The model based on range and Doppler equations (RD model) is the most precise model for SAR geolocation, and therefore SAR geolocation based on this RD model has become more and more popular. Unfortunately, the RD method requires iterative solution, in most case, which is time-consuming and prone to poor optimization due to observation errors of parameters. In face of the huge mass of measured data from global SAR measurements, how to improve processing speed while maintaining geolocation accuracy is an important problem. This paper examines how to solve the RD geolocation equations for single, interferometric, and stereo SAR. First, the RD geolocation equations for the three kinds of systems are abstracted into a unified equation form. Second, it is determined that the RD geolocation equation can be approximated as a mapping relationship using polynomials. Then a fast solution method for the unified geolocation equation is proposed based on the Range Doppler Polynomial Coefficient Model (RDPC). Third, the accuracy loss of the RDPC model is analyzed, and the precision differences among the three kinds of system are compared. Finally, several groups of TerraSAR-X measured data for the three modes are processed using the fast algorithm. The results show that the fast algorithm greatly reduces the amount of calculation while the geolocation accuracy loss is small. Performance evaluation demonstrates that the proposed method is efficient and correct.
Composites of rice husks and carbon nanotubes (RHCNTs) are an innovation in improving the absorption of microwave signals. Rice husks, which are an agricultural waste material, have been found to possess a significant propensity for absorbing microwave signals. Studies have shown that both rice husks and carbon nanotubes (CNTs)have high percentages of carbon. Thus, in this paper, we present the results of our experimental study in which we varied the ratios of rice husks and CNTs in the composite materials and determined the dielectric properties of the composites and measured their abilities to absorb microwave signals. The experimental microwave absorber was fabricated using rice husks and CNTs, which increased the dielectric constant and the loss factor.Complex permittivity was measured using an Agilent dielectric probe.The RHCNT compositeswere investigated to determine their reflection loss and absorption performance as microwave absorbers. For the fabricated microwave absorber,we used the rectangular waveguide measurement technique to study reflection loss, transmission loss, and absorption performance in the frequency range of12.4 - 18 GHz. Carbon has an essential role in the absorber due to its ability reflect/absorb microwave signals.Thus, we compared the abilities of a pure rice-husk (PRH) absorber and RHCNT composites absorbers to absorb microwave signals.
In this work, a subharmonic frequency mixer for millimeter wave applications has been designed. The mixing and multiplication phenomena are simultaneously achieved via a nonlinear component consisting in a microstrip line gap covered by a graphene film coating. The circuit structure is made up of various filters, which have been optimized to ensure high port-to-port isolation. The nonlinear behavior of the subharmonic frequency mixer has been experimentally evaluated within the 39-40.5 GHz RF frequency band. The frequency downconversion is achieved by mixing the RF signal with the second harmonic component of a 17.9 GHz LO signal. Conversion losses are minimized by generating a return path for IF, through the use of a quarter wavelength open-ended stub.
For ultra-wideband synthetic aperture radar (UWB SAR), there often exist a lot of clutters in the image, and the weak targets are easy to be masked by them. However, using the prior scattering knowledge of targets, enhanced imaging can be realized and beneficial improvements in image quality and detection performance can be expected. In this paper, an enhanced imaging method for body of revolution (BOR) has been researched. Since the BOR target has the unique feature of aspect-invariant characteristic, the aspect scattering entropy (ASE) is proposed to describe the diversity of aspect scattering and used in the BOR-enhanced imaging method. Then the application of the proposed method in landmine detection is discussed. The experimental results show that the BOR targets are effectively enhanced and the clutters are surpressed and thus the probability of landmine detection increases under the same false alarm rate.
In monostatic radars systems, only the micromotion signatures projected onto the radar line-of-sight (LOS) can be observed from echoes. As a result, the obtained micromotion signatures (e.g., the radius length of rotation) are sensitive to the radar LOS. In this paper, we propose a method for the accurate estimation of three-dimensional (3-D) micromotion signature with the orthogonal frequency division multiplexing - linear frequency modulation (OFDM-LFM) multi-input multi-output (MIMO) radar technique, which makes use of the advantages of the multi-view of MIMO radar systems and the broad bandwidth of the OFDM-LFM signals. In the proposed method, the Hough transform and Orthogonal Matching Pursuit (OMP) algorithm are introduced to extract the m-D curve features from echoes, and then the 3-D micromotion signatures of the rotating targets are obtained by solving nonlinear multivariable equation systems. The extracted 3-D micromotion signatures are no longer sensitive to the radar LOS, and can provide realistic feature information for target recognition. Simulations are given to validate the effectiveness of the proposed method.
