Rectangular Stub Research Articles

Circularly polarized CPW fed MIMO/Diversity antenna for Wi-Fi and WLAN applications

Abstract In this paper, circular polarized two-element and eight-element CPW fed MIMO/Diversity antenna with defected ground is presented. The dimension of the two-port antenna is 30 mm × 30 mm whereas the edge-to-edge gap between radiating elements is 5.65 mm. The |S11| in dB varies from 4.95 to 5.95 GHz with a gain up to 4.1 dB and efficiency is more than 90%. The isolation of two-element CPW antenna is more than 20 dB with open and diagonal stub in the ground whereas more than 18.7 dB for eight-element antenna without decoupling network. The circular and rectangular stub perturbs the surface current in the ground and is responsible for RHCP and LHCP in two-elements and eight-elements antenna where it covers the complete operating band. The acceptable ECC, TARC, DG, and CCL values of the antenna are determined which represents the diversity characteristics of the antenna. The Wi-Fi/WLAN applications can be fulfilled with the proposed two and eight-element antenna.

Numerical Investigation of Composite Behavior and Strength of Rectangular Concrete-Filled Cold-Formed Steel Tubular Stub Columns.

The objective of this study was to investigate the composite behavior of rectangular concrete-filled cold-formed steel (CFS) tubular stub columns under axial compression. A fine finite 3D solid element model of rectangular concrete-filled cold-formed steel tubular stub column was established by ABAQUS, which utilized a constitutive model of cold-formed steel considering the cold-forming effect and a triaxial plastic-damage constitutive model of the infilled concrete. Good agreement was achieved and the average discrepancy between the experimental and FE results was less than 5%. Based on the verified models, a further parametric analysis was carried out to reveal the influence of various factors on the strength and behavior of the concrete-filled rectangular cold-formed steel tubular stub columns. The factors included constitutive models adopted for cold-formed steel, length over width ratio of the rectangular section, wall-thickness and width, and concrete strength and yield strength of the cold-formed steel. A total of 144 FE models were analyzed. The stress nephogram was reasonably simplified in accordance with the limit state and a theoretical formula considering confinement coefficient was proposed to estimate the ultimate bearing capacity of concrete-filled rectangular cold-formed steel tubular stub columns using the superposition method. The calculated results showed satisfactory agreement with both the experimental and FE results, which proved the validity and accuracy of the formula proposed in this paper. In the proposed formula, the confinement coefficient of square concrete-filled cold-formed steel tubular stub columns is larger than that of hot-rolled steel counterparts but smaller than that of the stainless steel counterparts.

A high sensitivity nanosensor of ring resonator with inner stubs for multifunctional sensing

Herein, a novel nanosensor consisting of a ring resonator with two rectangular stubs and a metal–insulator–metal waveguide with two triangular stubs is proposed. By adopting the finite element method, a Fano resonance is found in the transmission spectrum, which results from the coupling between the discrete narrowband mode and the continuous wideband mode. The physical mechanism is analyzed by the normalized magnetic field distribution, and the effects of structural geometric parameters on the transmission characteristics are studied carefully. The results demonstrate that the maximum sensitivity could reach 2660 nm RIU−1 with the corresponding figure of merit of 66.5. The applications of the structure for hemoglobin concentration detection and temperature measurement are discussed, and the sensitivity of the two applications can reach up to 2.524 nm·l g−1 and 0.831 nm °C−1, respectively. The proposed structure with extremely high sensitivity and compactness can provide an excellent case for designing high-performance integrated plasmonic devices.

Dual-Band Antenna With Large Frequency Ratio Based on Dual-Mode Transmission Line

A dual-band antenna with large frequency ratio for microwave and millimeter-wave applications based on the dual-mode coplanar waveguide (CPW) transmission line is investigated in this letter. The dual-mode operation of the transmission line is obtained by introducing a rectangular stub to traditional CPW, which can provide different phase shift in different frequency bands. In the millimeter-wave band, the dual-mode transmission line can support odd mode while it supports even mode in the microwave band. Based on this, the dual-band antenna which operates as monopole antenna in the microwave band and Vivaldi antenna in the millimeter-wave band is realized using the same aperture. Moreover, the radiation structure for monopole in the microwave band is designed to enhance the radiation performance of the antenna in the millimeter-wave band. For verifying, the prototype of the antenna is fabricated on a Rogers 4003 substrate with an overall size of 45 × 20 × 0.508 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> and the measured results agree well with the simulated ones.

