This paper presents low cross-polarization single-layer reflectarray elements for dualpolarization use. These elements have an omega-shaped symmetrical structure to realize the crosspolarization reduction and also provide parallel linear reflection-phase properties with almost the same slop characteristics for the frequency, thereby achieving the desirable reflection phase range more than 360˚ over the wide frequency range. To verify effectiveness of the proposed elements, a reflectarray antenna with an offset feed is constructed by them, and wideband frequency characteristics are also confirmed at Ku-band numerically and experimentally.
An antenna array system configured to offer directional dependent modulation has the capability to prevent eavesdroppers' attacks, thereby enhancing the security level of data transmission. In this paper, we propose artificial-noise-aided directional modulation transmitter utilizing a 4×4 Butler matrix with a four-element 2-D (i.e., range and angle) frequency diverse array (FDA) antenna to achieve secure transmissions, which outperforms the 1-D (i.e, angle) phased array scheme. The proposed scheme utilizes FDA Butler matrix excited by information data and injected artificial noise interference which radiates along all directions except the main information data direction. Thus, the radiation pattern during a particular transmission period will be range-angle dependent. The proposed scheme is evaluated by using constellation points in IQ space, bit error probability (BER), and secrecy capacity. Simulation results demonstrate that: 1) our scheme scrambles the constellation points along undesired direction(s) in both amplitude and phase, while preserving a clear constellation points along the pre-specified direction(s); 2) the scheme achieves better BER and secrecy capacity than that of the phased array based directional modulation scheme and other existing scheme; 3) the scheme significantly improve security performance especially in the range dimension.
Microwave Staring Correlated Imaging (MSCI) is a high-resolution radar imaging modality, whose resolution is mainly determined by the randomness of radiation source. To optimize the design of random radiation source, a novel concept of temporal-spatial relative distribution entropy (TSRDE) is proposed to describe the temporal-spatial stochastic characteristics of radiation source. The TSRDE can be utilized as the optimization criterion to design the array con guration and signal parameters by means of optimization algorithms. In this paper the genetic algorithm is applied to search for the best design. Numerical simulations are performed and the results show that the TSRDE is an effective method to characterize the randomness of radiation source, and the source parameters optimized by this method can dramatically improve the imaging resolution.
A two-step method is proposed to estimate the direction-of-arrivals (DOAs) of quasi-stationary source signals, with a partlycalibrated uniform linear array (PC-ULA). The special structure of Toeplitz matrix is utilized to estimate the sensors' uncertainties. Then, a Khatri-Rao (KR) based multiple signal classification (MUSIC) algorithm is proposed to estimate the DOAs of source signals. Simulation results show that the proposed method renders lower root-mean-square-error (RMSE) than existing KR-based ESPRIT algorithms, especially under low signal-to-noise-ratio (SNR) and small angle separation between DOAs. It is also shown that the proposed method increases the degree-of-freedom (DOF) by one, as compared to the counterpart ESPRIT methods.
For energy harvesting applications a new design of a coplanar waveguide (CPW) fed monopole antenna is presented. It covers almost all useful band ranges from 900 MHz-9.9 GHz (Radio, GSM, ISM, UWB bands). It also provides band reject characteristics for the range 3.1 GHz-5.6 GHz (HIPERLAN, C-Band, and W-LAN) to avoid interference from this range. The new design is based on the modification of coplanar waveguide (CPW) structure and optimizing the gap between patch and CPW ground for covering the ultra wideband (UWB) range and other useful ranges (Radio, GSM and ISM). Bandwidth enhancement and impedance matching for UWB range have been obtained by chamfering the corners, cutting two slots in CPW ground and dual stubs. The new design incorporates a parasitic patch above the antenna patch for tunning the desired band rejection. The entire design has been optimized at various stages during its evolution. The structure is compact in size 50×40×1.6 mm3. It may also be used for mobile, military and satellite applications.
