This paper presents a closed-form analysis of composite right/left handed transmission lines. The ladder network structure of the transmission line allows to obtain a rational form of any twoport network representation. As a consequence of the rational form of the transfer functions, poles and residues are easily computed and the dominant ones selected leading to an efficient time-domain macromodel. The numerical results confirm the robustness and the accuracy of the proposed method in capturing the physics of composite right/left handed transmission lines.
The modular toroidal coil (MTC) is composed of several solenoidal coils (SCs) connected in series and distributed in toroidal and symmetrical forms. In this paper, we present an accurate approach for calculation of the mutual and self-inductance between all the SCs of MTC with any arbitrary section. We use Biot-Savart's and Neumann's equations to calculate the self- and mutual inductance between two filamentary circular rings with inclined axes that lie in the same plane, respectively. Their centers are either displaced along the axis of one coil or displaced along one axis of the first coil and then displaced sideways. We use the extended three-point Gaussian algorithm to solve the numerical analysis of the integrations resulting from these equations. Additionally, we apply the filament method to calculate the inductance of the MTC coil. Moreover, the finite element method (FEM) is employed to obtain SC inductance. The results obtained using the FEM confirms the analytical and empirical results. Furthermore, the comparison of the behavior of SC inductance, when the dimensional parameters of the SC are changed, with the FEM results shows an error of less than 0.2%. In this approach, we clarify how the presented equations have to be used for different coil combinations in the filament treatment. Thus, the presented approach can be easily used to calculate the mutual and self-inductance of a MTC between any two MTC rings in three dimensions.
Two different approaches for compensating the probe positioning errors in a near-field-far-field transformation with cylindrical scanning using a nonredundant number of measurements are presented and experimentally validated in this paper. In order to evaluate the uniformly distributed samples from the irregularly spaced ones, the former makes use of the singular value decomposition method, whereas the latter employs an iterative technique. In both the cases, the near-field data needed by a standard nearfield-far-field transformation are efficiently evaluated via an optimal sampling interpolation algorithm.
A simple field analysis was developed for helical slow-wave structure symmetrically supported by rectangular shaped discrete dielectric support rods partially embedded in the metal segments projecting radially inward from a metal envelope for wideband traveling-wave tubes. The tape helix model was used for the prediction of the dispersion relation and the interaction impedance characteristics. The closed form simplified expressions are obtained by combining the tape model dispersion relation for free-space helix and the dielectric loading factor obtained for the loaded helix in the sheath model. The dispersion characteristics and the interaction impedance characteristics obtained by the present analysis were compared with other more involved analytical method reported in the literature for the similar helical slow-wave structure and found to be in close agreement. The present analytical results were also validated against HFSS simulation with an agreement within 5% for both the characteristics for a wide range of structure parameters. An appropriate choice of the structure parameters (helix thickness, height of the metal segments, material of the dielectric support rods, wedge segments angle and helix pitch) provided the phase velocity varying with frequency corresponding to flat to negative structure dispersion with an appreciable interaction impedance values over a wide frequency band. The present analysis enjoys simplicity and establishes the potential of theproposed helical interaction structure for its employment in wideband traveling-wave tubes.
Intelligent compression is important to image transmission in real time over bandlimited channels for synthetic aperture radar (SAR) payloads deployed on unmanned aerial vehicles (UAV), where target areas are encoded with high fidelity, while background data are encoded with lesser fidelity. A target-aided SAR image intelligent compression (TAIC)system is presented in this paper, which utilizes robust fixed-rate trellis-coded quantization (FRTCQ) to encode target sequences and FRTCQ to encode background sequences. Multiresolution constant false alarm rate (CFAR) detector in wavelet domain using db4 based on the multiscale model of target is embedded. Generic region of interest (ROI) mask is created. In order to achieve better quality of target areas decoded, ROI mask is modified. The improved performance using TAIC system by compressing target chips from training set and testing set in Moving and Stationary Target Acquisition and Recognition (MSTAR) database is demonstrated.
