Circular Waveguide Research Articles

Buried Depressed-Cladding Waveguides Inscribed in Nd3+ and Yb3+ Doped CLNGG Laser Crystals by Picosecond-Laser Beam Writing.

Buried depressed-cladding waveguides were fabricated in 0.7-at.% Nd:Ca3Li0.275Nb1.775Ga2.95O12 (Nd:CLNGG) and 7.28-at.% Yb:CLNGG disordered laser crystals grown by Czochralski method. Circular waveguides with 100 μm diameters were inscribed in both crystals with picosecond (ps) laser pulses at 532 nm of 0.15 μJ energy at 500 kHz repetition rate. A line-by-line writing technique at 1 mm/s scanning speed was used. Laser emission at 1.06 μm (with 0.35 mJ pulse energy) and at 1.03 μm (with 0.16 mJ pulse energy) was obtained from the waveguide inscribed in Nd:CLNGG and Yb:CLNGG, respectively, employing quasi-continuous wave pumping with fiber-coupled diode lasers. The waveguide realized in RE3+-doped CLNGG crystals using ps-laser pulses at high repetition rates could provide Q-switched or mode-locked miniaturized lasers for a large number of photonic applications.

Bound states in the continuum in circular waveguides: toward the on-chip integration of nanofiber on silicon platform.

In previously reported researches on bound state in the continuum (BIC) waveguides, almost all of them are demonstrated with top-down fabrication procedures, leading to inconvenience for post-manipulation and size tuning. Nanofibers with circular cross sections are the fundamental components to transport energy due to their intrinsic advantages of high flexibility and adjustability, which is replaceable and can be readily manipulated over size and position on the substrate. In this work, we explore the possibility of achieving on-chip integration of silica nanofiber onto a silicon-on-insulator platform. By constructing additional leakage channels in coupled nanofiber waveguides, coherently destructive interferences are successfully achieved. The heavy leakage losses from the low-index nanofiber to a high-index silicon substrate are completely eliminated with BIC, and the propagation length of the nanofiber waveguide is significantly improved.

Production of genuine multimode entanglement in circular waveguides with long-range coupling

Production of genuine multimode entanglement in circular waveguides with long-range coupling

Thrust measurements of a waveguide electron cyclotron resonance thruster

Direct thrust measurements are performed on a circular waveguide electron cyclotron resonance (ECR) thruster working at 5.8 GHz using a pendulum thrust balance with mechanically amplified displacement. Thrust levels between 1 and 3.5 mN are found for power levels in the range of 60–350 W and xenon flow rate between 2 and 8 SCCM. A maximum thrust efficiency of 3.5% is reached at 2 SCCM and 60 W. Plasma plume diagnostics are used to estimate the thruster partial efficiencies to understand the main losses, and to perform a comparative analysis between directly and indirectly measured thrust. Results suggest that the low energy conversion efficiency and propellant utilization efficiency (<6.4% and < 53%, respectively) are the key factors spoiling the ECR thruster performance. Finally, retarding potential analyzer measurements show the presence of energetic electrons with energy tail up to about 300 eV.

Computational Design of an In-Line Coaxial-to-Circular Waveguide Adapter with More Than an Octave Bandwidth

This paper presents a computer-simulation-based design of an in-line, coaxial-to-circular waveguide adapter for converting the coaxial transverse electromagnetic (TEM) mode to the circular waveguide TE11 mode over more than a one-octave bandwidth. The proposed adapter consists of a coaxial-to-rectangular waveguide transformer employing a stepped-ridge converter and a rectangular-to-circular waveguide transformer employing a curved transition. The proposed adapter has been optimized using a commercial simulation tool. The dimensions of the designed adapter are given so that it can be verified by anyone who is interested. The designed adapter operates from 8.00 GHz to 22.95 GHz (2.87:1 bandwidth) with a reflection coefficient of less than −20 dB and a higher-order mode level of less than −25.0 dB.

