In this work a 12 element patch planar antenna array is designed, fabricated and tested along with its radio frequency (RF) feed network at 2.45 GHz. The array is designed to be embedded in the wing structure of a fixed wing hobby-type UAV. The planar array allows for beam steering with two degrees of freedom (θb,Φb). The maximum mutual coupling between antenna elements was -25 dB. The RF combiner was phase compensated to minimize the phase imbalance between its branches. The maximum measured antenna gain was 21.4 dB. The 3D Radiation pattern at several steering angles was measured at an outdoor antenna range facility. Measured and simulated values were in good agreement.
The waveguide has a perfectly conducting surface. Its cross section domain is bounded by a singly-connected contour of a rather arbitrary but enough smooth form. Possible waveguide losses are modeled by a homogeneous conductive medium in the waveguide. The boundary-value problem for the system of Maxwell's equations with time derivative is solved in the time domain. The real-valued solutions are obtained in Hilbert space L2 in a form of transverse-longitudinal decompositions. Every field component is a product of the vector element of the modal basis dependent on transverse coordinates, and the modal amplitudes dependent on time and the axial coordinate. Three examples are included. The dynamic properties of the modal waves and concomitant energetic waves are studied and their dependence on time illustrated graphically.
A compact multiband handset antenna including MIMO antenna operation for LTE 13 band (746~787 MHz) applications is proposed. The proposed antennas are separately located on the top and bottom portions of a mobile handset in order to use the antenna area more effectively. The proposed antenna achieves isolations of higher than 14 dB, enveloped correlation coefficients (ECC) of less than 0.25, and total efficiencies of greater than 40%. The operating frequency bands of Antenna 1 and Antenna 2 include the LTE 13 (746~787 MHz)/DCS/PCS/UMTS (1710~2170 MHz) bands and the LTE 13 (746~787 MHz)/GSM850/900 (824~960 MHz) bands, respectively.
In this work, we present a new design of a tunable nanofocusing lens using a circular grating of linear-variant depths and nonlinear-variant widths. Constructive interference of cylindrical surface plasmon launched by the sub-wavelength metallic structure forms a sub-diffraction-limited focus, the focal length can be adjusted by varying the geometry of each groove in the circular grating. According to the numerical calculation, the range of focusing points shift is much more than other plasmonic lens, and the relative phase of emitting light scattered by surface plasmon coupling circular grating can be modulated by the nonlinear-variant width and linear-variant depth. The simulation result indicates that the different relative phase of emitting light lead to variant focal length. We firstly show a unique phenomenon for the linear-variant depths and nonlinear-variant widths of the circular grating that the positive change and negative change of the depths and widths of grooves can result in different of variation trend between relative phases and focal lengths. These results paved the road for utilizing the plasmonic lens in high-density optical storage, nanolithography, super-resolution optical microscopic imaging, optical trapping, and sensing.
Ground-based microwave radiometer is the main device to remotely sense atmosphere passively which can detect the water vapor density, temperature, integral water vapor, etc. Because of the influence of liquid water in cloud on the brightness temperature measured by microwave radiometer, the cloud needs to be modeled to retrieve the parameters of atmosphere. However, the difference between cloud model and actual cloud may bring on error in retrieval. Based on the relation between absorption coefficient of liquid water and frequency, a dual-frequency method of eliminating liquid water radiation which is not based on modeling cloud is put forward to retrieve the parameters of cloudy atmosphere. Historical radiosonde data are employed in the calculation of retrieval coefficients to profile the water vapor. The simulation and experiment results show that the dual-frequency method can eliminate the affection of liquid water effectively. So the error in modeling cloud can be avoided to improve the retrieval precision. The integral water vapor in cloudy atmosphere is also retrieved by the dual-frequency method, and the precision is almost the same with the method of modeling cloud.
A novel switchable beam textile antenna (SBTA) for wireless body area network (WBAN) applications is proposed. The SBTA is centrally-fed by a coaxial probe and the power distributed over four circular radiating elements. Four RF switches are integrated through which the SBTA is able to generate beam steering in four directions: 0°, 90°, 180°, and 270°, with a maximum directivity of 6.8 dBi at 0°. Its small size (88 mm x 88 mm) and flexibility enables the structure to be easily integrated into safety jackets, rain coats, etc., for tracking, and search and rescue communication purposes. The structure successfully integrates reconfigurability into a wearable textile antenna.