Improved Refractive Index-Sensing Performance of Multimode Fano-Resonance-Based Metal-Insulator-Metal Nanostructures.

This work proposed a multiple mode Fano resonance-based refractive index sensor with high sensitivity that is a rarely investigated structure. The designed device consists of a metal–insulator–metal (MIM) waveguide with two rectangular stubs side-coupled with an elliptical resonator embedded with an air path in the resonator and several metal defects set in the bus waveguide. We systematically studied three types of sensor structures employing the finite element method. Results show that the surface plasmon mode’s splitting is affected by the geometry of the sensor. We found that the transmittance dips and peaks can dramatically change by adding the dual air stubs, and the light–matter interaction can effectively enhance by embedding an air path in the resonator and the metal defects in the bus waveguide. The double air stubs and an air path contribute to the cavity plasmon resonance, and the metal defects facilitate the gap plasmon resonance in the proposed plasmonic sensor, resulting in remarkable characteristics compared with those of plasmonic sensors. The high sensitivity of 2600 nm/RIU and 1200 nm/RIU can simultaneously achieve in mode 1 and mode 2 of the proposed type 3 structure, which considerably raises the sensitivity by 216.67% for mode 1 and 133.33% for mode 2 compared to its regular counterpart, i.e., type 2 structure. The designed sensing structure can detect the material’s refractive index in a wide range of gas, liquids, and biomaterials (e.g., hemoglobin concentration).

Miniaturized quad‐band filter with improved selectivity using split ring resonators and metallic strips

A miniaturized bandpass filter of quad-band response with high selectivity is reported in this paper. The developed filter utilizes two sets of symmetric open-ended split-ring resonators (SRR), L-shaped and C-shaped strips along with rectangular stubs. Initially, open-ended SRR is connected with a C-shaped metallic strip to serves as a dual passband filter. Then by adding another SRR along with L-shape metallic strip and rectangular stub, it was converted into triple band and quad-band respectively. The operating frequency of the proposed filter structure can be controlled with the variation in the length ratio of resonators. In addition, transmission zero can be increased because of coupling between source/load and resonators which improves selectivity. The quad-band bandpass filter operates at 0.6/1.1/2.25/3.1 GHz, along with 3-dB fractional bandwidths of 17.9% (0.56-0.67 GHz), 17.7% (1.03-1.23 GHz), 5.8% (2.20-2.33 GHz), and 13.3% (2.88-3.29 GHz). It offers compactness with an electrical footprint area of 0.11λg × 0.10λg (23.5 mm × 21.0 mm) without feedline, where λg denotes the guided wavelength at 0.6 GHz. The measured and simulated outcomes were in virtuous correlation.

Prediction of Mechanical Properties of the Stirrup-Confined Rectangular CFST Stub Columns Using FEM and Machine Learning

In this study, a machine learning method using gradient boost regression tree (GBRT) model was presented to predict the ultimate bearing capacity of stirrup-confined rectangular CFST stub columns (SCFST) by using a comprehensive data set and by adjusting the selected parameters indicated in the previous research (B, D, t, ρsa, fcu, fs). The advantage of GBRT is its strong predictive ability, which can naturally handle different types of data and very robust processing of outliers out of space. The comprehensive data set obtained from the FEM method which has been verified the accuracy and rationality by the existing literature. In order to make the data group closer to the engineering example, a large amount of experimental data collected in the literature was added to the data group to enhance the accuracy of the model. We compare a few regression models simply and the results show that the GBRT model has a good predictive effect on the mechanical properties of CFST columns. In summary, it can help pre-investigations for the CFST columns.

