In this paper, the applications of chiral layers and metamaterials as radar absorbing materials are investigated. A perfect electric conductor plate covered by a chiral metamaterial is considered and after the formulation of the problem, reflection of the structure under an oblique plane wave incidence of arbitrary polarization is investigated. Then several examples of the applications of chiral layers in nondispersive, dispersive, and chiral nihility conditions are provided to design of zero reflection coatings. Finally, application of chiral metamaterial structures as microwave absorbers is discussed. In some of the provided examples, the method of genetic algorithm is used to optimize chiral coatings for the minimization of co- and cross reflected power.
In this paper, we present an efficient Artificial Neural Network (ANN)-based model to estimate both azimuth and elevation arrival angles of a signal source. To achieve this goal, the ANN model is constructed using measurement data obtained by a rectangular antenna array in the space-frequency domain. Unlike classical super-resolution algorithms such as 2D MUSIC, the proposed model is capable to account for imperfections of measurement equipment as well as mutual couplings between array elements. The neural model has been verified for several angular positions and frequencies. It is shown that use of ANN model to estimate angular positions of a signal source yields more accurate results when compared to 2D MUSIC. Moreover, the neural model significantly outperforms 2D MUSIC in terms of speed of computation.
It is potentially useful to perform target identification using micro-Doppler features because they contain information on the geometrical structure of the target. In this paper, the m-D effect of the rotationally symmetric ballistic target (BT) is analyzed which reveals that the m-D is not a form of sinusoidal modulation due to the sliding-type scattering. Inspired by the extended Hough transform (EHT), a method to extract all the six parameters of the BT is proposed. The m-D effect and the performance of feature extraction algorithm are demonstrated by the measured data in a microwave anechoic chamber.
The theory and design of a new family of multifrequency monopole antennas by smartly loading a set of complementary metamaterial transmission line (CMTL) unit cells are investigated. The distributed CMTL elements, epsilon negative (ENG) or double negative (DNG) through incorporating additional capacitive gaps, contain a Koch-shaped extended complementary single split ring resonator pair (K-ECSSRRP) etched on the signal strip. The K-ECSSRRP features dual-shunt branches in the equivalent circuit model, rendering a distinguished resonator with dual zeroth-order resonant (ZOR) modes. By smartly controlling the element layout and loading different numbers of unit cells, ten antennas covering different communication standards (GSM1800, UMTS, Bluetooth, DMB and WIMAX) are designed and four of them are fabricated and measured. At most of operating frequencies, the antennas exhibit impedance matching better than -10 dB and normal monopolar radiation patterns. Numerical and experimental results both confirm that the single-cell or dual-cell ENG and DNG CMTL-loaded monopoles exhibit almost identical dual ZOR modes. Moreover, the loaded elements also contribute to the radiation, which is the major advantage of this prescription over previous lumped-element loadings. These antennas are compact and the multiple operating bands can be arbitrarily engineered, enabling an alternative and easy avenue toward monopoles with multifunction and high integration.
The need to find ways to effectively utilize the large quantities of agricultural waste that are produced is indicative of the huge potential associated with producing an alternative pyramidal microwave absorber for anechoic chamber-testing applications. We propose the development of a pyramidal microwave absorber that can use sugar cane bagasse (SCB), a byproduct from the production and processing of sugar cane, as the absorbent. In this paper, we report the results of our use of dielectric probe measurement to determine the dielectric constant and loss tangent of SCB. These values were used to model and simulate an SCB pyramidal microwave absorber in Computer Simulation Technology's (CST's) Microwave Studio. This absorber was operated in the microwave frequency range between 0.1 GHz and 20.0 GHz.
In the applications of synthetic aperture radar (SAR) data, a crucial problem is to develop precise models for the statistics of the pixel amplitudes or intensities. In this paper, a new statistical model, called simply here GΓΓ, is proposed based on the product model by assuming the radar cross section (RCS) components (texture components) of the return obey a recently empirical generalized Gamma distribution. Meanwhile, we demonstrate theoretically that the proposed GΓΓ model has the well-known K and g0 distributions as special cases. We also derived analytically the estimators of the presented GΓΓ model by applying the "method-of-log-cumulants" (MoLC). Finally, the performance of the proposed model is tested by using some measured SAR images.