A Compact Circular Waveguide Directional Coupler for High-Order Mode Vacuum Electronic Devices

In this paper, a compact circular waveguide directional coupler for high-order mode vacuum electronic devices is presented and investigated. To reduce the size, the primary and secondary waveguides of this coupler are connected in an orthogonal way by two coupling holes. Moreover, to improve the directivity and operating bandwidth, a method of loading adjustable metal stubs on the isolating port is proposed and introduced in design. A Ka-band TE01-mode circular waveguide directional coupler was designed, and the structure parameters were optimized by electromagnetic simulation. To verify the design, a prototype sample was fabricated, assembled, and tested. The experimental results show good agreement with the simulations, and the directivity are improved by adjusting the metal stubs on the isolating port. In the experiment, a 26.7 dB directivity at 35 GHz was obtained, and the bandwidth of directivity above 20 dB was higher than 7 GHz, corresponding to a relative bandwidth higher than 20%. Meanwhile, the TE01° mode maintained good transmission efficiency in this compact high-order mode directional coupler.

Multilayer circular substrate-integrated waveguide cavity band-pass filters with ultrawide stopband characteristics

AbstractThis paper presents a methodology to design band-pass filters having ultrawide stopband characteristics using multilayer circular substrate-integrated waveguide (SIW) cavities. The orthogonal microstrip feedlines are used as input and output ports that are present at the top and bottom layers, while the middle layers are used to couple the SIW cavities. Higher-order spurious modes of the circular SIW cavity are suppressed by using orthogonal feeding mechanism and properly adjusting the arc-shaped slots between the cavities. To validate the present approach, two filters (second- and fourth-order) have been designed and fabricated and their characteristics are measured. The second-order filter exhibits a stopband rejection below 25 dB up to nearly 5.07f0, while the fourth-order filter has a stopband characteristic of nearly 5.05f0 with 20 dB rejection. The filters allow only TM010 mode propagation and attenuate the higher-order spurious modes of the cavity.

High-directivity far-field radiation of quantum dot-based single-photon emitter coupled to polymeric circular waveguide resonant grating

Solid-state single-photon emitters (SPEs) commonly encounter the limitation of quasi-omnidirectional radiation patterns, which poses challenges in utilizing their emission with conventional optical instruments. In this study, we demonstrate the tailoring of the far-field radiation patterns of SPEs based on colloidal quantum dots (QDs), both theoretically and experimentally, by employing a polymer-based dielectric antenna. We introduce a simple and cost-effective technique, namely low one-photon absorption direct laser writing, to achieve precise coupling of a QD into an all-polymer circular waveguide resonance grating. By optimizing the geometry parameters of the structure using 3D finite-difference time-domain simulations, resonance at the emission wavelength of QDs is achieved in the direction perpendicular to the substrate, resulting in photon streams with remarkably high directivity on both sides of the grating. Theoretical calculations predict beam divergence values below 2°, while experimental measurements using back focal plane imaging yield divergence angles of approximately 8°. Our study contributes to the evaluation of concentric circular grating structures employing low refractive index polymer materials, thereby expanding the possibilities for their application.

Laser emission from buried depressed-cladding waveguides inscribed in Nd:YAG ceramics by picosecond-laser beam writing

Buried, depressed-cladding waveguides were inscribed in a 1.1-at.% Nd:YAG ceramic by direct writing with a picosecond-laser beam. Laser emission performances were investigated under the pump with fiber-coupled diode lasers. For quasi-continuous-wave pumping, a circular waveguide with 100 μm diameter yielded laser pulses at 1.06 μm with 2.4 mJ energy for 12.8 mJ pump pulse energy at 807 nm (corresponding to an overall optical-to-optical efficiency of 0.19); the slope efficiency was 0.22. Continuous-wave output power of 0.35 W at 1.06 μm with overall optical-to-optical efficiency of 0.09 was obtained from the same waveguide; the slope efficiency amounted to 0.12. Furthermore, the circular waveguide yielded laser pulses at 1.32 μm with 0.4 mJ energy (at an overall optical-to-optical efficiency of 0.03); the slope efficiency amounted to 0.03.