The fine-grained parallel micro-genetic algorithm (FGPMGA) is developed to solve antenna design problems. The synthesis of uniformly exited unequally spaced array is presented. Comparison with the micro-genetic algorithm (MGA) has been carried out. It is seen that the FGPMGA significantly outperforms MGA, in terms of both the convergence rate and exploration ability. The FGPMGA can also reduce the optimization time. Then the FGPMGA and the body of revolution finite-difference time-domain (BOR-FDTD) are combined to achieve an automated design process for conical corrugated-horn antenna. Numerical simulation results show that the horn antenna has good impedance matching (the VSWR is less than 1.5), stable beamwidth and gain, as well as good rotation symmetry patterns over the whole band 8~13 GHz.
A compact quad-band hybrid antenna for Compass/WiMAX/WLAN applications is proposed. The hybrid antenna is designed based on the method of combining a composite right/left-handed transmission line (CRLH-TL) unit cell with a meandered monopole and wide multi-band characteristics are achieved by merging some of resonance frequencies of the CRLH-TL unit cell and meandered monopole together. Coplanar waveguide (CPW) is used as a parallel excitation for both the CRLH-TL unit cell and meandered monopole. A prototype of the proposed hybrid antenna has been constructed and experimentally studied. The measured results show that four distinct operating bandwidths with 10 dB return loss are about 30 MHz (1.25-1.28 GHz), 290 MHz (2.44-2.73 GHz), 650 MHz (3.17-3.82 GHz) and 1130 MHz (5.03-6.16 GHz), covering the Compass B3, 2.5/3.5/5.5 GHz WiMAX and 5.2/5.8 GHz WLAN bands. Furthermore, the antenna has a single-layer planar structure with a small volume of only 31 × 21 × 2 mm3. Acceptable radiation patterns and peak realized gains are obtained over the operating bands.
The uniform expressions of scalar fringe waves which are based on the physical theory of diffraction (PTD) were obtained for the impedance half plane in terms of the Fresnel integrals. Asymptotic and uniform forms of the fringe fields were compared. The radiated fields of the fringe expressions were analyzed numerically.
This paper proposes an Extended Inverse Chirp-Z Transform (EICZT) algorithm to handle the high squint FMCW SAR data, where the conventional Inverse Chirp-Z Transform (ICZT) cannot work due to the failure in dealing with the range-variance of second- and higher-order range-azimuth coupling terms. A pre-processing operation is implemented in the azimuth-Doppler and range-time (Doppler-time) domain, where a perturbation function consisting of second-order and third-order range time variables is implemented to compensate the range variance of the second order range terms. Moreover, a new scaling factor is formulated to represent the Range Cell Migration (RCM), and further corrected by the presented EICZT approach. The proposed approach is analyzed and compared with the conventional ICZT. The simulated high squint SAR scene with nine targets is well focused by the proposed approach and the quality is greatly improved with respect the conventional ICZT. The proposed algorithm is also validated by the X-band high-resolution real SAR data.
State-of-the-art radomes exploit frequency selective media so as to be transparent for the frequencies of the antenna protected by them and opaque to other frequencies. This feature helps in reducing the radar cross section of the antenna and in protecting it from interference. The study of a frequency selective radome is a daunting task, since the radome is usually large in terms of wavelengths, hence full wave analyses are prohibitive. In this paper an approximate technique, based on the physical optics concept, is proposed to attain an estimation of the behavior of a radome shielded antenna in a short time with a commonly available computer. Results are validated against a full wave technique over a relatively small radome.
