Two extended doublet bandpass filters with compact size and good spurious suppression characteristic are proposed. One is built up by a dual-mode microstrip resonator with a full-mode substrate integrated cavity, while the other is composed of a microstrip resonator and a half-mode cavity. The relationship between the location of their transmission zeros and the impedance ratio of the microstrip resonator is analyzed theoretically. Our proposed filters only occupy the areas of 0.69λ02/εr and 0.51λ02/εr, and they also have wide upper stopband. The predicted performances are demonstrated by the reasonable agreement obtained between their simulated and measured S-parameters.
A novel adaptive Wireless-Fidelity (Wi-Fi) system is the combination of radio frequency identification (RFID) technology, programmable intelligent microcontroller development board (PIDB) and reconfigurable antenna with beam shape characteristics. The system is capable to sustain a Wi-Fi signal adaptively above its threshold level (-81 dBm) within a range up to 100 m across three different buildings with variety indoor environments and floors. It is found that the modified ground reflection model has successfully predicted the total path loss of the test-bay buildings which consist of corridors, several floors and windows. The modified propagation model is extremely crucial in determining the projection and height of reconfigurable antenna to efficiently cover the scattered measurement points across the three buildings. The need of comparable signal strength is compulsory since the signal strength between 2.4 GHz of reconfigurable beam shape antenna and 0.433 GHz of RFID tag is different within the same distance. When reconfigurable beam shape antenna radiates with a minimum gain of 4.85 dBi, the measured signal strength shows that most of the measurement points are below Wi-Fi‟s threshold level which is from -69.001 dBm to -115.4530 dBm. However, the proposed system is able to boost all the signal strength above the threshold level with three different gain of reconfigurable beam shape antenna, 7.2 dBi, 9.9 dBi and 14.64 dBi through the activation of mobile RFID tag at different measurement points at one time. The boosted signal strengths are within the range of -69 dBm to -73.056 dBm. The capability of the mobile RFID tag in producing certain level of signal strength has been successfully exploited as a wireless stimulator for the system to adaptively activate certain PIN diode switches of reconfigurable beam shape antenna in this finding. The proposed system also has a great potential in realizing a new smart antenna system replacing the conventional switching beam array (SBA) antenna.
Early detection of tumor tissue is one of the most significant factors in the successful treatment of breast cancer. Microwave Breast Imaging methods are based on the dielectric contrast between normal and cancerous tissues at microwave frequencies. When the breast is illuminated with a microwave pulse, the dielectric contrast between these tissues can result in reflected backscatter. These reflected signals, containing tumor backscatter, are spatially focused using a beamformer which compensates for attenuation and phase effects as the signal propagates through the breast. The beamformer generates an energy profile of the breast where high energy regions suggest the presence of breast cancer. Data-Adaptive (DA) beamformers, use an approximation of the desired channel response based on the recorded signal data, as opposed to Data-Independent (DI) algorithms which use an assumed channel model. A novel extension of the DA Robust Capon Beamformer (RCB) is presented in this paper which is shown to significantly outperform existing beamformers, particularly in a dielectrically heterogeneous breast. The algorithm is evaluated on three anatomically accurate electromagnetic (EM) breast models with varying amounts of heterogeneity. The novel beamforming algorithm is compared, using a range of performance metrics, against a number of existing beamformers.
In this paper, based on different influences of the lattice symmetry, the geometry of dielectric rod, and the structure of unit cell to absolute gaps we propose a so-called three-order-effect method for the construction of two-dimensional (2D) photonic crystals (PCs) with larger absolute gaps. As an example, by means of our approach we fabricate a 2D hexagonal lattice of cylinder with an optimal rod adding at the center of the unit cell, where the absolute gap is larger than that of the PC with similar structure studied by other group previously. On the other hand, we also find that many of the 2D PCs with larger absolute gaps reported previously possess optimal first-order and second-order substructures. Our three-order-effect method would be useful for the design of 2D PCs with larger absolute gaps.
This paper proposes a novel design criterion for optimal pyramidal horns. According to it, the optimal aperture phase error parameters of a pyramidal horn are determined from the minimization of the horn's lateral surface area. We present two families of curves that illustrate the optimal aperture phase error parameters for frequency and directivity values in the area of practical interest. We also discuss two simple approximate design methods for the calculation of the optimal horn parameters. Comparisons with well-known design methods demonstrate the efficacy of our approach. The proposed criterion produces the lightest horn for a given directivity; as a result its fabrication requires less material compared to other structures. Moreover, the designed horns have smaller aperture area and occupy less space. The present approach is a useful design tool when the size and weight of a pyramidal horn or its manufacturing cost are of concern.
