Waveguide Simulator Research Articles

A Two-Bit Reflectarray Element Using Cut-Ring Patch Coupled to Delay Lines

In this paper, a two-bit element for reflectarray applications is presented. The proposed element is based on the cut-ring patch coupled to delay lines through an annular slot. The four states of the reflection phase with a step of 90◦ are achieved with two switches. This reported work is the first step towards the 2-bit active reflectarray element. Prototypes of the element have been fabricated and characterized in X-band using waveguide simulator. Measured results show good characteristics with low magnitude losses and the bandwidth of 1.7-bit resolution is over 5%.

Computer-Aided Design and Simulation of Spatial Opto-Mechatronic Interconnect Devices

Optical technologies become increasingly important in modern sensor and communication applications. Nevertheless, manufacturing and design methods in the field of spatial opto-electronics have not been investigated intensively yet. A new approach is to print polymer waveguides on spatial carriers to use the full design freedom of opto-mechatronic assemblies. Up to now, no specific design tools and validation methods are available. The article describes possible technology-specific methods for designing spatial opto-mechatronic applications with the focus on computer-aided design (CAD) and raytracing simulation of spatial waveguides.

1-Bit Reconfigurable Unit Cell for Ka-Band Transmitarrays

This letter presents an electronically reconfigurable, linearly polarized unit cell for transmitarray applications in Ka-band. A 1-bit phase resolution (namely with two phase states 0 ° and 180 °) is obtained using two p-i-n diodes mounted on a slot-loaded patch antenna. The design, realization, and experimental characterization in a standard waveguide simulator are reported. The measured insertion losses only reach 1.09 and 1.29 dB for the two-phase states, respectively, with a 3-dB transmission bandwidth of about 11.2%.

Optimization of optical waveguide for optical DEMUX at optical windows

Abstract This paper investigates the structure, operation and simulation of Optical Waveguide for Optical Demultiplexer (DEMUX) at three optical communication windows. Optical waveguide is realized by 2D photonic crystal structure with 3 × 3 silicon rod. Photonic band gap of 2D photonic crystal structure is simulated by plane wave expansion method. Here, two types of reflections, external and internal are considered to obtain the photonic band gap. Simulation results reveal that lattice parameter and diameter of silicon rod play vital role to design the optical Demultiplexer. Again, this result showed that photonic crystal having diameter of silicon rod of 129 nm and lattice spacing of 428 nm allows wavelength, 850 nm, diameter 97 nm and 194 nm allows wavelength, 1310 nm, diameter 36 nm and lattice spacing of 180 allows wavelength, 1550 nm.

Active Dual-Band Frequency Selective Surfaces with Close Band Spacing Based on Switchable Ring Slots

This letter presents active dual-band frequency selective surfaces (AFSS) with close band spacing based on two switchable ring slots loaded by PIN diode switches. The close band response is achieved by splitting the outer ring slot, and then shifting upward its fundamental resonance beyond the resonance of the inner ring slot. The proposed AFSS can provide four states of operation including lower single-band, upper single-band, dual-band with close band spacing, and reflective mode. Experimental results based on the waveguide simulator show that a frequency ratio of 1.14, with insertion loss lower than 0.82 dB at resonant frequencies, is obtained in the X-band.

Fourier methods for harmonic scalar waves in general waveguides

A set of semi-analytical techniques based on Fourier analysis is used to solve wave scattering problems in variously shaped waveguides with varying normal admittance boundary conditions. Key components are newly developed conformal mapping methods, wave splitting, Fourier series expansions in eigen-functions to non-normal operators, the building block method or the cascade technique, Dirichlet-to-Neumann operators, and reformulation in terms of stable differential equations for reflection and transmission matrices. For an example the results show good correspondence with a finite element method solution to the same problem in the low and medium frequency domain. The Fourier method complements finite element analysis as a waveguide simulation tool. For inverse engineering involving tuning of straight waveguide parts joining complicated waveguide elements, the Fourier method is an attractive alternative including time aspects. The prime motivation for the Fourier method is its added physical understanding primarily at low frequencies.

