Nonradiative Dielectric Waveguide Research Articles

A wideband multi-bit reflectarray antenna with low cross-polarization based on nonradiative dielectric waveguide

This paper presents a wideband reflectarray antenna (RA) based on a nonradiative dielectric (NRD) waveguide with an inserted metal blade for muti-bit phase quantization. The proposed design eliminates the need of resonant components that typically exist in traditional RAs. Additionally, low cross-polarization is achieved by exciting the appropriate propagation mode in NRD waveguide. The beam scanning performance based on multi-bit phase quantization is verified by a series of static prototypes. Compared to traditional rectangular waveguide RAs, the proposed design possesses collimated beam scanning up to 60° without grating lobes, due to the compact unit cell dimensions. At a collimation beam angle of 20°, a 1-dB gain bandwidth of 18 % is achieved with an aperture efficiency of over 40 % and a cross-polarization level of below −40 dB.

Substrate-Integrated Nonradiative Dielectric (SINRD) Waveguide for THz Integrated Circuits and Systems

Substrate-Integrated Nonradiative Dielectric (SINRD) Waveguide for THz Integrated Circuits and Systems

Substrate-Integrated Hybrid Metallo-Dielectric Waveguide Architecture for Millimeter-Wave and Terahertz Applications

In millimeter-wave (mmW) and terahertz (THz) applications, the transmission behavior along circuit structures and components, such as radiation and leakage losses, is critical for their overall performances. It is imperative to develop low-loss interconnect and transmission techniques that should be used for the construction of building circuit blocks and elements. In this work, a hybrid metallo-dielectric (MD) waveguide architecture is proposed and studied for the first time. The scheme is made of mixed substrate-integrated dielectric waveguide (SIDW) and substrate-integrated nonradiative dielectric (SINRD) waveguide, which are deployed for the design of specific building parts in consideration of respective transmission properties of the two waveguides. A back-to-back WR3-band prototype based on this hybrid scheme is investigated theoretically and validated experimentally. The hybrid MD waveguide architecture with SINRD is found to outperform the hybrid MD waveguide architecture with substrate-integrated waveguide (SIW) in terms of transmission performance and manufacturing complexity because of the advantageous features of metallized-via-free structure. The presented hybrid MD waveguide architecture shows its potential for developing low-loss highly integrated mmW and THz circuits and systems.

Vertically Stacked Double-Layer Substrate-Integrated Nonradiative Dielectric Waveguides for THz Applications

Nonradiative dielectric (NRD) waveguides have been studied and exploited to address the leakage issue in dielectric waveguides caused by discontinuities. With the proliferation of substrate integration technologies, planarized substrate-integrated NRD (SINRD) waveguides have emerged, which are found to be more suitable for terahertz (THz) integrated circuits and systems. However, in the making of SINRD waveguides, a process-related conflict may arise between the air-hole perforation of a hosting substrate and its essential residual metallic coating on the perforated region. In this work, a solution to this problem using a multilayer topology is formulated, where the size difference between entrance and exit of the drilled air holes is reduced. Moreover, the exposed metallic coating over both sides of the multilayer SINRD waveguide is well preserved. Therefore, a dense air-hole perforation is allowed when needed. In this letter, a vertically stacked double-layer guiding structure is presented, studied, and experimentally verified, which demonstrates the interesting features of this technique.

Research on a Novel Ka-Band Low Insertion Loss Transmission Line Based on H-Guide

H-guide and nonradiative dielectric (NRD) waveguide have more favorable prospects in the millimeter wave and even terahertz bands comparing to other waveguides, such as surface plasmon polaritons transmission lines and Goubau line. Basically, the H-guide described in this letter can avoid many of the disadvantages of the other more-conventional guides, such as high losses, low <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$Q$</tex-math> </inline-formula> -factors, poor field confinement and leakage, low power rating, small dimensions leading to severe tolerance problems, and expensive fabrication. In this letter, we analyze the characteristics of H-guide and design an adapter from microstrip line to H-guide. The experimental results are in good agreement with the simulation ones. The measured insertion loss of H-guide with back-to-back transitions ranges from 1.8 to 3.1 dB during 33–37 GHz, where the length of the H-guide reaches 200 mm.

Function expansion based topology optimization of NRD guide device using hybrid method of harmony search and gradient method

In recent years, optimization technique has attracted a lot of attention to develop high performance electromagnetic devices and various kinds of design strategies have been reported. Among them, topology optimization method has potential to develop innovative devices. In this paper, the function expansion based topology optimization method, which has been developed for design of photonic devices, is extended to be applied to design of nonradiative dielectric waveguide (NRD guide) devices. In the optimal design of NRD guide devices, solution search sometimes tends to fall into local minimum compared with the design of photonic devices. Therefore, we develop a novel hybrid optimization method combining harmony search which is one of the evolutionary algorithm and gradient method using adjoint variable method for robust and efficient design of NRD guide devices.