A probe-compensated near-field - far-field (NF-FF) transformation with spherical spiral scanning, which makes possible to lower the number of needed measurements, as well as the time required for the data acquisition when characterizing quasi-planar antennas, is experimentally verified in this paper. Such a technique, based on the nonredundant representation of electromagnetic fields, has been achieved by properly applying the unified theory of spiral scans for nonspherical antennas and adopting a very flexible source modelling, formed by two circular "bowls" with the same aperture diameter but different bending radii. A two-dimensional optimal sampling interpolation formula allows one to reconstruct the NF data at any point on the measurement sphere and, in particular, at those required by the classical NF-FF transformation with spherical scanning. The reported NF and FF reconstructions, obtained from the nonredundant samples acquired on the spiral, assess the accuracy of the proposed technique.
In the framework of wide-band and ultra wide-band array antennas, an Optical Time Steered Antenna (OTSA) is presented, by considering the design strategies of a new True Time Delay (TTD) Control Unit in the Beam Forming Network (BFN). The unit has high reliability, low crosstalk, low switching time and potential low cost, being based on a low cost technology. Furthermore, due to its compactness and modularity, it can be easily grouped with other ones to make a control unit of large arrays. Different strategies and working configurations of the TTD control unit are presented as a trade-off among hardware complexity, insertion loss reduction and beam control capability. The design of an OTSA prototype is discussed by considering a realistic model simulating the behavior of a real world antenna and accounting for unavoidable non-realities, such as random, periodic and systematic errors introduced by each device exploited in the OTSA as well as mutual coupling between radiating elements. An optimal trimming strategy, able to compensate at best for BFN errors and based on the use of suitably located trimmers, is presented. Among other cases, to enlighten the potentialities of the OTSA, an all optical architecture providing a difference beam squint free pattern is also proposed.
Circularly arced Koch fractal curve (CAKC) is originally proposed. Then, a novel wire dipole is formed with Ki-iterated CAKC. The dipole is experimentally studied for fractal electrical characteristics revealing. It manifests many unique properties, such as multiband resonance at odd times of half-wavelength. In particular, it unprecedentedly presents normal mode (0.5.λ) and axial mode (1.5.λ) simultaneously. Thus, K2 CAKC wire is configured into folded monopole with circular disc ground for omni-directional and directive radiation. Five matched bands (S11≤-10 dB) are obtained within 1 GHz-10 GHz, of which f1=1.31 GHz, f2=3.14 GHz, f3=3.63 GHz, f4=4.65 GHz, and f5=7.71 GHz. Compared with conventional wire monopole (0.25.λ), this fractal monopole shows 31% height reduction. It has dipole-like patterns at f1 and f2, endfire patterns at f3 and f4 with high gain (10 dBi), and off-endfire patterns at f5. Moreover, the fractal antenna possesses compactness, lightweight, simplicity, and low cost. So, it is an attractive candidate for multiband and multifunction antennas, such as satellite antennas, of which omni-directional normal mode and directive axial mode are needed for beaconing and communication respectively.
A multiband Fractal Koch dipole textile antenna is proposed for wearable applications. The antenna is designed to operate at 0.9 GHz, 2.45 GHz and 5.8 GHz. Denim materials as the substrate are selected aiming to obtain robustness, flexible and lightweight textile antenna. The antenna model is designed, simulated, optimized and analyzed using Microwave Studio CST software. Two types of multiband antenna prototypes are fabricated and evaluated with different conducting elements (Shield It fabric and copper foil tape). Antenna performance is observed in term of return loss, bandwidth, radiation pattern and realized gain. Three different comprehensive analyses are taking into considerations which are measurement antenna with different bending sizes, on-body measurement and under wet condition. The antenna performances are evaluated based on resonant frequency (fo) and bandwidth (BW). The antennas performance with bending on the human body (arm & forearm) is compared and investigated. A suitable placement on the body has been discovered between chest and backside of human body. The antennas have also been tested under wet conditions to ensure the stable characteristic under the influence of water.
To solve the low-frequency breakdown inherent from the electric field integral equation (EFIE), an alternative new form of the EFIE is proposed by using the Coulomb-gauge Green's function of quasi-static approximation. Different from the commonly adopted Lorentz-gauge EFIE, the Coulomb-gauge EFIE separates the solenoidal and irrotational surface currents explicitly, which captures inductive and capacitive responses through electrodynamic and electrostatic Green's functions, respectively. By applying existing techniques such as the loop-tree decomposition, frequency normalization, and basis rearrangement, the Coulomb-gauge EFIE also can remedy the low-frequency breakdown problem. Through comparative studies between the Lorentz-gauge and Coulomb-gauge EFIE approaches from mathematical, physical and numerical aspects, the Coulomb-gauge EFIE approach shows the capability of solving low-frequency problems and achieves almost the same accuracy and computational costs compared to the Lorentz-gauge counterpart.
