Resonance in open coaxial cylindrical resonators

A study of the electrodynamical properties of open coaxial cylindrical resonators using a partially conical inner rod is made along with experimental verification. On the basis of a geometrical criterion for the occurrence of high-Q resonances, it turns out to be possible to discriminate certain classes of TE modes by keeping to a minimum value their diffrationQ factors. In particular, for an especially designed cavity only TE_0.2 and TE_1.3 modes appear to have strong resonance in the 6 · 14GH _z range as a result of the action of the coaxial insert.     

Theory of gyrotrons with coaxial resonators

In the development of powerful gyrotrons capable of long-pulse or continuous wave operation the cardinal problem is to provide stable, single-mode highly efficient operation at the desired mode with an acceptable level of ohmic losses in the resonator walls. In the present paper the selective properties of various coaxial resonators as well as ohmic losses of the microwave power in outer and inner conductors are considered. The start-up scenario in powerful gyrotrons is discussed. The results of numerical simulations of a 1 MW, 280-GHz coaxial gyrotron are presented which demonstrate that successive excitation of a number of modes during the voltage rise may not hinder the stable operation of the desired mode on the top of the voltage pulse. An electronic efficiency of 48% is predicted     

Propagation and radiation properties of corrugated cylindrical coaxial waveguides

A theoretical study is given for the behavior of cylindrical coaxial waveguides having reactive (corrugated) surfaces. After a general analysis assuming independent values for the surface reactances, the propagation and radiation properties for specific surfaces are considered. These include the case where 1) both surfaces are smooth-walled; 2) one surface is smooth-walled with the other corrugated; and 3) both surfaces are corrugated such that they have equal values for the surface reactance.     

Theory and experiment of dual-mode microstrip triangular patch resonators and filters

In this paper, we report on the results of an investigation into dual-mode operation of microstrip triangular patch resonators and their applications for designing dual-mode bandpass filters. It has been found theoretically that the dual modes can result from the rotation and superposition of a fundamental mode. The characteristics of the dual modes and their mode splitting are described. The applications of this new type of dual-mode microstrip patch resonator in the design of microwave planar filter are presented. A circuit model for operation of this type of filter is proposed. Two- and four-pole filters of this type are demonstrated for the first time. Both theoretical and experimental results are presented.     

Theory and experiment of a coaxial probe fed hemisphericaldielectric resonator antenna

A hemispherical dielectric resonator antenna fed by a coaxial probe is studied both theoretically and experimentally. The Green's function for the evaluation of the input impedance is derived rigorously and expressed in a form convenient for numerical computations. The method of moments is used to obtain the probe current from which the input impedance of the DR antenna is calculated. Both delta gap and magnetic frill source models are considered. Moreover, the results using a reduced kernel as well as the exact kernel are presented. Both entire basis (EB) and piecewise sinusoidal (PWS) expansion modes are used and the results are compared. The effects of the probe length, feed position, and dielectric constant on the input impedance are discussed. Finally, the theoretical radiation patterns for the first three resonant modes (TE₁₁₁, TM₁₀₁, and TE₂₂₁) of the DR antenna are presented     

Axisymmetric modes of cylindrical resonators with cascadedinhomogeneous dielectrics

A generic numerical scheme is developed to calculate the resonant frequency of axisymmetric modes in an inhomogeneous cylindrical dielectric resonator. The resonator consists of sections of cylindrically stratified dielectrics within a cylindrical waveguide. In each section, the TM_0m and TE_0m waveguide modes are solved by expanding the H_φ and E_φ components in terms of the eigenmodes in an empty waveguide. The fields in each section are then expanded in terms of these TM_0m and TE_0m modes. The transverse resonance technique is then applied to obtain the resonant frequencies. Comparison with literatures validates the effectiveness of this approach. Results with continuous dielectric profiles are also obtained     

A novel numerical synthetic technique for determination of the TMon dispersion relation in a coaxial corrugated cylindrical waveguide

