Dielectric Posts Research Articles

A W-Band SPDT Photoconductive Evanescent-Mode Waveguide Switch

This letter presents the design, fabrication, and measurement of a silicon micromachined photoconductive evanescent (EVA)-mode waveguide switch operating in a single-pole double-throw (SPDT) configuration. Two EVA-mode waveguides loaded with silicon posts are placed in a Y configuration with a common feeding waveguide. In the absence of photoexcitation, the dielectric posts and EVA channel exhibit a bandpass filter response that allows low-loss propagation of signals on the order of 2.0 dB at 96.7 GHz. When photoexcited, the low conductive posts and EVA channel yield a very high isolation of 36.5 dB up to 102.4 GHz within <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$W$ </tex-math></inline-formula> -band. The proposed design shows promise for 5G and 6G communication backhaul devices.

A Dual-Band Tunable Balanced Filter With Independently Tuning Bands

A dual-band tunable balanced filter based on one hybrid microstrip-cavity structure is proposed in this paper. The cavity acts as one multimode resonator, and the differential feeding networks are printed on the PCBs. According to the electromagnetic (EM) field theory, TE101 and TE011 modes are generated under differential-mode (DM) excitation, and highly suppressed under common-mode (CM) excitation. The dielectric posts in the cavity can independently shift the resonant frequencies of the two modes. Moreover, the inter-resonator coupling of each band is independently controlled by the cross-shaped coupling slot. Therefore, good filtering differential response can be realized with in a wide band. For demonstration, a dual-band tunable balanced filter is designed and measured. The measured results indicate that the center frequencies of the two bands are tuned from 7.51 GHz to 8.22 GHz and 9.34 GHz to 10.56 GHz, respectively. Over the tuning range, the insertion losses vary from 0.5 dB to 1.5 dB and the CM suppressions in both passbands are under 50 dB and 42 dB. In this way, the proposed hybrid microstrip-cavity structure is feasible to design a reconfigurable balanced filter with wide tuning range and high CM suppression.

All-optical diffractive neural networked terahertz hologram.

Holography has garnered an explosion of interest in tremendous applications, owing to its capability of storing amplitude and phase of light and reconstructing the full-wave information of targets. Spatial light modulators, metalenses, metasurfaces, and other devices have been explored to achieve holographic images. However, the required phase distributions for conventional holograms are generally calculated using the Gerchberg-Saxton algorithm, and the iteration is time-consuming without Fourier transform or other acceleration techniques. Few studies on designing holograms using artificial intelligence methods have been conducted. In this Letter, a three-dimensional (3D)-printed hologram for terahertz (THz) imaging based on a diffractive neural network (DNN) is proposed. Target imaging letters "THZ" with uniform field amplitude are assigned to a predefined imaging surface. Quantified phase profiles are primarily obtained by training the DNN with the target image and input field pattern. The entire training process takes only 60 s. Consequently, the hologram, that is, a two-dimensional array of dielectric posts with variational heights that store phase information, is fabricated using a 3D printer. The full-wave simulation and experimental results demonstrate the capability of the proposed hologram to achieve high-quality imaging in the THz regime. The proposed lens and design strategy may open new possibilities in display, optical-data storage, and optical encryption.

Applying additive manufacturing to integrate coaxial connectors with 3D printed waveguides for cascaded RF link applications

This paper explores the use of additive manufacturing as a low-cost method to integrate coaxial SubMiniature version A (SMA) connectors with waveguides operating at X-band. The integration of coaxial connectors into the filter and waveguide designs via 3D printing eliminates the need for two additional bulky external SMA-to-waveguide transitions, and allows for customizable integrated SMA-to-waveguide transitions that minimize impedance mismatch. Four designs, including air-filled and polycarbonate (PC) dielectric-filled waveguides and two-pole filters, are modeled and manufactured using additive manufacturing to demonstrate this integrative approach. Placement of the coaxial connector in terms of depth and location is optimized in the designs for good match using simulation. PC dielectric posts are also incorporated into the device to provide additional reinforcement to the coaxial connectors without impacting the radio frequency (RF) performance. Good RF performance is achieved with the variation less than 0.39 dB between simulated and measured insertion loss results at the center of the device passband.

