The consideration of electromagnetic wave propagation in open irregular waveguiding structures usually assumes either smooth varying of medium parameters or their rigorously periodical perturbation. Combination of smooth and oscillated parameter perturbations leads to additional peculiarities of Bragg scattering. Anisotropy of parameters causes coupling of waves with different polarization. In the present paper using complex form of asymptotic method of Krylov, Bogoliubov and Mitropolsky (KBM), mutual transformation of waves in open guided structures in the form of an impedance rod with spatially oscillated surface impedance has been theoretically considered. Influence of exiting of surface waves propagating along the impedance rod on scattering wave beams has been analyzed. For some types of perturbations the solutions of coupled-wave equations of KBM method have been obtained and expressions for perturbed wavenumbers of eigenwaves have been derived. In general case the differential equations with slowly varying coefficients are rather easily integrated by a numerical method. Longitudinal distributions of wave complex amplitudes describe combination of different physical phenomena in examined structure.
Powerful sources of coherent radiation in the sub-terahertz to terahertz frequency range are required for expanding number of applications in the physical research and in various advanced high power THz technologies. In recent years, a spectacular progress in the development of various gyro-devices and in particular, the powerful high frequency (sub-terahertz to terahertz) gyrotron oscillators has demonstrated a remarkable potential for bridging the so-called terahertz power gap and stimulated many novel and prospective applications. In this paper, we outline two series of such gyro-devices, namely the Gyrotron FU Series which includes pulsed gyrotrons and Gyrotron FU CW Series which consist of CW (continuous wave) or long pulse gurotrons. Both series are developed at Research Center for Development of Far Infrared Region, University of Fukui (FIR FU). We present the most remarkable achievements of these devices and illustrate their applications by some characteristic examples. An outlook for the further extension of the Gyrotron FU CW Series is also provided.
A radar sensor as part of the automatic shunting system has been developed for the remote control of track occupancy in the hump yard and railroad switch territories, enhanced by the speed control of rolling stock when it passes by the retarder. The sensors are equipped with systems of remote control. They are provided with systems of internal parameter diagnostics and transmission of the radar and service information to the control point and can work in information networks.
Studying of thermal balance of terrestrial atmosphere is substantially connected with results of measurements of tropospheric and stratospheric temperature profile. Now in the Russian Federation the system of quasi continuous monitoring of thermodynamic characteristics of atmosphere is carried out thanks to discrete start-up of radiosondes, their top working border seldom reaches stratospheric heights. However, continuous aerologic sounding may be realized by means of the remote methods using microwave atmosphere thermal radiation. Particularly, presence of strong lines and band of molecular oxygen in the atmospheric millimeter wave radiation spectrum make it possible to use them for thermal sounding from ground up to stratopause. For measurement of troposphere temperature profile in Institute of Applied Physics Russian Academy of Sciences 8-channel spectroradiometer is developed. It operates in a frequency range of 50-55 GHz which corresponds to a low-frequency slope of a 5-millimeter wave-band of molecular oxygen spectrum. The device represents heterodyne receiver with low-noise HEMT front end amplifier (LNA). The amplifier has in a working wave-band a gain about of 16 dB and a noise figure no more than 4 dB. The following LNA Shottky diode mixer works on the first harmonic of a local oscillator signal (fLO = 48 GHz) and converts RF input signal to the 2 - 7 GHz intermediate frequency band (IF). Conversion loss of the mixer is 8-10 dB. Local oscillator signal (48 GHz) is formed by means of a signal synthesizer (8 GHz) having output power of 50 mW by multipliers and band-pass filters circuit. Power level of local oscillator signal 48 GHz on a mixer input is not less than 10 mW with suppression of harmful frequencies not less than 50 dB.
We develop the analytical solution to the problem concerning the plane wave scattering from a double-periodic gyrotropic layer in quasi-static case, i.e. if the structure periods are much smaller than the wavelength and the field remains approximately constant over the period. Using the solution [1], obtained by the Method of Integral Functionals based on the rigorous integral-differential equations [2] we drived the analytical expressions for the scattered fields in the single-mode approximation, i.e. by retaining only the zero diffraction orders in the full-wave Floquet expansions.
Open dielectric resonators (DRs) as disk and ball with whispering gallery modes (WGMs) have well known advantages such as a high value of Q-factor in millimeter band of wavelength. However they have disadvantages when used in specific devices and appliances. 1. The open nature of the dielectric resonator is a source of electromagnetic noise interference. The shielding of DRs is the main method of combating such injurious electromagnetic effects. However, the shielding causes a significant concentration of the oscillation spectrum. At the same time the so-called ray modes can be excited in the shielded DRs with the WGMs. 2. It is known that the use of local elements of excitation placed in the resonator field is the most effective method for excitation of the WGMs in the DRs. However, in this case, the Q-factor is decreased due to high radiation losses at the local element of mode excitation. The solution of these two problems is the aim of this work.
