We propose single/dual circularly-polarized (CP) antennas based on reflective metasurfaces with cross-polarization conversion. By suspending a probe-fed printed bow-tie dipole or a crossed bow-tie dipole above the reflective polarization-conversion metasurface and appropriately tuning the distance between them, a single-CP or a dual-CP antenna is generated. The theoretical design principle on this novel CP antenna structure has been discussed. Simulations and experiments are conducted to validate the design principle. The measured results show that the proposed single-CP antenna has achieved a 3-dB axial ratio (AR) bandwidth of 8.0%, from 12.67 to 13.72 GHz, and a peak gain of 8.03 dBi, while the dual-CP antenna exhibits a dual-CP AR bandwidth of 7.1%, from 13.09 to 14.05 GHz, and peak gains of 8.49 dBi and 7.03 dBi for left-handed circular polarization (LHCP) and right-handed circular polarization (RHCP), respectively. The measured isolation between the two ports of the dual-CP antenna is less than -20 dB. The operating frequency of the proposed antennas can be easily scaled to other frequencies that are applied to some specific wireless applications.
This article present a synthesis modelling of isolation in a diamond-shaped fractal electromagnetic band gag (DSFEBG) based two-port multiple input and multiple-output (MIMO) antenna using the Gaussian Process Regression (GPR). A compact two-port MIMO antenna with 0.140λ inter-element spacing is considered for isolation improvement. To predict mutual coupling in two-port MIMO antenna supervised learning-based regression technique of GPR, the model is trained with 50 samples and tested on 125 samples. The model performs result prediction in less than 1 second with RMSE less than 0.0001%. For a better understanding of the isolation between elements of the MIMO antenna, the automatic relevance determination property of GPR is presented. The proposed model does faster computation and is efficient in predicting isolation in DSFEBG based antennas for lower and high-frequency bands of 5G communication system.
Reconfigurable intelligent surfaces (RISs) have recently attracted attention in the implementation of smart radio environment. In this paper, RISs are realized by the near-field focused antennas (NFF). A near-field channel gain model of RIS-assisted wireless communications is developed for an NFF reflectarray antenna based on the physics and electromagnetic nature of the RISs. The developed model entails the computation of the reflectarray aperture efficiency. Also, it takes into account reflectarray reconfigurablility to cope with varying environment, physical factors like the physical dimensions of the RISs, and the radiation patterns of the unit cells. Moreover, it is characterised by a reduction in the complexity. This model is further used in computing the positioning performance bounds and estimating the RIS optimal beamformer weights. For a validation purpose, the model is simulated by using Matlab software, and the results are compared to the simulation results of a near-field model discussed in literature. The comparison shows a very good agreement. Finally, the reflectarray antenna is thinned to achieve a performance comparable to a fully populated reflectarray antenna case using the full wave 3D electromagnetic solver CST Microwave Studio (CST MWS).
A coplanar waveguide fed asymmetric rectangular antenna with sufficient WLAN-band rejection is presented for ultra-wideband applications. The antenna uses an asymmetric rectangular patch, modified feedline, and defected coplanar ground plane for obtaining ultra-wideband performance. An inverted-L shaped slit in the radiating patch is used for realizing the WLAN band-rejection. The antenna is designed on 1.6 mm thick FR-4 substrate having an area of 12×16 mm2 (0.169λL×0.225λL). An impedance bandwidth of 11.49 GHz with a WLAN band-notch from 5.15-5.86 GHz is achieved. In addition to this, desirable radiation characteristics in terms of stable radiation patterns, peak realized gain of 4.5 dBi, and maximum total efficiency of 81% are achieved in the pass-band. In the notched-band, the peak gain and total efficiency reduces to -1.3 dB and 40%, respectively. Measured results agree well with simulated results. This antenna structure has fractional bandwidth of 115.18% and a bandwidth dimension ratio of 3029, which is comparable or better than that of similar structures available in the literature. The proposed antenna has desirable time domain performance in terms of fidelity factor, group delay, isolation and S21 phase.
The main intention to present this work is to miniaturize and gain enhancement of a tapered microstrip patch antenna, which resonates for Global Positioning System (GPS) of L1 band at 1.575 GHz. To accomplish this, we present a new design configuration of a Tap-Shaped Defected Ground Structure (TSDGS). It has been utilized to switch the resonant frequency from 14.5 GHz to 1.575 GHz with no adjustment of areas of the actual Tapered Microstrip Patch Antenna (TMPA). The prototype antenna is fabricated on a Roger RT Duroid substrate merely 58 × 22 mm2. Conclusively, a miniaturization allowed up to 89.31%, with regard to the TMPA, is excellently accomplished. The gain of the proposed antenna is successfully enhanced with properly locating the metamaterial superstrate onto the basic patch antenna. A gain of 7 dBi improvement has been achieved. The proposed design process is done with two different solvers, ADS and HFSS.
