In this letter, a near-field focusing method for generating patterned focusing is studied. A partially excited planar array antenna is proposed for patterned focusing, which effectively suppresses the side lobes of the focusing pattern. The phase of the array antenna is adjusted by a digital phase shifter. A prototype was made and tested to verify the effectiveness of the method. Both the full planar array and the partially excited array realize the ``.'' pattern, and the partially excited array effectively reduces the side lobes. The experimental results show that the method can achieve focusing in any area. This study can provide a reference for wireless energy transfer and microwave hyperthermia.
In this article, a metamaterial-inspired decagon-shaped antenna was designed with the dimensions of 30 x 30 x 1.6 mm3 for the vehicular applications that fall under GPS (Global Positioning System), LTE (Long-Term Evolution), UMTS (Universal Mobile Telecommunication System), WLAN (Wireless Local Area Network), Wi-Fi (Wireless Fidelity), INSAT (Indian National Satellite), etc. Initially, a conventional decagon-shaped monopole antenna was designed for the frequency of 4.5 GHz. Then, a decagon-shaped metamaterial unit cell was designed for the frequencies of 1.5 GHz, 2.4 GHz, and 3.5 GHz which were inspired on the monopole antenna to obtain the desired passbandcharacteristics under vehicular bands. All the simulations were done in the ANSYS High-Frequency Structure Simulator (HFSS) 2019 R2 version. In order to determine the metamaterial characteristics of the proposed unit cell, Scattering Parameter Retrieval Method has been used, and the values of permeability have been obtained through MATLAB. Further to examine the antenna performance in vehicular communication, it is placed on the rooftop and front side of the car model in simulation and on a physical car. Return loss characteristics were observed in the simulation as well as in the open space measurement, and the radiation pattern is analyzed with the SBR+ (Shooting and Bouncing Rays) method. The gain and radiation efficiency of the antenna get increased when it is mounted on the car model which is beneficial for the proposed application.
Metamaterial absorbers are widely used in sensing, cloaking, imaging, etc. Currently, most metamaterial absorbers are integrated with hard substrates, which limit their applications for non-planar and irregularsurfaces. In this paper, a flexible, foldable metamaterial absorber is proposed using a matrix-assisted catalytic printing method. The absorber is composed of periodically patterned eight-round sector copper arrays supported by a polyethylene terephthalate substrate. Experimental results show that the absorber exhibits one absorption peak near 10.2 GHz.
The performance of the Capon beamforming sharply decreases against strong directional and large deviation interference. In order to reduce the impact of the abnormal interference, this paper proposes a large degree of freedom null broadening beamforming for non-circular signals. The signal vector is first extended by a uniform linear conjugate array. The covariance matrix of the array is then reconstructed by projection transformation and diagonal loading technique. Finally, the beamforming is constrained by the characteristic subspace of the guide vector matrix, and the analytic expression of the optimal weights of the method is derived. The numerical simulations demonstrate that the proposed null broadening method has the advantages of high degrees of freedom and strong parameter selection robustness.
A frequency multiplexed coding metasurface controlling beam is proposed to enrich the functions of a single metasurface. A square F4B dielectric substrate with a copper-clad bottom surface and a V-shaped and quadrangular cross-shaped metal structure is used as the unit. Applying the different responses of x and y polarized waves and optimization of structural parameters, we can obtain 1-bit coding units for the two frequency bands. The reflection phase can be modulated independently of each other. The design of a dual-band metasurface with different beam splitting effects was realized, achieving the goal of different frequency multiplexing functions on a single metasurface. An RCS reduction of 11 dB at 12 GHz and a double beam splitting at 20 GHz with a pitch angle of ±47.6° are achieved by metasurface. The test results agree well with the simulation results. The proposed metasurfaces offer a simple structure, low cost, good performance, and promising great applications in areas such as frequency multiplexed communications.
An efficient 0.6-4.2 GHz GaN-HEMT power amplifier based on Klopfenstein taper is proposed in this letter. A method based on source-pull/load-pull simulation has been used to find the optimum source and load impedances across the broad band. Then the Klopfenstein taper is studied and adopted for the output matching circuit design to achieve broadband performance. The measured results show that our proposed power amplifier has a fractional bandwidth of 150%, with saturated output power ranging from 39.45 to 42.32 dBm, power added efﬁciency from 45.1% to 64.8%, and over 9 dB gain at the whole working band of 0.6-4.2 GHz. The fabricated power amplifier can cover most of the wireless communication frequency bands.