Design of a compact UWB MIMO‐diversity antenna incorporating fractal inspired isolation structure with band notch characteristics

AbstractIn this communication, a new compact ultra‐wideband (UWB) multiple‐input multiple‐output (MIMO) antenna with band notch characteristics is presented for wireless application. It comprises of two unique monopole antenna elements sharing a similar ground plane. To reduce the coupling between antenna elements, a modified T‐shaped stub equipped with Minkowski fractal shape elements are introduced on the ground plane which in turn establish a good isolation between radiating elements. A band notch is achieved at 5.45 GHz by adding two additional rectangular stubs at 45° where symmetric slots have been etched. The efficiency and gain of the antenna drops significantly at the centre of the notch band which indicates good interference suppression. Results show that the designed antenna delivers widest impedance bandwidth (−10 dB) throughout the operating band of 3.1–20 GHz (of 146% impedance bandwidth) which covers UWB as well as Ku‐band. The antenna also produces ‐18 dB isolation for most of the operating band and ‐16 dB up to 6 GHz. The optimized antenna is fabricated and tested showing |S11| characteristics below −10 dB from 3.1 to 20 GHz band. The dimension of the proposed antenna is 18 × 26 × 1.6 mm3. Results show that the simulated characteristics are in good agreement with the measured counterpart. The designed MIMO antenna is an appropriate candidate for UWB and other wireless applications.

A high-selectivity double-mode SIW bandpass filter utilizing the modified parallel coupled microstrip lines

ABSTRACT In this article, a high-selectivity double-mode substrate integration waveguide bandpass filter utilizing modified parallel coupled microstrip lines (MPCML) is presented. The designed method is analyzed in detail. Six metal vias are designed to perturb TE-101 mode and TE-103 mode. The resonant frequency of the perturbed TE-101 mode is shifted to high frequency, close to that of TE-102 mode, which caused the formation of passband. The resonant frequency of the perturbed TE-103 mode is shifted to high frequency, improving out-of-band performance. Simultaneously, the coplanar waveguide structure is used to adjust the external quality factor. Two rectangular slotlines are introduced to adjust center frequency and bandwidth slightly. Two rectangular stubs are designed for better source and load matching. Three transmission zeros (TZs) are obtained to improve the selectivity. The designed MPCML promotes the generation of TZs. Another TZ is obtained by the coupling between TE-102 mode and TE-103 mode. The designed filter operates at 14.4 GHz with bandwidth of 800 MHz. The measured return loss is better than 15 dB, and the minimum insertion loss is 1.60 dB. The measurement is agreed with the simulation.

Fano-resonance-based refractive index sensor with ultra-high sensitivity

In this paper, we propose a Fano-resonance-based refractive index sensor with ultra-high sensitivity. The sensor comprises a metal–insulator-metal (MIM) waveguide with two rectangular stubs coupled with a circular resonator embedded with a defective metal nanocube (CRMN). The transmission characteristics of the structure are simulated using the 2D finite element method. This analysis reveals that the Fano resonance mode splitting is affected by the geometry of the sensor. In addition, the modulation depth and position of the Fano resonance can be tuned by adjusting the width and length of the stub on the CRMN. Optimizing the structural parameters results in a peak sensing sensitivity of 10200 nm∙RIU−1 under the ultra-compact sensor size. This sensitivity allows the sensor to be used in the detection of hemoglobin concentration (HC). By processing simulation data, the linear relationship between the refractive index of three different blood groups (A, B, and O) and HC is obtained. Based on the sensing principle of the designed device, HC can be calculated from measuring the shift of the Fano resonance wavelength. These results provide critical developments for the application of nanoscale refractive index sensors in the biomedical field.

Circularly Polarized DR-Rectenna for 5G and Wi-Fi Bands RF Energy Harvesting in Smart City Applications

A smart city necessitates spectrum and energy efficiency with increasing applications which demand an increasing number of nodes in the Internet of Things (IoT) system networks. In recent years, radio frequency (RF) energy harvesting is best suited to enhance the energy efficiency required for self-sustained IoT networks incorporated in smart cities. This work proposes a rectangular dielectric resonator antenna (RDRA), that comprises a rectangular dielectric resonator (DR) and slots loaded ground plane. The proposed antenna operates efficiently at 3.5 and 5.8 GHz frequencies and also achieves circularly polarized characteristics at two operating bands. A microstrip feeding approach opts for excitation of the proposed antenna. The radiational properties of the proposed antenna show that the antenna is suitable to operate for radio frequency energy harvesting in smart city applications efficiently. An HSMS2860 Schottky diode has been chosen for the rectification at two bands of frequencies. A proper impedance matching is achieved using microstrip transmission lines and rectangular stubs connected to the rectifier circuit. The proposed rectifier circuit offers the maximum power conversion efficiency (PCE) of 54.53% and 41.26% at 3.5 and 5.8 GHz frequencies respectively for 5 dBm input power. The output voltages obtained at two frequencies are 1.31 V and 1.16 V, respectively.

