Open-ended Circular Waveguide Research Articles

Radiation of a TM mode from an open end of a three-layer dielectric capillary

Abstract Modern trends in beam-driven radiation sources include the interaction of Cherenkov wakefields in open-ended circular waveguides with complicated dielectric linings, with a three-layer dielectric capillary recently proposed to reduce radiation divergence being a representative example [Opt. Lett. 45 5416 (2020)]. We present a rigorous approach that allows for an analytical description of the electromagnetic processes that occur when the structure is excited by a single waveguide TM mode. In other words, the corresponding canonical waveguide diffraction problem is solved in a rigorous formulation. This is a continuation of our previous papers which considered simpler cases with a homogeneous or two-layer dielectric filling. Here we use the same analytical approach based on the Wiener–Hopf–Fock technique and deal with the more complicated case of a three-layer dielectric lining. Using the obtained rigorous solution, we discuss the possibility of manipulating the far-field radiation pattern using a third layer made of a low permittivity material.

Diffraction at the Open End of Dielectric-Lined Circular Waveguide

A rigorous approach for solving canonical circular open-ended dielectric-lined waveguide diffraction problems is presented. This is continuation of our recent paper [1] where a simpler case of uniform dielectric filling has been considered. Here we deal with the case of an open-ended circular waveguide with layered dielectric filling which is closer to potential applications. The presented method uses the solution of corresponding Wiener-Hopf-Fock equation and leads to an infinite linear system for reflection coefficients (S-parameters) of the waveguide, the latter can be efficiently solved numerically using the reducing technique. As a specific example directly applicable to beam-driven radiation sources based on dielectric-lined capillaries, diffraction of a slow TM symmetrical mode at the open end of the described waveguide is considered. A series of such modes forms the wakefield (Cherenkov radiation field) generated by a charged particle bunch during its passage along the vacuum channel axis. Calculated S-parameters were compared with those obtained from COMSOL simulation and an excellent agreement was shown. This method is expected to be very convenient for analytical investigation of various electromagnetic interactions of Terahertz (THz) waves (both free and guided) and charged particle bunches with slow-wave structures prospective in context of modern beam-driven THz emitters, THz accererators and THz-based bunch manipulation and bunch diagnostic systems.

Turbine blade tip clearance determination using microwave measurement and k-nearest neighbour classifier

Turbine blade tip clearance and deformation can be monitored by measurement of scattering parameters. In this research, a k-band microwave sensor has been simulated, optimized and implemented in computer simulation technology software which can detect tip clearance variations by measurement of the scattering parameters using a network analyzer. The open-ended circular waveguide with the tip of the turbine blades forms a cavity resonator known as a microwave sensor. Scattering parameters can be used as fingerprints of the blade that are altered due to changes in tip clearance and deformation in accordance with the theory of small perturbations in cavity resonators. In this research, a new method for interpretation of the measured scattering parameters is presented that is based on measuring indices and the k-nearest neighbor classifier. It has been shown that the k-NN classifier provides acceptable accuracy for detection and determination of the blade tip clearance and deformation.

Dual-Band Open-Ended Waveguide Feeder Antennas With Collinear Feed Design

This communication presents two classes of dual-band open-ended circular waveguide antennas with a compact collinear end-launcher-type feed design. The proposed antennas consist of an open-ended circular waveguide, radial cavities, and resonators. The collinear feed is connected to the body of the circular waveguide, providing a high power-handling capability. The proposed structures can generate a mixed mode close to TE11 on the aperture of the open-ended waveguide in both bands. As a result, stable broadside gains over each band of interest are achieved for both antennas. The proposed antennas are good candidates to be used as feeder elements in several high-gain antennas such as bull’s eye antennas, surface-wave antennas, and metasurface antennas.

Bunch Imaging at the Open End of an Embedded Circular Waveguide

We consider a charged particle bunch passing along the axis of a semi-infinite open-ended circular vacuum waveguide placed into a collinear infinite waveguide with larger radius. The rigorous solution of this problem is constructed using residue-calculus technique. Analytical expressions for the Fourier harmonics of the field components are obtained in each domain of the structure. Numerical integration over frequency is also performed and time-domain field dependencies are obtained. The analytical results are compared with the results of the numerical simulation and an excellent agreement is observed. In particular, we report on the effect of a “bunch image,” a radiation pulse is generated in the coaxial area and has the form of the transverse electric field correlating with the longitudinal charge distribution within the bunch.

AN EFFICIENT METHOD FOR COMPUTING THE INTERACTION OF OPEN ENDED CIRCULAR WAVEGUIDE WITH A LAYERED MEDIA

This article presents a new method for studying the near-field electromagnetic interaction between a dielectric filled open ended circular waveguide (OECW) and a layered dielectric structure. The p ...

Analysis and Design of a Metamaterial Lens Antenna Using the Theory of Characteristic Modes

A new single-layer metamaterial lens antenna aimed to operate at 10 GHz is proposed in this paper. The lens antenna consists of twelve capacitively coupled unit cells distributed along a ring and illuminated by an open-ended circular waveguide with a metallic resonant ring. The theory of characteristic modes is used to analyze the metamaterial lens, in order to provide an insight into the radiation characteristics of the antenna. The proposed antenna has been optimized, obtaining a large bandwidth and a maximum directivity of 12.88 dBi at 10 GHz.

