Rectangular Waveguide Research Articles

Design and Verification of a Miniaturized Multifunctional Transmitarray Unit Cell for the S-Band

In this paper, a miniaturized multifunctional unit cell structure of a transmitarray operating at S-band and its verification method using a waveguide structure is presented. The unit cell of a multifunctional transmitarray antenna is a critical component because it controls the phase and polarization of an incident wave. The proposed unit cell consists of three main parts: an Rx antenna, a Tx antenna, and a control circuit for phase and polarization. The performance of the designed unit cell is verified by a rectangular waveguide structure. The waveguide structure feeds an electromagnetic wave propagating in a TE<sub>10</sub> mode to a 1 × 2 unit cell array to verify polarization and phase shifting capability of the unit cell. The phase shifting and polarization conversion capabilities of the proposed unit cell are directly measured by the radiation patterns and polarization of the transmitted wave.

Terahertz photodiode integration with multi-octave-bandwidth dielectric rod waveguide probe.

Photonic integrated circuits play a vital role in enabling terahertz (THz) applications that require multi-octave bandwidth. Prior research has been limited in bandwidth due to rectangular waveguide (WRs) interconnects, which can only support single octave at low loss. To overcome this fundamental limitation, we exploit the ultra-wideband (UWB) near-field coupling between planar waveguides and silicon (Si)-based subwavelength dielectric rod waveguides (DRWs) to interconnect THz bandwidth uni-traveling-carrier photodiodes (UTC-PDs) at 0.08-1.03 THz. In a proof-of-concept experiment, the on-chip integrated UTC-PDs demonstrate a UWB operation from 0.1 THz to 0.4 THz. Furthermore, by employing Si DRWs as probes, multi-octave device-under-test characterization of UTC-PDs integrated with UWB transition is enabled with only one DRW probe. The proposed UWB interconnect technology is distinct from previously used WR-based ground-signal-ground probes or quasi-optical free-space coupling since it can provide multi-octave bandwidth and enable on-chip THz circuit integration.

A New Technique for Broadband Matching of Open-Ended Rectangular Waveguide Radiator.

The maximum reflection at an open end of a standard rectangular waveguide is about -10 dB in its operating frequency range. It is often used without matching. For critical applications, it is desirable to further reduce the reflection coefficient. In this paper, a new technique is presented for the broadband impedance matching of an open-ended rectangular waveguide. The proposed technique employs three thin capacitive matching elements placed at proper intervals via a low-loss dielectric material. The capacitance of, and distance between, the matching elements are optimized for broadband impedance matching using a simulation tool. Based on the proposed technique, two design examples are presented for the matching of a WR75 waveguide radiator. A reflection coefficient of less than -16 dB and -20 dB has been achieved over a ratio bandwidth of 2.13:1 and 1.62:1, respectively.

Additively manufactured rectangular waveguides for the electromagnetic characterization of materials using the transmission/reflection line method

PurposeRadio frequency (RF) technology relies on the electromagnetic properties of the materials used, which includes their complex permittivities and loss tangents. To measure these properties, techniques for material characterization such as the transmission/reflection method are used in conjunction with conversion techniques to calculate these values from scattering parameters. Unfortunately, these techniques rely on relatively expensive rectangular waveguide adaptors and components, especially if testing over large frequency ranges. This paper aims to overcome this challenge by developing a more affordable test equipment solution based on additively manufactured waveguide sections.Design/methodology/approachTo evaluate the effectiveness of using additively manufactured waveguides to perform electromagnetic characterization with the transmission/reflection method, samples of PLA Tough with varying infill percentages and samples made from several Formlabs photopolymer resins are fabricated and analyzed.FindingsResults show that the method yielded permittivity and loss tangent values for the measured materials that generally agree with those found in the literature, supporting its credibility.Originality/valueThe accessibility of this measurement technique will ideally allow for more electromagnetic material characterization to occur and expand the possible use of additive manufacturing in future RF designs. This work also provides characterization of several Formlabs photopolymer resins, which have not been widely analyzed in the current literature.

Advanced Modeling of Rectangular Waveguide Devices With Smooth Profiles by Hierarchical Model Reduction

We present a new method for the analysis of smoothly varying tapers, transitions, and filters in rectangular waveguides. With this aim, we apply a hierarchical model (HiMod) reduction to the vector Helmholtz equation. We exploit a suitable coordinate transformation and, successively, we use the waveguide modes as a basis for the HiMod expansion. This allows us to model the electromagnetic field efficiently and compactly without incurring on relevant simplifications. We show that accurate results can be obtained with an impressive speed-up factor when compared with standard commercial software based on a 3-D finite element discretization.