Full-Vectorial Bidirectional Beam Propagation Method for Nonradiative Dielectric Waveguides

Full-Vectorial Bidirectional Beam Propagation Method for Nonradiative Dielectric Waveguides

Analysis of NRD guide devices using rigorous two‐dimensional full‐vectorial FDTD method

AbstractIn this paper, a rigorous two‐dimensional full‐vectorial finite difference time domain (2D‐FVFDTD) method is developed for an efficient analysis of nonradiative dielectric waveguide (NRD guide) devices with three‐dimensional structure. A Convolutional perfectly matched layer is employed as an absorbing boundary condition. Furthermore, we have established a rigorous formulation for estimating the modal power of each and mode. We confirmed the validity of the proposed method through the analysis of NRD crossing and T‐branch guide devices. Excellent accuracy is achieved by the cross comparison of 2D‐FVFDTD results with recently developed two‐dimensional full vectorial finite element method.

Topology Optimal Design of NRD Guide Devices Using Function Expansion Method and Evolutionary Approaches

In order to increase communication capacity, the use of millimeter-wave and terahertz-wave bands are being actively explored. Non-radiative dielectric waveguide known as NRD guide is one of promising platform of millimeter-wave integrated circuits thanks to its non-radiative and low loss nature. In order to develop millimeter wave circuits with various functions, various circuit components have to be efficiently designed to meet requirements from application side. In this paper, for efficient design of NRD guide devices, we develop a topology optimal design technique based on function-expansion-method which can express arbitrary structure with arbitrary geometric topology. In the present approach, recently developed two-dimensional full-vectorial finite element method (2D-FVFEM) for NRD guide devices is employed to improve computational efficiency and several evolutionary approaches, which do not require appropriate initial structure depending on a given design problem, are used to optimize design variables, thus, NRD guide devices having desired functions are efficiently obtained without requiring designer's special knowledge.

Measurement Technique for Interface and Surface Conductivities at Millimeter-Wave Frequencies Using Dielectric Rod Resonator Excited by Nonradiative Dielectric Waveguide

Herein, we propose a new technique for measuring interface and surface conductivities, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{i}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{s}$ </tex-math></inline-formula> , of circuit substrates separately at millimeter-wave frequencies using a TE <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{0m\delta }$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$m =1$ </tex-math></inline-formula> , 2, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3, \ldots, \delta &lt; 1$ </tex-math></inline-formula> ) mode single-crystal sapphire rod resonator excited via nonradiative dielectric waveguide (NRD guide). Here, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{i}$ </tex-math></inline-formula> represents an effective conductivity of conductor at the dielectric side. On the other hand, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{s}$ </tex-math></inline-formula> represents an effective conductivity at the shiny side of the conductor. Evaluating <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{i}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{s}$ </tex-math></inline-formula> separately is essential for high-precision circuit design at microwave and millimeter-wave frequencies and the development of low-loss circuit substrates. The superiority of NRD guide excitation compared with the conventional loop antenna excitation was confirmed through both experiments and simulations for the dielectric resonator at millimeter-wave frequencies. The feasibility of the proposed technique was verified by measuring <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{i}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{s}$ </tex-math></inline-formula> of the two types of commercially available copper-clad substrates, which were liquid-crystal-polymer-based and polytetrafluoroethylene-based substrates, at approximately 62, 74, and 80 GHz. In addition, we confirmed that these data were consistent with respect to the frequency with the measured results obtained using the conventional technique via loop antenna excitation at microwave frequencies, demonstrating the validity of the proposed technique. The measured results from 2 to 80 GHz showed that <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{i}$ </tex-math></inline-formula> had a smaller value than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{s}$ </tex-math></inline-formula> and their values decreased with increasing frequency. Furthermore, it was found that the frequency dependence of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\sigma _{i}$ </tex-math></inline-formula> was very different for the two types of substrates.

A Monolayer Dually Polarized High-Order Space Harmonic Leaky-Wave SIW Antennas With Fixed and Scanning Beam Capability

In this work, the concept of high-order space harmonics (HSHs) applied to a hybrid form of nonradiative dielectric (NRD) waveguide and substrate-integrated square waveguide (SIW) involving both TE10 and TE01 modes is investigated with aim to develop multi-functional dually polarized leaky-wave antennas (DP-LWAs). A polarization-selective coupling (PSC) mechanism is used to guide the two orthogonally oriented modes in the hybrid structure to achieve a polarization diversity feature. The polarization effect on unit-cell geometrical structures is examined for different characteristics of LWA such as propagation constant behavior, leakage ratio, and scanning range variation. In addition, we demonstrate how the extrinsic characteristics of HSHs in a one-dimensional periodic LWA and its unit-cell analysis can provide design flexibility through two case studies. In the first case of demonstration, we show a dually polarized multi-beam LWA design with wide scanning capability in which we use both even and odd HSHs of n-1,-2). The second antenna design case is concerned with a DP-LWA having the capability of fixed and scanning beams operation by using a combinatory set of PSC and four HSHs of n-1,-2,-3,-4. Two DP-LWA prototypes are demonstrated as proofs of concept, and the obtained experimental results show a very good agreement with their simulation and analysis counterparts.