A scanning antenna at THz region is proposed and developed based on the quasi-optical techniques. It is composed of extended hemispherical lens/dielectric waveguide feed, inverse Cassegrain antenna, and transform lens. The extended hemispherical lens/dielectric waveguide feed is the key innovation of the scanning antenna. The inverse Cassegrain antenna is realized at THz region with special process and techniques, and the transform lens is used to match the input beam and the quasi-optical feed. The properties of the quasi-optical antenna are simulated with the FDTD method, and the experiments are carried out. The measured radiation pattern of the antenna is in agreement with the simulated result.
We present a rigorous 2D numerical study of the transmission, reflection and crosstalk coefficients of the perpendicular, identical dielectric crossing waveguide with various core-cladding index contrasts for both TE and TM polarizations. Our method is based on a hybrid frequency-domain finite-difference (FD-FD) technique computed with the cross-symmetry model. By varying the intersection profile, such as the circular, filleted, tapered and elliptical shapes, we achieve, even for a large 3.5 to 1.5 index ratio, a low 0.25dB insertion loss, a nontrivial reduction over the straight direct crossing case.
Both explicit analysis and FEM numerical simulation are used to analyze the field distribution of a line current in the so-called Maxwell's fish eye lens [bounded with a perfectly electrical conductor (PEC) boundary]. We show that such a 2D Maxwell's fish eye lens cannot give perfect imaging due to the fact that high order modes of the object field can hardly reach the image point in Maxwell's fish eye lens. If only zeroth order mode is excited, a good image of a sharp object may be achieved in some cases, however, its spot-size is larger than the spot size of the initial object field. The image resolution is determined by the field spot size of the image corresponding to the zeroth order component of the object field. Our explicit analysis consists very well with the FEM results for a fish eye lens. Time-domain simulation is also given to verify our conclusion. Multi-point images for a single object point are also demonstrated.
3-dimension finite-difference time-domain (FDTD) method is used to simulate the enhanced blue light emission of gallium nitride light emitting diode (GaN-LED) using the surface-plasmons (SPs) coupling with the quantum wells. The numerical simulation results demonstrate that when the silver film is coated on GaN-LED, the excited SPs play a key role in the enhanced blue light emission, and the enhancement depends on the geometries of GaN-LED and silver film. An enhancement factor is given to describe the enhancement effect of light emission. By changing the structure parameters of GaN-LED and silver film, the enhanced peak of the light emission in the visible region can be controlled. Under the optimal parameters, about 17 times enhancement at 460 nm can be obtained, and the enhancement effect is evidently demonstrated by the SPs field distribution.
Based on the altitude-dependent model of ITU-R slant atmospheric turbulence structure constant, the log-amplitude variance of laser beam propagation on the slant path through turbulent atmosphere is obtained with transmitter and receiver parameters and can be degenerated to the result of the horizontal path with atmospheric structure constant as a fixed value. These expressions are convenient tools for beam-wave analysis. Finally, we apply the ITU-R turbulence structure constant model to calculate collimated, divergent and convergent beam log-amplitude variance. The numerical conclusions indicate the log-amplitude variance of laser beam propagation on slant path is generally smaller than those on horizontal path.
This study investigates the effects of incorporating Doppler velocity measurements directly into track association and maintenance parts for single and multiple target tracking unit in a multi function phased array radar (MFPAR). Since Doppler velocity is the major discriminant of clutter from a desired target, the measurement set has been expanded from range, azimuth and elevation angles to include Doppler velocity measurements. We have developed data association and maintenance part of a well known tracking method, Interacting Multiple Model Probabilistic Data Association Filter (IMMPDAF), with the Doppler velocity measurements and demonstrated the performance improvement through simulations in terms of track update interval, track maintenance rate, RMS position estimation error, probability of detection and processing time. Since Doppler velocity measurements are employed in track maintenance, non-linear filters are used in the scheme leading to the use of Extended Kalman Filter (EKF) based PDAF. Comprehensive simulations have revealed that using Doppler velocity measurements along with 3D position measurements in heavy clutter conditions lead to an increase in track maintenance rate, track update interval; a decrease in position estimation error, processing time and no considerable effect on the probability of detection. This result is very significant for the efficient use of the limited resources of a multi function phased array radar.