Design of Microstrip Patch Antenna for Dual-band Operation using Metal Ring Superstrate

In this paper, a dual-band generation in rectangular microstrip patch antenna (RMPA) using a superstrate metal ring has been proposed. In this configuration, a metal ring is placed above the rectangular patch with the support of two dielectric posts. The metal ring behaves as a superstrate layer and resonator for the lower band, the other band is generated by microstrip patch and hence the combined configuration metal ring and patch gives dual-band characteristics. The lower band resonates at 9 GHz with an impedance bandwidth of 6.8% and higher band at 11.35 GHz with impedance bandwidth of 3.1%. The co-polarized peak gain values at these frequencies are 8.2 dBi and 10.1 dBi respectively. This may be used in applications like airborne and naval-radar. The prototypes are fabricated using commercially available dielectric substrate (RT-Duriod r = 2.2 and thickness h =1.6 mm). The measured results show good agreement with the simulated predictions

Efficient Analysis of Electromagnetic Scattering in Post-Wall Waveguides and Its Application to Optimization of Millimeter Wave Filters

Functional post-wall waveguides and waveguide based compact passive circuits - namely bandpass filters - that are formed by introducing additional metallic or dielectric posts inside the post-wall waveguide are analyzed. Scattering parameters (S-parameters) of the waveguide-based bandpass filters are calculated using the method of images combined with the lattice sums technique. The developed formulation is numerically very fast, hence it can be considered as one of the best-suited approaches for the analysis of multiple scattering in post-wall waveguides and for numerical structural optimization. A breeder genetic algorithm is employed as a global search heuristic in order to track down the optimal geometrical parameters for the introduced posts yielding a bandpass filter characteristic in the desired frequency bands. Comparison with other references validates the correctness and utility of our formalism. Different configurations for the specifications of post-wall waveguide-based bandpass filters are discussed.

A 3-D-Printed Wideband Circularly Polarized Parallel-Plate Luneburg Lens Antenna

This communication presents a 3-D-printed wideband parallel-plate circularly polarized Luneburg lens (LL) antenna. The proposed structure of dielectric posts truncated by two metallic parallel plates serves not only as a LL, but also as a wideband linear-to-circular polarizer. The permittivity variation of the LL is realized by positioning dielectric posts with various radius (r) based on the optics theory and the effective medium theory (EMT). On the other hand, the desired circular polarization is realized by exciting two orthogonal propagating modes with different phase constants thanks to the integrated parallel plates. To verify our concept, a prototype was fabricated using 3-D-printing technology. Based on the measurement results, the proposed antenna achieves an overlapped bandwidth of 43% (21–32.5 GHz) in terms of the reflection coefficients lower than −10 dB and the axial ratios smaller than 3 dB. Good agreement between simulation and measurement is obtained.

On the analysis of capacitive rectangular waveguide discontinuities close to arbitrarily shaped conducting and dielectric posts

In this work, we propose an integral equation technique for the efficient analysis of capacitive step discontinuities in rectangular waveguides. The method allows for the inclusion of a number of arbitrarily shaped posts in the vicinity of the step discontinuity. The posts can be both metallic or composed of homogeneous dielectric materials. The integral equation formulation is based on the Surface Equivalence Principle, and uses the parallel plate Green’s functions that take into account for the boundary conditions imposed by the host waveguide. The formulation is written in the mixed spatial-spectral frequency domain, and takes advantage of the symmetry of the problem by reducing the original three dimensional (3D) problem to a so called 2.5D problem. The numerical technique has been validated with simulation examples, namely, two lowpass filters that use conducting and dielectric posts of different shapes as impedance inverters. The results provided by the method that we propose have been also compared to those obtained with a commercial full-wave software tool (ANSYS HFSS), showing in all cases a very good agreement with substantially higher computational efficiency.