The Coefficient of Variation (CoV) is investigated, studied, and proposed as an alternative and important performance metric to describe the effects of handset orientation on the capacity of Multiple-Input-Multiple-Output (MIMO) systems. We combine 3-D simulated radiation patterns of a base station and handset and their associated scattering parameters in two anisotropic propagation environments. The capacity is evaluated as the handset rotates about the X-Y-Z axes using standard Euler's angles. The coefficient of variation is numerically derived by rotating the handset over the Euler angles (φ, θ, ψ) in each direction every 15° about each axis over a full sphere where each rotation involves the creation of numerous instances of the propagation environment depending on the statistical robustness of the results sought. Three antenna array geometries operating at a frequency of 2.45 GHz are examined using two different propagation channel models (TGnB and TGnF) to verify the validity of the proposed approach. The derived results suggest that the proposed CoV is an effective and practical reasonable metric in selecting the best antenna system design, where ``best'' here refers to the design with the ability to reach the highest throughput of the designs considered.
A tri-band negative group delay (NGD) microwave circuit for multiband wireless applications is proposed and self-matched without the need for external matching networks. The frequency range can be influenced by the characteristic impedance of the microstrip lines. Under the condition that the microstrip circuit can be implemented with the common printed circuit board (PCB) fabrication technology, the frequency ratio of the highest NGD band to the lowest NGD band can vary between 3.8 and 10.9. For verification, a 1.2/3.5/5.8-GHz tri-band NGD circuit for Beidou B2, WiMax, and WLAN application is designed, fabricated, and measured. From the measured results, the NGD times are -1.08 ns, -1.19 ns, and -1.09 ns at three NGD central frequencies with insertion losses of 16.4 dB, 24.6 dB, and 18.9 dB, respectively. And the measured NGD bandwidths are 12.40% for the lower band, 8.60% for the center band, and 3.59% for the upper band, in which the return losses are greater than 16 dB.
A segmented three-dimensional wire monopole antenna is proposed and optimized to operate in both the Wi-Fi and Wi-Max frequency bands (2.4-2.48 and 3.3-3.7 GHz). The fabrication of the antenna employs both three dimension printing and foundry techniques. The design occupies a total volume of 33.8 mm × 30.4 mm × 37.4 mm, which is equivalent to 0.28λ0 × 0.25λ0 × 0.30λ0, where λ0 is the central wavelength of the lower band. The measurements agree with the simulations and show that the antenna has a -10 dB impedance bandwidth of 7.53% (2.36 to 2.55 GHz) and 53.87% (2.78 to 4.43 GHz) and a measured -3 dB axial ratio bandwidth of 19.06% (3.18 to 3.85 GHz) for the second band. For the first band, simulations indicate that the polarization is elliptical. The radiation pattern is a near hemispherical coverage toward the upper hemisphere. The measured maximum gain values are 5.6 and 7.3 dB for the lower and upper bands, respectively. The simulated radiation efficiency is higher than 98%.
Corrugated substrate integrated waveguide (CSIW) based bandpass filter is designed and developed for the microwave interferometer (7.0 GHz) and ISM band (5.7 GHz-5.9 GHz) application. CSIW structure provides a cost-effective solution counter to substrate integrated waveguide (SIW). Initially, the CSIW structure is designed from the design methodology of SIW. Vias are replaced with a quarter wavelength open stub. A metallic inductive post is used for the realization of the bandpass filter from the CSIW structure. Computer simulation technology (CST) software is used for design and simulation of the proposed model. Two structures are implemented for the microwave interferometer and ISM band frequency application. The first structure resonates at the center frequency of 7.023 GHz with the fractional bandwidth of 5.26%. It provides an insertion loss value of less than 1.5 dB and a return loss better than 14 dB. Similarly, the second structure provides passband frequency, from 5.6 GHz to 6.0 GHz, with the insertion loss value less than 1.5 dB and return loss better than 18 dB at the center frequency. It can be used for the ISM band frequency application. The frequency tuning approach is also shown to change the resonance frequency for different applications. For the proof of concept, the proposed filter is fabricated and tested. The measured results are quite similar to the simulation results.