In this paper, we present a broadband out-of-phase power divider with high power-handling capability. The proposed device consists of several sections of double-sided parallel-strip lines (DSPSLs), a mid-inserted conductor plane, and two external isolation resistors, which are directly grounded for heat sinking. A through ground via (TGV), connecting the top and bottom sides of DSPSLs, is employed. The special metal via is realized to short the isolation resistors at full-frequency band when the odd-mode is excited. Meanwhile, it can be ignored as the excitation is even-mode. This property is efficiently utilized to improve the bandwidth. To examine the proposed power divider in detail, a set of closed-form equations are derived. Meanwhile, the power operation analysis illustrates that the proposed power divider is a good candidate for high power applications. The design charts show that the proposed device can support a wide frequency ratio range (1-1.7). Furthermore, broadband responses can be obtained when proper frequency ratios are adopted. For verification, an experimental power divider operating at 1.25/1.75 GHz is implemented. The measured results exhibit a bandwidth of 44.3% with better than 15 dB return loss and 18 dB port isolation is achieved.
This paper proposes a novel synchronous wideband frequency domain method for measuring time domain response of long-distance channel. Its core consists of: (1) baseband signal generators at the transmission terminal and the reception terminal respectively are used to generate the wideband signal of the same frequency; (2) the two GPS clock frequency reference sources locked on the same satellite are used to yield the high-stability 10MHz signal as the external reference source of the baseband signal generator so that the initial phases of the wideband signals are basically the same; (3) the pulse per second (PPS) signal generated by the GPS clock frequency reference source is used as trigger signal to ensure that the baseband signal generator and the vector network analyzer (VNA) can transmit and receive signals synchronously; (4) the time domain response of the channel is indirectly obtained through the inverse Fourier transform of amplitude and phase of the frequency domain response. To verify the measurement method, experiments were performed, in which the sea surface evaporation waveguide which is tens of kilometers apart from each other was selected as the channel. The experimental results, given in Figs. 4 and 5, and their analysis show that the measurement method can obtain amplitude and phase of the signal whose band is hundreds of MHz and whose equivalent pulse width reaches 5ns. The measurement method is used to obtain the time domain response of the long-distance channel, verifying that the measurement method is effective.
Current advanced spaceborne synthetic aperture radar (SAR) systems may operate at multiple imaging modes, including conventional modes as stripmap, ScanSAR and spotlight, as well as the state-of-the-art SAR modes, e.g., sliding spotlight, TOPS (Terrain Observation by Progressive Scans) and inverse TOPS, etc. A novel image formation scheme for unified processing spaceborne SAR data was proposed, which significantly simplified complexity of SAR processor sub-system. The unified-model-coefficient (UMC) was defined for modeling all SAR modes by means of analyzing both imaging geometry and time-frequency diagram corresponding to each imaging mode, respectively. The unified mathematical formula for modeling all SAR modes echo signal was derived as a function of UMC. Consequently, a unified image formation scheme for accurately focusing spaceborne SAR data in an arbitrary mode was proposed, which integrates all of SAR image formation procedures into a standard three-step processing framework, namely, de-rotation, data focusing and re-sampling, which evidently improve efficiency and robustness of data processing sub-system. Computer simulation experiment results verify the effectiveness of the proposed scheme.
In this paper, a new method that called the ``Stepped Cut at Four Corners'' is introduced to design a multi-mode/broadband modified rectangular microstrip patch antennas (MRMPAs). In order to become acquainted with the new method, the design process of a monopole broadband MRMPA suitable for multifunctional wireless communication bands is explained. The methodology of the proposed broadband MRMPA design is presented in six stages. The first stage is designing a single-mode RMPA. Subsequently, by creating a step at the corners using the proposed method a dual-mode antenna is obtained at the second stage, while the triple-mode and multi-mode antennas are designed, at the third and fourth stages respectively. Two types of broadband antennas are obtained, the stepped line and straight line antennas. By increasing the number of steps, the antenna's operating bandwidth (BW), with return loss less than −10 dB, covers the frequency range from 900 MHz to 2.6 GHZ, which is suitable for GSM (900 MHz and 1.5 GHz), WiFi (2.4 GHz) and LTE (2.6 GHz) applications. In addition, the antenna prototype has been fabricated and measured in the all stages, in order to validate the simulation results, and there is a close agreement between the simulated and measured results.