It is shown how the linear Gouy phase of an ideal nondiffracting beam of ±(k-kz)z form, with kz being the projection of the wavevector of modulus k of the plane wave spectrum onto the propagation axis z, is built from a rigorous treatment based on the successive approximations to the Helmholtz equation. The so much different families of nondiffracting beams with a continuum spectrum, as Bessel beams, Mathieu beams and Parabolic ones, as well as nondiffracting beams with a discrete spectrum, as kaleidoscopic beams, have an identical Gouy phase, which fully governs the beam propagation dynamics. Hence, a real beam whose Gouy phase is close to that linear Gouy phase in a given range, will have nondiffracting-like properties on such a range. These results are applied to determine the effective regime in which a physically realizable beam can be treated as a nondiffracting one. As an fruitful example, the Gouy phase analysis is applied to fully establish the regime in which a Helmholtz-Gauss beam propagates with nondiffracting-like properties.
In order to obtain a super-resolution non-diffraction beam, we propose a fast searching method to design a ternary optical element combined with the circularly polarized light. The optimized results show that a beam with a spot size of 0.356λ and depth of focus of 8.28λ can be achieved by focusing with an oil lens of numerical aperture NA = 1.4 and refractive index of oil n = 1.5. The analysis reveals that the spot size of transverse component is 0.273λ, indicating that the super-resolution effect mainly comes from the transverse component. The spot size inside the media can theoretically reach down to 0.273λ because the spot size inside the media is mainly determined by the transverse component.
As key components of the train control system, balise and Balise Transmission Module (BTM) cooperate with each other and fulfill the ground-train information transmission to ensure the safety and reliability of train operation. Aiming at the requirements for future developments of high-speed railway, this paper builds the model for the dynamic transmission process of the balise tele-powering signal using finite element method and electromagnetic field theory, respectively. The paper analyzes the change law of the magnetic flux density distribution within the balise receiving antenna, and derives expressions for the balise induced voltage amplitude envelope based on train speed. Then, the paper carries out the performance optimization to the existing balise system from two perspectives of the balise mounting style and the BTM mounting height. Experiments show that the proposed optimization measures can substantially enhance the system's adaptability to the ever-increasing train operation speed from the existing 448 km/h to 523 km/h. Furthermore, a potential optimization scheme with respect to the BTM mounting angle which enables huge promotion of the system performance is also discussed and proposed.
The investigation of finite ground coplanar fed ultra-wideband (UWB) antenna and the influence of its curvature and the proximity of planar and circular metalic screen on the reflection coefficients and radiation characteristics is presented. The antenna is composed of two circular coplanar strips which enclose slot aperture of similar shape and is designed on a thin and flexible substrate which allows its bending. The antenna configuration has been modeled and experimentally tested, showing good performance in 2-15 GHz frequency with return losses less than -10 dB. It is shown that the bending of antenna does not significantly affect its performance. The existence of metalic screen deteriorates its radiation pattern and reflection coefficient, however with the correct choice of the distance between screen and antenna the required level of return losses can be provided.
The electro-magnetic torque production in the reluctance machine is highly influenced by the magnetic linkages in the air-gap area. The conventional machines derive the drawback of reduction in the air-gap area to a minimal due to influence of mechanical unbalancing thereby restricting the effective energy conversion area. In order to increase the magnetic linkage area the dual-air-gap structure is introduced. The dual-air-gap structure is realised through the division of the magnetic circuit area into two-air-gap while still maintaining the net air-gap length value. A double-rotor with single-stator structure is used to attribute the above concept. The electro-magnetic analysis of such a structure is developed and investigated through numerical analysis. In order to validate the proposed structure the electro-magnetic characteristics are compared with that of the conventional structure at similar operating conditions. The maximum torque generated by the selected dual-air-gap structure is 1.7549 Nm and for conventional structure is 1.2723 Nm. The evaluation of the proposed machine is done at the same operating conditions and it is found that the dual-air-gap structure exhibit 65% increase in average torque value in comparison with that of the conventional single-air-gap structure.
In this paper, a novel compact quadruplexer is implemented by using slotline stepped impedance stub loaded resonators (SISLRs) in ground plane. Four folded dual-mode slotline SISLRs with one input and four output coupled line structures are designed at different frequencies for the quadruplexer operation. By properly adjusting the geometrical parameters of a single dual-mode slotline SISLR, its first two resonant frequencies can be controlled, and thus it can be utilized to implement a second-order bandpass filter when these resonant frequencies are suitably assigned. Furthermore, because the proposed quadruplexer utilizes the distributed coupling technique, a small circuit size can be obtained. As a result, the proposed quadruplexer occupies an extremely small area, i.e., 0.22λ0 × 0.25 λ0(0.36λg × 0.41λg). Finally, good agreement between measurement and EM simulation verifies the design method successfully.