With rapid development of satellite technology in monitoring the ocean, a good understanding of the physical processes involved in the electromagnetic ocean-surface interaction is required. The composite surface models are usually applied in the analysis of the interaction, hence a systematical check of their region of validity is desirable. Based on a generalized minimal residual procedure which is right preconditioned (GMRES-RP) that we have recently developed which has demonstrated the desirable properties of a numerical algorithm: robust and efficient, in this paper, for bistatic scattering from one dimensional ocean surfaces, we carry out a systematic assessment of the performance of the popular two-scale model and the advanced three-scale model under different conditions of ocean surface wind speeds, polarizations, frequencies, and incidence angles. It is found that the two-scale model in general captures the bistatic scattering pattern, yet the accuracy of geometrical optics (GO) for the large scale wave brings considerable impact on the overall accuracy. If the evaluation of the contribution of the large scale wave is instead using direct numerical integration for the corresponding Kirchhoff integral, impressive improvements are frequently observed, especially at low frequency (L and C bands) and low wind speed (3 m/s). But care should be taken when apply two-scale method with numerical integration, since there are cases where visible discrepancy with method of moment (MoM) are observed. On the other hand, the three-scale model is found in very good agreement with MoM across the considered ocean surface wind speeds, polarizations, frequencies, and incidence angles, hence represents a much advanced model over the two-scale model.
This paper presents an effective method for reconstructing the rotation-induced micro-Doppler (m-D) from a signature corrupted by noise. An adaptive low-pass filter is employed as a preprocessor of empirical mode decomposition (EMD) in order to effectively extract the first chopping harmonic component of the rotation-induced m-D. Then the extracted component is used for reconstructing the original m-D signature in the joint time-frequency domain. Although it is difficult to interpret the time-frequency representation of the noise-corrupted signature, the reconstruction of the m-D enables the acquisition of related information and can be used for complementing other traditional analysis methods. By validating the applicability of the proposed method with measured jet engine modulation (JEM) signatures, we demonstrate that the reconstruction process presented in this paper is expected to be significantly helpful for radar target recongnition in real environments.
Multi-path time delay spread is a very important factor in the bit error rate of high-frequency ionospheric communication channels and in the target detection performance of over-the-horizon radars. In this study, the probability density distribution of multi-path time delay and Doppler shift of ionospheric radio signal are derived using Rayleigh fading. Moreover, the probability density distribution of time delay, average power of the received signal, and received signal variance are discussed in detail. Using a designed experimental circuit, the measured value of the multi-path time delay spread is obtained from three given radio paths by the sweep-frequency pulse sounding technique. The average value of the multi-path time delay spread that changes with the ratio K, which is the operating frequency of the basic maximum usable frequency, is also analyzed and fitted using the least-squares fitting method. Theoretical and statistical research shows that for a given radio path and specific frequency, the multi-path time delay spread approximately follows a normal distribution. The average time delay spread decreases with the increase in the ratio K; however, it eventually approaches a steady value. The results of this research provide an empirical reference for further prediction and estimation of the time delay spread of a radar wave propagating through the ionosphere.
Numerical calculations based on finite-difference timedomain (FDTD) simulations for metallic nanostructures in a broad optical spectrum require an accurate modeling of the permittivity of dispersive materials. In this paper, we present the algorithms behind BCALM (Belgium-CAlifornia Light Machine), an open-source 3D-FDTD solver simultaneously operating on multiple Graphical Processing Units (GPUs) and efficiently utilizing multi-pole dispersion models while hiding latency in inter-GPU memory transfers. Our architecture shows a reduction in computing times for multi-pole dispersion models and an almost linear speed-up with respect to the amount of used GPUs. We benchmark B-CALM by computing the absorption efficiency of a metallic nanosphere in a broad spectral range with a six-pole Lorentz model and compare it with Mie theory and with a widely used Central Processing Unit (CPU)-based FDTD simulator.
A research of a quasi-optical Bessel-Gauss resonator (QOBGR) at millimeter (MM) and submillimeter (SubMM) wavebands is presented in this paper. The design is based on the quasi-optical theory and technique. The iterative Stratton-Chu formula (ISCF) algorithm is employed to analyze the output characteristics of the cavity, including the resonant modes, phases, power losses and phase shifts. Analysis of the results demonstrates that the present design of the QOBGR can support zero order or any high order mode of the pseudo Bessel-Gauss beam. At the output plane the intensity distributions of these modes are modulated by a Gauss-shaped envelope, and their phase patterns have an approximate block-like profile. Tolerance analysis for the designed QOBGR is also done. Lastly, a comparison of resonating modes is made between QOBR (quasi-optical Bessel resonator) and QOBGR when both are configured with the same geometric parameters.