The design of hexadecagon circular patch (HDCP) antenna for dual band operation is presented In this paper. The proposed antenna operates at two resonating frequencies 13.67 GHz, 15.28 GHz with return loss of -42.18 dB, -38.39 dB, and gain 8.01 dBi, 6.01 dBi respectively. An impedance bandwidth of 854 MHz (13.179-14.033 GHz) and 1140 MHz (14.584-15.724 GHz) is observed for dual-bands respectively. To produce the circular polarization, the HDCP antenna is incorporated with ring and square slots on the radiating patch. The defected ground structure (DGS) is considered for enhancement of gain. The proposed antenna, axial ratio is less than 3 dB and VSWR ≤ 2 for dual bands. The measured and simulated (HFSS, CST) results of of the HDCP antenna are in agreement. The HDCP antenna has work at Ku band for satellite communications.
This paper presents two novel miniaturized broadband Quasi-Yagi antennas which adopt compact layouts and two different modified bowties as driven dipoles. In these antennas, the microstrip feed and λ/4 impedance transformer are placed horizontally and rearranged in a same horizontal line with balun to reduce the vertical size. The horizontal size is reduced by loading the vertical metallic strips at the sides of bowtie driven dipole and ground patch. Compared with the conventional Quasi-Yagi antenna, the sizes of the two proposed antennas are decreased to approximately 50%. The experiment results exhibit that they have wide bandwidths of 2.27-3.35 GHz and 2.14-3.3 GHz for reflection coefficient below -10 dB. Their gains reach 4dBi over the operation frequency band, which indicate that they can be applied conveniently in wireless communications and recognition fields like WLAN, RFID, WiMAX and LTE frequency bands.
In this study, a new slot embedded microstrip antenna for dual-band dual-polarization operation is proposed. The antenna comprises a single layer structure with a square radiating patch where the feed port is located along a diagonal line of the patch. Two narrow slots parallel and close to the radiating edges of the patch are loaded on the patch. Patch without slots is resonated for X-band and another resonant frequency at Ku-band is obtained by loading the slots. Moreover, the loading of slots helps to produce two orthogonal modes of equal amplitudes at X-band. Furthermore, the feed port along the diagonal line of the square patch makes it possible to radiate di erent polarization at the two bands. The antenna can radiate circular and linear polarization at X- and Ku-band, respectively. Current distributions of the antenna at both bands are observed to explain the behavior of the antenna and con rm the polarization characteristics at X- and Ku-band. A 3-dB axial ratio bandwidth of 1.35% is achieved. Measured gains of 6.60 dBic and 5.80 dBi with good radiation performances are achieved at X- and Ku-band, respectively. Moreover, good measured cross-polarization levels of 27.6 dB at X-band and 15.6 dB at Ku-band are obtained. The measured performances of the fabricated antenna are consistent with simulated results.
Frequency selective surfaces (FSS) lter specific electromagnetic (EM) frequencies that are defined by the geometry and often fixed periodic spacing of a conductive element array. By embedding the FSS pattern into an origami structure, we expand the number of physical configurations and periodicities of the FSS, allowing for fold-driven frequency tuning. The goal of this work is to examine the fold-dependent polarization and frequency behavior of an origami-inspired FSS under normal incidence and provide physical insight into its performance. The FSS is tessellated with the Miura-ori pattern and uses resonant length metallic dipoles with orthogonal orientations for two primary modes of polarization. A driven dipole model with geometric morphologies, representative of the folding operations, provides physical insight into the observed behavior of the FSS. Full-wave simulations and experimental results demonstrate a shift in resonant frequency and transmissivity with folding, highlighting the potential of origami structures as an underlying mechanism to achieve fold-driven EM agility in FSSs.
In this paper, a single band-notched at 5.2 GHz with complementary split ring resonator (CSRR) ultra-wideband (UWB) antenna and its implementation in designing of two element multiple-input multiple-output (MIMO) with high and uniform isolation are experimentally demonstrated. The proposed UWB MIMO consists of T-shaped stub in ground plane in between antenna elements of the size of λat 3.1 GHz/4 to achieve minimum 20 dB isolation, which is almost uniform in entire UWB band. The size of the UWB MIMO antenna is 0.31λat 3.1 GHz×0.434λat 3.1 GHz×0.008λat 3.1 GHz mm3 and it is printed on RT/duroid 5880 substrate (ɛr = 2.2, tanδ = 0.0009), which leads to good gain and high total efficiency of the antenna in operating bands. The simulated and measured result shows good agreement for the impedance bandwidth (|S11| < -10 dB) and isolation (|S21| < -20 dB) most of the operating band, excluding the notched band at 5.2 GHz in UWB range. The simulated, measured and calculated MIMO antenna diversity parameters proves that the antenna is suitable for UWB MIMO systems.