In this work a non-linear efficiency optimization method for its application to an Injection-Locked High Efficiency Voltage Controlled Oscillator is presented. The proposed approach is based on the control of the harmonic content of the oscillator autonomous signal, which is accomplished through the use of an Auxiliary Generator and several multi-harmonic loads based on Arbitrarily Width-Modulated Microstrip Lines. The presented technique has been applied to the design of a 2.5 GHz high efficiency Voltage Controlled Oscillator, which has been manufactured and experimentally characterized, obtaining a good agreement between the simulated and measured results.
Based on quantum Stokes operators and non-Kolmogorov spectrum model of index-of-refraction fluctuation, the analytical formulas for the quantum degree of depolarization of quantization Hermite-Gaussian (QHG) beams propagating in a turbulent atmosphere slant channel are derived. The nonclassical polarization properties of QHG beams propagating in turbulent atmosphere are studied numerically. It is found that the polarization fluctuations of QHG beams are dependent of the turbulence factors such as spectrum powerlaw exponent, refractive index structure parameter at the ground and zenith angle. The degree of depolarization of QHG beams has a saltation and reaches the minimum value at spectrum power-law exponent α = 11/3, the refractive index structure parameter at the ground of the turbulent atmosphere slightly affects the polarization degree of QHG beams which have travelled a long distance, and the change of polarization degree decreases with the increasing zenith angle. Furthermore, the numerical simulations show that QHG beams with higher photonnumber level, lower beam order, shorter wavelength are less affected by the turbulence. These results indicate that One can choose low-order QHG beams with wavelength λ = 690 nm as optical carrier, increase photon number, set the size of transmitting aperture ω0 as about 0.1 m, and detect communication signals at the central region of beams to improve the performance of a polarization-encoded free-space quantum communication system.
A multi-band ferrite-based metamaterial has been investigated by experiments and simulations. The negative permeability is realized around the ferromagnetic resonance (FMR) frequency which can be influenced by the saturation magnetization 4πMs of the ferrites. Due to having multiple negative permeability frequency regions around the multiple FMR frequencies, the metamaterials consisting of metallic wires and ferrite rods with various 4πMs possess several passbands in the transmission spectra. The microwave transmission properties of the ferrite-based metamaterials can be not only tuned by the applied magnetic field, but also adjusted by the 4πMs of the ferrite rods. A good agreement between experimental and simulated results is demonstrated, which confirms that such a ferrite-based metamaterial possesses a tunable multi-band behavior. This approach opens a new way for designing multi-band metamaterials.
In a recent study, we proposed improved quasi-static expressions for the electromagnetic field components excited by a vertical electric dipole lying on the surface of a flat and homogeneous lossy half-space. The present paper introduces an analytical approach to derive analogous formulas for the case of the horizontal electric dipole. The procedure is based on the expansion of the integral representations for the fields into power series of the ratio between the wavenumbers in free-space and in the conducting medium. Later, the terms in the expansions up to the second order can be reduced to known tabulated integrals. Numerical results are presented to illustrate the improvement in accuracy that follows from using the second-order approximations for the fields in place of the zeroth-order ones. In the quasi-static frequency range and beyond, use of the new formulation makes it possible to reduce the maximum relative error in the calculation of the fields from about 23% down to less than 7%.
In this paper, a K-band ground-based hyperspectral microwave radiometer for atmospheric sounding is proposed, which improves the profile error and vertical resolution of moisture profiling under the high water vapor condition. The hyperspectral microwave radiometer (80 K-band spectral channels) can observe the rapidly changing weather with high sensitivity and accuracy of brightness temperature by using a stable high-speed receiver and an improved tipping calibration method. By combining several advantages of traditional microwave receiver, the MMIC receiver has good ultra-wideband performance, high linearity, and short measuring time. Moreover, through correcting the calibration parameters of traditional tipping calibration, the proposed calibration method can increase calibration accuracy based on the radiative transfer equation in the atmosphere. Measurement results demonstrate that the radiometer achieves a sensitivity of 0.1 K for 2 s of integration time and an accuracy of better than 0.77 K. For the water vapor profile, the variational retrievals method is used to extract the redundant information under the microwave hyperspectral condition. Preliminary comparisons of measured water vapor profiles with traditional results show good improvement of the profile error and vertical resolution.
In this paper, a multilevel time domain fast dipole method (TD-FDM) is proposed for solving time-domain magnetic field integral equations. It is the extension of TD-FDM to the multilevel. This proposed scheme starts by multilevel grouping. At each level, the far-field interaction can be expanded through the Taylor series and reconstructed via aggregation-translation-disaggregation procedure, which reduces the memory requirement and the computational cost of the marching-on in-time (MOT) method. Numerical results about the electromagnetic scattering from perfect electric conductor (PEC) objects are given to demonstrate the validity and efficiency of the proposed scheme.