In this paper, two-dimensional time-stepping finite-element (TSFE) method is performed for modeling and analyzing of a salient pole synchronous generator with different degree of dynamic eccentricity (DE) fault. TSFE analysis is used to describe the influence of DE fault on the flux distribution within the generator and no-load voltage profiles at low and high field current is obtained for healthy and faulty cases. Comparing the magnetic flux distribution of healthy and faulty generators helps to detect the influence of DE fault. Also, it can be seen at no-load condition with low excitation current, the effect of the eccentricity is considerable compared to that of the rated excitation current. Since the calculation of inductances of the machine is the most important step for fault analysis and diagnosis, the self- and mutual-inductances of the stator phases and rotor windings are calculated in the eccentric generator. Double periodic phenomenon is observed in inductances profile of stator phases due to the DE fault. Finally, spectrum analysis of stator current of two generators with different design parameters is used to diagnosis the significant harmonics in the presence of DE fault.
In this paper, a novel microstrip structure is developed to realize a dual-band bandpass filter. The proposed bandpass structure uses a microstrip resonator with two independently controlled resonance frequencies producing two frequency bands of interest controlled by adjusting the dimensions of the resonator. Parametric analysis is performed on the structure to determine the optimum dimensions to obtain the desired frequency response and is explained in the paper. The dual-band bandpass filter developed in this paper exhibits dual operating frequencies at 1390 MHz and 2520 MHz with 9.85% and 9.92% fractional bandwidths respectively. We achieved a compact second-order dual-band bandpass filter with controllable resonance frequencies and low insertion losses in the passband with high selectivity. The measured results are in good agreement with simulated results. Additionally, it can be easily fabricated and can be used in applications where miniaturization and compatibility with microstrip technology are of primary concern.
In this paper, the designed of triple-band printed dipole antennas are incorporated with single-band artificial magnetic conductor (AMC). The single-band AMCs are designed to resonate at 0.92 GHz, 2.45 GHz and 5.8 GHz using TLC-32 dielectric substrate. The four important parameters in AMC high impedance surface (HIS) design are also described in this paper. By simulating a unit cell of the AMC structure using a transient solver in Computer Simulation Technology (CST) software, the characteristic of the AMC can be characterized. The AMC condition is characterized by the frequency or frequencies where the magnitude of the reflection coefficient is +1 and its phase is 0°. It has high surface impedance (Z_{s}) and it reflects the external electromagnetic waves without the phase reversal. This characteristic of AMC enables the printed dipole to work properly when the antenna with AMC ground plane (GP) is directly attached to the metal object. The performances of the antenna with and without AMC structure as a ground plane to the antenna such as return loss, realized gain, radiation efficiency, radiation pattern and directivity are studied. Reported results show that the performances of the antenna are improved. Hence, the designed dipole tag antenna can be used for metal object identifications when the AMC structure is introduced as a ground to the antenna. The properties of the antenna are also remained well when the size of metal plate attached to them is increased.
Electromagnetic shields are designed to optimize the performance for shielding effectiveness and reflectivity. Multilayered laminates of different materials are developed to achieve excellent results in terms of not only in shielding effectiveness but also for reflectivity. In this paper, a three layered laminate is considered for estimation of the required parameters in the X-band frequency range. A sandwich of conductive polymer between a conductor and microwave absorber yields very good performance. Several investigations were carried out for the estimation of shielding effectiveness and reflectivity of the three layered laminate structure at different thickness of each layer and for a combination of different materials.
The modeling of quasi-static optimization problems often involves divergence-free surface current densities. In this paper, a novel technique to implement these currents by using the boundary element method framework is presented. A locally-based characterization of the current density is employed, to render a fully geometry-independent formulation, so that it can be applied to arbitrary shapes. To illustrate the versatility of this approach, we employ it for the design of gradient coils for MRI, providing a solid mathematical framework for this type of problem.