Reconfigurable reflectarray antenna using single‐layer radiator controlled by PIN diodes

A new type of pattern-reconfigurable reflectarray phased by reconfigurable unit cells that are centrally controlled by a laptop is presented. The proposed reflectarray with single-layer radiators employs a phasing element formed by a fixed-size circular ring attached by a variable-length arc phase delay line controlled by positive-intrinsic-negative diodes. The biasing network of the diodes is properly designed to minimise the interference between the radiating structure and the biasing circuit. To that end, the biasing circuit is placed on a substrate layer below the ground plane whereas the PIN switching diodes are embedded within radiators. The biasing signal is transmitted to the switching elements at the top layer using vias that penetrate the thin substrate layer, the foam layer and the ground plane. Investigations are carried out to verify the performances of the phasing element using a waveguide simulator. A reflectarray, which includes a C-band offset fed 8 × 8 elements, is configured to switch its main beam between 20° and 30° from the broadside direction. A biasing control unit is added to the fabricated reflectarray and activated using a laptop. The measured radiation patterns of the proposed reflectarray demonstrate a beam-switching characteristic from the broadside direction, which confirm the proposed design method.

Omni-directional Slotted Waveguide Antenna with Low Omni Ripple at MM Wave

The paper describes the design, simulation, and realisation of a slotted waveguide based horizontally polarized omni-directional antenna at millimeter wave frequency. This design has been optimised for minimum ripple in omni pattern and wide elevation coverage. It is based on radiating slots on both sides of waveguide for generating omni pattern and reduced height waveguide along with metallic wings on both sides used to obtain minimum omni pattern variation. The designed antenna has been simulated on finite element method-based ANSYS’s HFSS EM Simulator software using proper boundary conditions. A metallic strip on both side of slot on upper face of antenna has been used to provide flatness as well as strength to antenna. The antenna has the advantages of being robust, low cost, and easy to fabricate being in waveguide configuration. Measured VSWR of antenna is less than 2.0 over the frequency band of 37-40 GHz and minimum omni gain of the antenna is 0 dBi over the frequency band. Defence Science Journal, Vol. 65, No. 2, March 2015, pp.159-162, DOI:http://dx.doi.org/10.14429/dsj.65.8025

X-Band Tunable Frequency Selective Surface Using MEMS Capacitive Loads

A tunable frequency selective surface (FSS) based on slotted ground is presented. Tuning of the resonance frequency is achieved by using a metallic MEMS bridge over the slot. The bridge acts as a capacitive load, increasing the equivalent capacitance, and so decreasing the resonance frequency. Electromagnetic and electromechanical simulations are performed to investigate the designed FSS. S-parameter measurements of the FSS unit cell are performed in a waveguide simulator, showing more than 1.7 GHz frequency shift in the X-band, achieved by using only one MEMS bridge. A measured bandwidth of 400 MHz at the resonance frequency of 9.59 GHz is achieved. The designed MEMS bridge benefits from an unconventional method of using SU-8 as the sacrificial layer, resulting in low loss at high frequencies (3.2 dB loss at the resonance frequency of 9.59 GHz). Devices with different heights of the MEMS bridge were fabricated to study the variation in the resonance frequency. The MEMS bridge was tested at fixed heights. Simulated and measured results show excellent agreement. An FSS array is designed based on the FSS unit cell results. The design procedure to maximize the quality factor and controllable frequency range, and improve the radiation characteristics of the FSS array is discussed. Further simulations are performed to examine the performance of the FSS array with regards to grating lobes, oblique incidence and tunability.

Reconfigurable Nested Ring-Split Ring Transmitarray Unit Cell Employing the Element Rotation Method by Microfluidics

A continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell employing the element rotation method is designed and fabricated. The unit cell comprises a double layer nested ring-split ring structure realized as microfluidic channels embedded in Polydimethylsiloxane (PDMS) using soft lithography techniques. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is air. Movement of the liquid metal together with the split around the ring provides 360 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> linear phase shift range in the transmitted field through the unit cell. A circularly polarized unit cell is designed to operate at 8.8 GHz, satisfying the necessary phase shifting conditions provided by the element rotation method. Unit cell prototypes are fabricated and the proposed concept is verified by the measurements using waveguide simulator method, within the frequency range of 8-10 GHz. The agreement between the simulation and measurement results is satisfactory, illustrating the viability of the approach to be used in reconfigurable antennas and antenna arrays.

