N. Popenko

Broadband omnidirectional circular patch antenna

This paper presents an omnidirectional microstrip circular patch antenna with conical radiation pattern. Geometric parameters of the antenna such as metal disk radius, thickness and permittivity of the substrate have been selected on the basis of theoretical predictions. It has allowed us to provide a desirable resonant TM/sub 01/ mode excitation. The results have shown that the antenna of this kind with VSWR/spl les/2 and bandwidth of 18% has a conical radiation pattern oriented 36/spl deg/ to the zenith. The antenna also has a level of side radiation as well as a cross-component level less than -25 dB. The radiation pattern width and the direction of maximum radiation change within the working frequency band of 17% and 40%, respectively. This antenna can be successfully applied for mobile system, wireless indoor communications, etc.

Compact broad-band SHF direction finder for WiMax applications

The original design of the compact broad-band direction finder is presented in this paper. Unusual arrangement of the cylindrical monopole antenna as a sub-reflector of the reflector-type antenna gives new opportunities to the direction finder systems. The results of model experiments demonstrate the high spatial resolution and sensitivity of the proposed direction finder.

Size effect of the ground plane and axial coupling aperture on the monopole antenna performance

Our systematic and detailed investigations of the X-band cylindrical monopole antennas allowed us to clarify the physical nature of oscillating dependencies of antenna characteristics such as the resonance frequency, elevation angle, and gain for the quarter-wavelength monopole. For the first time we have demonstrated the role of the finite ground plane and the axial coupling aperture on the cylindrical monopole antennas performance. In contrast to the quarter-wavelength monopole the radiation of the grounded three quarter-wavelength monopole is formed at the angle near zenith thereby diminishing the edge effects. The optimal radii of the axial coupling aperture providing the maximum antenna efficiency have been determined for all the AUTs. Furthermore, it has been shown that the axial coupling aperture radius variation is accompanied by the resonance frequency shift of the antenna. The quarter-wavelength monopole antenna with the best characteristics and permissible minimal ground plane radius R=λ/4 demonstrating the mono-beam radiation pattern, −10dB impedance bandwidth of 1.6GHz, and the gain G=4dBi has been presented.

Wide-angle antenna array with the novel radiating element

In this paper the results of computational modeling of the antenna array with a wide beam steering and the experimental investigations of the individual radiator characteristics are presented. The characteristics of the compact radiator prototype as the open-ended waveguide with a dielectric insertion comprising a special exciting pin are analyzed. The novel radiator has the wide beamwidth and the frequency band around 21%. Following the computational modeling the characteristics of antenna array for scan angles up to 50deg are discussed.

Waveguide antenna with a hybrid dielectric insertion

In this paper, the aperture X-band antenna with a hybrid dielectric insertion has been proposed. It is shown that the use of cylinders with different permittivities inside the dielectric matrix and a specific topology in their location gives rise to the significant extension of the operational frequency band up to 2.3GHz and varying the elevation angle of peak directivity in the H-plane.

Features of spin dynamics in HgCrCdSe and HgCrSe crystals in the vicinity of phase transitions

The inhomogeneously broadened EPR lines of the solid solutions Hg1–x–yCrxCdySe and Hg1–xCrxSe are represented in the form of spin packets and their temperature evolution is analyzed upon the transition of the crystals to ferromagnetic ordering. In this case, the spin packets being introduced into the consideration are identified with allowed transitions of the localized electrons and with the delocalized electrons. It is established that a characteristic feature of the subsystem of delocalized electrons is the anomalous behavior of the g-factor in the vicinity of the transition to the ferromagnetic state. The introduced spin subsystems, which characterize the localized and delocalized electronic states, allow for explaining the differences in scenarios of the transition to magnetic ordering of crystals with different cluster structures. Just significantly lower concentration of clusters in the HgCrSe crystal leads to a slowing down of flip-flop processes that explains the longer relaxation times of spin p...

X-band resonator for studying the various axially symmetric inhomogeneities in the frequency band

The problem related to the choice of an adequate microwave resonator for measuring the dielectric constant of substances with the high permittivity and losses is considered. Numerical modeling and experimental investigations of a rectangular X-band resonator with the axially symmetric inhomogeneities, such as a dielectric cylinder and the dielectric capillary filled with the solutions, which have the different dielectric permittivity, are carried out. Both optimal sample sizes depending on their dielectric permittivity and the geometric parameters of dielectric capillaries for studying the various liquids are determined.

Definition permittivity of weakly concentrated solutions in the microwave range

In this paper a modification of the well-known method of resonance dielectrometry is proposed with the aim to define a real part of the permittivity of weakly concentrated solutions in the microwave frequency band. By using the results of numerical simulations, the optimized electrodynamical module has been fabricated and tested. The experimental verification of the proposed method points out the high sensitivity and accuracy of measurements.

Original Ka-band fractional spiral antennas

The original fractional

Numerical modeling the resonance X-band structures with local inhomogeneities inside

-shape spiral antenna being fed from the Ka-band metal waveguide is proposed. The impedance bandwidth of such an antenna is 6.7GHz. Herewith, the axial ration does not exceed 3dB level within the limits of 34.2 - 37 GHz. The radiation pattern of such an antenna is similar to the monopole antenna with zero-radiation intensity in the antenna axis and with an elevation angle of peak directivity equal to about θ=20°. It is important, that the radiation pattern shape does not undergo any visible deformations through the operational frequency band. The use of near-field technology allows for explaining the basic reasons of the axial ratio changing through the antenna bandwidth. The proposed antenna seems to be very attractive for various practical applications in the millimeter range.