A study is made of the electrodynamic characteristics of an antenna having the form of a perfectly conducting, infinitesimally thin, narrow strip located at a plane interface of an isotropic medium and a cold collisionless magnetoplasma. The antenna is perpendicular to an external static magnetic field superimposed on the plasma medium and is excited by a time-harmonic given voltage. Singular integral equations for the antenna current are obtained in the case of an infinitely long strip conductor. Based on the solution of these equations, the current distribution and input impedance of the antenna are found for nonresonant and resonant frequency ranges of the magnetoplasma. The limits of applicability of an approximate approach employing the transmission line theory for determining the antenna characteristics are established. Within the framework of this approach, the results obtained are generalized to the case of a finite-length strip antenna.
An E-shaped printed monopole antenna with loaded resonant elements suitable for penta-band multi-input multi-output (MIMO) application is proposed. The simple E-shaped monopole antenna results in a single resonance, and by loading the vertical arm of the antenna with narrow slots and stubs, a multi-band antenna can be obtained. The slots so placed on the antenna create L-shaped resonance paths which are multiples of λg/4, and stubs resonate at λg/4. The antenna is designed for operation over the UMTS, WiMAX and WLAN frequencies 2.1, 2.5, 3.5, 5.2, 5.8 GHz. A two element array of such antennas with close spacing of λg/15 is suitable for MIMO application. The array has low mutual coupling, low envelope correlation, high efficiency and good radiation patterns over all five frequency bands. Simulation and measurement results are compared and discussed.
Curved trajectories of traditional navigation satellites limit their performance in bistatic radar imaging system. Instead of using common Inclined Geosynchronous Orbit (IGSO)/Medium Earth Orbit (MEO) satellites in motion, a new global navigation satellite system (GNSS) imaging system based on Beidou geosynchronous orbit (GEO) satellites is presented to deal with this problem. The most prominent feature of GEO satellites is that they are stillrelative to the earth. This work includes three parts. First, a reasonable parallel assumption is provided to simplify the geometric topology of the imaging system, and the relevant path delay formula is deduced. Second, the principle of imaging based on multiple GEO satellites is proposed, and the simulation result is presented. Third, the entire signal processing, which uses a multi-correlator, is designed to improve the range resolution. Two imaging experiments targeting at the trees are described and conducted in Wuhan University to verify the imaging system. The first experiment is targeted at isolated trees, and the second experiment is focused on groves along the road. Conclusion can be obtained: the imaging result is highly consistent with the imaging area, which validates the feasibility of the method and confirms the potential use of GNSS imaging system in forest monitoring.
For slower computation speed and lower classification accuracy of the traditional image classification methods, wavelet transform, multi-strategy, particle swarm optimization (PSO) algorithm and support vector machine (SVM) are introduced into image classification in order to propose a new remote sensing image classification (RIWMPS) method. First of all, wavelet transform method with multi-resolution characteristics is used to extract the features of remote sensing image. Then the steepest descent strategy, corrective decline strategy, random movement, aggregation strategy and diffusion strategy are used to improve the PSO algorithm to obtain an improved PSO (MSPSO) algorithm, which is used to optimize the parameters of the SVM model in order to construct an optimized SVM classifier for realizing remote sensing classification. Finally, the remote sensing image of Chongming Island is select to test the effectiveness of the RIWMPS method. The experiment results show that the RIWMPS method has higher classification efficiency and accuracy, and takes on better superiority and effectiveness. This study provides a new classification method for processing the remote sensing image.
Body worn antennas generally face the problem of isolation when operated in close proximity to human body. Use of magneto-dielectric material as substrate for antenna makes the system compact and reduces the influence of body on performance of antenna. In addition, miniaturization of antenna size also takes place. 7 wt.% of nano-sized Ni0.5Zn0.5 Fe2O4 is dispersed as magnetic filler in flexible linear low density polyethylene matrix. Beyond 7 wt.%, the sample stiffens and loses flexibility because of percolation limit of the polymer. Verification of the composite as a potential substrate for a body worn antenna is carried out by fabricating a coplanar waveguide fed simple rectangular monopole antenna, using transmission line model at 6 GHz. Antenna performance is studied by wearing the patch on human wrist. S11 of -21.78 dB at 5.32 GHz and -10 dB bandwidth of 49.62% is observed. For comparison, an antenna at the same resonant frequency is developed on linear low density polyethylene with magnetic inclusions. The antenna on magneto-dielectric substrate shows better performance than dielectric substrate. The magnetic and dielectric properties of the Nickel Zinc Ferrite-linear low density polyethylene composite magneto-dielectric substrate reduces the influence of the human body which makes the antenna system compact and robust as additional techniques are not required for shielding of human body influence on antenna performance.