An ultra compact antenna for low frequency application is presented. The resonant frequency band of the proposed antenna is centered at 403.5 MHz, employed for medical implant communication service (MICS) band. The proposed antenna is designed and fabricated on a substrate with εr = 4.4, tanδ=0.02 and thickness h = 1.6 mm. The size of the antenna is only 0.04λ0 x 0.022λ0 x 0.002λ0 (29 mm x 16.5 mm x 1.6 mm), making it very compact for low frequency of operation. The antenna is evolved from a CPW transmission line. During the process of evolution of the proposed antenna, dual-composite right left handed (D-CRLH) behavior is confirmed from the dispersion diagram. The equivalent lumped circuit model for the antenna is also developed, and the D-CRLH behavior is also confirmed from the circuit model.
A wideband compact shark-fin antenna operating in a frequency band from 2.86 GHz to 7.68 GHz is presented. The proposed design is realized on a substrate material of ``Rogers 4003C'' with εr = 3.48, tanδ = 0.0027, and substrate thickness 0.81 mm. The antenna is designed to operate at a center frequency of 5 GHz with an operating bandwidth of 4.82 GHz (96.4%). The bandwidth covers the lower band and mid band of 5G at resonant frequencies of 3.5 GHz and 5.8 GHz, respectively. The realized gain of the proposed antenna is 4.1 dBi and 5.35 dBi in the lower band and mid band, respectively. The proposed antenna is designed and simulated. It is also fabricated using photolithography techniques and measured using an R&S vector network analyzer. Good agreement is obtained between the simulated and measured results.
In this paper, a standard ray tracing model based on Geometrical Optics (GO) is proposed for predicting the signal strength of Wireless Sensor Network (WSN), ZigBee nodes, in an indoor environment. The signal strength is calculated analytically. The results are compared with numerical analysis implemented in FEKO computational electromagnetic software, and agreement is demonstrated. Also, the model is verified by a simple measurement campaign in a straight corridor section of commercial building, and results agreement is obtained. The results show that the proposed technique is capable of predicting the signal strength of WSN sensors in a corridor section of indoor environment with good accuracy, fast calculation time, and low computational resources and complexity. The proposed analytical model and measurement dataset can help WSN designers select the best locations of ZigBee nodes in a straight corridor section with good signal quality.
The electromagnetic wave perfect absorption of metamaterial is focused on by scientists currently. Conventional studies typically use a basic unit cell and then develop the entire structure in production. In this paper, we study and use a full-sized twisted metamaterial structure with the expectation that this structure will reveal outstanding advantages and possess excellent electromagnetic absorption properties. The structure of the twisted metamaterial consists of two coincident layers of cyclic lattice stacked on top of each other. When one lattice layer rotates at a specified angle relative to the other, it generates a new lattice configuration and increases the absorption of the structure. Therefore, the frequency band widens up to 6 GHz.
In this article, we focus on metric space in Finsler geometry and propose a method of ship detection in synthetic aperture radar (SAR) amplitude image based on Finsler information geometry. This provides deep unified perspectives of Finsler geometric application. The proposed method consists of three stages: The Weibull manifold model is used to represent the statistical information of intensity SAR images; then the Finsler metric is constructed to realize the distance measurement between probability distributions in Weibull manifold space; finally, Finsler metric space is used to achieve saliency representation and detection of ships. Theoretical analysis and comprehensive experimental results demonstrate the robustness and effectiveness of the proposed approach using typical real SAR images.
A high-selective wideband bandpass filter (BPF) with a notched-band and harmonic suppression is proposed in this paper. Firstly, a uniform impedance resonator with an embedded open-circuited stub square loop is applied in the filter design. By adopting parallel-coupling structure at I/O ports, such a resonator can generate a notched-band within the passband due to the counter-phase cancellation of two dissimilar signal paths. The width of the square loop can be adjusted to select the location of the notched-band. Secondly, by introducing an L-shaped open-circuited stub to one input feed line, a transmission zero (TZ) is created. It can be used to suppress higher harmonic passband. The filter is designed and fabricated with the notched-band centered at 8.1 GHz, and two TZs are implemented at the both sides of the passband. Simulated and measured results show that the filter has a good selectivity and a wider stopband characteristic.