A fast inhomogeneous plane wave algorithm is developed for the electromagnetic scattering problem from the composite bodies of revolution (BOR). Poggio-Miller-Chang Harrington-Wu (PMCHW) approach is used for the homogeneous dielectric objects, while the electric field integral equation (EFIE) is used for the perfect electric conducting objects. The aggregation and disaggregation factors can be expressed analytically by using the Weyl identity. Compared with the traditional method of moments (MoM), both the memory requirement and CPU time, are reduced for large-scale composite BOR problems. Numerical results are given to demonstrate the validity and the efficiency of the proposed method.
In this paper we study the optimization process of a novel hybrid antenna, formed by a Planar Inverted-F Antenna (PIFA) and a coplanar patch in the same structure, and intended to be used in mobile communications and WIFI applications simultaneously. This hybrid device has been recently proposed and characterized in the literature, and it has been shown that it allows a bandwidth of 850 MHz (49%) in the lower band and 630 MHz (11.25%) in the upper band. In spite of these good performance results, the fine tuning of the joint PIFA-patch parameters in the hybrid antenna is a hard task, not easy to automatize. In this paper we propose the use of an Evolutionary Programming (EP) approach, an algorithm of the Evolutionary Computation family, which has been shown to be very effective in continuous optimization problems. We use a real encoding of the antenna's parameters and the CST Microwave Studio simulator to obtain the performance of the antenna. The simulator is therefore incorporated to the EP algorithm as a part of the antenna's evaluation process. We will show that the EP is able to obtain very good sets of parameters in terms of the designer necessities, usually a larger bandwidth at the design frequencies. In this case, the bandwidth of the EP optimized antenna results in 980 MHz (55%) for the lower band and 870 MHz (17%) for the upper band.
We analyzed the microwave emission from a rough soil surface with exponential correlation by characterizing its dependences of polarization, look angle, and frequency. Using the same set of physical surface parameters of rms height and correlation lengths, results are obtained for a wide range of frequencies at 1.4 GHz, 5 GHz, 10 GHz, 18 GHz, and 36.5 GHz. Accurate simulations for the 2-D scattering problem are conducted by Galerkin's method with the rooftop basis function, followed by near-field integration, fine discretization, and cubic spline interpolation of surfaces. The multilevel UV method was employed to accelerate the solution. Accuracy is ensured by energy conservation check. Simulation results are compared with SPM, KA and AIEM. Results suggest that there exists distinct emission characteristic between the exponential and the Gaussian correlated surface. These charcateristics should be very useful in developing retrieval algorithm of the soil moisture from emissivity measurements.
The objective of this paper is to analyze the behavior of specular scattering for different soil texture fields at various soil moisture (mv) and analyze the data to retrieve the soil moisture with minimizing the effect of the soil texture. To study the soil texture effect on specular scattering 10 different soil fields were prepared on the basis of change in soil constituents (i.e, percentage of sand, silt and clay) and experiments were performed in both like polarizations (i.e., HH-polarization and VV-polarization) at various incidence angles (i.e., varying incidence angle from 25°to 70°in step of 5°). Angular response of specular scattering coefficients (σ°hh in HH-polarization and σ°vv VV-polarization) were analyzed for different soil texture fields with varying soil moisture content whereas the surface roughness condition for all the observations were kept constant. The changes in specular scattering coefficient values were observed with the change in soil texture fields with moisture for both like polarizations. Further, copolarization ratio (P=(σ°hh/σ°vv) study was performed and it was observed that the dependency of copolarization ratio for change in soil texture field at constant soil moisture is less prominent whereas the value of copolarization ratio is varying with variation of moisture content. This emphasizes that copolarization ratio may be minimizing the effect of soil texture while observing the soil moisture on specular direction. Regression analysis is carried out to select the best suitable incidence angle for observing the moisture and texture at C-band in specular direction and 60°incidence angle was found the best suitable incidence angle. An empirical relationship between P and mv was developed for the retrieval of mv and the obtained relationship gives a good agreement with observed mv. In addition, mv was also retrieved through the Kirchhoff Approximation (SA) and a comparison was made with the retrieved results of empirical relationship. The empirical relationship outperformed the SA.