This paper presents a novel compressed sensing based track before detect (CS-TBD) algorithm. The proposed algorithm reconstructs the whole radar scenario (direction of arrival (DOA)-Doppler plane) for each range gate at consecutive scans using an improved stagewise orthogonal matching pursuit (StOMP) algorithm, resulting in a three-dimensional range-DOA-Doppler space. It then performs temporal tracking in the newly built three-dimensional range-DOA-Doppler space, based on the information from multiple illuminations during each scan, as well as among consecutive scans. In the proposed CS-TBD algorithm, the improved StOMP algorithm together with the temporal tracking, can effectively distinguish true targets from false targets and clutter based on information from multiple illuminations.
In this paper, a double-layer split-ring resonator structure chiral metamaterial was proposed which could exhibit pronounced circular dichroism (CD) effect and negative refractive index at microwave frequencies. Experiment and simulation calculations are in good agreement. The retrieved effective electromagnetic parameters indicate that the lower frequency CD effect is associated with the negative refractive index property of the left circularly polarized (LCP) wave, and the upper one is to the right circularly polarized (RCP) wave. The mechanism of the giant CD effect could be further illustrated by simulated surface current and power loss density distributions.
In this study, we report the simulation, fabrication and characterization of a dual-band fractal metamaterial used for terahertz sensing application. By applying the fractal structures of square Sierpinski (SS) curve to the split-ring resonators (SRRs), more compact size and higher sensitivity can be achieved as privileges over conventional SRRs. The influence of different geometrical parameters and the order of the fractal curve on the performances are investigated. Then overlayers are added to the fractal SRRs in order to explore the performance of the entire system in terms of sensing phenomenon. The changes in the transmission resonances are monitored upon variation of the overlayer thickness and permittivity. Measured results show good agreement with simulated data. At the second resonance of the second-order SS-SRRs, maximum frequency shifts of 19.8 GHz, 26.3 GHz and 37.8 GHz were observed for a 2 μm, 4 μm and 10 μm thickness of photoresist. The results show good sensitivity of the sensors suggesting they can be used for a myriad of terahertz sensing applications in biology and chemistry.
An accurate characterization of the wave propagation inside tunnels is of practical importance for the design of advanced communication systems. This paper presents a five-zone propagation model for large-size vehicles inside tunnels. Compared with existing models, the proposed model considers the influence of the large size of the vehicle, and covers all propagation mechanism zones and their dividing points. When a large-size vehicle is passing the transmitter, the received power suffers a deep fading as the direct wave is blocked by the vehicle itself. This zone is called the near shadowing zone. Then, when the vehicle has moved past the transmitter, the line of sight is recovered. If the vehicle is still close to the transmitter, the free space propagation zone starts. Then, as the distance increases, the vehicle enters the multi-mode propagation zone, where higher order modes are significant. Further away, when high order modes are greatly attenuated, guided propagation is stabilized. Finally, when the vehicle is extremely far from the transmitter, the waveguide effect vanishes because of the attenuation of reflected rays. Two sets of measurements are employed to validate the model. Results show good agreement, and therefore, the model presents an effective way to predict the propagation inside tunnels for large-size vehicles.
This paper analyzes and discusses the effect of the electromagnetic absorption by human head against variation of head dielectric properties at 900, 1800 and 1900 MHz. The characteristics of helical antenna and its substrates with variation in human head dielectric properties are simulated by implementing finite-difference time-domain (FDTD) method using CST Microwave studio. The variations in human head dielectric properties were manipulated by increasing and decreasing 10% and 20% of each of the human head dielectric properties. In this paper, SAR values increase with increment of head conductivity, and increment of head permittivity and head density lead to decrement of SAR values. Helical antenna with substrate of FR4 results in higher SAR values in all frequency exposures. The head SAR values are higher with higher frequency exposures. The helical antenna with substrate of Rogers RO3006 (loss free) is found to be better over FR4 and Rogers RO4003 (loss free), which contributes towards much lower SAR values in all GSM frequency bands exposure.