SRR and Rectangular Stubs Loaded Novel Fractal Antenna Realization for Multiband Wireless Applications

This manuscript presents the novel design of Split Ring Resonator (SRR) and rectangular stubs loaded Circular Fractal Antenna for multiband wireless applications. Initially, the antenna is designed by introducing various fractal iterations from 0th to 3rd and the final iteration is designated as Antenna-I. This antenna exhibits the maximum bandwidth of 8.35 GHz from 4.12 to 12.47 GHz. Further, this bandwidth has been enhanced and inflated as 10.29 GHz from 2.07 to 12.36 GHz, by introducing the SRR structure in the geometry of 3rd iteration of the designed antenna and designated as Antenna-II. Similarly, to further improve the performance parameters the rectangular stubs are introduced in the structure of Antenna-II to obtain the proposed antenna final geometry called Antenna-III. The final structure of the proposed antenna shows improved impedance matching and exhibits the bandwidth of 11.43 GHz (1.30–12.73 GHz) and 5.17 GHz (14.83–20.0 GHz) in 1 to 20 GHz frequency range. The total dimensions of the proposed antenna is 36 × 32 mm2 and can be valuable for different multiband wireless applications such as a DCS, PCS, UMTS, Bluetooth, WiMAX, GSM, IEEE 802.16e, ITU, IEEE802.11a (WLAN)/b/g, C/S/X/Ku and K band.

A compact dual-polarized co-radiator MIMO antenna for UWB applications

AbstractIn this research study, a compact dual-polarized co-radiator ultra-wideband (UWB) multiple-input multiple-output (MIMO) antenna with improved impedance bandwidth and isolation is proposed for wireless applications. The designed co-radiator has an overall area of 0.3λo × 0.3λo mm2 (where, λo is free space wavelength corresponding to the lower cut-off frequency, i.e., 3.1 GHz). The proposed resonator comprises of a hybrid geometry which is created with the combinations of a circular-shaped patch, a square, and two rectangular stubs. It is centrally aligned between two 50 Ω micro-strip feed lines that are positioned orthogonal to each other. Further, the modified ground plane is attached with the end-loaded line which provides broadband isolation over entire UWB frequency band. The simulated results of the proposed antenna exhibit wideband characteristics with impedance bandwidth of 3.1–16.9 GHz with minimum isolation of −15 dB. Moreover, all the radiation performance parameters are analyzed and discussed. Some important diversity parameters such as envelope correlation coefficient, mean effective gain, effective diversity gain, and channel capacity loss have also been evaluated. Furthermore, all the measured results of proposed antenna agree well with the simulated results which make the proposed antenna a suitable candidate for UWB-MIMO wireless applications.

High strength steel square and rectangular tubular stub columns infilled with concrete

This paper presents the experimental and numerical investigations of high strength steel square and rectangular tubular stub columns infilled with concrete. Firstly, a series of tests was conducted on cold-formed high strength steel (CFHSS) square and rectangular tubular sections infilled with three different concrete compressive strengths, i.e., 40, 80 and 120 MPa. The CFHSS tubular sections had the nominal 0.2% proof stress (yield stress) up to 900 MPa. Secondly, an extensive numerical study accounting for the confinement effect, as well as the non-linearities of materials, geometry and contacts was performed. Upon validation against the test results, a parametric investigation was conducted. The structural behaviour of concrete-filled CFHSS stub columns was investigated, including the ultimate load, end shortening, strength enhancement index and ductility index. Finally, the experimental and numerical results were used to assess the suitability of the design rules specified in the current American Specification (AISC) and European Code (EC4) for the compressive strength of the concrete-filled CFHSS square and rectangular stub columns. It was found that the predictions from EC4 were generally unconservative while those from the AISC were conservative. However, the predictions by EC4 became conservative if the effective strength of infilled concrete or the effective area of outer steel tubes were considered in the design. In addition, the predictions by EC4 became less scattered for different infilled concrete strengths when the effective concrete strengths were used. However, using the effective concrete strengths or the effective areas did not lead to the improvements of for the AISC specifications.