Higher-Frequency Permeability Measurement by Harmonic Resonance Cavity Perturbation Method

A new combination of electric field antenna and coupling hole plates are introduced to extend the measurable frequency range of rectangular waveguide type harmonic resonator to evaluate complex relative permeability of magnetic composites by perturbation method from 18 GHz to 38 GHz (K/Ka-band). The noise suppression performance parameter ωμ”=2πfμ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> ” [kΩ/m] is useful to estimate the performance of magnetic powder composite sheets especially beyond 10 GHz range where relative permeability is as small as 0-2. The ωμ” exhibited the maximum of 166 kΩ/m at 27 GHz for a carbonyl iron powder composite sheet, and as high as 510 at 38 GHz for Sendust sheet. These values meet ωμ”≥100 kΩ/m criteria that some commercially available noise suppression sheets exhibit in their recommended frequency range. These performance match Sub-6 GHz band and 28 GHz band used for 5G telecommunication equipment.

The Singlet: Direct Synthesis of Pseudo-Elliptic Inline Filters With Frequency Variant Couplings

A general and direct synthesis of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{p}$</tex-math> </inline-formula> poles pseudo-elliptic inline filters having <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$N_{p}$</tex-math> </inline-formula> purely real and/or imaginary frequency transmission zeros is presented. Using an appropriate model of the resonators (bandpass distributed or lumped element) and shifting the reference planes at the input and output of the filter network, a novel direct synthesis and realization of filters based on frequency variant coupling (inductive or capacitive) in the distributed domain is demonstrated for accurate modeling of narrow and broadband filters. First, a complete general synthesis procedure is described that allows for flexible or mixed topologies realizing transmission zeros anywhere on the frequency plane (including complex and infinite frequencies). Furthermore, by exploiting the power of modular design, a synthesis procedure that enables simultaneous extraction of reflection zero (a pole) and a transmission zero in the form of a symmetrical and physically realizable singlet as an elementary unit is showcased. The physical dimensions of the extracted singlets are independently determined in any chosen technology, and the overall filter is obtained by directly cascading the physical singlets. To validate this novel synthesis technique, three design examples are shown: a narrowband four-pole, four transmission zeros (fully canonical) filter from literature is synthesized and physically dimensioned, a wideband three-pole, three transmission zero (fully canonical) filter, and a broadband three-pole, one transmission zero, filter. In the first two examples, each of the singlet blocks was implemented in an overmoded rectangular waveguide cavity operating at the TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{201}$</tex-math> </inline-formula> mode coupled at the input and output to the fundamental nonresonating TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{10}$</tex-math> </inline-formula> mode. The third example was implemented in a re-entrant coaxial resonator operating at the fundamental mode. The simulation of the electromagnetic (EM) high-frequency structure simulator (HFSS) models of the overall example filters was in excellent agreement with the synthesized models, thereby validating the effectiveness of the proposed synthesis technique. Furthermore, the measured results of the fabricated wide bandpass filter showed close agreement with synthesis and EM model.

Experimental study on microwave-induced puffing, micro-explosion, and combustion characteristics of ammonium dinitramide-based liquid propellant droplets

Microwave ignition technology has the advantages of high ignition energy, stable ignition, and spatial multi-point ignition. These advantages make this technology promising for future application in green single-component propellants. In this paper, the ignition characteristics of ammonium dinitramide (ADN)-based liquid propellant droplets under the influence of microwaves at room temperature are investigated using experimental methods. The effects of microwave power on puffing, micro-explosion, and combustion behavior of ADN-based liquid propellant droplets were studied. The droplet and flame diameters were statistically related to time, and the microwave-assisted droplet ignition mechanism was analyzed. A new rectangular waveguide resonant cavity was designed in which the droplet is placed at the maximum electric field strength of the device. The droplet morphology and flame profile inside the resonant cavity were photographed with a high-speed camera. The experimental results showed that the microwave positively influenced the puffing, micro-explosion, and combustion behavior of droplets. When the microwave power was increased from 200 to 280 W, the total droplet evaporation time and ignition delay time were reduced by 56.5% and 35.2%, respectively. The positive effects of microwaves on combustion have been summarized as the thermal effect of microwaves on polar molecules and the promotion of fuel oxidation reactions by microwave-induced plasma. The plasma was found to control the development of the initial flame propagation front and to influence the temperature during the combustion reaction process. In this paper, we propose the mode of droplet combustion under microwave induction as a plasma discharge and several stages of the droplet combustion process. This research provides novel insight into the study of the microwave ignition mechanism of liquid fuels.