In order to analyze the Doppler spectrum of three-dimensional (3-D) moving targets above a time-evolving sea surface, a hybrid method with acceleration techniques is proposed to simulate the electromagnetic (EM) scattering from the composite moving model. This hybrid iterative method combines Kirchhoff approximation (KA) and the multilevel fast multipole algorithm (MLFMA) to solve the EM backscattering from the rough sea surface and the targets, respectively, then mutual EM coupling effects between them are taken into account through an iterative process. To overcome the vast computational cost in the iterative process, acceleration approaches which can greatly reduce the calculation time are applied. Coupling area on the sea surface is truncated according to geometrical optic principle. Then a fast far-field approximation (FAFFA) is applied to speed up the mutual interactions between the targets and the sea surface. A successive iteration method is proposed to reduce the convergence steps for the MLFMA process. The accuracy and efficiency of this hybrid method with accelerations are demonstrated. Doppler spectra of backscattering signals obtained from such numerical EM simulations are compared for different incident angles, target velocities and surface models. The broadening effects of the Doppler spectra due to the mutual EM coupling interactions are studied.
A high linearity down-conversion mixer for the application of the fourth generation (4G) mobile communication systems is presented. The presented 2.3 to 5.8 GHz broadband mixer adopts current-reused and bulk-controlled techniques. The linearized transconductor stage is composed of the CMOS amplifiers and the bulk-controlled compensation (BCC) transistors. The bulk-controlled voltage is applied to adjust the threshold voltage of the BCC transistor. Thus, the equivalent third-order intermodulation (IM3) term of the CMOS amplifiers and the BCC transistors can be mitigated so as to improve the linearity. Furthermore, the current-reused architecture enhances the conversion gain of the proposed mixer and compensates the loss caused by the shunt feedback matching network. The presented mixer consumes 4.8 mA from a 1.5 V power supply. The measurement results of the mixer exhibit the maximum power conversion gain of 11.3 dB. The input third-order intercept point (IIP3) of 4.7 dBm over the entire 2.3-5.8 GHz band is observed.
We propose a general rule that can be used to design multibranch high-order mode converters. We used the modal theory to analyze the proposed structure rigorously and presented the general principles. The well-established finite-difference beam propagation method was used to simulate the proposed device. The numerical results show that the proposed devices could really function as an all-optical mode converter device. It would be developed to quantify the applications and benefit applications of optical signal processing and computing systems.
A map of a building using through-the-wall radar imaging (TWRI) can be best obtained by detecting and identifying its internal principal scatterers, where estimation of the pose angle of a trihedral formed by the wall-wall-floor structure is important in this application. In this paper, an image-domain based method is proposed to estimate the pose angle of trihedral using a feature called amplitude ratio (AR). The estimated pose angle of a trihedral is determined according to AR. Firstly, the imaging geometry of the radar with a multiple-input multiple-output (MIMO) array and the definition of AR in the echo-domain are described. Secondly, a parametric back-scattering model based on geometrical theory of diffraction (GTD) is applied to analyze AR in the echo-domain when a trihedral is in different pose angles. Thirdly, a virtual aperture imaging model is developed to describe the imaging procedure using MIMO array. Based on the imaging model, the AR of each trihedral can be calculated in the image-domain instead of the echo-domain. Finally, the proposed estimation method is validated by the real data collected in an anechoic chamber.
Transmission tunneling properties and frequency response of multilayer structure are theoretically presented by using transfer matrix method. The structure is composed of double-negative and double-positive slabs which is sandwiched between two semi-infinite free space regions. Double-negative layers are realized by using Lorenz- and Drude-medium parameters. The transmission characteristics of the proposed multilayer structure based on the constitutive parameters, dispersion, and loss are analyzed in detail. Finally, the computations of the transmittance for multilayer structure are presented in numerical results. It can be seen from the numerical results that the multilayer structure can be used to design efficient filters and sensors for several frequency regions.
A compact tri-band power divider based on triple-mode resonator is proposed in this paper. This tri-mode resonator comprises a conventional half-wavelength resonator, a short stub and an open stub. The interdigital coupled-lines are introduced at the input and the output to improve the performance of this power divider. The proposed tri-band power divider working at 1.57 GHz, 2.45 GHz, 3.50 GHz is simulated and fabricated, and good agreement between the simulated results and the measured results are observed.