Superconducting circuit boundary conditions beyond the dynamical Casimir effect

We study analytically the time-dependent boundary conditions of superconducting microwave circuit experiments in the high plasma frequency limit, in which the conditions are Robin-type and relate the value of the field to the spatial derivative of the field. We give an explicit solution to the field evolution for boundary condition modulations that are small in magnitude but may have arbitrary time dependence, in a formalism that applies both to a semiopen waveguide and to a closed waveguide with two independently adjustable boundaries. The correspondence between the microwave Robin boundary conditions and the mechanically moving Dirichlet boundary conditions of the dynamical Casimir effect is shown to break down at high field frequencies, approximately 1 order of magnitude above the frequencies probed in the 2011 experiment of Wilson et al. Our results bound the parameter regime in which a microwave circuit can be used to model relativistic effects in a mechanically moving cavity, and they show that beyond this parameter regime moving mirrors produce more particles and generate more entanglement than their nonmoving microwave waveguide simulations.

UNCERTAINTY QUANTIFICATION FOR MAXWELL'S EQUATIONS USING STOCHASTIC COLLOCATION AND MODEL ORDER REDUCTION

Modeling and simulation are indispensable for the design process of new semiconductor structures. Difficulties arise from shrinking structure sizes, increasing working frequencies, and uncertainties of materials and geometries. Therefore, we consider the time-harmonic Maxwell's equations for the simulation of a coplanar waveguide with uncertain material parameters. To analyze the uncertainty of the system, we use stochastic collocation with Stroud and sparse grid points. The results are compared to a Monte Carlo simulation. Both methods rely on repetitive runs of a deterministic solver. To accelerate this, we compute a reduced model by means of proper orthogonal decomposition to reduce the computational cost. The Monte Carlo simulation and the stochastic collocation are both applied to the full and the reduced model. All results are compared concerning accuracy and computation time.

Reflectarray Element Using Cut-Ring Patch Coupled to Delay Line

In this letter, new phase-shifter cells for reflectarray applications using the cut-ring patch coupled to the delay line through an annular slot are presented. The new configuration allows the phase shift to be obtained by adjusting the length of a single or two different delay lines. Various prototypes of the elements have been fabricated and measured in X-band using the waveguide simulator technique. A good agreement between the measurement and simulation for both reflection phase and magnitude is achieved. Experimental results indicate good characteristics of the reflectarray element with a wide range of reflection phase and good linearity of the phase curve.

A Dual Linearly Polarized Transmitarray Element With 1-Bit Phase Resolution in X-Band

In this letter, we propose a dual linearly polarized unit cell with 1-bit phase resolution for transmitarray application in X-band. It consists of two-layer metallic patterns connected by a metallized via-hole. One layer of the metallic pattern is a rectangular patch with two p-i-n diodes loaded in O-slot along electric field polarization direction, which is utilized as a receiver-antenna to achieve 1-bit phase tuning. The other metallic pattern is a dual linearly polarized transmitter-antenna that adopts a square ring patch with two p-i-n diodes distributed at the cross-polarization directions. The simulation results show that the designed antenna can achieve 1-bit phase tuning and linearly polarization reconfiguration at 10.5 GHz with insertion loss of about 1.1 dB. The characteristic of the designed transmitarray element is then experimentally validated by an ad-hoc waveguide simulator. The measured results agree with the simulated ones.

English

A compact dumbbell shaped defected ground structure (DGS) is applied to reduce the mutual coupling between microstrip arrays elements for ISM band and wireless applications with 0.47 λ0 elements spacing. The dumbbell DGS with new distribution is inserted in the E-plane between the adjacent arrayscoupled elements to suppress the pronounced surface waves. A four-element array with dumbbell shaped DGS is designed, fabricated on a substrate with dielectric constant of 10.2 and thickness of 1.27mm, and measured. The results show that a reduction in mutual coupling of 35.6 dB is obtained between elements at the operation frequency of the array. The surface current distribution with and Without DGS for the array is discussed. The microstrip array with and without DGS are studied by the waveguide simulator method and fabricated by photolithographic technique.