Fano resonance in a MIM waveguide with double symmetric rectangular stubs and its sensing characteristics

In this paper, a metal–insulator–metal (MIM) type surface plasmon waveguide structure is designed, which is composed of a circular split-ring resonance cavity (CSRRC) and a double symmetric rectangular stub waveguide (DSRSW). The finite element method (FEM) is used to investigate the transmission characteristics of the structure. The results show that the interference between the wide-band continuous state excited by the DSRSW and the narrow-band discrete state excited by the CSRRC produces double Fano resonances. The resonance wavelength and line shape of the Fano resonance can be tuned by the geometric parameters of the structure. After optimizing the geometric parameters, the sensitivity of the structure can be up to 1180 nm/RIU, and the figure of merit (FOM) can be up to 5585.3. Meanwhile, the structure can produce a maximum optical delay of about 0.128 ps, and the corresponding group refractive index is about 42.67. This structure has potential applications in refractive index sensors and slow light devices.

Simulation and fabrication of a high-isolation very compact MIMO antenna for ultra-wide band applications with dual band-notched characteristics

In this paper a very compact dual band-notched two-port multiple-input multiple-output antenna with low mutual coupling is presented for portable ultra-wideband systems. This antenna with overall size 18 × 35 × 1.6 mm3, consist of two identical monopole elements which fed by two 50 Ω coplanar waveguide lines and fabricated adjacent to each other on the top side of a FR-4 substrate with shared ground plane. To reduce the mutual coupling between elements, a rectangular stub was introduced between them and then it modified to a T-shaped stub. For further reduction, a rectangular slot etched out of the connected ground plane. Due to the results, proposed antenna achieves wide impedance bandwidth at each port, from 2.3 to 12 GHz covering the whole UWB spectrum except at two eliminating bands. Although this antenna has small size and simple structure, the mutual coupling between elements is lower than −20 dB. By etching out two rectangular single complementary split-ring resonators from the radiating patch, dual band-notched characteristics are obtained in WiMAX and WLAN bands. Envelope correlation coefficient of less than 0.035, nearly omnidirectional pattern, 90% radiation efficiency despite lossy substrate, high multiplexing efficiency (>−1 dB) except at two notches and peak gain near 6dBi are some other characteristics of this design.

A wideband compact antenna with quad‐circular polarized bands in its operating regions

This article presents the design of an offset CPW-fed slot antenna which exhibits a narrow impedance bandwidth (IBW; |S11| ≤ −10 dB) extending from 1.20 GHz to 1.45 GHz and another wide impedance bandwidth from 1.86 GHz to 8.4 GHz thus covering almost all the conventional operating frequencies. The antenna is loaded with semicircular and rectangular stubs and meandered microstrip lines to realize circular polarization at 1.35 GHz, 3.3 GHz, 4.9 GHz, and 7.5 GHz with axial ratio bandwidth (axial ratio ≤ 3 dB) of 19.25% (1.2-1.46 GHz), 4.24% (3.24-3.38 GHz), 4.1%(4.8-5 GHz), and 5.2% (7.3-7.69 GHz) respectively thus covering the GPS, WiMAX, WLAN, and X-band downlink satellite communication application bands. The mechanism of generation of CP is discussed using vector analysis of surface current density distribution. The gain is fairly constant in the wide IBW region with maximum fluctuation of 1.2 dB. The structure is compact with an overall layout area of 0.27λ × 0.27λ, where λ is the free-space wavelength corresponding to the lowest circular polarized (CP) frequency. A comparison of the proposed antenna with previously reported structures is performed with respect to impedance bandwidth, compactness, number of CP bands, LHCP to RHCP isolation and gain to comprehend the novelty of the proposed design. A prototype of the proposed antenna is fabricated and the measured results are in accord with the simulated results.