A novel, highly accurate numerical synthetic technique for determining the complete dispersive characteristics of electromagnetic modes in a spatially periodic structure is presented. The numerical method based on the coupling of the finite difference method in time domain with the discrete fourier transform is applied to calculate the eigenfrequencies and eigenfield distribution of a resonant cavity which is an appropriately shorted periodic slow wave circuit of N periods at both ends. The analytical synthetic technique, which is based on the intrinsic characteristic of spatially periodic structure, is used to derive the complete dispersion relation using the numerically measured resonances. The method was successfully applied for the case of TM_on modes in a coaxial corrugated waveguide and is applicable to slow wave structures of arbitrary geometry.     

Ohmic selection in open coaxial resonators: An experimental study

A study of ohmic selective properties of open coaxial cylindrical resonators has been conducted experimentally and compared with theory. The resonator consists of an inner cylinder made of silicon carbide symmetrically located inside an outer cylindrical, tube shaped waveguide. Several fundamental TE modes were identified over the range 9 to 17 GHz through measurements of the resonant frequencies and the associated quality factors. Mode discrimination is achieved both by exploring selective ohmic effects and examining the electrodynamical properties of the coaxial cylindrical waveguide. The effectiveness of a silicon carbide coaxial insert in providing ohmic mode selection is demonstrated in that the totalQ factors of TE _mp modes with radial indexp≥2 become well below the quality factors for surface TE _m1 modes. It has been verified that both structure and number of resonant modes are strongly dependent on the diameter and the resistivity of the coaxial insert.     

Azimuthal selection of modes in free-electron masers with coaxial Bragg resonators

A comparative analysis of the selective characteristics of Bragg resonators with various types of periodic corrugation is performed. In the simplest case of the azimuthal symmetric corrugation in a highly overmoded resonator (a large ratio of the perimeter to the wavelength), the Q factors of modes with different numbers of azimuthal variations are almost equal and the mode frequencies are close on the scale of the gain band of electron flow. A certain rarefaction of the mode spectrum can be attained using the helical corrugation when the traveling wave is coupled with the whispering-gallery modes and the frequency interval between the high-Q modes of the resonator with different azimuthal indices is determined by the interval between the critical frequencies of the whispering-gallery modes. The doubly periodic corrugation employed in the 2D Bragg resonators at the same (as in the case of the helical corrugation) intermode distance allows the Q-factor selection of a single azimuthal symmetric mode. The analysis is based on the method of coupled waves and the direct numerical simulation using standard codes.     

Bandpass filter with an ultra-wide stopband designed on miniaturized coaxial resonators

Characteristics of a new miniaturized coaxial resonator are theoretically investigated. It is shown that the first resonant frequency of the resonator can be significantly lowered relative to the second one and the resonator dimensions can be considerably decreased as compared to those of a traditional dielectric-filled quarter-wavelength coaxial resonator. Based on the investigated resonator, a fourth-order bandpass filter has been designed and fabricated. The filter stopband at a level of no worse than ?90 dB extends to the frequency that exceeds the passband center frequency by a factor of 47. Calculated frequency responses are in good agreement with those measured on the fabricated filter prototypes.     

Electric, magnetic and open-wall cylindrical gyromagnetic resonators

Half wavelength, axially magnetised, ferrite filled, cylindrical cavities with electric, magnetic or open side walls all exhibit hybrid dominant modes with split radial wavenumbers. The geometrical dependence of the frequency splitting is studied for each case under the same magnetic conditions.<>     

Theory of Fabry-Perot resonators with dielectric medium

A Fabry-Perot resonator filled with a dielectric slab is investigated using the Vainshtein method. Simple and explicit formulas are obtained for the diffraction loss, phase shift, and field distributions for both strip and circular mirrors. It is found that the presence of the dielectric reduces the diffraction loss, and causes mode confinement to certain degrees.     