A filtering dielectric resonator antenna (FDRA) using an inductive CPW (coplanar waveguide) feed structure is proposed. Simultaneously, a pair of slotline stubs are respectively loaded on the signal line and ground of the CPW feed structure, which is used to generate radiation nulls near the edges of the passband. Furthermore, the two radiation nulls can be controlled independently by adjusting the length of the loaded two pairs of slotline stubs. In addition, it is interesting that TE111 mode is split due to the different loading effects of slotline stubs in feed network, thereby three resonances in the passband are formed. Finally, an FDRA with quasi-elliptic function response is realized without additional filtering circuit. The prototype of the FDRA operating at 3.53 GHz was fabricated and measured to verify the design validity. The measured results show that the impedance bandwidth is 13.6% (3.29-3.77 GHz); the gain is basically stable at 5.7 dBi wihtin the passband; and the two radiation nulls are located at 3.05 GHz and 3.88 GHz, respectively.
A frequency- and pattern-reconfigurable cone antenna utilizing liquid metal is investigated. It contains a cone antenna, four reflectors, and a circular ground plane. The transparent resin is processed into a mold for the cone and reflective poles to store the liquid-metal. By controlling the poles height in the mold, the proposed antenna can realize four radiation patterns. Meanwhile, the cone height could be adjusted by the reflective poles, thereby achieving frequency tuning. The simulation and measurement results show that, by tuning and switching the liquid-metal radiator and reflectors, a wide frequency tuning bandwidth of 43.2% is achieved, and a pattern reconfigurable with five types of beam steering over 360° coverage is realized. The prototype is fabricated, assembled, and measured, with good agreement between the simulated and measured results. The design of indoor coverage antenna system must have comprehensive measurement indexes such as multi-bands, multi-beams, high gain, and low cost.
In the paper, a compact wideband power divider (PD) which consists of a λ/4 unequal width three-coupled-lines, four short-circuited stubs and an airbridge resistor is presented. By connecting the four short-circuited stubs to the input and output ports of the PD, two additional transmission poles are obtained, which results in enhanced bandwidth and improved selectivity. Rigorous design equations are given according to the even-odd mode analysis, and the design parameters are obtained based on particle swarm optimization. For validation, a prototype operating at 1 GHz is fabricated and tested. The experimental results indicate that the proposed power divider exhibits a return loss of more than 17.5 dB and an isolation of larger than 18.8 dB isolation in the fractional bandwidth of 91%.
The integration of directed energy weapons (DEWs) into modern military platforms is of considerable interest to those examining the impact of emerging technology on the future fighting force. Hence the performance prediction of DEWs is of importance. The purpose of this study is to develop a simple framework where the minimum number of DEWs deployed in an operational setting can be determined, to achieve a desired level of performance.
A compact Sub-6 GHz Multiple-input Multiple-output (MIMO) antenna based on a complementary split-ring resonator (CSRR) and electromagnetic bandgap (EBG) is proposed in this paper. The antenna has an interesting structure and a compact size of 38×38 mm2. Four identical antenna elements are deposited orthogonally to each other, using polarization diversity and adding decoupling structures, so that good isolation and miniaturized size can be obtained. The isolation is less than -17.5 dB in the operating bandwidth of 3.28-3.62 GHz and -19.5 dB in 4.78-5.04 GHz. The simulation results are consistent with the measured ones, indicating that the antenna is suitable for Sub-6 GHz communication equipments.
A novel dual-band filter power divider (DB-FPD) with controllable transmission zeros (TZs) is designed using a slotline multimode resonator (SLMR) in this letter. Using the stub loading technology, each resonator mode of the SLMR can be easily controlled. Accordingly, a dual-band bandpass filter is realized. Four TZs are generated due to the loaded stubs on the SLMR and feeding network, which can improve the out-of-band selectivity. Finally, without introducing additional circuits, a DB-FPD with good performance is realized. For verification, a prototype operating at 2.01 and 4.79 GHz is fabricated and measured. The measured results are basically consistent with simulated ones. The 3-dB fractional bandwidths are 29.7% (1.72~2.32 GHz) and 7.99% (4.58~4.96 GHz), respectively, and the isolation in each band is better than 14 dB.
A novel high-selectivity bandpass filter based on a defected ground structure and substrate integrated coaxial line is proposed. Three transmission zeros near the passband are achieved by introducing a divergent-shaped resonator and two spindle-shaped defected ground structures, resulting in a high selectivity. To verify the proposed structure, one prototype with a center frequency of 4.94 GHz is designed and fabricated. The measured results show that three transmission zeros respectively located at 3.92, 4.36, and 6.00 GHz are obtained. The 3-dB passband bandwidth is 14.2% from 4.59 to 5.29 GHz. The upper stopband rejection is better than 20 dB from 5.71 to 11.31 GHz.