Magneto-Optical Isolator Based on Ultra-Wideband Photonic Crystals Waveguide for 5G Communication System

This paper presents a novel magneto-optical isolator based on an ultra-wideband and high efficiency photonic crystals (PCs) waveguide and gyromagnetic ferrites. The three-dimensional numerical simulation finds that the photonic crystals waveguide’s (PCW) transmission efficiency rises with its height and width. The corresponding experiments are performed by using a triangular lattice Al2O3 dielectric posts array in 5G millimeter wave band. The measured transmission efficiency is up to 90.78% for the optimal PCs waveguide structure, which has ultra-wide operating bandwidth from 23.45 to 31.25 GHz. The magneto-optical isolator is designed by inserting two rectangular gyromagnetic ferrites into the PCs waveguide. Due to the contrast between the effective permeability of the left and right circular polarization waves passing through the magnetized ferrite sheets, the ferromagnetic resonance absorption of the forward and reverse waves is different. By using finite element method, the isolation is optimized to be 49.49 dB for the isolator and its relative bandwidth reaches 8.85%. The high isolation, broadband, and easy integration indicate that our designed magneto-optical isolator has significant advantage in 5G communication systems.

3-D Printed Circularly Polarized Modified Fresnel Lens Operating at Terahertz Frequencies

In this paper, a novel 3-D printed circularly polarized (CP) modified Fresnel lens antenna operating at 300 GHz is introduced. By virtue of the superior geometric flexibility of the 3-D printing technique, a modified Fresnel lens consisting of subwavelength discrete dielectric posts in the odd-numbered Fresnel zones is proposed. It is further demonstrated that by integrating dielectric anisotropic metamaterial, the modified Fresnel lens can realize CP radiation fed by a simple linearly polarized (LP) open-ended waveguide (OEWG). The 3-D printing approach is also investigated to push the performance envelops of the 3-D printer for realization of the terahertz CP lens. The measured results show that the axial ratios (ARs) of the fabricated antenna prototype are smaller than 3 dB from 265 to 320 GHz. Moreover, the modified Fresnel lens has a maximum gain of 27.4 dBic, which is 0.9 dB larger than that of the conventional Fresnel zone plane antenna (FZPA). These validate the concept, the design, and the fabricated prototype.

High-Gain Circularly Polarized Lens Antenna for Terahertz Applications

A high-gain circularly polarized (CP) lens antenna fed by a standard linearly polarized (LP) pyramidal horn operating at 300 GHz is proposed in this letter. The high-gain CP lens consists of discrete variable-height dielectric posts and grating. The height of each dielectric post is tuned to realize the required transmission phase, forming a planar wavefront above the lens aperture. By integrating the bottom dielectric grating with anisotropic characteristic, the dielectric lens can transform the incident LP waves from the feed source into CP radiation waves. Three-dimensional (3-D) printing technique is utilized to fabricate the terahertz (THz) CP lens for simplifying the fabrication process and reducing the cost. Measured results show that the designed lens can realize right-hand circular polarization radiation with a gain of 30.8 dBic at 300 GHz. The measured 1 dB gain bandwidth and 3 dB axial-ratio bandwidth of the THz CP lens can reach 13.3% and 18.8%, respectively. 3-D printed dielectric CP lens for use at THz frequencies is demonstrated, opening new possibilities for future high-speed wireless communications.

Magnetic photonic crystal circulator based on gradient changing width waveguide

In this paper, a novel Y-shaped photonic crystal circulator based on a photonic crystal gradient changing width waveguide is proposed. The gradient changing width waveguide is constructed by triangular lattice photonic crystals with dielectric cylindrical posts. Simulation results show that the waveguide has well transmission characteristics with low ripple and high efficiency. The Y-shaped photonic crystal circulator is envisaged based on the waveguide with three ferrite posts in waveguide junction. Insertion loss and isolation of the circulator are 0.0028 dB and 53.36 dB respectively, which were theoretically analyzed through FEM method.