Enhancing interaction efficiency in traveling-wave devices with multiple beamlets and beam–beam interference

We demonstrate that beam–beam interference can significantly enhance the efficiency of multi-beam traveling-wave devices. Our theoretical analysis explains that a positive coupling of the space-charge field enhances the beam–wave interaction, resulting in increased efficiency in multi-beam devices with beam–beam interference. We validate this mechanism by performing particle-in-cell simulations on 670 GHz grid-loaded rectangular waveguide backward-wave oscillators. Both the multi-beam and single-beam devices exhibit the same dispersion of operating modes and operate under identical conditions. The simulation results indicate that the efficiency of the multi-beam device is up to 1.58 times higher than that of the single-beam device. Additionally, simulations are performed on the same structure at 340 and 1030 GHz, demonstrating efficiency improvements that support the proposed mechanism. These findings present a novel approach for increasing the efficiency of traveling-wave devices.

Resonator-Loaded Waveguide Notch Filters with Broad Tuning Range and Additive-Manufacturing-Based Operating Frequency Adjustment Procedure

This article presents a new class of ring-resonator-loaded waveguide notch filters with a broad tuning range, low cost, and improved performance. The proposed approach employs a complementary asymmetric split-ring resonator coupled to a microstrip transmission line and excited in a rectangular waveguide. An equivalent circuit model is proposed to explain the working principle of the proposed notch filter. The adjustment of the operating frequency is based on the additive manufacturing of a metallic copper patch allocated on the microstrip transmission line, which enables extensive tuning capabilities and consistent performance with minimum variations across the tuning window. For demonstration purposes, a filter employing a WR-28 waveguide and photolithography-manufactured resonator is prototyped and experimentally validated. The measured results indicate a broad 8 GHz tuning range with a consistent insertion loss, ranging from 23.4 to 31.4 GHz. An inverse regression model is constructed using measurement data obtained for tuning patches of various sizes, which allows for determining the relationships between the operating frequency and the copper patch size. The resulting calibration curve enables rapid filter tuning to the required frequency by inserting metallic patches of the model-predicted size.

Simple and Easily Connectable Transition from Empty Substrate-Integrated Waveguide to a 3D Printed Rectangular Waveguide

3D printing is one of the most promising manufacturing methods in the most developed technological fields, including microwave hardware fabrication. On the other hand, the well-known manufacturing methods of planar substrate integrated circuits allow high-quality prototypes to be made at low cost and with mass production capabilities. The combination of both manufacturing methods, 2D or 2.5D (substrate integrated circuits) and 3D (3D printed structures), will allow us to take advantage of the main strengths of each technology and minimise disadvantages. In this article, for the first time, a transition structure between the Empty Substrate-Integrated Waveguide (ESIW) technology—a planar waveguide integrated on a printed circuit board—and a standard rectangular waveguide manufactured by 3D printing is proposed. This transition will make it possible to combine planar circuits with 3D structures, thus taking advantage of the benefits of both types of technologies. The fabricated prototype presents low losses (0.6 dB for the transmission coefficient and 15 dB for reflection coefficient), good electrical response (very flat), and simultaneously good mechanical stability and robustness to manufacturing and assembly errors. The proposed design for this transition piece is easily realisable for a wide range of affordable 3D printers. Repeatability is guaranteed and the proposed transition allows us to combine different SIC structures to 3D printed circuits. Hence, this transition will enable advancements in the fabrication of microwave devices, particularly with regard to satellite communications.