This paper presents a novel design approach to design in-line microstrip bandstop filter with accurate design theory and sharp skirt selectivity. This kind of bandstop filter is based on a simple coupled-line structure, indicating compact and flexible circuit layout for microstrip implementation. For a single-section bandstop filter, the scattering parameters and their constrain conditions are achieved, which provides an effective design guide for multi-section bandstop filters. Theoretical analysis indicates that the even-mode and odd-mode characteristic impedances can be easily used to determine the desired bandstop performance while the total circuit layout keeps very compact. For demonstration, seven numerical examples are designed, calculated, and compared. Finally, both experimental and simulation results of a two-section two-cell microstrip bandstop filter operating at 1 GHz are presented to verify the theoretical predications.
Label-free optical biosensors are important tools to study the kinetics, interaction and presence of (bio)chemical compounds in various fields such as biotechnology, pharma, diagnostics as well as environmental and food quality monitoring. Systems based on planar optical waveguides with input/output grating couplers are of interest as they offer multiple tuning parameters for the chip design and their high sensitivity. In the present paper, an algorithm based on the Finite-Elements Method (FEM) is proposed for finding the chip response and optimizing the sensitivity of the sensor system. Total field and scattered field coupled with the Transmission Line Transfer Matrix Method (TLTMM) are compared for the FEM. Unlike some widely used approximations, the impact of the grating depth, shape, duty cycle as well as losses and surface roughness are taken into account. Another advantage of the presented method is the possibility to implement a large part of the algorithm with commercially available FEM solver. Several practical situations are treated proving the validity of the approach against the Local Interference Method (LIME). The waveguide losses appear to be a decisive parameter for the chip design.
Time domain reflectometry (TDR) offers the advantage of distributed sensing using a single transmission line sensor. In the present study, a parallel plate type non-invasive TDR sensor for structural health monitoring (SHM) of composite has been designed, modeled and experimentally tested. Five layer unidirectional glass fiber/epoxy composite specimens are fabricated. Specimens included a damage initiator in form of a cut in the central ply. The TDR sensor detects sub-surface damage in the composite non-invasively as the effective dielectric constant of the composite decreases due to the presence of delamination cracks. Previous work done on dielectrostriction is used to model the TDR response to strain changes. Qualitative agreement between theory and experimental results for strain sensing are found.
In this paper, a novel planar inverted-F antenna (PIFA) with slotted ground structure is proposed for multiband mobile communication application. The multimode performance is applied for multiband operation in our design. The proposed antenna has good impedance matching characteristics for GSM850/900, DCS1800/1900, LTE2300/2500, IEEE 802.11a/b. The measured radiation efficiency of proposed antenna is all higher than 69% in GSM (824-960 MHz)/DCS (1710-1880 MHz)/PCS (1850-1990 MHz)/LTE (2300-2400 MHz, 2500-2690 MHz)/802.11b (2.4-2.48 GHz), and is up to 50% in IEEE 802.11a (5.15-5.825 GHz).
We investigate the wave propagation properties in lossy structures with graded permittivity and permeability involving left-handed metamaterials. An exact analytic solution to Helmholtz' equation for a lossy case with both real and imaginary parts of permittivity and permeability profile, changing according to a hyperbolic tangent function along the direction of propagation, is obtained. It allows for different loss factors in RHM and LHM media. Thereafter, the corresponding numerical solution for the field intensity along the composite structure is obtained by means of a dispersive numerical model of lossy metamaterials that uses a transmission line matrix method based on Z-transforms. We present the expressions and graphical results for the field intensity along the composite structure and compare the analytic and numerical solutions, showing that there is an excellent agreement between them.
The ability to control the scattering property of an object is important in many applications. In this paper, we propose and study the scattering characteristics of a circular array of split-ring resonators (SRRs). By calculating the scattered energy spectrum, we show that the proposed structure has a localized surface plasmon resonance like behavior, which makes it useful as a super scatterer. Furthermore, in a special case, the proposed structure exhibits transparency to the illuminated waves, i.e. it does not scatter any energy at all and thus acts as a zero electromagnetic scattering object.
Time domain analysis of electromagnetic wave propagation is required for design and characterization of many optical and microwave devices. The FDTD method is one of the most widely used time domain methods for analysing electromagnetic scattering and radiation problems. However, due to the use of the Finite Difference grid, this method suffers from higher numerical dispersion and inaccurate discretisation due to staircasing at slanted and curve edges. The Finite Element (FE)-based meshing technique can discretize the computational domain offering a better approximation even when using a small number of elements. Some of the FE-based approaches have considered either an implicit solution, higher order elements, the solution of a large matrix or matrix lumping, all of which require more time and memory to solve the same problem or reduce the accuracy. This paper presents a new FE-based method which uses a perforated mesh system to solve Maxwell's equations with linear elements. The perforated mesh reduces the requirement on memory and computational time to less than half of that compared to other FE-based methods. This paper also shows a very large improvement in the numerical dispersion over the FDTD method when the proposed method is used with an equilateral triangular mesh.