A combined analysis method for determining the structural and electrical performance of very-low-frequency (VLF) T-type transmitting antennas with a complex structure is proposed. By using the finite element method for analyzing the antenna's structural performance and the moment method for determining the antenna's electrical performance, the structural entity model of the antenna is transformed into an electrical model by extracting the position and displacement information of the antenna curtain, thereby determining the electrical performance index of the transmitting antenna. An actual VLF T-type transmitting antenna is analyzed using this method. A comparison between the calculated results and the measured data shows that this method is effective and feasible. In addition, by optimizing the sag of the antenna's curtain, it is demonstrated that the radiation efficiency of the transmitting antenna can be further improved using this method, and the radiation patterns of the initial state and optimized antenna stay almost the same. This method provides guidance for the synthesis design of other VLF transmitting antennas with complex structures.
This paper solves the problem of minimizing losses in the stator magnetic core of high-speed electric machines with the use of amorphous iron. A fundamentally new technology for manufacturing of a stator magnetic core from segments of amorphous steel is developed by the authors. The feature of the new stator design is the possibility to use technological ducts located inside the stator as cooling ducts. This aspect significantly improves the heat dissipation from the active zone of the stator and, accordingly, minimizing temperature. The efficiency of this solution was studied using two power generators of 100 kW and 200 kW and rotational speeds of 60,000 rpm and 45,000 rpm respectively in the software complex Ansys Maxwell. Harmonic compositions of currents and voltages, flux density distributions in active elements of the generator in various operating modes were studied: under load, in a three-phase short-circuit and at idle. Also, the obtained data were compared with analogous models of an electrogenerator made of electrical steel. The results of the study showed the operability and effectiveness of the proposed technology. Based on the results of the research, a prototype of the stator magnetic core made from amorphous iron was created. Losses in the generator were experimentally measured. Also the results of experimental studies of aerodynamic losses are presented.
Permanent magnet linear synchronous motors (PMLSM) are well known for its high thrust performance. However, such high thrust can be distorted by the existence of cogging force due to the attraction between stator core and permanent magnet (PM). To improve its performance, two parts of the PMLSM structure were considered during the design. They are PM magnetization arrangement on mover side and stator slot opening parameters on stator side. The designed models were simulated by using FEM software, and the performances of the models are then compared. The aim of the design is to achieve high thrust and low cogging force characteristics. Apart from average thrust Fave and cogging force Fcog, the performance of the PMLSM is also evaluated using average thrust, Fave to cogging force ratio Fcog, called as thrust ratio. Based on the design, the highest thrust ratio Fave: Fcog, obtained from radial, axial and Halbach models, are 2.5032, 2.6262 and 1.8437, respectively.
This paper evaluates the effect of glasses on the Specific Absorption Rate (SAR) and the absorbed power in the human head exposed to microwave from wireless eyewear device at phone call state. Due to the sensitivity of eyes to microwave, this paper mainly concentrate on the SAR and the absorbed power in ocular tissues. The calculated results indicate that wearing glasses can obviously increase the maximal SAR and the absorbed power in ocular tissues. Glasses has almost doubled the maximal SAR in ocular tissues. The absorbed power with glasses is about 3.1-4.5 times as big as that without glasses. Furthermore, we find that the maximal SAR and absorbed power are sensitive to the width of glass leg and the thickness of spectacle lens, while variation trends with the varying glasses size are quite different. Hypermyopia patient might suffer from higher risk of getting the oculopathy due to the larger SAR caused by the thicker spectacle lens. In conclusion, wearing glasses may pose higher health risk on eyes of wireless eyewear device user. This paper would provide valuable reference data for the future evaluation of microwave biological effect on eyes.