DESIGN OF A REFLECTOR ANTENNA IN THE FORM OF A TRUNCATED PARABOLOID

One of the fastest developing areas of radioelectronics are antennas and microwave devices. Antennas are one of the most important functional blocks of different radio engineering systems. Parabolic antennas are the most common unidirectional microwave antennas in radar systems, radio communication and radio astronomy. A parabolic antenna in the form of truncated paraboloid is developed. The antenna is designed, and its characteristics are calculated using one of the most modern software for electrodynamics modeling, FEKO, which represents a new approach to the design of three-dimensional microwave devices. The visualized results of calculations of a parabolic antenna in the form of a truncated paraboloid, which are displayed in the form of graphs. As a radiator for the designed antenna a circular open-ended waveguide is chosen, which consists of two parts – the rectangular and the circular waveguides. For the developed antenna, the radiation patterns in the polar system in E and H planes, and the gain and voltage standing wave ratio (VSWR) are presented, designed in FEKO software. The value of the main lobe of the pattern at half power 〖2θ〗_0,5 and 〖 2φ〗_0,5 is calculated. The structure of the real antenna is shown. The results of comparisons of the values of dependency of VSWR on the frequency and radiation patterns of real and designed antennas are introduced. The parameters of the developed antenna were measured using the NI PXI-5630 network vector analyzer and the NI USRP-2901 radio device. The results of experimental studies have shown their compliance with the results of modeling. The developed antenna operates in the 4.6...6 GHz frequency range.

ВЛАСНІ КОЛИВАННЯ В ПЛАНАРНО-КІРАЛЬНИХ ДВОШАРОВИХ ОБ’ЄКТАХ ПОРОДЖУЮТЬ ШТУЧНУ ОПТИЧНУ АКТИВНІСТЬ

Subject and Purpose. The research focuses on how the resonance frequencies, the Q-factor of resonances, and the polarization plane rotation ability are influenced by the topology of individual components of a planar-chiral double-layer object consisting of a pair of con- jugated irises having rectangular slots and accommodated in a circular waveguide. Methods and Methodology. All the numerical results are obtained by the mode-matching technique (MMT) and the transverse reso- nance method on the basis of our own proprietary MWD-03 software package. Results. By the waveguide example, it has been shown that the internal structure of individual components and dihedral symmetry of the conjugated bilayer allow all the conclusions of the spectral theory (theory of eigen-oscillations) to be carried over to all the objects of the type. On the other hand, these objects behave as symmetric two-port waveguide components with conventionally "symmetric" and "antisymmetric" eigen-oscillations. The mutual coupling of these eigen-oscillations depends on the bilayer parameters. Where the frequen- cies of these eigen-oscillations are close enough, the polarization plane rotation and the transmission bandwidth reach their highest. It has been demonstrated that as a slot number increases, the resonance frequency decreases. The theoretical results have been confirmed by the measurements at the X range of frequencies for pairs of conjugated irises with various numbers of rectangular slots. Conclusions. A pair of conjugated chiral irises can rotate the polarization plane. The iris topology, iris spacing, and the mutual ro- tation angle alter resonance frequencies. The resonance frequencies can be reduced by increasing the rectangular slot length and/or slot number. Even though they have not longitudinal symmetry, such objects have properties of two-port waveguide components. In particular, the phase shift of their reflection and transmission coefficients is modulo 90. Besides, a possibility exists to divide eigen-oscillations into conventionally "symmetric" and "antisymmetric" based on the proximity of their fields to those whose type of symmetry is known before- hand. This makes it possible to approximate the reflection and transmission coefficients through corresponding eigenfrequencies.

Spectral approach with iterative clarification of a radiation boundary conditions for modeling of quasimodes of a gyrotrons open cavities