A closed modified V-shaped uniplanar triple band ACS fed antenna for wireless applications

In the proposed paper, a uniplanar asymmetric coplanar strip (ACS) fed antenna with closed V-shaped radiating patch of size printed on FR4 substrate with loss tangent ( =0.02, height (h)=1.6mm, and dielectric constant of 4.4 covering WiMAX, X-band and WLAN applications is presented. The proposed closed V-shaped radiating patch is formed by joning two rectangular stubs. The resultant shape of the radiating patch is obtained by adding rectangular strips to feed line until desired multiband results are achieved. The advantage of this structure is that it forms simple configuration as well as helps the overall antenna in attaining three distinict useful frequency band with good impedance matching for S11-10 dB criteria. The proposed ACS fed antenna operates at 3.1 (WiMAX), 5.0 (WLAN) and 9.9 (X-band) GHz with impedance bandwidth ranging from 2.7-3.9 GHz, 4.4-5.5 GHz and 9.5-10.3 GHz in simulation. Under measurement the proposed antenna shows multiband phenomenon at 3.2, 5.3 and 9.7 GHz with impedance bandwidth ranging from 2.8-3.7 GHz, 4.6-5.4 GHz and 9.4-10 GHz, respectively. The antenna exhibits simulated gain of 2.51, 1.18 and 1.96 dB at the corresponding frequency bands of 3.1, 5.0 and 9.9 GHz. The key parameters of the antenna like length and width of the multi-branched strips are optimized to get the multiband operation. The deisign simulation is carried out in Ansys HFSS (High frequency Simulation Software) where different characteristics of the proposed antenna are investigated. The evolution and optimization process is dealt in detail with the help of S11, VSWR, current distributions, radiation patterns and gain.

Sensing Features of the Fano Resonance in an MIM Waveguide Coupled with an Elliptical Ring Resonant Cavity

In this article, a novel refractive index sensor composed of a metal–insulator–metal (MIM) waveguide with two rectangular stubs coupled with an elliptical ring resonator is proposed, the geometric parameters of which are controlled at a few hundreds of nanometer size. The transmission feature of the structure was studied by the finite element method based on electronic design automation (EDA) software COMSOL Multiphysics 5.4 (Stockholm, Sweden). The rectangular stub resonator can be thought of as a Fabry–Perot (FP) cavity, which can facilitate the Fano resonance. The simulation results reveal that the structure has a symmetric Lorentzian resonance, as well as an ultrasharp and asymmetrical Fano resonance. By adjusting the geometrical parameters, the sensitivity and figure of merit (FOM) of the structure can be optimized flexibly. After adjustments and optimization, the maximum sensitivity can reach up to 1550 nm/RIU (nanometer/Refractive Index Unit) and its FOM is 43.05. This structure presented in this article also has a promising application in highly integrated medical optical sensors to detect the concentration of hemoglobin and monitor body health.

Design of compact patch antenna with enhanced gain and bandwidth for 5G mm‐wave applications

A super compact parasitic patch loaded patch antenna with enhanced gain and super wide band is proposed in this study for 5G millimetre-wave (mm-wave) applications. The proposed antenna has hybrid geometry and is constructed using circular and two rectangular driven patches with two semi-circular parasitic patches fed by stepped impedance microstrip line. The two rectangular stubs are incorporated on driven patch to improve the voltage standing wave ratio (VSWR) bandwidth. The two semi-circular parasitic patches are added on the fundamental radiator (driven/main patch) to further enhance the bandwidth to cover the entire Ka-band spectrum for 5G mm-wave requirements and covers 24–40 GHz frequency spectrum with VSWR ≤2. This designed radiator is feasible to be placed inside the multilayered housing systems or can be integrated along with the electronic components existing on the printed circuit board. Furthermore, a four-element modified corporate feed array configuration is constructed and their enhanced gain performances are compared with proposed radiator (single element). Both the prototypes are fabricated and experimentally validated for impedance and radiation characteristics and it is observed that, the simulated and measured responses are in good arrangement. The presented radiating element finds its applications in future 5G mm-wave, 5G base station controlling networks and 5G wideband code division multiple access.