Circular waveguide TE 11 -HE 11 mode transducing antenna loaded with radial double mediums

A circular waveguide TE11-HE11 mode transducing antenna loaded with radial double mediums is reported based on measurements and simulations. The mode transducing antenna includes a novel broadband circular waveguide TE11-HE11 mode converter and a radiator. The circular waveguide TE11-HE11 mode converter is inserted with radial double mediums, and the radiator adopting an open circular waveguide or a small angle conical horn will radiate out HE11 mode. Using the commercial software HFSS to simulate and optimize two kinds of circular waveguide TE11-HE11 mode transducing antennas, the numerical results show that the two antennas have a highly symmetrical radiation pattern and a relatively low sidelobe level, no matter they work at linear polarization or circular polarization. The standing wave ratio (VSWR) and the gain of the two kinds of mode transducing antennas are tested by using the vector network analyzer and the spectrum analyzer. The measured results reveal that the gain of the antenna which uses an open-ended circular waveguide as the radiator is 11.21 dB, the gain of the antenna which uses a small angle conical horn as the radiator is 15.58 dB, and the VSWR is less than 1.05 at the center frequency of 9.4 GHz. The experimental results are in agreement with the simulation results, which validates the feasibility and correctness of the antenna technology of the mode conversion. 

A Novel Dual-Mode Dual-Polarized Circular Waveguide Feed Excited by Concentrically Shorted Ring Patches

There are a number of applications where an adaptive dual-mode dual-polarized reflector antenna feed is required, such that the mode excitation and polarization can be controlled externally. This paper presents one such feed. The modes are excited by two concentric shorted microstrip ring patches placed at the bottom end of an open-ended circular waveguide. It is shown that the proposed feed is capable of producing two perpendicular polarizations within a single hardware with excellent isolation between the excitation ports. A prototype antenna is fabricated and tested. The measured results satisfactorily validate the numerical ones.

Reflection of ${\rm TE}_{0{n}}$ Modes at Open-Ended Oversized Circular Waveguide

Reflection of circular symmetric TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> modes ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = 1-6) at an oversized, open-ended circular waveguide (C76-waveguide, inner diameter=27.79 mm, 70 GHz) radiating into free space has been investigated theoretically employing two scattering matrix codes (SMCs), the finite-difference time-domain code EMPIRE and the uniform geometrical theory of diffraction (UTD) as well as the first time experimentally. The measurements utilized mode converters for generation of pure TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> modes and a wavenumber spectrometer for mode analysis in the oversized waveguide. The total power reflection computed by EMPIRE is 4.1 to 13.4 dB lower than calculated from free-space wave and waveguide mode impedances. In all cases, most of the reflected power is carried by the backward traveling TE <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">06</sub> mode, which is the mode closest to cutoff. Experiments are in very good agreement with theoretical results.

Circular Aperture Antenna With Conical Beam

A novel circular aperture antenna with a conical beam fed by a coaxial line is presented. Three printed ring slots have been employed as the transition between the coaxial line and the open-ended circular waveguide. Through optimal design, the gain of 8-9.3 dB and elevation angles of 24°-31° have been achieved in the -10 dB impedance bandwidth of 12.2% at the center frequency 35 GHz, respectively. A rigorous analysis of the antenna using the mode-matching method is conducted. Good agreement has been observed between simulated results and measured ones.

RADIATION FROM OPEN-ENDED CIRCULAR WAVEGUIDES: A FORMULATION BASED ON THE INCOMPLETE HANKEL FUNCTIONS

An analytical formulation based on physical optics is employed to determine the field and the radiated power distribution by open-ended circular waveguides. Using the incomplete Hankel functions, the line integrals yielding the electromagnetic field are evaluated in closed analytical form along the waveguide axis. It is shown that cylindrical waves are generated by the surface currents flowing on the waveguide walls, while spherical waves are produced by the currents and charges excited at the waveguide truncation. Cylindrical and spherical waves are shown to be responsible for the field synthesis in terms of waveguide modes and scattered fields at the waveguide mouth. Numerical results concerning the spatial distribution of the electromagnetic field and associated power density are compared with previously published results, showing the advantage of the incomplete Hankel functions formulation. Finally, the uniform asymptotic representation of the incomplete Hankel function is shown to be suitable to compute the field distribution on the waveguide axis except for the TE 11 and TM 01 modes.

Analysis of Open-Ended Circular Waveguides Using Physical Optics and Incomplete Hankel Functions Formulation

The spatial distribution of the electromagnetic field excited in semi-infinite open-ended circular waveguides is analyzed using a physical optics (PO) and incomplete Hankel functions formulation. Using the incomplete Hankel functions, the PO surface integral employed to compute the field quantities is reduced to a simple line integral along the waveguide contour. Such a superposition integral, which describes the elementary field contributions having spherical and cylindrical character, is then evaluated in closed analytical form along the waveguide axis. It is shown that cylindrical waves are generated by the surface currents flowing on the waveguide walls, while the spherical waves are produced by the currents and charges excited at the waveguide truncation. Cylindrical and spherical waves are responsible for the field synthesis in terms of waveguided modes and scattered fields at the waveguide mouth. Numerical examples, demonstrating the accuracy of said field representation in the near-and far-field region of truncated circular waveguides, are finally provided.