A wideband circularly polarized antenna with wide half power beamwidth (HPBW) and 3 dB axial-ratio beamwidth (ARBW) is proposed in this paper. The circularly polarized (CP) radiation is realized by feeding two crossed printed dipoles through a wideband feeding network with broadband 90º phase shift. By adding a thick substrate layer and a notched-corner metal cavity around the antenna, the impedance bandwidth (VSWR < 2) is greatly enhanced. The HPBW of the proposed antenna are greater than 110º while the ARBW are greater than 130º in the operating band, simultaneously. The overall dimension of the antenna is only 70×70×36 mm3. The measured results show that the impedance bandwidth of the proposed antenna reaches 54.7% (1.06 GHz-1.86 GHz) while the AR bandwidth (AR<3 dB) is 48.6% (1.08 GHz-1.78 GHz). As such, the proposed antenna can be widely used in various global navigation satellite system (GNSS) applications.
This work presents an enhanced rectenna with a differential source feeding scheme for radio frequency (RF) energy harvesting at 2.45 GHz frequency. A circularly polarized (CP) microstrip antenna with embedded slots is designed which efficiently attains harmonics suppression. By modifying size and position of two diametrically opposite triangular projections in the top patch, two orthogonal modes that have equal magnitude and are in phase quadrature are excited. The four radial slots embedded in the antenna can block 2nd and 3rd harmonics which is suitable for onboard rectenna design without harmonics filter. A microstrip tapered feed line is used to match antenna element with 50-ohm impedance. The designed antenna is then tested for RF energy harvesting in two ways. One is conventional single source fed rectenna (SSFR), and the other is proposed differential source fed rectenna (DSFR). In the DSFR, the designed antennas are differentially operated by making a difference of λg/2 path length (λg Guided wavelength), and the ports are then connected to a differentially driven optimized rectifier circuit. For comparison, an SSFR and a DSFR are fabricated and tested. The circuit parameters in each case are optimized in Agilent Design System (ADS) 2011 software to maximize RF to direct current (DC) conversion efficiency. The proposed DSFR has a maximum efficiency (RF-DC) of 41.63% at 10 dBm RF input power. In the input power range from -20 dBm to 10 dBm, the DSFR has improved performance and higher efficiency over the SSFR.
A miniaturized ultra-wideband (UWB) antenna based on Sierpinski square slots is reported. The antenna has a compact dimension of only 0.32λl×0.32λl (28×28 mm2), at a lower frequency of 3.4 GHz. Antenna miniaturization is achieved by etching Sierpinski square slots in the radiating decagonal shaped monopole, and UWB operations are accomplished by utilizing double truncations in the ground plane. The designed antenna has a fractional bandwidth of about 127.3% (3.41-15.37 GHz) in simulation and about 124.7% (3.50-15.1 GHz) in measurement. The time domain characteristics of the designed antenna are discussed in detail. Good radiation characteristics and impedance matching are exhibited by the designed fractal antenna in the entire UWB range.
Within the framework of the higher-order Kirchhoff approximation, the properties of the electromagnetic scattering from sinusoidal water waves are presented, and the theoretical formulas up to third-order for describing the scattering field and its spectrum are derived. It shows that not only the spectral peaks which correspond to phase velocity of the water wave but also other discrete harmonic peaks can be found from the theoretical spectrum model. And the Doppler shifts of the spectral peaks are all integral multiple of the sinusoidal wave's frequency. For the backscattering field from a sinusoidal wave, the higher-order resonant peaks would also be found at different scattering angles, and the values of these peaks decrease with the scattering angle. On the other hand, the comparisons with the MoM demonstrate that the contributions of the slope-dependent terms can be generally neglected if the amplitude of the sinusoidal wave is small. However, if the waves slope is larger, the impact of the second order scattering becomes obvious and cannot be omitted.