Magnetic response based on a two-level magnetic dipole transition in rare earth ions doped crystals was studied. Semi-classic theory and Wigner-Eckart theorem were used to calculate the magnetic permeability. It is found that negative permeability can be attained near the transition frequencies. In order to realize simultaneously negative permittivity and negative permeability, an electric dipole transition at the same frequency was also adopted, and a negative refraction region with a bandwidth of 0.57 MHz is demonstrated in (Yb0.02 Sm0.02Y0.96)3Al5O12 crystal. This explores a new route to obtain magnetic response and negative refraction at optical frequencies with nature-existed materials instead of metamaterials.
The relationship between specific absorption rate (SAR) and antenna gain inside the head due to the metal-frame spectacles was investigated. The radio frequency (RF) energy source considered is the smartphone used in the frontal face. A computer simulation using CST Microwave Studio 2012 was used for the investigation. Two sets of dipole antennas, operated at 900 MHz and 1800 MHz for GSM applications, were used as representative radiation sources from a mobile phone. Parametric studies were conducted to determine the optimum length of the metal rod, and the length was used to study the possibility of RF irradiation of the metal spectacles model. Then, the spectacles model was used as an analysis tool to study the interaction between gain and SAR in the head. The radiation pattern was plotted to identify the causes of the interactions. The gain decreased when the energy source was very close to the spectacles, and SAR increased enormously.
Application of electric field in normal to aligned carbon nanotubes creates Coulomb forces at intertube junctions and tubes become closely packed. Packed structure facilitates intertube transfer of carriers and reduced resistance is found to scale with field strength. Aggregated nanotubes are therefore used as field sensors and sensitivity is evident by drastic fluctuations of resistance. Sensing mechanism is discussed and verified.
The periodic structure like electromagnetic band gap (EBG) is a hot research topic in the academia and RF-microwave industry due to their extraordinary surface wave suppression property. This study involved in designing a compact uni-planar type EBG structure for a 2.4 GHz resonant frequency band. Double folded bend metallic connecting lines are successfully utilized to realize a low frequency structure while a size reduction of 61% is achieved compared to the theoretically calculated size. From the transmission response, the surface wave band gap (SWBG) is found to be 1.2 GHz (1.91-3.11 GHz) whereas the artificial magnetic conductor (AMC) characteristic is observed at 3.3 GHz. The FEM based EM simulator HFSS is used to characterize the EBG structure. The SWBG property is utilized for alleviation of mutual coupling between elements of a microstrip antenna array. A 2 x 5 EBG lattice is inserted between the E-plane coupled array which reduced the coupling level by 17 dB without any adverse effect on the radiation performances.
We propose a balanced frequency tripler scheme for millimeter-wave and submillimeter-wave application, in which double-sided suspended stripline is adopted. Two arms of Schottky diodes are mounted on the upper side of the substrate, and the other two arms of diodes are mounted on the lower side. The diodes are DC biased without bypass chip capacitor, which is essential in the common used balanced tripler scheme. Furthermore, the numbers of the diodes are doubled as there are only two arms of diodes in the common balanced tripler scheme, and this will double the power handling capability of the tripler. A W-band frequency tripler is designed according to the proposed scheme with commercial Schottky Varistors. The output power is from 2.9 to 5.7 dBm at the frequencies from 89.7 to 94.8 GHz, with the conversion efficiency from 1.95% ~3.7%.
This paper presents a structured model of the dielectric properties of the corneal tissue at microwave frequencies, based on the fine structure and chemical composition of its constituents. This is accomplished by appropriately combining the known properties of tissue substructures using mixing rules, in order to obtain the effective macroscopic properties of the medium. The presented approach is multi-scale: it begins from the microscopic scale and derives the macroscopic properties after several scale-steps. The predictions of the model agree with the existing measured data in the literature. Verification and analysis of the model sensitivity to input parameters has been presented. The model is expected to find application in non-invasive medical sensing where it can relate dielectric response to pathological structural changes in the tissue. The model is also useful for the prediction of dielectric properties for high-frequency computational dosimetry, and for understanding the physical mechanisms behind the macroscopic dielectric behaviour in general.