In this paper, an analytical method to characterize the frequency behaviour of Composite Right/Left Handed (CRLH) loaded printed dipole antenna is presented. One needs to determine the parameters of ungrounded reactive components realizing CRLH structures. Efficient resonant RLC circuit models based on Partial Elements Theory are presented to calculate inductance of meander line inductor and inter digital capacitor, while their capacitance is determined by Conformal Mapping Method. By using these circuit models and dispersion relation of balanced CRLH TL, negative resonance modes of antenna can be obtained. In addition, to validate the accuracy of the proposed analytical method, a prototype of the CRLH loaded printed dipole antenna is simulated, fabricated and measured.
In homeland security and law enforcement situations, it is often required to remotely detect human targets obscured by walls and barriers. In particular, we are specifically interested in scenarios that involve a human whose torso is stationary. We propose a technique to detect and characterize activity associated with a stationary human in through-the-wall scenarios using a Doppler radar system. The presence of stationary humans is identified by detecting Doppler signatures resulting from breathing, and movement of the human arm and wrist. The irregular, transient, non-uniform, and non-stationary nature of human activity presents a number of challenges in extracting and classifying Doppler signatures from the signal. These are addressed using bio-mechanical human arm movement models and the empirical mode decomposition (EMD) algorithm for Doppler feature extraction. Experimental results demonstrate the effectiveness of our approach to extract Doppler signatures corresponding to human activity through walls using a 750-MHz Doppler radar system.
A new antenna structure is formed by combining the concept of reconfigurable planar antenna array (RPAA) with the parasitic elements to produce beam steering patterns. The antenna has been integrated with the PIN diode switches that enable the beam to be steered in the desired direction. This has been done by changing the switch state to either on or off mode. In this work, a number of parasitic elements have been applied to the antenna, namely reflectors and directors. They are placed in between the driven elements, which is aimed to improve the beam steering angle. With such configuration, the main beam radiated by the array can be tilted due to the effect of mutual coupling between the driven elements and parasitic elements (reflectors and director). The unique property of this antenna design is that instead of fabricating all together in the same plane, the antenna's feeding network is separated from the antenna radiating elements (the patches) by an air gap distance. This allows reducing the spurious effects from the feeding line. The optimization results for the resonant frequencies of the antennas with variable air gap heights are also been studied. The antenna is made for 5.8 GHz. Good agreement is achieved between the simulation and measurement.
A geometrically based channel model is proposed to describe radio propagation in an indoor environment with directional antennas. In conventional geometric channel models (GCMs), distribution of scatterers does not take into account the antenna properties. A different approach is taken here for directional channel modeling. The locations of scattering objects are defined using non-Cartesian coordinates comprising an auxiliary geometric parameter ρ and angle-of-arrival (AOA) φ. Subsequently, we present a systematic method to study the influence of antenna pattern on scatterer distribution by applying two heuristic rules, which underpin the connection between the physical wave-propagation process and its canonical GCM. Provided with model preliminaries, important channel parameters including power azimuthal spectrum (PAS), power delay spectrum (PDS), mean effective gain (MEG), and antenna-decoupled PAS are derived and compared against the published data in the existing literature to demonstrate the usefulness of the proposed model.
Three novel shapes of mushroom-like electromagnetic band-gap (EBG) structures are presented in this paper. The three shapes are based on rectangular metal strip with different combinations. The performances of the three-shape structures are studied by using both incident plane wave method and transmission coefficient approach. The effect of height and via location are also studied to achieve multi or wide band gap. These shapes are embedded in microstrip patch antenna substrate. The performance of the MPA is improved as increasing the antenna gain by 5 dBi, decreasing the surface current so improving the antenna radiation pattern as well as reducing the antenna size by more than 70% compared to the original size. The new shapes of EBG structure are integrated with MPA as a ground plane, where the conducting ground plane is replaced by a high impedance surface EBG layer. Parametric studies are conducted to maximize their impedance bandwidth and gain. It is found that the antenna bandwidth increased by about four times than original band and its gain is similarly increased. Sample of these antennas are fabricated and tested, to verify the designs.