Microwave induced thermo-acoustic tomography (MITAT) has great potential in early breast cancer detection because it utilizes the advantages of both microwave imaging and ultrasound imaging. In this paper, we develop a fast and efficient simulation approach based on a hybrid method which combines finite integration time domain (FITD) method and pseudo-spectral time domain (PSTD) method is developed. By using this approach, energy deposition of biology tissue illuminated by electromagnetic fields can be accurately simulated. Meanwhile, acoustic properties of the tissue can be efficiently simulated as well. Compared to traditional methods, such as finite difference time domain (FDTD), et al, the developed method can well process real 3-D electromagnetic-acoustic complex models. Based on this approach, a MITAT model is created and some simulated results are analyzed. Furthermore, some real breast tissues are adopted to perform the thermo-acoustic imaging experiment. Comparisons between experimental and simulated results are made. The feasibility and effectiveness of the proposed approach are demonstrated by both numerical simulations and experimental results.
The influence of beam convergence on the photonic band-gaps, or stop-bands (SBs), of onedimensional photonic crystals (1D PCs) is investigated. The investigation is based on an analysis of the gap map obtained from reflection spectra, calculated by the transfer matrix method for various angles of light incidence, φ, The calculated data is compared with reflection spectra taken using Fourier Transform Infrared microspectroscopy. It was found that the introduction of the parameter, Δφ to account for the focused light beam, for angles up to 20°, has little effect on the first, or lowest SB and the SBs adjacent to it. However, an increase in the order of the SB causes an increase in the influence of this parameter.
A frequency dependent model of sheet resistance of transparent conductive mesh coatings is proposed based on transmission line theory and vilified by experiments. And the effect on shielding effectiveness of frequency dependent sheet resistance is analyzed. Simulation results of shielding effectiveness are compared with the experimental data of a mesh-coated window sample with equivalent parameters fabricated and measured by Exotic Electro-Optics. The agreement between experiment and simulated proves the validity of the proposed sheet resistance model. So it can be therefore concluded that the frequency dependent model can be used to reasonably evaluate sheet resistance and shielding effectiveness of transparent conductive mesh coated windows.
Adaptive beamforming methods degrade in the presence of model mismatch. In this paper, we develop a modified interference covariance matrix reconstruction based beamformer that is robust against large array calibration errors. The calibration errors can come from the element position errors, and/or amplitude and phase errors, etc. The proposed method is based on the fact that the sample covariance matrix can approximate the interference covariance matrix properly when the desired signal is small, and a reconstructed covariance matrix based on the Capon spectral will be better than the sample covariance matrix when the desired signal is large. A weighted summation of two covariance matrices in references is used to reconstruct the interference covariance matrix. Moreover, a computationally efficient convex optimization-based algorithm is used to estimate the mismatch of the steering vector associated with the desired signal. Several simulation cases are applied to show the superiority of the proposed method over other robust adaptive beamformers.
Properties of wave transmission in a photonic quantum well (PQW) structure containing superconducting materials are theoretically investigated. We consider two possible PQW structures, (AB)P(CD)Q(AB)P-asymmetric and (AB)P(CD)Q(BA)P-symmetric, where the host photonic crystal (PC) (AB)P is made of dielectrics, A = SrTiO3, B = Al2O3, and the PQW (CD)Q contains C = A and superconducting layer D = YBa2Cu3O7-x, a typical high-temperature superconducting thin film. Multiple transmission peaks can be seen within the photonic band gap (PBG) of (AB)P and the number of peaks is directly determined by the stack number of PQW, i.e., it equals Q-1. Additionally, the results show that symmetric PQW structure is preferable to the design of a multichannel transmission filter. The effect of stack number of photonic barrier is also illustrated. Such a filter operating at terahertz with feature of multiple channels is of technical use in superconducting optoelectronic applications.
We perform the long time monitoring of nanoparticle-cell membrane interaction with high spatial and temporal resolution. The 2,3-bis(4-(phenyl(4-(1,2,2-triphenylvinyl) phenyl)amino)phenyl) fumaronitrile (TPE-TPA-FN) is doped in organically modified silica (ORMOSIL) to be a biocompatible nanoprobe, which displays an aggregation-induced emission (AIE) effect. Photobleaching resistance of this synthesized nanoparticle is tested and compared with its similar counterpart, which proves its superiority and capability of long term fluorescence emission. We utilize the objective-based total internal reflection microscopy combined with the living cell incubation platform to investigate the cell uptake process of this nanoparticle in real time.
To obtain Electromagnetic Compatibility (EMC), we would like to study the worst-case electromagnetic eld-induced voltages at the ends of Printed Circuit Board (PCB) traces. With increasing frequencies, modelling these traces as electrically short no longer suffices. Accurate long line models exist, but are too complicated to easily induce the worst case. Therefore, we need a simple analytical model. In this article, we predict the terminal voltages of an electrically long, two-wire transmission line with characteristic loads in vacuum, excited by a linearly polarised plane wave. The model consists of a short line model (one Taylor cell) with an intuitive correction factor for long line effects: the modified Taylor cell. We then adapt the model to the case of a PCB trace above a ground plane, illuminated by a grazing, vertically polarised wave. For this case, we prove that end-fire illumination constitutes the worst case. We derive the worst-case envelope and try to falsify it by measurement in a Gigahertz Transverse Electromagnetic (GTEM) cell.