A modified differential evolution algorithm (MDE) for pattern synthesis of antenna arrays is proposed in this paper. By employing the novel strategies of best of random mutation and randomized local search, the convergence of standard differential evolution algorithm (SDE) is significantly accelerated. Five standard benchmark functions are optimized to testify the proposed algorithm by comparison with several other optimization algorithms. The numerical results verify the superior performance of the proposed MDE. Furthermore, the MDE is applied to two pattern synthesis examples, including a linear array and a cylindrical conformal array. Experiment results demonstrate that the proposed MDE has better performance than the other optimization methods in both of these two examples, which indicate the proposed algorithm is a competitive optimization algorithm in pattern synthesis.
In this work, near infrared filtering properties in a transmission narrowband filter are theoretically investigated. The filter is a defective photonic crystal of (LH)ND(HL)N, where N is the stack number, L is SiO2, H is InP, and defect layer D is an extrinsic semiconductor of n-type silicon (n-Si). It is found that there are multiple transmission peaks within the photonic band gap (PBG) as the defect thickness increases. The filtering position can be changed by varying the doping density in n-Si. That is, the peak (channel) wavelength is blued-shifted when the doping density increases. In the angle-dependent filtering property, the channel wavelength is also blued-shifted as the angle of incidence increases for both TE and TM waves. These filtering properties are of technical use in the applications of semiconductor optoelectronics.
We propose a novel signal model by combining the sparse stepped frequency signals with chaotic signals, i.e. the sparse stepped chaotic signal (SSCS) model, as well as the corresponding compression algorithm based on compressed sensing. In SSCS, the chaotic signals are modulated to sparse stepped frequencies to compose a transmitting burst. When receiving, the echo signals are demodulated to the baseband and then can be sampled directly at a rate much lower than the Nyquist rate determined by the bandwidth of chaotic signal of each subpulse. Compared with radars using conventional stepped frequency waveforms, the SSCS radar can transmit fewer subpulses in a burst and directly use lower speed ADC next to the receiver. Both simulated and real radar data are processed to demonstrate the effectiveness of the proposed SSCS as well as the compression algorithm by which high resolution range profiles are very well reconstructed.
The purpose of this paper is to discuss the applicability of the TGn radio channel models in estimating the performance of WLAN transmission. The specificity of the indoor radiowave propagation is first discussed, then TGn models are introduced together with a deterministic propagation model created by the authors for predicting the radio channel higher-order parameters. Intensive WLAN measurements have been carried out in two representative propagation environments and compared to theoretical predictions obtained in four configurations: beginning with the original TGN channel models, then enhancing them by including deterministically simulated pathloss and impulse responses and eventually by generating the channel impulse response on a purely random basis. The obtained results should indicate how accurately the general TGn channel models match measurements in real environments and how they compare to proposed successive modifications.
DRFM (Digital Radio Frequency Memory) is now widely utilized by modern radar jammers due to its high efficiency in jamming generation. However, its jammer structure is somewhat complex, since the up-conversion and down-conversion processes must be included. This paper proposes a new Synthetic Aperture Radar (SAR) jammer architecture utilizing Direct Radio Frequency Processing (DRFP), wherein both the up-conversion and down-conversion modules can be excluded. DRFP has a very compact hardware structure which employs Direct Digital Synthesizer (DDS), phase shifter, and delay lines for jamming modulation. Finally, the performances of DRFP are shown by both the inner-field test and a rail-way SAR experiment to be rather effective in jamming generation.
A novel triple-band single-fed compact microstrip antenna with varied polarization states and radiation patterns is proposed based on two-dimensional artificial metamaterial transmission line (TL). The TL element is composed of complementary split ring resonators (CSRRs) etched in the ground plane and a capacitive gap embedded in the stepped-impedance conductor line. By inserting a 2×2 array of the original element in conventional patch and feeding the resultant structure with an annular-ring slot along the diagonal, an antenna working in three resonant modes (n = -1, n = 0, and n = +2) is engineered at three specific well-separated frequencies f-1 = 1.5, f0 = 2.4 and f+2 = 3.5 GHz, respectively. As a result, both the numerical and experimental results illustrate that the antenna exhibits a patch-like radiation with pure linear polarization in the n = -1 mode, a monopolar radiation with circular polarization in the n = 0 and also an asymmetric quasi monopolar radiation with a hybrid linear polarization in the n = +2 mode. The antenna features compact whose patch occupying only an area of 0.246λ0×0.246λ0×0.03λ0 at f-1 and exhibits groups of advantages such as high radiation efficiency. Moreover, the proposed prescription, free of any metallic via, perturbation structure and complicated feeding network, is of practical value and opens an alternative avenue toward new types of antenna with agile polarization capability and versatile radiation patterns.