Measurement of RCS of cylindrical and rectangular dielectric resonators

The results of the precise measurement of the RCS of dielectric bodies of cylindrical and rectangular shape at the resonance frequencies are reported. The measured results are compared with those predicted by the asymptotic theory of Van Bladel (1975).<>     

Modeling of cylindrical dielectric resonators in rectangularwaveguides and cavities

The mode matching method is used to accurately model a generalized cylindrical dielectric resonator structure in a rectangular waveguide or cavity. The field distributions of different modes in cavities are given. The resonant frequencies of the cavities are calculated and compared to the measured data, showing very good agreement. The resonator structure can be a dielectric disk resonator, a ring resonator, a dielectric resonator with support, etc. This structure can be used in filter design as the basic element, providing very good mechanical stability. The slot coupling between cavities is also analyzed, showing some interesting results     

Resonant modes in shielded cylindrical ferrite and single-crystaldielectric resonators

The Galerkin-Rayleigh-Ritz method is applied for computing the first few lowest resonant frequencies of cylindrical anisotropic resonators in a cylindrical cavity. The resonators are allowed to have gyromagnetic and uniaxial dielectric anisotropy with respect to the z-axis of the cylinder. Results of computations of the resonant frequencies are compared to exact solutions for many simple resonant structures and to results of experiments for more complicated structures, with good agreement. A new method of measuring permeability tensor components is presented. The method utilizes two parallel-plate cylindrical resonators operating in the HE⁺-/₁₁₁ and H₀₁₁ modes. A method of measuring the permittivity tensor components of single crystals using one parallel-plate cylindrical resonator operating in two different modes is proposed     

Aperture coupling to a coaxial air line: theory and experiment

Coupling through a circular aperture in the shield of a coaxial air line is studied theoretically and experimentally. Polarizability theory is used to compute the effective dipole moments that excite the coaxial line in the internal region. Measurements of shielding effectiveness were made in a reverberation chamber over wide frequency ranges. Agreement between theory and measurements is generally within ±10 dB. Recommendations for improvements in the measurements and theory are made for achieving the closer agreement that would be desirable for an artifact standard for shielding effectiveness measurements     

Resonant frequencies and quality factors in lossy NRD cylindrical resonators

In this paper the fundamental effects of losses on resonant parameters (frequencies and quality factors) are analyzed for circular-cylindrical dielectric resonators inserted between metal plates, in the configuration also called NRD (Non-Radiative Dielectric). Power dissipations are considered both in the dielectric and in the conductors. Complex resonant frequencies and closed-form expressions for the relevant quality factors are derived rigorously for arbitrary resonant modes, even without circular symmetry. Numerical results are presented and discussed, making also use of experimental data obtained by means of a suitable NRD set-up. The present analysis accurately provides the basic information for a more realistic design of up-to-date millimeter-wave frequency-selective devices in NRD circuitry.     

Theory and analysis of leaky coaxial cables with periodic slots

Frequency band and coupling loss are the two important parameters of leaky coaxial cables with periodic slots. The frequency band can be predicted by analyzing the arrangement of the slots on the outer shield of the cable, but the coupling loss is not so easy to determine by classical methods. In this paper, the finite-difference time-domain (FDTD) method is used to calculate the electric field distribution in the slot cut in the outer conductor of the coaxial cable. The dyadic Green's function is then used to calculate the radiation field of the equivalent surface magnetic current densities. By these two methods, the coupling losses of the leaky coaxial cables with different periods, sizes and shapes of the slots can be accurately obtained. Some results in this paper were verified by the experimental results of leaky coaxial cables designed for railway mobile communications with a frequency band of 100-500 MHz     

The coaxial collinear antenna: Current distribution from the cylindrical antenna equation

A theoretical model and computer simulations of the current on the coaxial collinear (COCO) antenna are presented. Comparisons between numerical results and measurements are made for 24- and 26-element COCO antennas at 50 MHz and for six- and eight-element COCO antennas at 915 MHz. The results show reasonable agreement between first-order theory and measurements.