A single-fed compact circularly polarized quarter-mode substrate integrated waveguide (QMSIW) antenna with improved bandwidth is designed based on a single-layer structure. The antenna consists of four QMSIW elements. Instead of using a complex power divider to excite each element, an inset microstrip line is employed to excite the driven QMSIW element, while the parasitic QMSIW elements are excited by means of gap and direct couplings. Moreover, the phase and magnitude of the electromagnetic fields in each QMSIW element are controlled by gaps and short sections of microstrip line to obtain a circularly polarized radiation. A prototype of the proposed antenna is fabricated and measured, and the measured results are in good agreement with the simulated ones. The measured 10-dB impedance bandwidth is 6.23%, from 5.13 GHz to 5.46 GHz, and the 3-dB axial-ratio bandwidth is 3.62%, from 5.15 GHz to 5.34 GHz. The measured maximum gain of the antenna is 6.46 dBic.
Due to a recent growth in three-dimension (3D) printing technology, engineers can fabricate affordable and versatile antennas; however, lossy conductive materials, inadequate antenna terminations, and simplistic designs which do not adequately utilize the available volume continue to limit the capabilities of 3D printed antennas. In this work, the dielectric constants of three polylactic acid (PLA) materials, dielectric PLA, magnetic PLA and conductive PLA, were measured using the coaxial transmission line method, and the results were compared with measurements using the commercially available coaxial probe method. Based on published dielectric constants for solid non-printed PLA, a variety of antenna designs were simulated and fabricated. Each of these antenna designs addressed a certain shortcoming faced by 3D printed antennas. The antennas were designed with a target resonant frequency of 2.45 GHz, an impedance bandwidth of at least 500 MHz, and a gain greater than 1.5 dBi. The three antennas presented here are a fractal bow-tie antenna (FBTA), a spiral antenna, and a Yagi-Uda antenna.
In this paper, a four switchable beam antenna dedicated to Wireless Sensor Network (WSN) nodes in the 2.4 ISM band (2.4-2.485 GHz) is presented. It consists of two fed monopoles and two loaded parasitic ones. The nature and value of the load are obtained using the Uzkov equations, allowing to determine current weighting coefficients in the case of two separately fed antennas, in order to maximize the gain and the directivity in a given direction. Reconfigurability is achieved using reflector and director elements activated by PIN diodes to reduce the back radiation and pointing in the desired direction. Thus, a first system is obtained which consists of two elements, one fed and the other loaded with an inductor, with a maximum gain of 5.2 dBi in simulation and 4.7 dBi measured at 2.4 GHz in azimuthal directions of 90˚ and 270˚. Then, the system is compared with another, composed of two antennas fed separately. Finally, the same methodology is applied to an array of four antennas, in which two antennas are fed, and two are loaded. This last structure is capable of steering its radiation pattern in the azimuth plane, covering a 360˚ angle with four beams (0˚, 90˚, 180˚ and 270˚). The total gain achieved is 4 dBi for each beam in the azimuth plane.
Bearingless brushless DC (BBLDC) motor in the flywheel energy storage system has advantages of low energy consumption, high critical speed and better speed adjustment performance. However, torque ripple exists inevitably due to the current commutation of the BBLDC motor and the wide range of speed changes when the flywheel energy storage system charges and discharges. In this frame, an approach of combining the direct torque control (DTC) with the current prediction control (CPC) is proposed to suppress torque ripple in wide speed regulation range. In this paper, the mathematical model of the BBLDC motor is given, and the principle of DTC scheme is introduced. On the basis of analyzing the causes of commutation torque ripple when using DTC scheme, CPC scheme is employed to minimize the commutation torque ripple by controlling the changes of phase current during commutation. During the non-commutation, the DTC is selected, and the CPC is selected during the commutation. Results show that the proposed approach is feasible, and torque ripple is effectively suppressed both in high speed and low speed. Moreover, this method has no effect on the suspension performance.
This paper presents a planar, compact 8-element frequency-reconfigurable multiple-input-multiple-output (MIMO) antenna system. The proposed design can be utilized as a communication antenna for cognitive radio (CR) front-end applications. The proposed antenna design contains 8 elements on a single substrate board. Frequency reconfigurablility is achieved using varactor diode in the middle of each antenna element by varying the capacitive reactance of the slot. The proposed antenna system provides very wide frequency tunable characteristics from 1.6 to 2.48 GHz. The proposed design covers several well-known frequency bands like LTE, GSM-1800, PCS-1900, WLAN along with several others. Moreover, rectangular defected ground slots are used between vertically placed antenna elements to enhance the isolation. The complete antenna system is realized on single FR-4 substrate of dimensions 120×60×1.56 mm3. The performance of proposed design is demonstrated by presenting both the simulated and measured results with close agreement achieved between the two which validates the proposed design.