In this paper, we presents a cost effective method to generate a high-quality quadruple frequency optical millimeter-wave (MMW) signal using an integrated dual-parallel MachZehnder modulator (IDP-MZM). Not only does the method minimize the complication of the central station (CS) and its frequency demand for the devices, but the generated optical MMW signal as well has good transmission performance. By properly adjusting the direct current (DC) bias, modulation index, and using two radio frequency (RF) driving signals with 135° phase delay, a high quality dual tone optical MMW at 60 GHz is generated from a 15 GHz RF local oscillator (LO) with optical sideband suppression ratio (OSSR) as high as 32 dB and radio frequency spurious suppression ratio (RFSSR) exceeding 33 dB without optical filter when an integrated IDP-MZM with 30 dB extinction ratio is utilized. Furthermore, the influences of a number of non-ideal parameters, such as the impact of imperfect extinction ratio, non-ideal RF driven voltage and phase difference of RF-driven signals applied to two sub-MZMs of the integrated DP-MZM, on OSSR are studied through Simulation. Finally, we build a Radio over fiber (RoF) system through simulation, and the transmission performance of the generated optical MMW signal is presented. The eye patterns still clear and keeps open even after 60 km transmission.
We propose an effective way to realize the ultra-low loss in a split ring resonator (SRR) by suppressing the electric dipole moment approach. To tremendously reduce the loss, the loss mechanism of the SRR is theoretically analyzed in detail. The nonuniform current distribution on the SRR loop results in the residual electric dipole moment and thus brings the high radiation losses. Three different SRR configurations that the lumped capacitor, the distributed capacitor and the dielectric medium are incorporated into the SRR metamaterial are conceived, by which the uniform current distribution can be observed. This leads to in a finite bandwidth deviated from the resonance frequency where the SRR's loss performance dramatically improves owing to suppression of the residual electric dipole moment. The proposed the loss reduction mechanism has potential applications in negative and zero index memataterials, especially at THz frequencies and in the optical regime.
We address the performance analysis of the natural frequency-based radar target detection in this paper. We show how to calculate the detection performance recursively by making a polynomial approximation of the probability density function (PDF) of the standard normal distribution. Why we make a polynomial approximation of the PDF of the standard normal distribution is that the PDF of the standard normal distribution is not analytically integrable but that the polynomial is definitely analytically integrable, which makes it possible to calculate the detection performance without look-up table. The Taylor polynomial is used for an approximation of the PDF of the standard normal distribution. We derive the error of the approximation, the bound of the error of approximation, and the optimal polynomial approximation in the sense that the bound of the error of the approximation is minimized. We validate the derived expressions via numerical simulation.
In this paper, a novel circularly polarized Spidron fractal slot antenna array developed for broadband satellite communication in the Ku-band is discussed. A Spidron fractal slot configuration was utilized as a single radiating element to achieve circularly polarized radiation. The effects of altering the feeding position on the resonance behavior and the radiative characteristics were assessed. As a consequence, the design was expanded from a single element to a 2×2 subarray and further to a 4×4 array in order to enhance the bandwidth performance of the antenna when integrated with a sequential feeding network. Two prototype arrays were fabricated and tested, and measurements revealed that the 2×2 subarray has a 10-dB reflection coefficient bandwidth between 10 and 14.28 GHz, 3 dB axial ratio bands between 10.15 and 11.15 GHz and between 11.75 and 13.92 GHz, and a maximum gain of 11.4 dB at 13 GHz. The results for the 4×4 array indicated that both the 10-dB reflection coefficient and 3 dB axial ratio bandwidths cover the entire operating frequency from 10 to 15 GHz in the Ku-band. The maximum gain for the 4×4 array was 15.63 dB at 12.6 GHz.
In multidimensional numerical simulations of optoelectronic devices the rigorous Maxwell equations are solved in different ways. However, numerically efficient incoherent propagation of light inside the layers has not been resolved yet. In this paper we present two time- and resource-efficient approaches for optical simulations of incoherent layers embedded in multilayer structures: (a) phase matching and (b) phase elimination approach. The approaches for simulating the incoherent propagation of light in thick layers are derived from Maxwell equations. Both approaches can be applied to any layer in the structure regardless of the position inside the structure and the number of incoherent layers. In rigorous simulations, for low absorbing thick layers scaling down the thickness and increasing extinction coefficient of the layer proportionally is implemented to shorten computational time. The simulation results are verified with the experiment on two types of structures: a bare glass incoherent layer and an amorphous silicon solar cell.