Inverse synthetic aperture radar (ISAR) images represent the two-dimensional (2-D) spatial distribution of the radar cross-section (RCS) of an object and, thus, they can be applied to the problem of target identification. The traditional approach to ISAR imaging is the range-Doppler algorithm based on the 2-D Fourier transform. However, the 2-D Fourier transform often results in poor resolution ISAR images, especially when the measured frequency bandwidth and angular region are limited. Instead of the Fourier transform, high resolution spectral estimation techniques can be adopted to improve the resolution of ISAR images. These are the autoregressive (AR) model, multiple signal classification (MUSIC), and matrix enhancement and matrix pencil MUSIC (MEMP-MUSIC). In this study, the ISAR images from these high-resolution spectral estimators, as well as the FFT approach, are identified using a recently developed identification algorithm based on the polar mapping of ISAR images. In addition, each ISAR imaging algorithm is analyzed and compared in the framework of radar target identification. The results show that the dynamic range as well as the resolution of the ISAR images plays an important role in the identification performance. Moreover, the optimum size of the subarray (i.e. covariance matrix) for MUSIC and MEMP-MUSIC in terms of target identification is experimentally derived.
A novel dual-wideband microstrip bandpass filter (BPF) with improved upper-stopband performance is presented. With the use of some special structures such as E-shaped microstrip Stepped-Impedance Resonator (SIR) and input-output cross-coupling feed structure, this filter can generate five transmission zeros which are beneficial for improving its frequency selectivity and upper-stopband performance. Finally the microstrip dual-wideband BPF has been simulated, fabricated and measured. Measurement results show that the two passbands are centered at 3.7 GHz and 5.8 GHz with the fractional bandwidth of 31% and 13% respectively. Meanwhile more than 50% relative upper stopband bandwidth with 20 dB rejection has been realized. The simulated and measured results are in good agreement.
In this paper, a new hybrid classification method using both range profile (RP) and time-frequency image is proposed. The time-frequency image is obtained using the short-time Fourier transform before calculating the RP and this image is used for classification. 2-Dimensional Principal Components Analysis (2DPCA) is used to further compress the time-frequency image and to derive useful features from the image. The proposed method achieves a higher correct classification ratio than existing methods, especially when the signal-to-noise ratio is low.
A comprehensive review has been done on the types of electromagnetic transients that may affect low voltage electrical systems. The paper discusses various characteristics of lightning, switching, nuclear and intentional microwave impulses giving special attention to their impact on equipment and systems. The analysis shows that transients have a wide range of rise time, half peak width, action integral etc. with respect to both source and coupling mechanism. Hence, transient protection technology should be more specific with regard to the capabilities of the protection devices. Furthermore, we discuss the components and techniques available for the protection of low voltage systems from lightning generated electrical transients and the adequacy of International Standards in addressing the transient protection issues. The outcome of our analysis questions the suitability of 8/20 μs test current impulse in representing characteristics such as the time derivative and the energy content of lightning impulses. The 10/350 μs test current impulse better represents the integrated effects of the energy content of impulse component and long continuing current. A new waveform is required to be specified for testing the ability of protective devices to respond to the fast leading edges of subsequent strokes that may appear 100s of millisecond after the preceding stroke. The test voltage waveform 1.2/50 μs should also be modified to evaluate the response of protective devices for fast leading edges of induced voltage transients. A surge protective device that is tested for lightning transients may not be able to provide defense against other transients.
We present fast and accurate solutions of electromagnetics problems involving realistic metamaterial structures using a lowfrequency multilevel fast multipole algorithm (LF-MLFMA). Accelerating iterative solutions using robust preconditioning techniques may not be sufficient to reduce the overall processing time when the ordinary high-frequency MLFMA is applied to metamaterial problems. The major bottleneck, i.e., the low-frequency breakdown, should be eliminated for efficient solutions. We show that the combination of an LF-MLFMA implementation based on the multipole expansion with the sparse-approximate-inverse preconditioner enables efficient and accurate analysis of realistic metamaterial structures. Using the robust LF-MLFMA implementation, we demonstrate how the transmission properties of metamaterial walls can be enhanced with randomlyoriented unit cells.
