array that is optimal according to the criterion of minimum standard deviation. New properties of an optimal spatial filter are revealed, namely, an additional correlation component of the interference sum at the filter

We constructed an adaptive modal rank-reduction algorithm for acoustic source localization with a vertical sensor array operating under conditions of incomplete information on the spatial variability of the waveguide propagation channel. It has been established by means of statistical modeling that the proposed estimator gives a significant advantage in the accuracy of the source position finding as

Based on the results of the experiments performed in 2005–2010 within the framework of the Sura—DEMETER program, we analyze the features of the precipitations of energetic electrons (with energies E ≈ 100 keV) from the Earth’s radiation belt. The modification of the ionospheric F2 region was conducted by means of high-power HF O-mode radio waves radiated in the CW regime. The precipitations were detected

By simulations and experiments we develop a method for generation phase locking of a Ka-band subgigawatt nonstationary relativistic backward-wave oscillator (BWO) with an external radio pulse, the duration of which is considerably greater than the pulse duration of a driven BWO. The level of input power (about 20 kW), which provided phase locking with a total spread of about 1.2 rad, is determined

The concept of Compton-type free-electron lasers (FELs) operating in short wavelength ranges with a high efficiency and power level is currently underway at the IAP RAS (Nizhny Novgorod). This concept is aimed at reducing the energy of a driving relativistic electron beam and thereby increasing the efficiency of the electron–wave interaction in FELs, as well as making the oscillator relatively compact

We demonstrate the possible implementation of the chirped pulse amplification (CPA) method, which is widely used in optics, for the microwave frequency band. This method is based on the preliminary elongation of the incident pulse in the stretcher, sequential amplification of spectral components in a wideband amplifier, and final compression in a line with negative dispersion (compressor). A circuit

The radiation-frequency locking by an external signal is experimentally studied for a megawatt gyrotron. An external signal from a magnetron is applied to the operation space of the gyrotron at a frequency of 35 GHz via a synthesized two-mirror quasioptical converter developed at the Institute of Applied Physics of the Russian Academy of Sciences. The radiation spectra are measured for both the frequency

We show that the radiation patterns of two-dimensional systems in the form of arrays depend on the duration of the emitted pulses. To study such systems, we propose to use the correlation length depending on the pulse duration and the emission direction. The obtained formula for the length of correlation in two-dimensional systems is convenient for description of distortions in the radiation patterns

We propose and study a scheme of a microwave pulse generator operating in the frequency ranges near 37 and 73 GHz, in which the electron interaction with both the (−1)st harmonic of the counterpropagating TM02 mode and the synchronous slowed-down TM01 mode is combined in a sectionalized slow-wave system with an average diameter of 2.5λ. An efficient current modulation at the input of the slow-wave

We present the results of theoretical and experimental studies of the resonant properties of a single cell of a receiving system based on cold-electron bolometers (CEBs) with a double-slot antenna and curved coplanar lines, which is intended for receiving a signal in the range 220–240 GHz with a bandwidth of 5%. The resonant properties of a CEB located on the cryostat plate with a temperature of 0

The Institute of Applied Physics of the Russian Academy of Sciences has for many years been developing sub-terahertz and terahertz large-orbit gyrotrons that permit selective oscillation at higher cyclotron harmonics than is possible in the conventional gyrotrons. Currently, experimental studies are conducted at two specialized facilities. A prototype universal sub-terahertz source for magnetic resonance

We consider the influence of an external quasi-monochromatic signal on a multimode gyrotron in the case where the signal frequency is close to the frequency of the operating mode of the gyrotron. The influence of the mode competition on the generation regime at a harmonic frequency modulation is studied. The calculations were performed for a high-power 170 GHz gyrotron developed at the Institute of

We present the results of the development and study of the field emitters for high-voltage electronic devices operating in technical vacuum. The main attention is paid to estimating the possibilities of using distributed field emitters under the conditions of intense ion bombardment.

We discuss the results of the atmospheric absorption studies on the territory of the Kara-Dag radio astronomy station in Crimea in the millimeter-wavelength transparency windows. Critical analysis of the hardware system and measurement techniques is carried out, which permits one to create a more perfect radiometric system for long-term atmospheric measurements. Connection between atmospheric absorption

The gyrotron traveling-wave tube (gyro-TWT) is a wideband version of gyrotron amplifiers, which produce pulsed or continuous-wave radiation in the millimeter-wavelength band at a power level that exceeds the powers produced by conventional TWTs with slow-wave structures and rectilinear beams by 1–2 orders of magnitude. Since 1996, researchers at the Institute of Applied Physics of the Russian Academy

We analyze the possibility to create new generation continuous-wave gyrotrons operating in the Kband (at frequencies of 28-30 GHz) at the fundamental cyclotron resonance with an output power of 25–30 kW and more. For a gyrotron with a magnetically shielded solenoid, the electron-optical and electrodynamic systems have been optimized, which ensures generation with high efficiency (about 50%) at acceptable

We have developed, manufactured, and tested a waveguide mixer in the range 211–275 GHz on the basis of the superconductor–insulator–superconductor (SIS) tunnel structures. The methods of manufacturing high-quality tunnel structures on quartz substrates have been worked out. To extend the receiver band, the Nb/AlOx/Nb and Nb/AlN/NbN tunnel junctions with a high current density of up to 20 kA/cm2 are