Purpose. The article presents a new method for numerical simulation of quasi-eigenmode oscillations in open resonators of gyrotrons — powerful vacuum generators of electromagnetic waves in the millimeter and submillimeter ranges. The gyrotron cavity has the shape of a weakly inhomogeneous hollow circular metal waveguide. Methods. The proposed approach uses the inhomogeneous string equation with radiation boundary conditions to formulate a nonlinear spectral boundary value problem describing oscillations in a resonator, neglecting the couplings of waves with different radial indices. By linearizing with respect to frequency the radiation boundary conditions, the boundary value problem is reduced to a linear boundary value problem. To discretize this boundary value problem, the finite difference method is used and a linear generalized matrix eigenvalue problem is formulated. This problem is solved by the Arnoldi method with eigenvalues calculation in a shift-invert mode. An iterative algorithm is proposed that makes it possible to sequentially calculate a given number of frequencies and quality factors of quasi-eigenmodes of oscillations. Results. The computer program was developed written in the Wolfram Language and Fortran using the algorithms proposed in the work. The results of test calculations for real gyrotron resonators are presented, which demonstrate the high accuracy of the obtained values of frequencies, quality factors and field distributions of quasi-eigenmode oscillations in the studied resonators. Conclusion. The methods, algorithms and created program proposed in the article can significantly facilitate the process of developing gyrotrons intended for various practical applications and operating in new frequency ranges. The method of iterative refinement of boundary conditions can be generalized to the case of equations of the linear theory of a gyrotron and used to develop new methods for analyzing the starting conditions for the soft self-excitation in gyrotrons — generators.

Cherenkov diffraction radiation dielectric button characterization via a slab-line

Cherenkov diffraction radiation is generated when a charged particle beam passes in close proximity to a dielectric target, and is currently being studied and developed for various non-invasive beam instrumentation applications at CERN. One such instrument is a beam position monitor (BPM) composed of four cylindrical dielectric inserts. A challenge of using the conventional stretched wire technique to characterize the BPM up to high frequencies is the coupling of unwanted higher order modes (HOM) into the inserts that are dielectric-loaded circular waveguides. To minimize the generation of HOMs and excite mainly the transverse electromagnetic (TEM) mode as a model of the beam field, a set-up comprising a dielectric insert mounted on a slab line with 50 Ω characteristic impedance was tested. The results and comparison with numerical simulations in CST are be presented.

Dielectric Measurement for Liquids Using a Coaxial-Feed Type Large-Bore Cut-Off Circular Waveguide with Good Repeatability

Dielectric Measurement for Liquids Using a Coaxial-Feed Type Large-Bore Cut-Off Circular Waveguide with Good Repeatability

ÇİFT-BANT İRİS POLARİZÖR TASARIM VE OPTİMİZASYONU

The structure that transforms a linear polarized signal into right-hand or left-hand circularly polarized signals is called a polarizer. In this study, a dual-band waveguide polarizer used in satellite communications is presented. The waveguide polarizer is designed using iris structures on a square waveguide. The purpose of the polarizer is to transmit the ±45° tilted linearly polarized signal at its input to the output as a right-hand or left-hand circularly polarized wave, and vice versa. At the input of the polarizer, a transition is designed between the WR42 waveguide and the square waveguide. At the output stage, a transition from square waveguide to circular waveguide is designed. In this paper, the design steps of both the polarizer and the transition sections, the optimization parameters, and simulation results are presented in full detail. The simulations are performed with a commercial electromagnetic simulation software, CST Studio Suite. The design operates within the Ka-band, specifically at 17.2 – 21.2 GHz and 27.5 – 31 GHz frequency bands. The insertion loss of the iris polarizer is 23 dB, and the phase difference is less than 15° around 90° for both bands.

High-efficiency and compact microwave heating system for liquid in a mug

The demand for efficient and compact heating for dynamic dielectric liquid has grown significantly. Compared with traditional heating, microwave heating has the advantages of being fast and efficient. Moreover, the demand for outdoor portable heating and industrial compact heating is increasing. To address this limitation, this study proposes a compact heating system based on a metamaterial-based circular waveguide. First, asymmetric propagation theory is introduced, and an asymmetric propagation circular waveguide is designed in detail according to the discretisation of the relative permittivity. Then, a multi-physics model using a circular waveguide and a mug for high heating efficiency is developed by coupling Maxwell's equations and the heat transfer equation. Furthermore, heating experiments are performed for liquids with different relative permittivity and the experimental results consistently validated an efficiency rate of over 88 %, which agrees with the simulation results. Finally, the effects of the dielectric properties of the material and mug on the heating efficiency are discussed to highlight the robustness of the proposed heating system, with heating efficiency consistently maintained at 75 % or higher. In summary, the proposed design features a compact structure that is suitable for practical microwave heating applications.