A form of a novel adaptive antenna system that combines radio frequency identification (RFID) technology, programmable intelligent computer (PIC) microcontroller and reconfigurable beam steering antenna is proposed. Localization and adaptive response are the most challenging issues in smart antenna system. In this research, the localization technique relying on the received signal strength (RSS) signals has been done intensively where the capability of the RFID tag in producing certain level of signal strength has been exploited as a stimulator for the system to adaptively activate certain PIN diode switches of reconfigurable beam steering antenna. It is found that the detecting ability of the RSSI signals is extremely influenced by the 45°angle of the RFID reader's directive antenna. The combination of four 90°triangles which have 'adjacent' and 'opposite' angle of 45°forming pyramid antenna which has four sections; 1, 2, 3 and 4 enable the RFID readers to receive the RSS signals from the angles of 0°/360°, 90°, 180°and 270°respectively. When the RFID tag is directly facing a certain section, certain RSS signals will 'flow' from particular section into their respected RFID readers to automatically detect the range and angles' location of the RFID tag through the input ports of PIC microcontroller: A1, A4, C4 and C7. The PIN diode switches of the reconfigurable beam steering antenna are then activated by the output ports of PIC microcontroller: B0 up to B4, to steer the beam adaptively towards the RFID tag at four different angles: 0°/360°, 90°, 180°, and 270°according to the algorithm programmed in the microcontroller. It is found that the Ground Reflection (Two-Ray) propagation model is very crucial in determining the projection and height of reconfigurable antenna to efficiently cover the scattered measurement points of 1 up to 10 at four angles with different ranges of distance. The proposed antenna has a great potential in realizing the new smart antenna system replacing the conventional adaptive array antenna and Wimax application.
Generalized synthesis of the rat race ring coupler is developed with its four arms being allowed to have different characteristic impedances. The transmission line theory incorporated with the even-odd analysis is used to formulate the conditions for solving the circuit parameters. The solution shows that a rat race ring with a normalized area of 41.82% or 0.97λ-circumference can be achieved. Based on the solutions, simulated bandwidths of the new ring hybrids are reported. Two experimental circuits are measured for validation check. One uses stepped-impedance sections to realize the four arms for further size reduction. This circuit occupies only 13.12% of that of a conventional hybrid ring at 1 GHz. It is believed that this implementation has the best size reduction for a microstrip ring hybrid in open literature. Measured scattering parameters show good agreement with the simulated results.
In this paper, we present the design, simulation, and measurement of a dual-band metamaterial absorber in the microwave region. Simulated and experimental results show that the absorber has two perfect absorption points near 11.15GHz and 16.01GHz. Absorptions under different polarizations of incident EM waves are measured with magnitude of over 97% at low-frequency peak and 99% at high-frequency peak respectively. Current distribution at the dual absorptive peaks is also given to study the physical mechanism of power loss. Moreover, it is verified by experiment that the absorptions of this kind of metamaterial absorber remain over 90% at the low-frequency peak and 92% at the high-frequency peak with wide incident angles ranging from 0° to 60° for both transverse electric wave and transverse magnetic wave.
Compact dual-mode dual-band bandpass filters are realized with a single periodic stepped-impedance ring resonator. Neither extra resonator nor substrate layer is required for implementing the second passband. Based on the transmission line theory, a transmission zero design graph consisting of the transmission zeros together with the resonant frequencies of the resonator is developed against the space separation angle between the input and output ports. Based on this graph, when the line-to-ring feed structure is implemented, the space angle can be determined for the dual-mode dualband design with designated zeros near the two passbands. It is believed that this is the first design graph for designating the transmission poles and zeros of a dual-mode ring resonator filter before the excitation structure is realized. Three dual-mode dual-band bandpass filters are carried out for demonstration. All circuits occupy only 60% of the area of the conventional ring resonator bandpass filter at the first frequency. Measured results of experimental circuits show good agreement with simulated responses.
A Message Passing Interface (MPI) parallel implementation of a hybrid solver that combines the Method of Moments (MoM) with higher order basis functions and Physical Optics (PO) has been successfully used to solve a challenging problem including a 2160-slot waveguide array on an airplane with a maximum dimension larger than 1000 wavelengths. The block-partitioned scheme for the large dense MoM matrix combined with the process-cyclic scheme for the PO discretized triangles is designed to achieve excellent load balance and high parallel efficiency. To break the limitation of physical memory, the parallel out-of-core technique is introduced to tackle large dense systems generated using the MoM formulation. This research provides a solution with reasonable accuracy for solving large on-board antenna problems but has very low memory usage.