Bandwidth Enhancement of Dielectric Resonator Reflectarray Antenna

Aperture-coupled dielectric resonator antenna is proposed using a novel reflectarray antenna unit cell structure. It is shown that a bowtie-shaped slot can enhance the bandwidth performance of a reflectarray antenna. The unit cell's reflection phase response was verfified experimentally using the waveguide simulator method. An array comprising of 256 elements was simulated using the finite integration technique based on the proposed unit cell. The array exhibits a 3-dB gain bandwidth of 28% and radiation efficiency of 43.8%. These results were validated using the transmission-line method.

Imaging surface plasmon polaritons using proximal self-assembled InGaAs quantum dots

We present optical investigations of hybrid plasmonic nanosystems consisting of lithographically defined plasmonic Au-waveguides or beamsplitters on GaAs substrates coupled to proximal self-assembled InGaAs quantum dots. We designed a sample structure that enabled us to precisely tune the distance between quantum dots and the sample surface during nano-fabrication and demonstrated that non-radiative processes do not play a major role for separations down to ∼10 nm. A polarized laser beam focused on one end of the plasmonic nanostructure generates propagating surface plasmon polaritons that, in turn, create electron-hole pairs in the GaAs substrate during propagation. These free carriers are subsequently captured by the quantum dots ∼25 nm below the surface, giving rise to luminescence. The intensity of the spectrally integrated quantum dot luminescence is used to image the propagating plasmon modes. As the waveguide width reduces from 5 μm to 1 μm, we clearly observe different plasmonic modes at the remote waveguide end, enabling their direct imaging in real space. This imaging technique is applied to a plasmonic beamsplitter facilitating the determination of the splitting ratio between the two beamsplitter output ports as the interaction length Li is varied. A splitting ratio of 50:50 is observed for Li∼9±1 μm and 1 μm wide waveguides for excitation energies close to the GaAs band edge. Our experimental findings are in good agreement with mode profile and finite difference time domain simulations for both waveguides and beamsplitters.

Low Frequency Ultra-Thin Compact Metamaterial Absorber Comprising Split-Ring Resonators

We present a design of a low frequency ultra-thin compact and polarization-insensitive metamaterial absorber (MA). The designed MA is a two-layer structure, a periodic array of novel split-ring resonators (SRRs), which are constructed in an FR4 dielectric layer, and another ultra-thin grounded sheet is attached to the bottom. Numerical simulated results show that the proposed MA can realize effective absorption at the frequency 281.9 MHz, and its overall thickness is just only 0.29% of the resonant wavelength, the unit space is only 2.57%, and the absorbance is kept well for a wide range of incident angles for different polarizations. In addition, the proposed MA is changed into a more compact one when the inter-digital structures are introduced in the SRRs. One convenient experiment is carried out in a rectangular waveguide simulator.

Frequency selective surface for radio frequency energy harvesting applications

A novel application for frequency selective surfaces (FSSs) is presented. The novel FSS design can harvest power from arbitrarily polarised incident waves. The design does not involve a matching network, which results in a simple, polarisationindependent power harvester. An accurate analytical procedure, to calculate the impedance of the commercially available Schottky rectifiers, is presented. The results are validated by full-wave simulations and by measurements. A simple equivalent circuit model to predict the transmission and reflection characteristics of the gridded-square-loop FSS is employed. The design method is validated for different polarisations and for different incident angles. The addition of lumped elements (R, L, C) in the metallic conductive grid of the FSS is investigated. The waveguide simulator method and full-wave simulations are employed to validate the derived analytical equations. A 3 x 3 and a 5 x 5 RF harvesting FSS have been designed, simulated, fabricated and validated. A radio frequency (RF) to DC conversion efficiency of 25% for the 3 x 3 RF harvester and 15.9% for the 5 x 5 RF harvester is measured at an RF input power level of -6 dBm.

True‐blue laser diodes grown by plasma‐assisted MBE on bulk GaN substrates

AbstractWe present nitride based laser diodes (LDs) grown by plasma‐assisted molecular beam epitaxy. In this work we investigate influence of epitaxial structure on LDs pa‐rameters. In particular we compare LDs with and without AlGaN cladding layers operating at 430 to 460 nm. We show results of waveguide simulations which explain the increasing threshold current density of longer wavelength LDs. The PAMBE LD with InGaN waveguides and AlGaN bottom cladding has threshold current density of 4.3 kA/cm2 and slope efficiency of 0.56 W/A. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)