Contour reconstruction and accurate identification of dielectric objects placed on a conducting surface are the aims of the millimeter-wave Synthetic Aperture Radar (SAR) imaging processing system presented in this paper. The method uses multiple frequencies, multiple receivers and one transmitter in a portal-based configuration in order to generate the SAR image. Then, the information in the image is used to estimate the contour of the body under test together with the permittivity of the dielectric region. The results presented in this paper are based on synthetic scattered electromagnetic field data generated using an accurate Finite-Difference Frequency-Domain (FDFD)-based model and inversion based on a fast SAR inversion algorithm. Representative examples showing the good behavior of the method in terms of detection accuracy are provided.
In this paper, an efficient method is proposed to reduce the peak transient grounding resistance (P-TGR) of a grounding system. By surrounding the lifting line with a material volume, the P-TGR of the grounding system is greatly reduced. The effect of the surrounding volume conductivity and relative permittivity on the P-TGR is also tested. Second, the rectangular surrounding material volume is shielded with a metallic pipe to reduce the P-TGR further. Third, the shielding metallic pipe is connected to the grounding electrode with thin wire, and the effect of the number of the wires on the P-TGR is also analyzed. It is demonstrated that the P-TGR of the grounding system has been reduced significantly.
A novel band-pass filter (BPF) with lower and upper stopband zeros is proposed. The filter mainly consists of two antisymmetric modified anti-parallel coupled-lines and double pairs of transmission lines. Compared with the traditional anti-parallel coupled-line, the new filter has a better performance at both pass band and stop band. On the basis of even-odd mode method and network theory, the filter has been analyzed in detail. In addition, a simple method to create transmission zeros is investigated, which is beneficial for controlling the stopband zeros. The proposed filter is implemented on RT/Duroid 4350 substrate. Measured results show low insertion loss of less than 1.6 dB in the pass band and good suppressing of more than 22 dB in the lower stop band. Measured results show a good agreement with simulated results.
Inverse synthetic aperture radar (ISAR) imaging is one of the most well-known techniques of radar target recognition. One of the most important issues in ISAR imaging is the improvement of the image smeared by a target with complicated motion. In this paper, we propose the discrete Gabor representation (DGR) in an oversampling scheme as an effective means of obtaining a well-focused ISAR image with a short calculation time. In contrast to other linear time-frequency transforms, the DGR obtains Gabor coefficients using the analysis window frames derived from the clearly defined synthesis window. The oversampling scheme of the DGR leads to accurate calculations of the Gabor coefficients, which denote signal time-frequency amplitude. Since each Gabor coefficient is compartmentally assigned to the associated unit cell of the time-frequency grid, the DGR can show an excellent time-frequency concentration and can effectively discriminate the Doppler components of prominent point-scatterers. The simulation results demonstrate that the DGR not only has enhanced focusing performance but also retains computational efficiency. The DGR in the oversampling scheme is expected to facilitate high-quality ISAR imaging in radar target recognition.
We consider MUltiple SIgnal Classification (MUSIC)-type imaging of perfectly conducting cracks arising in inverse scattering problems. We first explore the structure of a MUSIC-type imaging function by finding a relationship between it and the Bessel function of order zero of the first kind. Then, we design multi-frequency based MUSIC-type imaging in order to improve the traditional one, and establish a relationship with the Bessel function of integer order of the first kind. Some numerical experiments are presented to support the results of our investigation.
We propose a loop switching technique to improve the efficiency of wireless power transfer (WPT) systems using magnetic resonance coupling. The proposed system employs several loops with different sizes, one of which is connected to the system with various distances between the transmitter and the receiver. It enables the coupling coefficient to be adjusted with the distance, which allows high efficiency over a wide range of distances. The proposed system is analyzed using an equivalent circuit model, and electromagnetic (EM) simulation is performed to predict the performance. It is shown from the experimental results at 13.56 MHz that the proposed loop switching technique can maintain high efficiency over a wide range. The efficiency is measured to be 50% at 100 cm, which corresponds to a 46% increase compared to a conventional WPT system without the loop switching technique.
This paper presents herein experiments and calculations of electromagnetic induction between jointless track circuits (JTCs) and track-circuit readers (TCRs). The paper uses transmission-line theory to simulate JTC currents ahead of shunt points and electromagnetism to calculate voltages induced in the TCR antenna. Based on these calculations, the JTC-to-TCR range is defined. The paper derives expressions for the amplitude and phase of the voltage induced in the TCR antenna by the JTC current and uses them to quantitatively analyze the train control system. Experiments verify the conclusions reached based on the calculations.