Wireless technology plays a vital role in data transfer. There is an acute need of smart wireless devices which could respond effectively for specific applications. This paper presents a defected ground plane based planar antenna. The presented antenna has the potential to operate at 2.47 GHz, 3.55 GHz, and 5.55 GHz frequencies with gains of 3.88 dBi, 3.87 dBi, and 3.83 dBi having impedance bandwidths of 14.61%, 5.42%, and 5.40% respectively. Flame Retardant 4 (FR4) is employed as a substrate. The agreement between simulated and measured results points out the utilization of the presented structure for Wi-Fi/WiMAX/WLAN applications.
This manuscript presents the design of an antenna based on nested square shaped ring fractal geometry with circular ring elements for multi-band wireless applications. The impedance bandwidth and reflection coefficient of the antenna are improved with the design of different iterations from the 0th to 2nd. The performance parameters of the antenna like reflection coefficient, VSWR, bandwidth, bandwidth ratio and current density are improved in the final iteration. It also achieves the enhanced bandwidth greater than 3 GHz at three resonant frequency bands and exhibits additional frequency band at 2.4 GHz. Likewise, the frequency band of designed fractal antenna shifts towards the lower end and helps in achieving the miniaturization of antenna. The proposed fractal antenna is designed and fabricated on a low-cost FR4 glass epoxy substrate and investigated using HFSS software. The proposed antenna is optimized for generating different parameters, and the last geometry is fabricated and tested. Further, these parameters are compared with the experimental results and found in good agreement with each other. Due to the multi-band behaviour and improved bandwidth, the proposed fractal antenna can be considered as a good candidate for several wireless standards.
This work presents the design and implementation of a four-section reconfigurable uniform impedance resonator (UIR) active filter. UIR active filter consists of λg/4 microstrip line resonators cascaded in series with parallel coupled lines (PCLs). An additional quarter wavelength section is added to the coupled line quarter wave resonator section and gives flexibility in the coupling length. The proposed active filter provides a gain as a means of compensation to loss incurred by passive circuitry. In addition, it gives high selectivity (-70 dB) and wide stopband. The wide stopband is the result of suppression of spurious frequencies which is accomplished by using shunt stub resonators at appropriate locations in the active filter. The bandwidth reconfigurability is achieved by varying the bias currents of the active devices as well as by tuning the varactor diodes. The UIR concept with active matching is implemented on an FR4 substrate (εr = 4.4), with passband gain of around 15 dB at 1.3 GHz, and out of band rejection is better than -35 dB at twice the centre frequency of 1.3 GHz.
In this paper, we study a double intelligent reflect surface (IRS) aided secrecy transmission design in multiple-input single-output (MISO) channel. Specifically, we investigate a joint active and passive beamforming design to maximize the secrecy rate, subject to multiple non-convex constraints. An alternating optimization (AO) method is proposed, where the unit modulus constraints are handled by the alternating direction of multipliers method (ADMM) and majorization-minimization (MM) methods. Simulation results show the superiority of the proposed design.
This study presents a differentially driven log-periodic dipole array system with high isolation between reception and transmission ports for wideband full-duplex applications. The antenna system is composed of two pairs of log-periodic dipole arrays operating in the X-band spectrum from 8 GHz to 12 GHz. The system offers a low cross-polarization between E-plane and H-plane (less than -25 dB). The simulation results show high isolation S21 < -60 dB through the entire X-band while the measured results reach S21 < -45 dB in a reflective lab room. Furthermore, in order to verify the measured values, a modified 180º out-of-phase wideband power divider is used to feed transmitting and receiving ports. The second measured outcomes also attain total isolation greater than 45 dB for the entire band of interest. The proposed design is able to cover both orthogonal transmitted and received directions with reasonable gain values, high efficiency, and good impedance matching.
This paper presents a high gain dielectric resonance antenna (DRA) array for vehicular wireless communication and 5G system in millimeter wave band, which takes the advantage of low side lobe level (SLL). The planar antenna array is composed of 8×8 rectangular DRA elements, whose operation mode is the fundamental mode TE111. The beamforming weights of the array are designed based on the principle of Dolph-Chebyshev distribution to suppress the antenna SLL. The planar array consists of 8 linear sub-arrays, which are fed with standing-wave series resonance method respectively. The excitations of sub-array elements are precisely adjusted based on the aperture coupling model. Furthermore, the series-parallel hybrid feed network and parallel-cascaded feed network are applied to unequally feed the sub-arrays in accordance with Chebyshev polynomials. The measurement results of prototype validate the design solution of antenna array. The impedance bandwidth is 570 MHz (25.77 GHz-26.34 GHz) for reflection coefficients less than -10 dB, and the antenna gain and SLL are 20.5±1 dBi and 20 dB, respectively. Due to the advantages of miniaturization and narrow beam, the proposed DRA antenna array is adequate for vehicle communication equipment.