Cladding waveguide fabrication by femtosecond laser in Yb-doped phosphate glasses

Cladding waveguides near sample surface were investigated in Yb-doped phosphate glass using a femtosecond laser. The propagation of LP11-mode and dark-hollow beam was achieved using the circular cladding waveguides by adjusting the pulse energy and diameter of the cladding structure without inducing any damage tracks to the guiding core. Furthermore, semi-circular cladding waveguides with large-area and uniform-intensity modes were fabricated just below the glass surface. The working mechanism of the surface waveguide was clarified by analyzing the influence of the writing depth, which involves an overlapping between the mode at the upper end of the damage line and the mode adjacent to the glass interface. Finally, we successfully operated a 1030 nm laser by pumping the surface cladding waveguide at 976 nm.

Rectangular Waveguide Radial Combiners With Coaxial or Circular Intermediate Waveguide Sections Based on Stub Matching

Rectangular Waveguide Radial Combiners With Coaxial or Circular Intermediate Waveguide Sections Based on Stub Matching

Design of a Dual-Mode Waveguide CP Antenna with a Symmetric Beamwidth Using Short Stub for Low-Orbit Satellite TC&R

In this study, a dual-mode waveguide circularly polarized antenna for TC&R (telemetry, command, and ranging) was proposed for the communication between a low-orbit satellite and a ground station. The proposed antenna required both a wide -10 dB bandwidth and axial ratio bandwidth of 7.1–7.3 GHz and 8.0–8.4 GHz. The antenna was designed with a stepped septum inside a square waveguide to obtain circular polarization and the axial ratio wide bandwidth. Next, a dual-mode synthesis method was adopted for link budgeting by combining square and circular waveguides. The requirement was that the co-polarization level with a symmetric -3 dB beamwidth of 39° must be -5 dBic or higher at ±76.5°, and the cross-polarization level must average -15 dBic or lower at ±76.5°. Finally, the corrugate structure attached to the outside of the extended circular waveguide was offset in multiple steps to suppress the back lobe of the crosspolarization As a result, the axial ratio maintained an average of 1.8 dB at 0° within each band of the required frequency. In addition, the co-polarization obtained an average of -4.52 dBic in the 7.2 GHz band and -5.31 dBic in the 8.2 GHz band at ±76.5°. Finally, in the case of the cross-polarization pattern, the back lobe level was suppressed by 9.89 dB at 7.2 GHz by the corrugate structure, and an average value of -19.9 dBic or less was obtained at ±76.5°. The proposed antenna was confirmed to be effective as a Korean low-orbit satellite TC&R antenna with a radiation pattern of a symmetric beamwidth.

Dual-Mode Conical Horn Antenna with 2-D Azimuthal Monopulse Pattern for Millimeter-Wave Applications.

In this paper, a novel concept of a three-dimensional full metal system including a Dual-Mode Converter (DMC) network integrated with a high-gain Conical Horn Antenna (CHA) is presented. This system is designed for 5G millimeter wave applications requiring monopulse operation at K-band (37.5-39 GHz). The DMC integrates two mode converters. They excite either the TE11cir or the TE01cir modes of the circular waveguide of the CHA. The input of the mode converters is the TE10rec mode of two independent WR-28 standard rectangular waveguide ports. By integrating the DMC with the CHA, the whole system, called a Dual-Mode Conical Horn Antenna (DM-CHA), is formed, radiating the sum (Σ) and difference (Δ) patterns associated to the monopulse operation. To adequately prevent the propagation of higher order modes and mode mutual coupling, this integration procedure is carefully designed and fabricated. To prove the performance of the design, the DMC network was fabricated using subtractive manufacturing by Computer Numerical Control (CNC) technology. The CHA was fabricated using additive manufacturing by Direct Metal Laser Sintering (DLMS) technology. Finally, the simulation and measurement results were exhaustively compared, including return loss, isolation, radiation pattern, and gain of the full DM-CHA structure. It is noteworthy that this system provided up to ±11° per beam in the angular of arrival detection to support the high data rate operation for 5G satellite communications in the millimeter-wave band.