Ultra-wideband synthetic aperture radar (UWB SAR) is a sufficient approach to detect landmines over large areas from a safe standoff distance. Feature extraction is the key step of landmine detection processing. On one hand, the feature vector should contain more scattering characteristics to discriminate landmines from clutters; on the other hand, the dimension of feature vector should be lower to avoid the "curse of dimensionality". In this paper, a novel feature vector extraction method is proposed. We first obtain the scattering information in the four-dimensional domain, i.e., range, azimuth, frequency and aspect-angle, via the space-wavenumber distribution (SWD). Since the data after SWD are with higher dimension and local nonlinear structures, a typical manifold learning method, Isomap, is used to reduce the dimension. The validity of the proposed method is proved by using the real data collected by an airship-borne UWB SAR system.
This paper presents a fully integrated broadband low power high isolation subharmonic mixer. The proposed mixer achieves a double-balanced architecture by adopting a single-to-differential frequency-doubling technique, and improves port-to-port isolations. The mixer fabricated by tsmc 0.18 μm Mixed Signal CMOS process achieves maximum power conversion gain of 7.1 dB, input third-order intercept point (IIP3) of -6.9 dBm, input second-order intercept point (IIP2) of 33.5 dBm, and single side-band noise figure of -19.6 dB over the 2.3-5.8 GHz fourth generation of mobile phone communications standards (4G) frequency band. The LO-RF, LO-IF and RF-IF isolations are 82.8 dB, 66.5 dB and 62.3 dB, respectively. The measured power consumption is 2.95 mW at a 1.8 V power supply.
A transparent monopole antenna operating at 2.30 GHz is presented in this paper. The radiating element and ground plane are both designed using AgHT-4, while the substrate is made of glass. The simulated and measured impedance bandwidths (BWs) are 41.89% (2.00-3.06 GHz) and 90.91% (1.5-4.00 GHz), respectively. These results were obtained by using a suitable arc-shape slot on the ground plane; and the BWs cover the IEEE 802.16e standard for WiMAX application in the 2.30 GHz band. The gain of proposed antenna is 3.16 dBi, and there is close agreement between measurement and simulation results, in terms of return loss and radiation patterns.
A reconfigurable beam forming antenna prototype using a spiral feed line is proposed in this paper. The presented antenna is integrated with PIN diode switches at a specific location of spiral feed line. It is discovered that the beam steering ability is greatly influenced by the spiral arm feed network. Four PIN diode switches have been incorporated at four different arms of spiral feed line to realize a beam forming ability. The intelligence behaviour of this antenna is conferred when the switches are connected to programmable intelligent computer (PIC) microcontroller. Certain configurations of PIC allow the antenna's radiation patterns to be adaptively changed within 0.01 ms. Therefore, the proposed antenna is capable of electronically forming the beam up to four different angles of +176°, +10°, -1° and -12°. This antenna is small in size with 100 mm by 100 mm of substrate dimension. In this research, the site field antenna performance relying on the received signal strength (RSS) testing is tested intensively in Universiti Malaysia Perlis with varied distant points of line-of-sight (LOS) and non-line-of-sight (NLOS) propagation. With good simulation and measurement results, this antenna could be a promising candidate to be installed in applications such as a smart antenna system, cognitive radio, WiMAX and long term evolution (LTE).
This paper introduces a mobile switchable antenna for long term evolution (LTE) of the 4th generation (4G), applicable to all mobile service bands. The validity of this antenna is assessed by design, realization, and measurement. A new frequency-selecting method is used in the proposed antenna, based on capacitance switching among four states. Due to the limited antenna space in existing terminals, it is quite difficult to cover the entire low band with a single antenna. To overcome this difficulty, three single-pole double-throw (SPDT) switches, one 74HC04, and four capacitors are used. The resulting antenna covers the LTE (698-798 MHz) and GSM (824-960 MHz) bands in the low-band characteristic by realizing four capacitance states and at the same time covers the DCS (1710-1880 MHz)/PCS (1850-1990 MHz)/WCDMA (1920-2170 MHz) bands in the high-band characteristic. The antenna provides a gain of -1.04-6.00 dBi, a radiation efficiency of 32.73-74.99%, and omni-directional characteristics in the H-plane. Because of this outstanding performance, it is expected that the new frequency-selecting technique will be applied in 4G mobile communication terminals.