A lightweight multi-beam cylindrical Luneberg lens antenna loaded with multiple dielectric posts

A multi-beam cylindrical Luneberg lens antenna loaded with multiple light dielectric posts for the purpose of light weight is presented. The antenna is based on a parallel-plate waveguide and specifically composed of 10 E-shaped patch antennas feeds, 2 parallel plates, and 491 epoxy posts. The equivalent gradient index of the Luneberg lens antenna is realized via the positions of the epoxy posts between the parallel plates. The features of low-profile height (0.55λ) and large radiating area (4.4 × 0.55λ2) of the cylindrical Luneberg lens result in wide beamwidth in elevation plane and high gain while operating at 4 GHz. Consequently, the 3 dB beamwidth in the elevation plane is >65°. Furthermore, the multi-beams cover a wide scan angle of 120° in the azimuth plane. The measured aperture efficiency of the fabricated lens antenna is above 50% from 3.9 to 4.3 GHz. In addition to the good radiation performance, features of light weight and ease of fabrication have also been demonstrated for the proposed lens antenna.

Design and analysis of High impedance surface modified 3D antennas

Three dimensional (3D) antenna offers immense advantages such as improved radiation efficiency, wider bandwidth, reduced footprint, and a thermally efficient system when compared to planar antenna design. 3D antenna is designed by placing the radiation element on a top plane, with the electrical feed line on a lower plane. The 3D antenna mentioned in the past was designed to have a radiating element rest on an array of copper posts which are electrically driven from the feed line on a lower plane. This paper discusses on an improvement towards the 3D antenna design by modifying the ground plane to an high impedance surface (HIS). The HIS modified 3D antenna offers wide band and similar gains for a 2.4 GHz signal frequency for comparable antenna dimensions. The HIS modified through dielectric copper posts antenna was designed and analyzed with other 3D antennas.

Novel Spatial Domain Integral Equation Formulation for the Analysis of Rectangular Waveguide Steps Close to Arbitrarily Shaped Dielectric and/or Conducting Posts

AbstractIn this paper, a novel integral equation formulation expressed in the spatial domain is proposed for the analysis of rectangular waveguide step discontinuities. The important novelty of the proposed formulation is that which allows to easily take into account the electrical influence of a given number of arbitrarily shaped conducting and dielectric posts placed close to the waveguide discontinuity. For the sake of simplicity, and without loss of generality, the presented integral equation has been particularized and solved for inductive rectangular waveguide geometry. In this case, the integral equation mixed‐potentials kernel is written in terms of parallel plate Green's functions with an additional ground plane located on the waveguide step. Therefore, the unknowns of the problem are reduced to an equivalent magnetic surface current on the step aperture and equivalent magnetic and electric surface currents on the dielectric and conducting posts close to the discontinuity. The numerical solution of the final integral equation is efficiently computed after the application of acceleration techniques for the slowly convergent series representing the Green's functions of the problem. The numerical method has been validated through several simulation examples of practical microwave devices, including compact size band‐pass cavity filters and coupled dielectric resonators filters. The results have been compared to those provided by commercial full‐wave electromagnetic simulation software packages, showing in all cases a very good agreement, and with substantially enhanced numerical efficiencies.

Reconfigurable Positioning of Vertically-Oriented Nanowires Around Topographical Features in an AC Electric Field.

We report the effect of topographical features on gold nanowire assemblies in a vertically applied AC electric field. Nanowires 300 nm in diameter ×2.5 μm long, and coated with ∼30 nm silica shell, were assembled in aqueous solution between top and bottom electrodes, where the bottom electrode was patterned with cylindrical dielectric posts. Assemblies were monitored in real time using optical microscopy. Dielectrophoretic and electrohydrodynamic forces were manipulated through frequency and voltage variation, organizing nanowires parallel to the field lines, i.e., standing perpendicular to the substrate surface. Field gradients around the posts were simulated and assembly behavior was experimentally evaluated as a function of patterned feature diameter and spacing. The electric field gradient was highest around these topographic features, which resulted in accumulation of vertically oriented nanowires around the post perimeters when dielectrophoresis dominated (high AC frequency) or between the posts when electrohydrodynamics dominated (low AC frequency). This general type of reconfigurable assembly, coupled with judicious choice of nanowire and post materials/dimensions, could ultimately enable new types of optical materials capable of switching between two functional states by changing the applied field conditions.

