A Green's function based methodology has been developed and implemented with the view to optimize the focusing properties and thus the performance of a Microwave Radiometry Imaging System (MiRaIS). The system consists of an ellipsoidal conductive wall cavity and a sensitive radiometric receiver and its operation principal is based on the convergence of the radiation from one focal point, where the subject or phantom is placed, on the other, where the receiver antenna is positioned. A two-layered cylinder is used to model the human head with the semi-analytical Green's function technique. The imaging configuration is enhanced by different matching structures of various materials which are placed on the surface of both the human head model and the antenna inside the ellipsoidal. Numerical code executions have been realized and the results for the electric field distribution inside the head are presented for materials of various dielectric properties and for left handed materials at two different frequencies (0.5 GHz and 1.0 GHz). Increased sensitivity of the system focusing properties is observed using particular matching structures.
A compact Vivaldi antenna array printed on thick substrate and fed by a Substrate Integrated Waveguides (SIW) structure has been developed. The antenna array utilizes a compact SIW binary divider to significantly minimize the feed structure insertion losses. The low-loss SIW binary divider has a common novel Grounded Coplanar Waveguide (GCPW) feed to provide a wideband transition to the SIW and to sustain a good input match while preventing higher order modes excitation. The antenna array was designed, fabricated, and thoroughly investigated. Detailed simulations of the antenna and its feed, in addition to its relevant measurements, will be presented in this paper.
Abstract---In this paper we propose a circularly polarized (CP) microstrip antenna on a suspended substrate with a coplanar capacitive feed and a slot within the rectangular patch. The antenna has an axial ratio bandwidth (< 3 dB) of 7.1%. The proposed antenna exhibits a much higher impedance bandwidth of about 49% (S11 < -10 dB) and also yields return loss better than -15 dB in the useful range of circular polarization. Measured characteristics of the antenna are in good agreement with the simulated results. The radiation patterns indicate good cross polarization rejection and low back lobe radiations. The design proposed here can be scaled to any frequency of interest.
This article describes a compact UWB chip antenna using the coupling concept. The inclined slot is inserted on the rectangular radiating patch of the UWB chip antenna. From experimental results, the measured impedance bandwidth of the antenna (defined by -6 dB return loss) is 2.5 GHz (3-5.5 GHz). Also, the proposed antenna exhibits good radiation patterns with small gain variation (2.5-3.5 dBi) in the operating frequency band. Details of the proposed antenna design and the simulated and measured results are presented and discussed.
An inclined semi-circular slot cut in the narrow wall of a rectangular waveguide has been analyzed. By enforcing the boundary condition of continuity of the tangential magnetic field at the slot aperture, an integral equation with the aperture electric field as the unknown has been obtained and solved by the method of moments (MoM). The equivalent slot admittance is then determined. Different slot parameters, such as scattering coefficients, normalized resonant conductance, resonant length versus tilt angle, and radiation patterns, have been studied. The results obtained by the MoM have been verified by comparing them against those results obtained with HFSS.
A new integration technique based on use of Quasi Monte Carlo Integration (QMCI) technique is proposed for Method of Moments (MoM) solution of Integral equation for capacitance computation. The integral equation for unknown charge distribution over the capacitors is formulated. The solutions are obtained by MoM using the QMCI technique. It is observed that the proposed method is not only capable of dealing with the problem of singularity encountered in the Integral Equation efficiently but also provides accurate computation of the capacitances of parallel plate, cylindrical and spherical capacitors.
A novel scheme for detecting the location of a metallic mine (modeled as a perfectly conducting sphere and spheroid) in marine environment is presented. This technique takes into account Eddy-Current response (ECR) induced on the conducting marine mines as well as Current-Channeling response (CCR) associated with the perturbation of currents induced in the conductive marine environment. It leverages on the unique electromotive force (EMF) induced in a receiving coil through different orientations of a transmitting coil with respect to the marine mine. Unlike conventional EM sensing apparatus which is used to carry out the measurement at just one attitude at a fixed angle with respect to buried mine, our proposed scheme consists of angular scanning via the symmetry axes of a concentric sensor over the metallic mine in order to obtain a unique normalized induced voltage determining the mine's depth. Simulated results show that this technique has the potential of extending the depth detection range compared with the current method especially in conductive marine environment up to about 2 meters away from the sensor.
An analytical investigation has been presented of Au nano- coated dielectric optical fibers. The propagation constants of different transverse TE and hybrid EH modes are obtained corresponding to varying nano-coating thickness. It has been observed that the Au-layer has its profound effect on the number of propagating modes in the fiber, and the number of sustained modes is much reduced with the increase in Au-layer thickness. For the sake of comparative investigation, the modal behavior of three-layer dielectric fibers is also taken into account together with the Au nano-coated four-layer fiber. It is reported that the Au-layer has the effect of mode proliferation with simultaneous reduction in their propagation constant values.