Currently, the development of new methods for estimating the parameters statistically rough surfaces is an important task: in engineering, the manufacture of products at different stages of technological process, as well as in any industry where the need to control surface finishes. In the proposed work the two methods to estimate the parameters of a statistically rough surfaces. The first is to evaluate the two-dimensional correlation function of rough surfaces calculated by speckle interferometric images formed by reflected coherent radiation. In the second method, based on the analysis of the speckle pattern with both diffuse and specular registered component.
Design of efficient electrically small antennas is very important for miniaturization of radio communication devices. However besides some technical difficulties there is a fundamental problem: an antenna with the size much smaller than the wavelength cannot radiate efficiently. As a result for an antenna there exists a lower cut-off frequency fc. For frequencies f <; fc an antenna cannot radiate and all the fed energy is reflected back to the generator. The cut-off frequency fc depends on the size of an antenna, so the problem of miniaturization can be considered: for given size to design the antenna with the lowest possible cut-off frequency. From this point of view we are going to consider one of the simplest antenna geometries based on irregular biconical line with dielectric filling.
According to the approach based on the use of unsaturated transistor regime, the concept of low-noise amplifier on commercially available PHEMTs is proposed. It has been found that the power consumption of a few microwatts can be achieved at frequencies of hundreds MHz. The power consumption as low as about 3 microwatts for two-stage amplifier (20 dB gain) was obtained at 300 mK ambient temperature. This is at least an order of magnitude better than the figures known up to date. It is conclude that the GaAs PHEMT and relevant circuitry are an adequate electronics for the ultra-low-temperature readout amplifiers, especially for multi-canal cryoelectronics (such as bolometer arrays, SIS matrixes etc.), when the power consumption budget is critical requirement for the system.
When you create a radiometer to a fixed frequency band the mixing module, in which the radiation of signal and of local oscillator (LO) arrive at the non-linear element from both directions is preferable [1]. The filters may be installed from the side of LO and the side of antenna in such mixer module [2]. Filters have several functions The first filter transmits radiation LO to the nonlinear element and works as a matching backshort of signal, as well as rejects noise of LO in the frequency band of signal. The second filter transmits signal to the non-linear element and functions as a LO matching backshort, as well as stops the LO radiation.
In the field of terahertz technologies (ν ~ 0.1 - 10 THz), much attention is paid to the design of uncooled efficient detectors, because of their potential importance for numerous applications in vision systems, spectroscopy, medicine, security, etc. The new generation of multielement focal plane arrays (FPA) will enable real-time imaging, increase an information capacity of the video system, reduce the scanning time and increase the reliability of the video system by eliminating mechanical scanning components. Silicon CMOS field-effect transistor FPA are one of the most promising elements for integrated imaging system design, due to the possibility of integral implementation of THz detection system with the matrix of readout integrated circuits (ROICs). It is desirable to use planar antennas due to their low cost and ease of manufacture. For imaging system, the sensitivity of elements in the array should be uniform, so the gain and the input impedance should be the same for all elements. One of the problems in the design of CMOS multi-element detectors based on FET is the heterogeneity of the element characteristics in matrix or linear arrays, even for small array with rather identical FET properties. As it might be expected for the finite-size substrate with high dielectric permittivity (ε Si ≈12), every antenna gain depends on the element position on the substrate. In the present work, we perform numerical simulation of the linear array of eight elements with modified bow-tie antennas on a finite-size substrate.
Summary form only given. Within the wider terahertz (THz) frequency range (ca. 0.1 to 10 THz), the sub-millimetre wave frequency band (between 0.3 and 3 THz) is still considered to be a largely unexplored part of the electromagnetic spectrum. This `THz Gap', between conventional electronics and photonics, offers the real potential for both scientific and commercial exploitation. However, while the majority of THz groups focus on the former, it is the latter that offers the key to bridge the THz Gap to ubiquitous applications. To this end, new engineering solutions are needed in modelling (mathematical & numerical), design (synthesis & analysis) and fabrications (precision & volume production). As ubiquitous THz applications emerge, the costs of associated passive components, active devices and metrology will fall, creating a positive spiral of growth in all areas; enhancing our modern day living and with the prospect of a huge societal and economic impact.
Automated analyzers, based on six-port reflectometers (SPR), are widely used for measuring the parameters of the microwave devices. In the measurement transducer of SPR the matched multiport passive microwave connection is used for the complex composition of the reference wave generator and the wave reflected from the object. In this case the parameters of the measurement system are found by preliminary calibration using at least four standards of the complex reflection coefficient (RC).