An analytical technique referred to as the propagator matrix method (PMM) is presented to study the problem of electromagnetic (EM) waves interacting with the nonuniform magnetized plasma. In this method, the state vector is proposed to describe the characteristics of eigen waves in anisotropic medium, and state vectors at two different locations are related with each other by the propagator matrix. This method can be used to deal with the phenomenon of the transformation of EM wave polarization induced by anisotropic magnetized plasma, besides the conventional propagation characteristics through plasma slab, which overcomes the drawback of other analytical methods introduced in former studies. The EM problem model considered in this work is a steady-state, two-dimensional, nonuniform magnetized plasma slab with arbitrary magnetic declination angle, which is composed of a number of subslabs. Each subslab has a fixed electron density, and the overall density profile across the whole slab follows any practical distribution function. Based on PMM, a significant feature of strong transformation of EM wave polarization is addressed when an incident wave normally projects on the slab, which leads to the reflected or transmitted waves containing two kinds of waves, i.e., the co-polarized wave and the cross-polarized wave. The effects of varying the plasma parameters on the reflected and transmitted powers of co-polarization and cross-polarization, as well as the absorptive power for the typical bi-exponential density profile are investigatedin in detail, which provides a certain reference to various plasma technologies such as plasma stealth and communications through re-entry plasma sheath.
We propose a compact passive device as a super-concentrator to obtain an extremely high uniform static magnetic field over 50 T in a large two-dimensional free space in the presence of a uniform weak background magnetic field. Our design is based on transformation optics and metamaterials for static magnetic fields. Finite element method (FEM) is utilized to verify the performance of the proposed device.
Wireless capsule endoscopy (WCE) was developed as a painless diagnostic tool for endoscopic examination of the gastrointestinal (GI) tract, but, to date, the low operating power of the capsule and the high data rate of the RF telemetry system are still key concerns. Innovative, novel solutions must be developed to address these concerns before WCE can be used extensively in clinical applications. In this paper, we propose a novel RF transmitter for WCE applications that only requires 1.5 V to transmit the required data as opposed to using a DC power supply. Our proposed, direct-conversion transmitter system consists of a current reuse oscillator, an envelope filter, and an L-section matching network. The oscillator is powered by the transmitting data which keep the oscillator in turned on and off for the transmitting 1 and 0 bit respectively and results in the on-off keying (OOK) of the modulated signal at the output of the oscillator. The rate of data transmission at the modulated signal is limited by the transient period of the oscillator start-up. When the start-up time of the oscillator is optimized, an OOK modulation rate of 100 Mb/s can be attained. In order to eliminate the oscillator decay noise, we used an envelope filter connected in series with the oscillator to filter out the decay part of the oscillation. Finally, the output impedance of the envelope filter is matched to the 50-Ω antenna with an L-section, low-pass, matching network to ensure maximum power transmission. The entire transmitter system was simulated in a 0.18-μm Complementary metal-oxide-semiconductor (CMOS) process.
This paper presents a new type of a negative coupling structure for designing elliptic-response filters with cross-coupling. The proposed coupling structure consists of short-circuited coupled transmission lines. Using the fact that insertion phase of the coupled line structure is different from that of an inductive iris, it is shown that the proposed coupling structure can be used as the negative coupling structure. In order to verify the proposed coupling structure, we designed a 4th-order cross-coupled elliptic-response bandpass filter with substrate integrated waveguide resonators. A pair of transmission zeros in measurement and simulation results validates that the proposed structure can be used as the negative coupling structure.
As the distribution of the multiuser interference plus noise in time-hopping ultrawide bandwidth (TH-UWB) systems can not be reliably approximated by Gaussian probability density function (PDF), the bit error rate (BER) performance of the conventional matched filter receiver in TH-UWB multiuser systems degrades. In this paper we study a novel TH-UWB receiver based on two PDFs approximating the distribution of the multiuser interference plus noise. Firstly we investigate the difference between the distribution of the multiuser interference plus noise when the received pulse is collided by interfering pulses and that when it is not. Then two PDFs are developed to approximate the distribution of multiuser interference plus noise in these two cases respectively instead of using one PDF for both cases as done in other research works. Based on these two PDFs, a new detection scheme of TH-UWB receiver is proposed. The results show that BER performance of the proposed receiver is improved by 50% or more as compared to the conventional matched filter receiver, blinking receiver, Gaussian mixture receiver and p-order receiver using simulations.