Stochastic Reduced-Order Electromagnetic Macromodels in FDTD

To enable an efficient stochastic-based design optimization methodology for multiscale structures of electrical devices, circuits, and systems, we propose the infusion of stochastic modeling with the electromagnetic macromodel in the method of finite-difference time domain (FDTD). We enhance the computational efficiency of the stochastic macromodel by applying the model order reduction techniques to produce the stochastic reduced-order macromodel. In addition, we provide a methodology and algorithms for the efficient generation and application of the stochastic reduced-order macromodel in the FDTD grid. The proposed methodology quantifies the impact of uncertainty in the electromagnetic system response that is manifested as random material and structural variations, through modeling and simulation. We demonstrate the proposed methodology by applying it to the computation of the stochastic transient electromagnetic fields in a 3-D bandgap structure comprising a rectangular waveguide, which contains an array of dielectric posts that exhibit uncertainty.

Radio‐frequency performance comparison of several H ‐plane rectangular waveguide filters loaded with circular dielectric posts

The study presents a radio-frequency performance comparison between several H-plane geometry filters based on rectangular waveguide technology. The basic all-metal filter of resonant cavities is compared with filters loaded with circular dielectric resonators, either in propagative or evanescent mode. The use of these resonators is claimed to reduce the length of the filter, increase the rejection band until the first spurious frequency and to improve the voltage magnification factor (VMF), at the cost of increasing the losses. Therefore, in order to properly assess and quantify the possible advantages of these filters, an accurate analysis of six of them has been developed. All the filters have been designed to have the same electrical response, and the length, losses, rejection band, VMF, and fabrication cost for all the filters are compared.

Conductive, dielectric and amalgamated obstacles coupled waveguide based highly selective multiband bandpass resonators

This paper demonstrates transverse nonplanar resonators consisting of symmetrically placed obstacles (posts which made up of same or different type of materials) coupled into rectangular waveguide. Introducing posts inside a waveguide in proposed structure creates discontinuity and become a cavity resonator. Resonance is created at X band, Ku band and Ka band frequencies are reported. Simulation results demonstrates that resonators's results are matched to free-space as well as having a superior insertion loss and better return loss of conductive posts compare to dielectric posts. Moreover, obstructing the E-field (using conductive posts) compare to the H-field (using dielectric posts) are given better insertion loss and impedance match- ing characteristics. However, insertion of amalgamated obstacles into rectangular waveguide generates good transmission and reflection zeros compared to other two topologies at resonant frequencies which are described here. Posts coupled waveguide resonators having high power handling capacity so it can be utilized for Base transceiver station, Satellite Communication, Space applications, sensors as well as the fusion plasma diagnostics system. All the proposed structures are simulated with Ansoft's finite-element High Frequency Structure Simulator (HFSS) tool to demonstrate the characteristics of the resonators using a rectangular waveguide with center frequency of 11.2 GHz for X-band. In addition, the equivalent model of resonator is simulated in ADS (Advance designing system). It is observed that offered topologies are very sensitive to the parameters devia- tion (Post coupled waveguide resonator performance depends on diameter of conductive post, elevation of post and detachment between posts).

Multiple-band waveguide based band-stop filter

This paper presents a novel transversal coupling network for the design of multiple-band bandstop filters. In this proposed structure, multiple-band bandstop filter is design based on amalgamated (conductive and dielectric material) posts coupled rectangular waveguide to demonstrate the feasibility of proposed network. We have proposed two structures using four metallic windows placed at the corners of triangle inside a waveguide and symmetrical dielectric material posts placed at the center of the triangle made by metallic posts. By inserting dielectric post, the results are improved. The structures are simulated with Ansoft's finite-element High Frequency Structure Simulator tool and its equivalent circuit of Ansoft designer to demonstrate the characteristics of this notch filter using a rectangular waveguide with center frequency of 11.2 GHz. The proposed structure using amalgamated post is fabricated and tested using the Vector Network Analyzer and obtained results compared with the simulated results.