Novel substrate integrated waveguide bandpass filters are presented by using a complementary split-ring resonator. The proposed stepped impedance octagonal octagonal complementary split-ring resonator (SI-OCSRR) presents high miniaturization compared to the classical octagonal complementary split-ring resonator (O-CSRR). Additionally, two different filter configurations consisting of two cascaded cells with different coupling between the CSRR are proposed. A comparison between the proposed filters and the other ones reported in the literature has proven the advantages of the proposed filters, namely compact size, high in-band return loss, and ease of integration. A good agreement between the simulated and measured results has been reached, which verifies the validity of the design methodology.
This paper presents the design and fabrication of HE11 miter bend along with a TM11 to HE11 mode converter and corrugated up-taper, which are the integral parts of a transmission line system (TLS) that carries 200 kW microwave power at 42 GHz from Gyrotron to plasma or calorimetric dummy load. It has a hybrid (HE11) mode. The HE11 mode transmission loss in miter bend is derived using mode-matching techniques and gap loss theory. The gap length (L) in a waveguide of diameter (D = 2a) at a wavelength (λ) for the predicted loss (D ≥ λ) is approximately 1.7[Lλ/2a2]3/2 dB. The HE11 miter bend design incorporates a demountable cooling assembly with a flat mirror. The design and optimization of the proposed miter bend were carried out using CST-microwave studio software. Finally, HE11 miter bend was fabricated along with integrated assembly. The proposed HE11 miter bend with mode converter and corrugated up-taper gives the transmission efficiency of 95.64%.
Discovering governing equations for transmission line is essential for the study on its properties, especially when the nonlinearity is introduced in a transmission line system. In this paper, we propose a novel data-driven approach for deriving the governing partial differential equations based on the spatial-temporal samples of current and voltage in the transmission line system. The proposed method is based on the ridge regression algorithm to determine the active spatial differential terms from the candidate library that includes nonlinear functions, in which the time and spatial derivatives are estimated by using polynomial interpolation. Three examples, including uniform and nonuniform transmission lines and a specific type of nonlinear transmission line for soliton generation, are provided to benchmark the performance of the proposed approach. The results demonstrate that the newly proposed approach can inverse the distributed circuit parameters and also discover the governing partial differential equations in the linear and nonlinear transmission line systems. Our proposed data-driven method for deriving governing equations could provide a practical tool in transmission line modeling.
This paper proposes an SRLSM with segmental stator pole. The segmented SRLSM which is known as SSRLSM was designed for domestic lift application. The SSRLSM was designed to fulfill the design target requirement where the lift must be able to transport a maximum 200 kg payload. This payload requires a motor with more than 2000 N thrust force at rated power of 1.5 kW. The rated current is 2.5 A. However, for the excitation current, the maximum current is taken twice of the rated current which is 5.0 A. The design of the SSRLSM was completed in two stages. The first stage is to design the stator pole length, lst, while the second stage is to design the stator pole thickness, tst. The designed models were simulated with FEM software. The simulation results show that the highest thrust produced in first stage is 6773 N. The thrust is produced by the model with stator pole length, lst, of 120 mm. Meanwhile, in the second stage, the model with the stator pole thickness, tst, of 20 mm produced the highest thrust. The thrust obtained from the model is 6903 N. Based on the analysis, the final model was selected. The model has the stator pole length, lst, and stator pole thickness, tst, of 120 mm and 20 mm, respectively.
Measurements of the complex permittivity and permeability of solids at high electromagnetic field greater than 10 kV/m pose a significant challenge to RF connectors and input amplifiers of the measurement equipment. Specifically, difficulties arise in measuring materials with high imaginary permittivity or low impedance, which act as short circuits, either exceeding the measurement equipment damage threshold or that of the material under test, and/or inducing an unacceptable signal-to-noise in the collected data. In this work, we report the development of a new measurement technique where we introduce an outer air-gap between the material under test and the conductor of a coax airline. The introduced air-gap reduces the effective conductivity of the sample, mitigating damage to the materials under test and allowing for high power measurement. This study compares the ability of air-gap correction methods to recover the complex permittivity and permeability to within 10% of the value measured without an air-gap introduced.