By exploiting the micro-motion features of fast rotating targets, wideband radar has been successfully applied to high resolution imaging. However, due to the traditional fixed pulse repetition interval (PRI), the target image may suffer from aliasing in some practical situations. In this paper, under the compressed sensing (CS) radar framework, an efficient wideband imaging scheme with random PRI signal is introduced for aliasing reduction. Considering that direct application of the CS theory will result in large-scale dictionaries and high computational complexity, we firstly generate a low resolution image by applying modified generalized Radon transform on range-slow time domain and then scale down the dictionary column by reserving the atoms corresponding to those strong scattering areas. Simulation results show that this scheme can achieve aliasing-free images with acceptable computational cost.
Metal nanowires have drawn much attention due to the highly confined electromagnetic waves and relatively low propagation loss. With the increasing application potentials, we desire deeper insight into the mode behavior guided by metal nanowires for routing and controlling SPPs modes. Here, we apply the analytical solution for analyzing SPPs modes of metal nanowires. Single mode propagation condition and modes number are studied based on the analytical model. A universal formula of field diameters for all guided modes is presented, and mode field diameters are investigated. Finally, the intensity profiles of allowed guided modes are studied for specific dimensions.
This paper presents the study of an artificial material, made up of a periodic structure, defined by a unit cell, consisting of a finite number N of periodic layers of thin conducting cylinders placed between two dielectric planes. These artificial materials known as metamaterials can be regarded as a homogeneous material with effective constitutive parameters impossible to achieve with naturally occurring materials, such as negative values for both magnetic permeability and electric permittivity. An analytical model has been developed to study the effective electric permittivity of the whole system in terms of the unit cell dimensions and the frequency of the incident electromagnetic wave. Simulations of the effective electric permittivity of the metamaterial were performed by varying the geometry of the metamaterial. This analysis enables the design and construction of structures with properties that make them an attractive candidate for shielding applications in the range of microwave frequencies. The metamaterial has been constructed with four rows of 5 bronze conducting rods each. We have made experimental measurements of the shielding effectiveness of these materials when subjected to a electromagnetic plane wave with electric field polarized along the direction of the conducting rods, and conversely, with electric field polarized perpendicular to the rods. Non-zero values for shielding effectiveness were observed in the first polarization, and zero values in the second case.
A simple and compact diagonal matched feed structure is proposed for offset reflector antenna, which includes a square choke to radiate the desired conjugate mode (TE4: a higher order rectangular coaxial cable mode) for suppressing the cross-polar power of an offset reflector antenna when the reflector is illuminated by the dominant diagonal mode (TEVD: a linear combination of rectangular TE01 and TE10 modes) radiated from the aperture of a central diagonal waveguide. Square choke is excited by two identical slots on the central diagonal waveguide using the longitudinal magnetic field of main operating mode TEVD. Wideband conjugate matching as well as impedance matching for broadband operation can be achieved by such radiating main mode and conjugate mode from apertures which are spatially separated. Based on the above configuration, a J-band matched feed structure is designed using HFSS software for a given offset reflector geometry. The proposed matched feed structure is fabricated and measured. The measured results are compared with simulated ones, and close agreements are found.
The work presents a simple and novel design approach to extend the bandwidth of existing Dielectric Material Based Microwave Absorber (DMBMA). The design comprises planar square patches of DMBMA placed periodically on a metal-backed FR4 sheet. For demonstration purpose, the DMBMA is synthesized by adding conducting carbon fillers in polyurethane matrix, and its electromagnetic parameters are measured in X-band. A single reflection null is observed in DMBMA owing to λ/4 resonance. In comparison, the bandwidth of 8 GHz (10-18 GHz) is achieved for -10 dB reflection for square patch based DMBMA. The thickness of proposed absorber is 2.75 mm. An additional resonant mode is observed due to capacitive coupling between the square patches. The enhanced bandwidth is attributed to the overlapping of λ/4 resonance and induced coupling mode. A good agreement between the simulated and measured data is observed.
An innovative and general approach is proposed to the optimal, mask-constrained power synthesis of circular continuous aperture sources able to dynamically reconfigure their radiation behavior by just modifying their phase distribution. The design procedure relies on an effective a-priori exploration of the search space which guarantees the achievement of the globally-optimal solution. The synthesis is cast as a convex programming problem and can handle an arbitrary number of pencil and shaped beams. The achieved solutions are then exploited as reference and benchmark in order to design phase-only reconfigurable isophoric circular-ring sparse arrays. Numerical results concerning new-generation telecommunication systems are provided in support of the given theory.
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