We describe a four-layered model for near infrared light propagation in a human head based on the Monte Carlo method. With the use of three-dimensional voxel-based media discretization, photon migration in the brain is analyzed by both the time-of-flight measurement and the spatial sensitivity profile. In the measurement of brain activity, the selection of light wavelength and the distance between the source and the detector have a great influence on the detected signal. In this study, we compare the detected signals from the detectors with different source-detector spacing at wavelengths of 690 nm, 800 nm and 1300 nm, and find that in our model, the wavelength of 1300 nm is more appropriate for the measurement of brain activity because the signals at 1300 nm get better detection sensitivity and spatial resolution. Source-detector spacing is also optimized.
In this paper we present two simulation techniques for modeling periodic structures with three-dimensional elements in general. The first of these is based on the Method of Moments (MoM) and is suitable for thin-wire structures, which could be either PEC or plasmonic, e.g., nanowires at optical wavelengths. The second is a Finite Difference Time Domain (FDTD)-based approach, which is well suited for handling arbitrary, inhomogeneous, three-dimensional periodic structures. Neither of the two approaches make use of the traditional Periodic Boundary Conditions (PBCs), and are free from the difficulties encountered in the application of the PBC, as for instance slowness in convergence (MoM) and instabilities (FDTD).
In this paper, an electronically reconfigurable beam steering antenna using embedded RF PIN switches based parasitic array (ERPPA) is proposed for modern wireless communication systems that operate at 5.8 GHz frequency. In the proposed antenna, a single driven element is fed by a coaxial probe, while each of the two parasitic elements is integrated with an RF PIN switches that embedded inside the substrate. In the conventional reconfigurable antennas, the RF PIN switches are mounted on narrow slots created on the top or bottom layer of the radiator/parasitic elements, which could lead to the dimensional changes of the antenna and degrade the performance in terms of beam steering and return loss. However, this research proposes an exclusive solution where the RF PIN diodes at parasitic elements are embedded inside the substrate thus no additional slots have to be created to mount the SMCs on the antenna. In this regard, the proposed antenna is highly competent to eliminate the intermodulation effect generated by the RF PIN diodes and the other passive elements associated with the PIN diodes. In this research, extensive investigations revealed that the parasitic element dimension and the selection of RF PIN switches significantly influence the antenna's beam steering capability. Adopting certain ON/OFF condition of the embedded RF switches, three beam-steering angles of -30°, 0° and +30° are achieved in the xz-plane, with measured peak gains at θ = -30°, 0° and +30° are 6.5 dBi, 6.5 dBi and 4.9 dBi, respectively. The fabricated antenna with Taconic substrate provides a good agreement with the simulation result. Furthermore, the performance of ERPPA is further tested by outdoor measurement using a wireless bridging system to verify the functionality of the designed antenna at the angles of -45°, -30°, -15°, 0°, 15°, 30° and 45°. The analysis with the switched diversity combining scheme has demonstrated that a maximum diversity gain approximately of 12 dBi is offered by the proposed antenna. With a compact dimension of 32 mm by 76 mm, the proposed antenna is a potential candidate in point-to-point wireless applications such as WIFI application.
The asymmetric transmission of the linearly polarized waves at normal incidence through the lossy anisotropic chiral structure is demonstrated. The proposed chiral metamaterial structure is composed of bi-layered discontinuous cross-wire-strips, and it is utilized in order to realize polarization rotation. Firstly, the theoretical relations between the incident polarization and the polarization rotation are derived using transmission matrices. Secondly, a strong and dynamically asymmetric transmission of linearly polarized electromagnetic wave through the chiral metamaterial has been demonstrated for microwave region, both by simulation and experimentally. The experiment results are in good agreement with the simulation ones. It can be seen from the results that the proposed chiral metamaterial structure can be used to design novel polarization control devices for several frequency regions.