In this paper, a dual-band complementary split ring resonator (C-SRR) is used to improve the band-notch effect relative to the traditional SRR. Meanwhile, we employ a brand-new SRR unit cell as an isolator for decoupling among multiple bands without enlarging the dimensions of the multiple-input-multiple-output (MIMO) antenna. Therefore, a compact ultra-wideband MIMO antenna is developed. Compared with the previous work, the proposed MIMO antenna also has obvious advantages such as high isolation and miniaturization (the dimensions are only 13.5 mm × 34 mm). The metamaterial-inspired UWB MIMO antenna presented here is suitable for small scaled mobile devices.
A novel characterization method of OTA test setups for wireless communication systems on vehicles in the random line-of-sight (Random-LOS) environment is proposed. The measurement setup assumes a compact range and a test zone where the antenna under test (AUT) on the vehicle would be located. An ideal receiver is assumed for the reference measurement, which allows to perform a system analysis through evaluating the Probability of Detection (PoD) as the system figure-of-merit. The proposed method is aimed as an aid for test equipment designers to design OTA compact ranges, compare their performances, and define an ideal numerical reference. The requirements for OTA measurement ranges are different from those for conventional anechoic compact ranges. A compact cylindrical reflector system with an antenna array line feed is characterized using the proposed method, from 1.6-2.7 GHz, for two orthogonal polarizations, various AUT heights and reflector tilting angles, with and without ground plane in a test zone which is 2 m wide in diameter.
In order to solve a key issue about power and data wireless transmission of implantable medical devices, M-ary differentially-encoded amplitude and phase-shift Keying (MDAPSK) is employed to balance the frequency selective contradiction in this paper. Subsequently, bio-capacitor model and biological path loss model are introduced to improve the accuracy of conventional wireless power transmission efficiency model. Based on 16DAPSK modulation, biological channel error rate analysis model is set up. Compared with experiment data, accuracy of the model is proved. Error codes suppression and error codes correction methods are optimized, and the optimization results have been verified by experiments. Lastly, it can be found that the power and data synchronized wireless transmission scheme is feasible. This work provides a new solution and model reference for power and data wireless transmission of implantable medical devices.
In this paper, we propose a novel direction of arrival (DOA) and polarization estimation method to address the problem of a coprime polarization-sensitive array (PSA). For a PSA, there may be a zero element in the covariance matrix when the polarized signal comes from a specific direction. To overcome this problem, we utilize the reconstructed received data to obtain a new covariance matrix whose elements are all non-zero. Then, the coprime MUSIC and sparse signal reconstruction algorithms are used for DOA estimation. In addition, the power of noise can be estimated in this polarization model, which improves upon the sparse signal reconstruction algorithm. Compared with the normalized algorithm, the proposed method offers favorable performance in terms of accuracy. Furthermore, our method can identify the peaks of the true DOAs at a low signal-to-noise ratio (SNR). The simulation results demonstrate the effectiveness of the proposed method.
Statistical characteristics of scattered ordinary and extraordinary electromagnetic waves in the magnetized plasma are considered using the smooth perturbation method. Diffraction effects and polarization coefficients are taken into account. Second order statistical moments of scattered radiation are obtained for arbitrary correlation function of electron density fluctuations. The expressions of the broadening of the spatial power spectrum and displacement of its maximum are obtained. Wave structure functions and the angle of arrivals are calculated. Scintillation level of scattered radiation is analyzed for different parameters characterizing anisotropic plasma irregularities for the ionospheric F-region. Numerical calculations of the statistical characteristics are carried out for the three-dimensional spectral function containing anisotropic Gaussian and power-law spectral functions using the experimental data.
This paper presents a novel approach of sensing the defect response after craniotomy on cranial surgery phantom models utilizing a short pulsed radar technique. The proposed antenna has demonstrated that the short pulse can be radiated without antenna's own distortion, which is a desirable characteristic for sensing defect response. The layered microwave head phantom has been developed for the purpose of emulating the healing stages of cranial surgery after craniotomy. The fabricated phantom has been validated with reference values reported in literature. The longitudinal scan has been performed for various skull thicknesses as a preliminary study. The one-dimensional pulsed profile has been obtained to achieve the pulse compression so that the defect response can be highlighted. The results obtained in this paper have the potential that the microwave based technique can be utilized for monitoring the healing stages for the future work.