Phase radiation characteristics of an open-ended circular waveguide

General analytical expressions are derived for the far-field amplitude and phase radiation patterns of an open-ended circular waveguide (OE-CWG) regardless of its radius or the operation frequency for the dominant and symmetric higher-order excitation modes. The derivation is based on the rigorous solution to the problem of diffraction at an open end of a waveguide proposed by Weinstein. The near-field amplitude and phase patterns of an OE-CWG are then calculated using the spherical wave expansion technique. The measurement of the radiation pattern of an OE-CWG was carried out to verify the validity of the derived expressions and a good agreement was obtained.

Some properties of an open‐ended circular waveguide with one‐ and two‐sided ideal hard walls

AbstractThe problem of radiation from a hard open‐ended circular waveguide excited in the dominant TEM mode is solved. The cases of one‐sided and two‐sided hard‐wall surfaces are considered. The rigorous solution obtained shows that the reflected TEM mode field in the latter case, unlike that in the former case, is completely concentrated at the surface outside the waveguide. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 160–164, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20407

Performance of an array of circular waveguides with strip-loaded dielectric hard walls

An infinite planar periodic antenna array of radiating open-ended circular waveguides is considered. The conducting waveguide walls are covered with dielectric layers loaded with longitudinal conducting strips for providing the hard wall boundary condition. Analysis of the array is carried out by the mode-matching method. The waveguide modes involved in the method are calculated by using the asymptotic strip boundary condition. It is shown that they are split into an independent subsystem of TE modes for the whole cross section and two independent subsystems of TM modes: one is for the central region and another is for the layer region. The calculations show that the operation of the hard waveguides in an array with small element spacing is similar to that of the multimode smooth wall waveguides completely filled with dielectric. For large diameters and element spacing, the hard waveguides have significant advantages over the smooth ones. It is shown that unlike an individual hard waveguide, the aperture efficiency of such a waveguide in the array has a nonmonotonic dependence on the waveguide radius. The results characterizing the behavior of the aperture efficiency and cross-polarization level in a frequency band as well as the contribution of certain waveguide modes in the reflected power are presented and discussed. The examples of the element patterns corresponding to minimal cross polarization are also given.

An Open-Ended Circular Waveguide with an Infinite Conducting Flange Covered by a Dielectric Hemi-Spherical Radome Shell: Full-Wave Analysis and Green Dyadics

An Open-Ended Circular Waveguide with an Infinite Conducting Flange Covered by a Dielectric Hemi-Spherical Radome Shell: Full-Wave Analysis and Green Dyadics

Finite-element analysis of high-frequency axisymmetric device problems

A finite-element scheme for solving wave propagation problems in devices with complete azimuthal symmetry both in their material properties and in their geometry is presented. The phi -coordinate variation is restricted to sin(n phi + xi ), thus requiring only a two-dimensional space for the complete finite-element analysis. The open radiating boundaries inherent in many propagation problems are tackled through simulated absorption of the radiation by lossy materials. Also proposed for these kinds of boundaries is a hybrid FEM-BEM (finite-element-method-boundary-element-method) formulation, based on the vector Green's function for the Helmholtz equation. This method has been tested by application to an open-ended circular waveguide and by a comparison with the simulated-absorption results. >

Computation and Optimization of Beam Efficiency for Reflector Antennas*

ABSTRACT This paper presents several topics on the beam efficiency of a reflector antenna. (i) A simple definition for the “main beam” is suggested for calculating beam efficiency. This definition is related to the reflector aperture diameter, but is independent of the feed edge taper. Use of this definition allows a fair comparison of beam efficiencies due to different feeds to be made. (ii) Physical optics theory does not conserve power. Therefore conventional reflector pattern computation methods based on PO can calculate beam efficiency only within 2% to 3% accuracy. A method for calibrating out this PO error is described. (iii) Beam efficiency curves are presented for typical parabolic reflectors fed by open-ended circular cylinder waveguide feeds. While directivity is optimized by a 10 dB edge taper, beam efficiency is optimized for a higher edge taper of over 20 dB. (iv) Beam efficiency curves for cases in which the beam is scanned off-axis are presented. (v) A cluster feed is utilized to improve b...

Radiation and Dispersion Effects from Frequency-Modulated (FM) Sources

Abstract We consider the Far-zone field radiated bv a frequency-modulated (FM) source in open-ended circular waveguide. The source is uniformly distributed over the waveguide cross-section. Possible multimode effects are included. The radiated fields are derived from an eauivalent source in the aperture. Far-zone fields are first obtained in the frequency domain with time-domain results following through an inverse Fourier transform. Results are given first in standard time and frequency domain plots. These are followed by short-time Fourier transforms and spectrograms that clearly show frequency modulation effects from the source and from the dispersion inherent in the wave propagation.