This paper proposes an efficient parallel shooting and bouncing ray (SBR) method on the graphics processing unit (GPU) cluster for solving the electromagnetic scattering problems. At each incident direction, the parallel SBR method partitions the virtual aperture into sub-apertures, and distributes the computational process of each sub-aperture over GPU nodes. As ray tubes in the virtual aperture do not have the same computational time, the parallel efficiency highly depends on how to partition the virtual aperture. This paper addresses this issue by a dynamic partitioning scheme according to the computational time at the previous angle, which can achieve excellent load balance. Numerical examples are presented to demonstrate the accuracy, high parallel efficiency, good scalability and versatility of the proposed method.
The reduction in the radiation efficiency of an antenna in a mobile handset due to user's hand effects in the talking and data modes is studied. A parameter called "body loss" is defined to evaluate the degradation of the radiation efficiency. A C-fed on-ground (OG) PIFA antenna, which can cover two typical LTE bands of 0.75 GHz-0.96 GHz and 1.7 GHz-2.1 GHz, is used to study the property of the hand-effect body loss in two CITA test positions: the talking and data modes. Three different positions of the proposed antenna in the talking mode are compared, and the position with the antenna located on the bottom of the mobile handset and facing the head phantom is recommended for minimal body loss. A new modified design with a smaller antenna width is proposed to reduce the hand-effect body loss in the talking and data modes.
The pattern of each element in conformal array has a different direction for the curvature of conformal carrier, which results in polarization diversity of conformal array antenna. Polarization parameters of incident signals are considered in snapshot data model in order to describe the polarization diversity of conformal array antenna. It is required that the polarization parameters and direction of arrival (DOA) of incident signals are estimated together. An integrated frequency and DOA estimation method is proposed in this paper for cylindrical conformal array antenna. The frequency estimation of signal source is obtained by constructing state-space matrix. Through well-designed configuration of elements on cylindrical carriers along with estimation of signal parameters via propagator method (PM), the decoupling scheme for DOA and polarization parameters is implemented. A novel parameter pairing method for frequency and DOA of multiple sources utilizing the interpolation technique is given, based on which the fast frequency-DOA estimation algorithm is developed. Effectiveness of the proposed method is demonstrated by simulation experimental results.
This paper presents a novel synthesis technique for microwave bandpass filters with frequency-dependent couplings. The proposed method is based on the systematic extraction of a dispersive coupling coefficient using an optimization technique based on the zeros and poles of scattering parameters representing two coupled resonators. The application of this method of synthesis is illustrated using two examples involving four and five-pole generalized Chebyshev filters implemented in substrate-integrated waveguide (SIW) technology. As a dispersive inverter, a parallel shorted stub with an additional septum was used. The septum lends greater flexibility to the dimensional synthesis, in that it increases the allowable range of the coupling coefficients. The measured and simulated results are in excellent agreement, which confirms the validity of the proposed approach.
In this paper, we adopt the Levenberg-Marquardt (LM) algorithm to implement the nonlinear multivariable optimization for azimuth/elevation angle-of-arrival (AOA) estimation based on the Capon beamforming algorithm. The formulation is based on the fact that the cost function of the Capon algorithm can be expressed in a least-squares form. The performance in terms of the root mean square error (RMSE) and the computational complexity is illustrated via numerical results.
We propose an automatic and accurate technique for classifying normal and abnormal magnetic resonance (MR) images of human brain. Ripplet transform Type-I (RT), an efficient multiscale geometric analysis (MGA) tool for digital images, is used to represent the salient features of the brain MR images. The dimensionality of the image representative feature vector is reduced by principal component analysis (PCA). A computationally less expensive support vector machine (SVM), called least square-SVM (LS-SVM) is used to classify the brain MR images. Extensive experiments were carried out to evaluate the performance of the proposed system. Two benchmark MR image datasets and a new larger dataset were used in the experiments, consisting 66, 160 and 255 images, respectively. The generalization capability of the proposed technique is enhanced by 5 × 5 cross validation procedure. For all the datasets used in the experiments, the proposed system shows high classification accuracies (on an average > 99%). Experimental results and performance comparisons with state-of-the-art techniques, show that the proposed scheme is efficient in brain MR image classification.