Two-Dimensional Full-Vectorial Finite Element Analysis of NRD Guide Devices

Nonradiative dielectric waveguide (NRD guide) is a promising platform for realizing compact millimeter waveguide circuits. NRD guide devices have been simulated by several numerical simulation approaches so far and these approaches treat 3-D structure because electric and magnetic fields in NRD guides vary in whole directions. In this letter, we propose a 2-D full-vectorial finite element analysis for efficient simulation of NRD guide devices.

Response Improvement of Liquid Crystal-Loaded NRD Waveguide Type Terahertz Variable Phase Shifter

Liquid crystals, which have high dielectric anisotropy even in the terahertz region and are easily controllable for dielectric permittivity by applying an electric field, have become increasingly attractive in recent years. The non-radiative dielectric (NRD) waveguide has a structure in which a dielectric line is sandwiched between two metal plates and by replacing the dielectric part with liquid crystal, a low loss liquid crystal-loaded NRD waveguide type terahertz phase shifter can be obtained. However, since the thickness of the liquid crystal layer is several hundred micrometers, it has a response time of as long as several hundred seconds when the driving voltage is removed. It is necessary to devise improvements for practical application. By inserting two polyethylene terephthalate (PET) films and reducing the thickness of the liquid crystal layer, the decay time was improved well, but the phase change was significantly reduced. In this study, we report improving both decay time and phase change with aligned nanofiber/liquid crystal complex. In addition, we demonstrate liquid crystal-load phase shifter, which has 360° phase change and the response time below one second.

NRD waveguide-type terahertz phase shifter using nematic liquid crystal

Non-radiative dielectric (NRD) waveguides are known as a type of transmission line with advantages such as the restriction of undesired radiation at curved sections and discontinuities. A new type of terahertz phase shifter which uses liquid crystal as the dielectric material in an NRD waveguide is presented for the first time. The phase change is very large but the decay time is extremely long. By inserting a PET sheet into a nematic liquid crystal-loaded NRD waveguide, the thickness of the liquid crystal layer is reduced. Although the phase change decreases, the decay time is greatly improved, and the availability of the partial use of nematic liquid crystal in the dielectric material of an NRD waveguide is confirmed. By comparing dielectric response results of the ordinary sandwiched cells with the experimental results of nematic liquid crystal-loaded NRD waveguides, it is confirmed that the response time does not depend on the kind of device.

Tunable Liquid Crystal Filter in Nonradiative Dielectric Waveguide Technology at 60 GHz

This letter presents a continuously tunable nonradiative dielectric waveguide three-pole bandpass filter based on liquid crystal (LC) technology at 60 GHz. LC is used as tunable material to obtain a continuous tunable center frequency. For the LC’s orientation, an electrode network with parasitic mode suppressive structure is realized. The measurements are performed with magnetic and electric biasing to verify the performance of the filter design. A maximum fractional bandwidth of 1% and a tunability of 2.5% were measured with electrical biasing. Furthermore, the filter’s insertion loss is between 4.9 and 6.2 dB over the tuning range. The extracted unloaded quality factor for electrical biasing ranges from 96 to 141.

Modeling Effective Anisotropy of Substrate Integrated Dielectric Waveguides for Polarization Diversity

A field-based analytical procedure is presented and developed for accurate modeling of the effective parameters of substrate integrated nonradiative dielectric (SINRD) waveguide. This modeling strategy is based on the eigenmode analysis of a dielectric substrate material perforated with air holes and enclosed between two horizontal metallic plates. From this model, it is found that the resulting effective dielectric constant of the periodic geometry of the SINRD waveguide is dependent on the direction of an electric field vector with respect to the material periodicity. In other words, the guiding parts of the SINRD waveguides act as anisotropic materials. A full demonstration for the proposed analysis is supported with simulation results using a full-wave finite-element method. The proposed model provides a scheme for the isotropization of anisotropic substrates. This is in addition to clarifying the exact regimes of operation inside the SINRD waveguide based on the guiding mechanism. Validation examples are studied based on polarization-selective coupling and effective polarization-independent coupling. A prototype is realized and measured where good agreement is achieved between simulation and measurement results.