An efficient determination of field distributions in E-plane dielectric loaded waveguides

ABSTRACT This paper proposes a new, fast, and efficient method for determining the electromagnetic field distribution in two-port E-plane dielectric-loaded uniform rectangular waveguides. The analysis region is divided into individual blocks in the absence and presence of dielectric obstacles. The non-zero electric and magnetic field components are constructed throughout the system via the proposed method by utilizing the generalized scattering matrix method between blocks for unimodal or multimodal excitation. The resulting field distributions are compared to those obtained from commercial software, with very close agreement achieved, but with a significantly reduced computational time for the proposed method. The method is applicable in a straightforward manner and has been tested on both a filter device with relatively complex geometry and a disjoint system with a modal coupling challenge between its elements. The field components' accuracy is also tested by calculating the Poynting vector along the system. Additionally, this approach provides the global scattering parameters at the physical ports as a co-product. The proposed method has the potential to be applied to various two-port networks by using the proposed method according to the considered problem.

Design of dual-mode dual-band filter based on multilayer groove gap waveguide

This paper presents a novel dual-mode dual-band filter (DBF) based on multilayer groove gap waveguide (GGW). Unlike other published planar GGW filters, the proposed filter achieves a vertically stacked duplicate topology by introducing a rectangular aperture in the common wall and traditional inductive irises on the same layer, with perfect central symmetry in the overall structure. This reduces machining difficulty while having a smaller size. By optimizing the dimensions of the coupling structure and rectangular cavities, dual-mode resonators (DMRs) including even mode and odd mode are used to accomplish dual-bandpass response. Additionally, an efficient transition is presented and applied to achieve a good impedance matching from rectangular waveguide (RW) to GGW. To better demonstrate, a multilayer DBF with working center frequencies of 67.9 and 69.8 GHz is designed, fabricated and measured. Good consistency can be observed between the simulation result and the measurement result.

Design of a Broadband Transition from a Coaxial Cable to a Reduced-Height Rectangular Waveguide

For miniaturization, rectangular waveguides with a reduced height are often required, along with a coaxial transition for signal launching. We present a simulation-based design of a broadband transition from a coaxial cable to a rectangular waveguide with the height(b)-to-width(a) ratio b/a ranging from 0.125 to 0.375. The proposed transition consists of a coaxial probe with a cylindrical head or a disk and two symmetrically placed tuning posts. To extend the operating frequency range, three sections of the rectangular waveguide are employed with properly chosen dimensions. Design examples are presented for the WR75 waveguide transition with a b/a of 0.125, 0.25, and 0.375, having a bandwidth of 83.4%, 92.7%, and 84.4%, respectively. Compared with previous works, our design offers the largest bandwidth in a right-angle coaxial-to-rectangular waveguide transition employing the aforementioned structure.

Design of single-ended CPW to rectangular waveguide transition on InP at 300 GHz for 5G applications

Abstract In this paper, we present the development of coplanar waveguide to rectangular waveguide (CPW-WG) transition for broadband millimetre wave applications. The traditional approach for interfacing of components in pure electronics is not possible to implement in micorwave photonics at high frequency range due to some limitations like rigidity and increased loss. In order to overcome this problem, transition structures are usually designed within the waveguide model through split block mechanism. The models developed so far are complex with minimum space of interconnects and less stable due to vertical placement of waveguide. The waveguide structure proposed in this paper is placed along horizontal direction due to which stability of structure is increased and has more space for interconnects. The transition model is designed using indium phosphide (InP) to increase the efficiency and reduce the propagation loss at high frequency range. The simulated design can operate over a bandwidth of 14 GHz with a return loss of 10 dB.

Challenges in the microwave heating of structured carbon adsorbents

Microwave heating is a promising method for achieving energy-efficient electrification of temperature swing adsorption processes. However, to successfully design the adsorbent bed and the regeneration step, it is crucial to analyse the limited penetration depth of microwaves. In this study, we present the first comprehensive investigation of microwave heating applied to large structured activated carbon adsorbents. The experiments were conducted inside a monomode microwave applicator, which consists of a rectangular waveguide operated at a frequency of 915 MHz. monolithic adsorbents of various shapes and sizes (cubic, rectangular cuboid, cylindrical) with dimensions up to 10 cm, were placed inside the cavity and subjected to microwave powers ranging from 10 to 200 W. To maximise microwave absorption by the sample, the geometry and impedance of the cavity were modified. Temperature measurements were taken at different positions within the monoliths to investigate heating homogeneity. The combined influence of reflections and the limited penetration depth results in very different temperature profiles as the size and shape of the monolith vary, even after optimising the cavity. In general, thinner monoliths heat better at the centre, whereas thicker monoliths experience better heating at the point closer to the radiation source. Additionally, these materials were characterized in terms of their dielectric and textural properties and composition, and it was determined that variations in these properties result in significant differences in the heating behavior. The choice of adsorbent bed size and heating time can be adjusted accordingly to maximise energy efficiency and heating homogeneity. Furthermore, the rotation of monoliths within the monomode electromagnetic field to achieve heating homogeneity is examined and a comparison with a multimode device is established.