A novel kind of symmetrical backward-wave coupled-line coupler with arbitrary coupling level is proposed in this paper which is based on resonant-type composite right-/left-handed transmission lines (CRLH TLs). First, an equivalent circuit model and procedure for circuit parameters extraction are presented to reveal the inherent nature of the unit cell of the CRLH coupler. Then a CRLH TL composed of four cascaded unit cells is demonstrated to point out the way to achieve balanced condition. At last, even/odd modes analysis based on full-wave simulation is employed to explain the operating principle of the coupler. Both quasi 0-dB and 3-dB CRLH couplers are demonstrated experimentally. The quasi 0-dB backward coupling is achieved over the range from 1.69 GHz to 2.19 GHz (-3 dB bandwidth in measurement), which represents the fractional bandwidth 25.8%. The maximum coupling coefficient 0.52 dB is obtained at 1.96 GHz, where the directivity and isolation is 20.8 dB and 21.3 dB, respectively. The 3-dB couplers shows an amplitude balance of 2 dB and quadrature phase balance of 90±5 degree over the fractional bandwidth of around 11.4%, from 1.99 to 2.23 GHz.
This paper proposes a leaky wave slot antenna array for azimuthally omnidirectional coverage. Slot elements were arranged in cascade and series-fed by a coplanar waveguide (CPW). The most important novelty of this paper is that the whole array, including all the radiating elements and feeding structures, was arranged on a single metal layer. This simple structure has the merits of easy fabrication and low cost, especially at higher frequencies, such as millimeter wave band. Moreover, the proposed antenna array was folded around a center-hollowed columnar substrate to achieve omnidirectional radiation pattern in the azimuthal plane, with the gain variation less than 1.1 dB, which is similar to previous omnidirectional antenna array. In this paper, a prototype of the proposed antenna array at 2.3 GHz was built and tested to validate the design strategy. The measured results, including S parameters, radiation patterns, and gain, were found to agree well with the simulation ones.
A network analyzer with a bulk current injection (BCI) probe is proposed to measure the common-mode conversion coefficient for DC supply loops on a driver PCB of thin film transistor-liquid crystal display (TFT-LCD) panel. The proposed technique is used to predict the common-mode radiated emission caused by the DC supply loops, which highly correlates with the radiated emission measurements obtained for the TFT-LCD panel in a fully anechoic chamber (FAC). The proposed technique is also successful to estimate the reduction of a specific peak in the radiated emission spectrum by shielding the DC supply loops on a driver PCB of TFT-LCD panel. Electromagnetic simulation and equivalent-circuit modeling approaches are developed to confirm the common-mode radiation mechanism in this study.
The radiation characteristics of dielectric slabs over a transmission waveguide, based on the concept of spoof surface plasmons, are studied in this paper. The proposed structure can be used to control the radiation over a wide band of operation, whilst retaining low Side Lobe Levels (SLLs) and cross-polarization. Leaky modes, broadside radiation and directive beams at fixed angles can all be obtained using various configurations (utilising homogeneous or gradient index dielectric slabs). The proposed antenna design has attractive performance for THz detectors and transmitters.
This paper discusses performance improvement with the integration of an artificial magnetic conductor (AMC) into array antennas. An AMC with defected ground structure (DGS) was designed to construct the AMC ground plane and in-phase superstrate. The two distinguishable structures were integrated into an array antenna, which serves as a reference antenna at 5.8 GHz. The impedance bandwidth (BW) of the reference antenna significantly improved to 287% when integrated with an AMC ground plane and with 37% reduced size. On the other hand, the integration of in-phase superstrate effectively enhances the gain and BW of the reference antenna by 1 dBi and 44%, respectively. The effects of air gaps on the reference antenna with both the AMC ground plane and in-phase superstrate are discussed. The antenna performance factors, such as return loss and radiation pattern, are also discussed for the reference antenna, the reference antenna with the AMC ground plane, and the reference antenna with in-phase superstrate, respectively. There is satisfactorily good agreement between the simulation and measurement results. The proposed antenna is useful in WLAN (5.15-5.35 GHz and 5.725-5.825 GHz) and WiMAX (5.725-5.825 GHz) applications.
The purpose of this paper is to propose analytical and finite element method (FEM) designs of a novel three-phase Seven Layers Switched Reluctance Motor (SLSRM) for the applications which dictated by the performance with the total torque per volume as a key marker indicator. The introduced motor consists of seven magnetically independent stator layers, which each layer includes a set of 4 by4 stator/rotor poles. In this SLSRM, the three layers are energized together to produce high torque and also decrease the torque ripple in comparison with the one layer conventional SRM. Since each layer has its independent phase in the motor, the isolation problem of coils and cooling troublesome existing in conventional SRMs is solved. In addition, these types of SLSRM have some other advantages, like simpler configuration, cooling in easier way, etc. Firstly an analytical design is carried out to illustrate the design procedure and then three-dimensional (3-D) magneto static simulation analysis of the SLSRM and the one layer SRM is performed using 3-D FEM, to obtain and verify the flux-linkage, flux density and torque profiles. Also, the proposed motor is compared with a conventional one layer SRM with a same size and volume.