The Goos-Hachen (GH) shift at the surface of chiral negative refractive media is analyzed theoretically. GH shifts are observed for both perpendicular and parallel components of the reflected field near the respective critical angles. It is found that positive and negative shifts can be attained when the incident angle is larger than the first critical angle, whereas if the angle of incidence exceeds the second critical angle, only positive shifts can be observed. In addition, a Gaussian beam is further adopted to illustrate the effect of the GH shifts.
Practical interests arising from behind-the-wall target detection, surveillance and reconnaissance et al. claim for high capability of imaging in complicated environments. Time Reversal Mirror (TRM) technique, making use of the principle of reciprocity, emerges as a promising way to deal with such complex problem. In this paper, we investigate TRM in the ultra-wideband (UWB) through wall radar imaging (TWRI) through numerical simulation. The probing region is a square room, with walls of rough surface and random media parameters. TRM is used to image the target settled in the room. We evaluate the degradation of the images when the aperture of the array is decreased or the received signals are contaminated by noises. The back projection (BP) algorithm is employed here as a comparison for imaging quality. For the case in which the random walls are changed between the forward and inverse phase of time reversal, we check the imaging stability and applied an averaged Green's function to improve the imaging quality. Finally, some interesting conclusions are drawn.
In this paper, the hybrid physical optics/boundary integral-finite element-mode matching (PO/BI-FE-MM) method is proposed for the analysis of the horn antenna enclosed by the electrically large radome. The radome is modeled by the PO method, and the BI-FE-MM method is implemented to the horn region. The equivalent PO currents on the radome surface are coupled into the BI-FE-MM equation of the horn region to account for the effects of the radome on the horn. With this hybrid method, the mutual interactions between the radome and the horn are fully considered. The radiation patterns, field distributions, and the S-parameters of the horns enclosed by different kinds of radome are presented.
In this paper, an improved residual carrier frequency offset estimation scheme is proposed for ultra-wideband multiband orthogonal frequency division multiplexing (UWB-OFDM) systems. The basic idea of our approach is based on the fact that two adjacent OFDM symbols convey identical information in an UWB-OFDM system. The mean square error of the synchronization scheme is derived, and its simple expression is also calculated. Finally, simulation results are demonstrated to verify the theoretical analysis in this paper.
A novel compact four element multiple input multiple output (MIMO) antenna is proposed. The antenna is composed of four E-shaped patch elements and operates at 5.8 GHz. The E-shaped patch antenna, operate at this frequency is designed using the Invasive Weed optimization algorithm. This algorithm is then applied to design the two and the four element MIMO antenna for high degree of isolation. In order to measure the array performance under MIMO signaling conditions a multi-port metric is used to characterize the compact array rather than the scattering matrix characterization. The designed antennas have low profile, easy fabrication, low cost and good isolation. The simulation and measurement result of reflection coefficient, mutual coupling and radiation pattern is presented.
Electrical capacitance tomography (ECT) is a relatively mature non-invasive imaging technique that attempts to map dielectric permittivity of materials. ECT has become a promising monitoring technique in industrial process tomography especially in fast flow visualization. One of the most challenging tasks in further development of ECT for real applications are the computational aspects of the ECT imaging. Recently 3D ECT has gained interest because of its potential to generate volumetric images. Computational time of image reconstruction in 3D ECT makes it more difficult for real time applications. In this paper we present a robust and computationally efficient 4D image reconstruction algorithm applied to real ECT data. The method takes advantage of temporal correlation between 3D ECT frames to reconstruct movies 4D of dielectric maps, which enhance the noise performance of and its computational efficiency, improves the speed of ECT image reconstruction. The 4D image reconstruction results are presented for experimental data from fast moving object.
Adaptive beamforming, which uses a weight vector to maximize the signal-to-interference-plus-noise ratio (SINR), is often sensitive to estimation error and uncertainty in the parameters, such as direction of arrival (DOA), steering vector and covariance matrix. Robust beamforming attempts to mitigate this sensitivity and diagonal loading in sample covariance matrix can improve the robustness. In this paper, beamformer based on particle filter (PF) is proposed to improve the robustness by optimizing the diagonal loading factor in sample covariance matrix. In the proposed approach, the level of diagonal loading is regarded as a group of particles and optimized using PF. In order to compute the post probability of particles beyond the knowledge of noise, a simplified cost function is derived first. Then, a statistical approach is developed to decide the level of diagonal loading. Finally, simulations with several frequently encountered types of estimation error are conducted. Results show better performance of the proposed beamformer as compared with other typical beamformers using diagonal loading. In particular, the prominent advantage of the proposed approach is that it can perform well even noise and error in the steering vector are unknown.
The PMCT probe, saying, one kind of open-ended coaxial probe adopted widely in microwave coagulation therapy of cancer, has been used to measure the complex permittivity of freshly excised specimens of normal animal tissues. The RFM model for PMCT probe is developed to extract the anticipant permittivity of specimens under test. In addition, the effects of several factors on the measurement results have been considered and discussed, including different temperature and reference materials, as well as the sampling frequency range and intervals of the rational function model. All the experiments have been conducted at the microwave frequency range from 450 MHz to 14.5 GHz.