In this paper an inverse source problem is investigated. The measurement set-up is a reflector antenna covered by a radome. Equivalent currents are reconstructed on a surface shaped as the radome in order to diagnose the radome's interaction with the radiated field. To tackle this inverse source problem an analysis of a full-wave integral representation, with the equivalent currents as unknowns, is used. The extinction theorem and its associated integral equation ensure that the reconstructed currents represent sources within the radome. The axially symmetric experimental set-up reduces the computational complexity of the problem. The resulting linear system is inverted by using a singular value decomposition. We visualize how the presence of the radome alters the components of the equivalent currents. The method enables us to determine the phase shift of the field due to the transmission of the radome, i.e., the IPD (insertion phase delay). Also, disturbances due to defects, not observable in the measured near field, are localized in the equivalent currents.
We propose a mode based approach for developing a parametric model to characterize RF propagation in conduits. The model considers a conduit as a lossy waveguide and defines the total received power as the sum of powers excited in propagating modes. The model's parameters are estimated from both the physical properties of the conduit material and an empirical data set. Underground conduits have significant value as wireless communication channels for condition based monitoring within the conduit. An enabler for this wireless sensor network application is based on characterizing the expected coverage range of wireless transceivers operating in the 2.4 GHz ISM band. Previous studies on modeling RF propagation in underground conduits have focused on conduits with diameters larger than 1.05 m. This motivated our measurement campaign to collect empirical data from underground conduits with varying diameters from 0.30 m to 1.37 m. The empirical data is used to predict the mode coupled powers which are model parameters that are analytically intractable. We observe that the proposed model provides a good estimate of received power in terms of contribution from dominant propagating modes.
By taking inspiration from [1], a synthesis strategy is proposed for the case of planar arrays and ring shaped patterns which does not require the exploitation of global optimization procedures. In particular, the approach is able to determine a priori (that is, without solving the overall design problem) whether the given power pattern design constraints can be fulfilled or not, and, in the affirmative case, to determine the needed excitation coefficients. Although the approach does not apply to generic planar arrays and generic constraints, it may serve both as a reference solution for more general synthesis procedures, and as an elementary brick for more cumbersome synthesis problems.
Multiple-input multiple-output (MIMO) radar has superior performance to conventional one. It has been introduced to almost every application field of conventional radar in recent years. In practical application, MIMO radar also faces the problem of congested spectrum assignment, which makes it not possible to have a continuous clear band with large bandwidth. Sparse frequency waveform that contains several individual clear bands is a desirable solution to this problem. In this paper, we propose a method to design sparse frequency waveform set with low sidelobes in autocorrelations and cross-correlations by optimizing an objective function constructed based on Power Spectrum Density requirement and sidelobe performances of waveform set. Thus, besides the property of approximate orthogonality, the designed waveforms obtain the ability of avoiding spectrum interference to/from other users. The waveform is phasecoded and thereby has constant modulus. The effectiveness of the proposed method is illustrated by numerical studies. Practical implementation issues such as quantization effect and Doppler effect are also discussed.
This paper investigates the use of clonal selection principles based on our immune system for optimization applications in electromagnetics. This concept is based on our immune system's ability to respond to an antigen and produce a pool of anti-body secreting cells. In addition to the common implementations of this algorithm where the affinity maturation and cloning principles of clonal selection principles are used, we utilize memory and the cross-over concepts that are common to other bio-inspired methods. The performance of the algorithm is investigated for well known mathematical test functions and its potential is demonstrated in the context of the design of a radar absorbing material and a planar phased array antenna with specific radiation and null characteristics.