Substrate integrated non-radiative dielectric waveguide and its applications

In this article a Substrate Integrated Non Radiative Dielectric Guide (SINRD) has been realized with the concept of substrate integration circuits. In SINRD, a specific pattern of air holes have been used grooved in a dielectric substrate to reduce the effective dielectric constant of a particular region. Accordingly, design and implementation of SINRD guides and its applications in millimeter wave subsystems have been investigated by using published literatures. Thereby the concept has been utilized to develop an optimized design flow of SINRD transmission line. Design has been carried out at W band (85–110 GHz) on a high dielectric constant substrate and subsequently dispersion characteristics has been studied subject to transmitted and radiated field configuration.

Design Methodologies of Compact Orthomode Transducers Based on Mechanism of Polarization Selectivity

An orthomode transducer (OMT) design is presented and implemented for future RF and millimeter-wave applications. The novelty of the proposed OMT stems from a distinct concept of handling dual-polarized signals on the basis of a polarization-selective coupler (PSC). The theory of the PSC is developed and understood through analyzing its constituent waveguides. Such waveguides are hybrid forms of nonradiative dielectric waveguide and substrate-integrated waveguide. An equivalent circuit model is deduced for modeling dispersion characteristics of the PSC. Consequently, design methodologies supported with comprehensive theoretical study and simulation analysis for a PSC-based OMT are developed and examined. The general design of a PSC-based OMT basically depends on a dielectric slab coupler waveguide with a longitudinal periodic PEC polarizer wall in its middle. Practical limitations for this design is discussed and supported with solutions using a proposed top slot coupler instead of the dielectric slab coupler. Closed-form equations are obtained as design recipes for computing structure dimensions and bandwidth based on operating frequency and the material parameters. The proposed structure is prototyped and measured. Measured results show an acceptable agreement with simulation results.

Theory of Polarization-Selective Coupling and Its Application to Design of Planar Orthomode Transducers

With the rapid and continuous development of new generations of wireless technologies and networks, exploring the underutilized millimeter-wave (mm-wave) band becomes inescapable. Polarization diversity has been an essential factor in the performance and capacity enhancement of various wireless systems including cellular networks. Accordingly, the design and development of dual-polarized antenna feeding structures in the mm-wave band is a must. In this paper, a compact wideband orthomode transducer design in the Ka-band is proposed and explored. The proposed architecture and design are based on a forward mode polarization-selective coupling strategy between two unconventional waveguides. These special waveguides are a combination between two types of guiding structure, namely, nonradiative dielectric waveguide and substrate-integrated waveguide. Polarization-selective coupling can be achieved in these structures due to different mechanisms by which orthogonally oriented modes are guided. Theoretical coupling levels of 0 dB are possible in the designed structure. Analytical analysis and design steps are given in detail. This analysis facilitates a complete control on the single-mode operation for each polarization. This control, besides the structure being planar, represents the main advantages of the proposed structure. Finally, a prototype is implemented and measured where an excellent agreement is achieved with the simulation results.

Инженерный расчет и оптимизация параметров полуэкранированного диэлектрического волновода в неизлучающем режиме

The parameters of half-shielded dielectric waveguides optimized in terms of their frequency bandwidth are investigated as a supplement to the procedure for designing waveguide transitions. The half-shielded dielectric waveguide is a rectangular dielectric rod placed between two parallel metal plates. Such a waveguide is in its own way a "hybrid" of open and closed transmission lines. It simultaneously has the properties of both the types of transmission lines; these properties may exhibit themselves to a greater or lesser extent depending on the design. Under certain conditions, a so called non-radiating effect is observed in this waveguide, a phenomenon consisting in that the electromagnetic energy is held in the dielectric rod when it is bent or deformed (provided, however, that the plane symmetry is retained). The ratio of the distance between the metal plates to the dielectric rod width is called the rod form-factor. For a non-radiating mode, there exists a certain optimal form-factor, at which the maximum frequency bandwidth is reached. The frequency bandwidth as a function of the waveguide form-factor is presented. Dependences characterizing the optimum form factor (according to the largest frequency bandwidth criterion) versus the medium parameters are investigated, and empirical formulas for evaluating them are proposed. An engineering method is proposed for calculating the physical parameters of non-radiating dielectric waveguides, which is one of the stages in calculating waveguide transitions. Empirical formulas for estimating the dependence of optimal form-factor on the parameters of medium are investigated and proposed. Dependences of the optimal form-factor and the frequency bandwidth coefficient on the ratio of dielectric constants of the waveguide rod and external medium are presented. An engineering method for calculating the physical parameters of non-radiating half-shielded dielectric waveguides is suggested. It is found that the non-radiating dielectric waveguide's frequency ratio lies in the range from 24 to 30%. It is shown that materials with a dielectric constant higher than 5 are best suited for achieving the largest frequency bandwidth. A formula for approximating the dependence of the optimal form-factor on the rod dielectric constant in the range from 1.5 to 30 is proposed.