The design and evaluation of an active three dimensional (3D) millimeter wave imaging system for personnel security screening is presented in this work. The system is able to produce a highresolution 3D reconstruction of the whole human body surface and reveal concealed objects under clothing. Innovative multistatic millimeter wave radar designs and algorithms, which have been previously validated, are combined to significantly improve the previous reconstruction results. In addition, the system makes use of a reduced amount of information, thus simplifying portal design. Representative simulation results showing good performance of the proposed system are provided and supported by sample measurements.
Magnetic induction tomography (MIT) is a tomographic technique utilising inductive coils and eddy currents to map the passive electromagnetic properties of an object. Eddy current methods are widely used for non-destructive testing (NDT) in inspection of metallic structures. Eddy current based NDT uses a single coil or a pair of coils to scan the samples. As an emerging NDT technique, MIT scans the sample with a coil array through an eddy current based tomographic approach. In this paper, a planar array MIT system (PMIT) is proposed for 3D near subsurface imaging. This is of great importance as there are large numbers of potential applications for MIT that allow limited access to the materials under testing. The system development, practical implication, capability and limitations of PMIT are discussed. The fundamental principles are demonstrated through simulations. Experimental data are used to evaluate the capability and detectability this system has as a potential 3D subsurface imaging tool.
In high squint spotlight mode SAR, the coupling of the range and azimuth is very serious, which brings challenges to the imaging. In this paper, an extended frequency scaling algorithm is proposed, in which the range migration correction is divided into two steps. Firstly the range walk correction is implemented in 2D time domain. In the second step, the residual range migration is corrected by the frequency scaling and bulk shift operations. Though the second range compression does not consider the range space variance, the range compression is precise. In the azimuth compression, because of the range walk correction, the azimuth modulation frequency rate becomes dependent on the azimuth position. In order to equalize the azimuth modulation frequency rate, the azimuth nonlinear chirp scaling method is involved to remove the dependence. The simulation experiments verify the validity of the proposed algorithm. The comparison of the imaging quality among traditional frequency scaling algorithm, nonlinear frequency scaling algorithm and the proposed method indicates the proposed method is more suitable for the high squint spotlight SAR.
An improved UWB non-coplanar power divider is presented. Based on the theory of microstrip-to-slotline transition, the principle of this power divider is discussed. To improve the performances of the power divider, a tapered slot and a fan-shaped slot take the place of a circular slot in the circuit design. The simulated and measured results show a progressive return loss of input port.
An impedance-permeability (Z-μr) resonance phenomenon is firstly founded and numerically demonstrated when electromagnetic metamaterials with negative permeability are firstly introduced into inductance coil. Numerical results reveal that the impedance-permeability relationship exhibits an extraordinary self-resonant phenomenon at a certain negative value of relative permeability, which is related to the dimensions of the core but nearly independent to the coil size. Such a mechanism is proposed to increase the sensitivity of eddy current (EC) sensors up to about 270 times, offering a new method to greatly improve the sensitivity of EC sensors and the spatial resolution with micrometer scale.
In this paper an in-depth parametric analysis of shielding effectiveness obtained when using ferromagnetic or conductive screens to mitigate the field generated by duct banks is presented. Due to the need of a case-by-case approach, all the simulations, performed by a finite element software (GetDp), are applied to a case study composed by 9 (3x3) ducts, with six of them including high voltage single-core cables and the three left empty for eventual future expansion. Two shielding geometries are tested: horizontal and U-reverse, changing in each one the main parameters: width, thickness, clearance to conductors, etc. Moreover, the conductors are grouped in two balanced in-phase three-phase circuits arranged in three configurations: vertical, horizontal and triangular. The mutual phase ordering of both circuits is the one that minimizes the field, so no further field reduction can be obtained by simple methods. The power losses and cost of different shielding solutions are also presented, including the effect of adding a third circuit if required.
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