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Design of Circular Waveguide Annular Slot Coupled Two-layer DRA for Linear and Circular Polarizations
摘要： The design of a circular-waveguide coupled two-layer DRA configuration is presented. It is observed that besides a reduction in the layers compared to a rectangular waveguide coupled number of multilayer-DRA structure to achieve coupling and enhanced bandwidth, the current configuration significantly enhances the functionality of the design in the realization of dual-band and right-hand / left-hand circularly-polarized (RHCP / LHCP) configurations without the use of additional coupling or matching elements, which to the best of our knowledge has not been reported earlier. Radiation characteristics with low cross-pol are achieved for the linearly polarized dual-band antenna structure. For the circularly-polarized (CP) configurations, a good axial-ratio performance and a high isolation between the RHCP and LHCP fields are achieved. The computed results are obtained through a full-wave Green’s function analysis of the structure, with the thickness of the ground-plane modeled as an annular cavity.
关键词： Dielectric resonator antenna,dual-band,Green’s function,circular polarization,circular waveguide
更新于2025-09-23 15:21:01
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Electromagnetic Materials and Devices || Metal- and Dielectric-Loaded Waveguide: An Artificial Material for Tailoring the Waveguide Propagation Characteristics
摘要： In the present chapter a number of loaded structures are studied with circular cross-section to explore the deviation in their dispersion characteristics from their parent circular waveguide. The dielectric and/or metal loading to the waveguide tailors its dispersion characteristics. In general, the dielectric depresses and the metal elevates the dispersion characteristics from the characteristics of their parent circular waveguide. The axial periodicity results in periodic dispersion characteristics with a lower and an upper cut-off frequency (bandpass). However such a characteristic is not reported for the azimuthal periodic structures. The bandpass characteristic arises due to the shaping of the dispersion characteristics. Therefore the dispersion shaping is only possible with axial periodicity and not with the azimuthal periodicity. The sensitivity of the structure (geometry) parameters on the lower and upper cut-off frequencies, the extent of passband and the dispersion shaping are also included. In the axial periodic structures, the periodicity is found to be the most sensitive parameter for tailoring the dispersion characteristics and the disc-hole radius is the most sensitive parameter for shifting the dispersion characteristics over the frequency axis.
关键词： dispersion characteristics,dispersion shaping,metal and dielectric loading,disc-loaded circular waveguide,periodically loaded waveguide
更新于2025-09-23 15:21:01
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Broad-band measurements of dielectric permittivity in coaxial line using partially filled circular waveguide
摘要： The full-wave analysis was applied for a coaxial line (i.e., transmission line) that has a “short-circuited” discontinuity. The discontinuity has a radius less than or equal to the inner radius of the coaxial line. The “sample region” can be considered as a partially filled circular waveguide. Such a structure is very practical and is of particular interest for the dielectric spectroscopy applications. It takes into account the inhomogeneous field distribution, which is the limiting factor for the determination of high dielectric permittivity values at microwave frequencies. The direct problem was solved by using the mode-matching technique, and the relationship between the complex reflection coefficient and the dielectric permittivity of the cylindrical sample was obtained. By solving the inverse problem, it is possible to obtain the complex dielectric permittivity from the experimental values of the scattering matrix. The results were verified by the finite element modeling of the system and applied for particular materials. The correspondence between these approaches is excellent. This method is very suitable for the determination of permittivity, which exceeds several thousands (it is applicable for any type of material). It extends the frequency range where the permittivity can be determined reliably. There is no necessity to prepare samples with different geometries (i.e., surface area and thickness).
关键词： dielectric permittivity,coaxial line,circular waveguide,mode-matching technique,finite element modeling
更新于2025-09-23 15:21:01
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Multipactor Analysis in Circular Waveguides Excited by TM <sub/>01</sub> Mode
摘要： A series of detailed numerical simulations are used to investigate the properties of multipactor breakdown in circular waveguides propagating the TM01 mode. A Monte Carlo model is constructed to track the motion of the electrons, study the multipactor scenarios, and predict the multipactor thresholds. The theoretical and numerical analyses indicate that the product of the frequency and the gap (f· D) affects both the intensity of the ponderomotive force and its spatial distribution, which results from the nonuniformity of the radio frequency (RF) field and significantly influences the electrons’ trajectories and multipactor trends. The decrease in f· Dresults in a remarkable enhancement in the magnitude of the ponderomotive force, while the maximal intensity gradually moves toward the half radius R/2 area. Low values of f·Dcorrespond to high ponderomotive potential, which sustains the short-range electrons and triggers the single-sided multipactor. In contrast, high values of f· D correspond to low ponderomotive potential, contributing to long-range electrons and exciting the double-sided multipactor. Fitting to the susceptibility diagram produces the border line and a modified f · D threshold of (f · D)th ≈ 338.4 GHz mm, which separates the susceptibility diagram into single-sided, double-sided, and mixed-sided zones. The initial electron energy influences their trajectories at high f · D and low RF power. This effect tends to dominate the multipactor behavior in the mixed-sided region.
关键词： ponderomotive force,multipactor,TM01 mode,Circular waveguide
更新于2025-09-12 10:27:22