Thus, microwave surface impedance measurements of Fe-pnictide superconductors allow accurate finding reactive and real part of complex conductivity of these materials despite of their small dimensions. At present, microwave measurements do not disturb consensus regarding the wave symmetry in all studied Fe-based superconductors. In turns, the complex conductivity makes it possible to find the temperature dependence of not only the penetration depth, but also quasiparticle conductivity and the rate of quasiparticle scattering. Here we obtain a chance to find the absolute value of the rate. Obviously, we will have a lot of work in this direction in a wide range of lengths of electromagnetic waves. In addition, the complex conductivity of the pnictides in temperature range above Tc is of undoubted interest too.
Ozone is one of the most important minor gas constituents of the atmosphere. Global depletion of the protective ozone layer in the last decades accompanied with such anomalous events as ozone holes in Antarctic and Arctic [1, 2] requires reliable long-term monitoring of ozone and ozone-related minor atmospheric gases from both satellites and ground level. Ground-based millimeter-wave (MMW) monitoring of atmospheric ozone is low-dependent on weather conditions, covers broad altitude region from the lower stratosphere to mesosphere, and is possible in day and night time [3, 4]. These features of MMW measurements provide their advantages over traditional optical methods (UV spectrometers and lidars) and ozone sondes.
Modern high power gyrotron is capable to generate RF radiation of a power up to (1-1.5) MW with total efficiency of (45-60)% at a frequency range of (30-170) GHz in quasi-CW regime providing pulse duration up to 1000 s. These unique parameters can be achieved first of all due to effective interaction of stable helical electron beam transported through oversized cylindrical resonator in a strong magnetic field and adequate cooling of all heated surfaces inside tube. Gyrotron is rigged with such important components as depressed collector, high-efficient built-in quasi-optical converter of high-order operating resonator mode into paraxial wave beam, and output window with disc of CVD diamond. All these elements aimed to decrease power dissipation inside tube, and thus make long pulse/CW/1MW operation of gyrotron reliable enough.
The conventional approach to characterisation of the wave phenomena in metamaterials (MMs) is based upon the approximation of homogenised medium. When MMs are composed of the arrays of resonant scattering elements, with their sizes much smaller than the wavelength of the propagating electromagnetic wave, MMs can be described by the effective constitutive parameters of an equivalent continuous medium. Although a number of the homogenisation procedures have been proposed for the effective linear parameters of MM such as the effective permittivity and permeability, their physical meaning and applicability limits are still debated in the literature. In this paper, we present the results of the theoretical and experimental study of transmission spectra of electromagnetic waves propagating through a finite periodic layered structure, composed of the ferrite and semiconductor layers, which is subjected to external magnetic bias. We consider both fine-layered structure and that with the thickness of the layers being of the same order of magnitude as the length of incident electromagnetic wave. The aim of the presented work is to consider new types of waves formed in the area of transfer between photonic crystal (PC) and homogenized medium. Using results of theoretical and experimental investigations we compare the theoretical model outcomes with the real processes and define the conditions of applicability of the theory.
The paper presents the results of upgrading and description a two-wavelength “unambiguous” microwave interferometer for line integrated electron density measurements at the “COMPASS” tokamak. The probing signals in the frequency range of 131 and 133 GHz are generated by IMPATT diode oscillators. Double conversion heterodyne receivers are used for detection. Use of each oscillator is twofold: as a source for the probing signals and as a local oscillator for heterodyne detection. The plasma is probed with two separate waves of different wavelengths traveling along identical paths to meet each other. Each probing beam experiences a different phase shift φ 1 and φ 2 and the “unambiguous” interferometer determines the difference φ 1 -φ 2 . The phase measurement is realized by using the 3 pieces of phase detectors based on pairs of phase/gain evaluation boards (AD8302). Application of the phase detectors provides information on the average plasma concentration in real time and restore the values of plasma density in the case of phase jumps by an amount > 2π.
This article presents “Compass” TOKAMAK microwave diagnostics calibration and results accuracy enhancing experiment methodology. Main subject is microwave diagnostic system phase measurements description. Additional interest is mistakes, attendant to phase measurement. Emphasis is put on phase detectors measurements mistakes correction methodology; two different phase meter configurations are described. Phase detectors, based on AD8302 CPLD, results processing methodology are presented.
The authors perform a comparison between the accuracy of two numerical techniques those permit solving the direct Dirichlet boundary value problem in the 2D electrical impedance equation. The first technique is a variation of the Finite Element Method (FEM) for elliptic partial differential equations, whereas the second is a new technique based on the modern pseudoanalytic function theory.