Sensitivity Performance of Optical Waveguide Sensors with Different Shapes of Cladding Layer for Microplastics Detection

With microplastics pollution becoming a global concern, there comes a need for sensors to attain an optimal level of sensitivity to detect microplastics in water. This work investigated the effects of cladding layer shapes on the sensitivity performance of an optical waveguide sensor for microplastics detection in water. In this research, three different cladding shapes—C-shaped fiber, D-shaped fiber, and rectangular waveguide with circular core—were simulated by using Wave Optics Module-COMSOL Multiphysics® software. The results indicated that the C-shaped fiber exhibited significantly higher sensitivity, with a sensitivity value of 1.070x10−3 compared to the D-shaped fiber and rectangular waveguide with 3.845x10−4 and 3.842x10−4, respectively. The sensitivities of the D-shaped fiber and rectangular waveguide were relatively similar and did not exhibit any significant difference. The higher sensitivity of the C-shaped fiber is attributed to its larger exposed core area to the analyte, resulting in higher interaction of the evanescent wave with the analyte. However, fabricating the C-shaped fiber is more challenging compared to the other two shapes. This research highlights the significance of cladding shapes in optical waveguide sensor sensitivities and provides design optimization insights for microplastics detection in water.

Higher-order mode filtering by a resistive layer.

A method for filtering higher-order acoustic modes using a resistive layer is proposed and applied to a two-dimensional rectangular waveguide with a quiescent fluid. An analogue of Cremer's criterion is discussed and used to obtain the optimal modal attenuation of the non-planar waves while the plane wave is preserved. Numerical validation of the concept is performed for a straight waveguide and an abrupt expansion in a waveguide.

Effect of factors on dielectric properties of pineapple leaf for microwave application

Nowadays, dielectric materials are widely used in electronic applications, and their permittivity and loss tangent are important properties to consider. Dielectric materials made from waste can help reduce pollution and conserve resources. The aim of this work is to analyze the important factors in pineapple plantation waste preparation as dielectric materials using rapid two-level factor analysis in order to identify significant factors during preparation. It takes a short procedure to determine the optimum variable factor and leads to fast analysis. The dielectric material preparation process involves chemical treatment, sample fabrication, and sample characterization. Measurement of permittivity is performed by using a G-band rectangular waveguide. The highest dielectric permittivity is 3.31 where one of the suitable applications is used as an antenna substrate. The best factor in producing high dielectric permittivity is a 1:10 ratio of pineapple leaves to distilled water, 50 min of boiling time, using a heating effect, and 5 g weight of pineapple leaves powder. The most significant factor in producing high dielectric permittivity is the heating effect, which is contributed by the presence of carbon in the composite material.

Comprehensive Multimode Reflection Analysis of a Dielectric-Loaded Rectangular Waveguide Terminated by Semi-Infinite Dielectric Media

This article presents a comprehensive multimode reflection analysis of a dielectric-loaded rectangular waveguide terminated by semiinfinite dielectric media. A Fourier-based analysis approach is extended for different incident modes of the waveguide to calculate the amplitude coefficients of the reflected modes when the flange or the waveguide walls have different finite conductivities. We calculate the complex propagation constant using the method of perturbation of the boundary conditions. The modal scattering parameters are defined based on the voltage wave normalized amplitudes to be valid for both propagating and evanescent fields. The inclusion of coupled and noncoupled modes in the solution is evaluated in terms of calculation time and the accuracy of the results. An algorithm is presented to calculate the reflection coefficient of variations in terms of the coupled modes included in the solution. It is shown that these variations are dependent on the operating frequency and dielectric properties used in the geometry. Our results are compared with 3-D full-wave simulations, and an excellent agreement is achieved over a wide frequency range by using the primary coupled modes in the solution. The modal aperture admittance is calculated for different modes to show the coupled modes’ effect on the results. Also, the proposed algorithm is modified to find the effective coupled modes much faster. These modes are used to obtain accurate results for different dielectric-loaded structures.