A generalized GPS (GGPS) algorithm is proposed for the problem of reducing the bandwidth and profile of the stiffness matrix in finite element problems. The algorithm has two key-points. Firstly and most importantly, more pseudo-peripheral nodes are found, used as the origins for generating more level structures, rather than only two level structures in the GPS (Gibbs-Poole-Stockmeyer) algorithm. A new level structure is constructed with all the level structures rooted at the pseudo-peripheral nodes, leading to a smaller level width than the level width of any level structure's in general. Secondly, renumbering by degree is changed to be sum of the adjacent nodes codes to make a better renumbering in each level. Simulation results show that the GGPS algorithm can reduce the bandwidth by about 37.63% and 8.91% and the profiles by 0.17% and 2.29% in average for solid models and plane models, respectively, compared with the outcomes of GPS algorithm. The execution time is close to the GPS algorithm. Empirical results show that the GGPS is superior to the GPS in reducing bandwidth and profile.
This paper presents a novel method to enhance the pattern characteristics of the TEM horn antenna for 2-14 GHz frequency band. The conventional TEM horn antenna introduces some fluctuations in the main lobe radiation pattern over the higher frequencies, i.e., 10-14 GHz. This motivated us to propose a new method to remove the aforementioned impact by carving an arc shape to the open end of exponentially tapered plates. The associated curvature of this arc is optimized to completely remove the aforementioned fluctuation. The measurement results show that the improved TEM horn antenna structure exhibits low VSWR as well as good radiation pattern over 2-14 GHz frequency band.
This paper studies the loss effect of the line and the validity of a SPICE model for lossless transmission lines excited by an incident plane wave by using a simple structure --- a single line over an infinite perfectly conducting ground excited by an incident electromagnetic field. The frequency domain current responses calculated by the Baum-Liu-Tesche (BLT) equation with the loss ignored are compared with those through the BLT equation with loss considered to study the loss effect of transmission lines. The loss effect study shows that the SPICE model for lossless transmission line can be used for electromagnetic pulse interaction with electronic systems when the frequency is not very high or the systems are not very large. But for a sine wave of which the frequency equals the pole frequency of the line, the SPICE model may lead to significant error.
We review the research progress in reversed Cherenkov radiation in double- negative metamaterials (DNMs) starting from the first experimental verification of the DNMs reported in 2001, including theories, numerical computation and simulation and experiments. We also discuss the potential applications to particle detectors and highpower microwave or millimeter-wave devices, including the oscillators and amplifiers, and the formidable challenges needed to be resolved before the benefits of using such artificial materials can be harvested.
A heuristic particle swarm optimization (PSO) based algorithm is presented in this work and the novel hybrid approach is applied to linear array synthesis considering complex weights and directive element patterns so as to analyze its usefulness and limitations. Basically, classical PSO schemes are modified by introducing a tournament selection strategy and the downhill simplex local search method, so that the hybrid algorithms proposed combine the strengths of the PSO to initially explore the search space, the pressure exerted by the genetic selection operator to manage and speed up the search, and finally, the ability of the local optimization technique to quickly descend to the optimum solution. Four classical real-valued PSO schemes are taken as reference and synthesis results for a 60-element linear array comparing those classical schemes and the hybridized ones are reported and discussed in order to show the improvements achieved by the hybrid approaches.
A new design of feed for radial line slot antenna (RLSA) is presented. For better impedance match to the waveguide the effect of the various feed parameters is analyzed and their design sensitivity is studied. This paper emphasizes the advantages of using feed with a funnel below the connector entry and a conical segment over the entering probe.
A system level integration of simulation methods for high data-rate transmission circuit design applications is developed in this paper. While the elementary circuit theory was responsible for designing the circuits to meet the required performance specifications, three dimensional full-wave electromagnetic simulation technique was adopted to characterize the off-chip parasitic effects induce from the packages. The developed technique was applied for the design of optical Pick-Up Head (PUH) driver circuitry and a data transmission rate up to 640Mega bits per second (Mb/s) was achieved with standard 0.35 μm CMOS technology, showing the promising feature of applying such technique in successful design for high data-rate transmission circuits.
The ambiguity function of a kind of chaotic signal radar using Colpitts oscillator is investigated and compared in several aspects. The Colpitts oscillator with specific value of capacitance, inductance and resistance can generate chaotic signal with frequency band from direct current to several gigahertz. The chaotic signal is obtained from simulation and experiment. The auto-ambiguity functions of the chaotic signal show that the chaotic signal of such oscillator is ideal for radar application with both high range and range rate resolution. The cross-ambiguity function also indicates the chaotic signal has excellent capabilities in the electronic countercountermeasures (ECCM).We also present the resolution of range with the spectrum from experiment.
A broadband method is introduced to measure the effective constitutive parameters of artificial magnetic materials. The method is based on the microstrip line topology, thus making it easy to retrieve the constitutive parameters over a wide band of frequencies. To demonstrate the effectiveness of this method, artificial magnetic materials with Fractal Hilbert inclusions are fabricated and characterized. Good agreement between the experimental and numerical simulation results verifies the accuracy of the proposed method.