We propose a methodic approach to design Artificial Magnetic Materials (AMM) with desired magnetic properties. The design procedure is defined based on a novel formulation for characterizing AMMs. The employed formulation expresses the effective permeability and the magnetic loss tangent (MLT) in terms of the geometrical and physical parameters of the inclusions. The method comprised four steps. In the first step, the feasibility of the design is checked through a set of constraints. The second and third steps provide an iterative procedure to capture the desired magnetic properties. Finally, the geometrical elements, i.e., the area and perimeter of inclusions, are calculated. The technique is applied to design of an AMM structure based on Rose curve resonators. The design based on the proposed methodology is verified by the numerical simulation of the AMM.
This paper presents a new approach to calculate the accurate fourth-order Doppler parameters for Geosynchronous Synthetic Aperture Radar (Geo-SAR). To get exact calculation results, the Earth is modeled as an ellipsoid and the relative motion between the sensor in an elliptical orbit and the rotating Earth is analyzed. The J2, J3 and J4 orbital perturbation items and attitude steering are analyzed. Ignoring the perturbation force would produce errors of the Doppler parameters for spaceborne SAR because it can influence the six orbital elements. Since the Doppler parameters are related to the antenna beam pointing directions and influenced by attitude of SAR platform, the calculation results before and after attitude steering are shown. Furthermore, the Doppler parameter properties during the whole orbital periods of Geo-SAR are compared with those of Low-Earth-Orbital SAR (Leo-SAR). Finally, the effects on Doppler parameters stemmed from the radar beam pointing accuracy are analyzed.
Based on the observation that sparsity assumption is well satisfied in the synthetic aperture radar (SAR) imaging applications, there is increasing interest in utilizing compressive sensing (CS) in SAR imaging. However, there are still several problems which should be concerned in CS-based imaging approaches. Firstly, inevitable noise and clutter challenge the performance of CS algorithms. Secondly, the super-resolving ability of CS algorithms is not sufficiently exploited in most cases. Thirdly, nonideal characteristics of mutual coherence affect the performance of CS algorithms in complex scenes. In this paper, a novel CS imaging framework is proposed for the purpose of improving the imaging performance of stepped frequency SAR. Meanwhile, a super-resolving imaging algorithm is proposed based on the nonquadratic optimization technique. Simulated and rail SAR measured data are applied to demonstrate the effectiveness of the novel framework with the proposed super-resolving algorithm. Experimental results validate the superiority of this method over previous approaches in terms of robustness in low SNR, better super-resolving ability and improved imaging performance in complex scenes.
Linear array synthetic aperture radar (LASAR) is a promising radar 3-D imaging technique. In this paper, we address the problem of sparse recovery of LASAR image from under-sampled and phase errors interrupted echo data. It is shown that the unknown LASAR image and the nuisance phase errors can be constructed as a bilinear measurement model, and then the under-sampled LASAR imaging with phase errors can be mathematically transferred into sparse signal recovery by solving an ill-conditioned constant modulus linear program (ICCMLP) problem. Exploiting the prior sparse spatial feature of the observed targets, a new super-resolution sparse autofocus recovery algorithm is proposed for under-sampled LASAR 3-D imaging. The algorithm is an iterative minimize estimation procedure, wherein it converts the ICCMLP into two independent convex optimal problems, and joints l1-norm reweights least square regularization and semi-definite relax to find the optimal solutions. Simulated and experimental results confirm that the proposed method outperforms the classical autofocus techniques in under-sampled LASAR imaging.
This paper presents that the extra passband with two transmission zeros can be obtained by adding shunt open stubs to the asymmetric half-wavelength resonators structure. By using this method, a fourth or even higher passband with good selectivity and compact size can be obtained. Dual-band, tri-band and quad-band bandpass filters are demonstrated by using this method. The measured bandwidth is 80/180 MHz for the dual-band, 60/180/180 MHz for the tri-band and 130/360/170/70MHz for the quad-band filter, respectively. The measured insertion loss for the dual-band, tri-band and quad-band filter is less than 2.7 dB, 2.5 dB and 2.9 dB at the center frequency. All the simulated results and the measured results agree well.
Cognitive radio technology proposes the utilisation of under-utilised spectrum resources which may include time, frequency, geographical location, direction, polarisation et cetera. Frequency is the conventional spectrum resource, considered to be exploited for cognitive radio, especially in the field of antenna design. We address the unconventional directional resource for cognitive radio, from antenna design perspective. The design concept of a multi-band compact array, capable of providing separate and simultaneous access to frequency and directional resources, is presented. The initial explorations are carried out for three frequency resources (bands) and three directional resources, providing nine degrees-of-freedom altogether. Laboratory version of the proposed antenna system is then used to gain proof-of-principle through line-of-sight measurements in an over-the-air test-bed, followed by static outdoor measurements in a multipath scenario. At the end, simulations are performed for arbitrary arrays in heterogeneous propagation scenarios to study the influence of antenna radiation pattern on the availability of directional opportunity. Recommendations are made for possible antenna design based on the simulation results.