A three-dimensional (3D) time domain approach can be particularly valuable for the analysis of many different types of practical structures. In this regard, the finite difference time domain (FDTD) method is a popular technique, being used successfully to analyze the electromagnetic properties of many structures, including a range of optical or photonic devices. This FDTD method offers several major advantages: a minimum level of calculation is required for each of the cells into which the structure is divided, as well as data parallelism and explicit and easy implementation: however, the use of a cuboid grid makes the method very resource intensive for large simulations, especially those in 3D. Although the finite element (FE) approach is superior for the discretization of two-dimensional (2D) and 3D structures, most of the FE-based time domain approaches reported so far suffer from limitations due to the implicit or iterative form or the mass matrix formulation, for example. This paper presents an FE based time domain technique for 3D structures which uses a unique perforated mesh system. It calculated the numerical dispersion characteristics for the FDTD and the proposed method and compared. This paper finally discusses how to utilize the improved numerical dispersion characteristics of the proposed method to increase the simulation speed beyond the FDTD 3D method by using Intel micro-processors.
The paper introduces a new class of adaptive CFAR methods to cope with the problem of outliers due to the presence of clutter edges and interfering targets. A fundamental distinction between the proposed approach and existing adaptive CFAR approaches is that in order to maintain robust performance the former uses information on positions at which estimated outlier-free cells appear in the full reference window and the statistics of the sample in the cell under test. The performance of one of the possible implementations of new adaptive CFAR methods is studied and compared with that of an existing adaptive CFAR approach. The results show significant advantages of the proposed class of adaptive CFAR methods in both the false alarm regulation property and detection performance.
We prove the existence of complex eigenfrequencies of open waveguide resonators in the form of parallel-plate waveguides and waveguides of rectangular crosssection containing layered dielectric inclusions. It is shown that complex eigenfrequencies are finite-multiplicity poles of the analytical continuation of the operator of the initial diffraction problem and its Green's function to a multi-sheet Riemann surface, and also of the transmission coefficient extended to the complex plane of some of the problem parameters. The eigenfrequencies are associated with resonant states (RSs) and eigenvalues of distinct families of Sturm-Liouville problems on the line; they form countable sets of points in the complex plane with the only accumulation point at infinity and depend continuously on the problem parameters. The set of complex eigenfrequencies is similar in its structure to the set of eigenvalues of a Laplacian in a rectangle. The presence of a resonance domain in the form of a parallel-plane layered dielectric insert removes the continuous frequency spectrum and gives rise to a discrete set of points shifted to (upper half of) the complex plane.
A single layer, single feed microstrip antenna with multifrequency operation in compact size is proposed. A modified inverted π-shaped slot is introduced at the left side radiating edge of the patch to reduce the size of the antenna by reducing the resonant frequency. Multiple resonant frequencies with increased frequency ratio are also obtained by cutting the modified inverted π-shaped slot. The measured result shows that the proposed antenna resonates at 3.3, 4.55, 5.56 and 6.08 GHz in microwave S and C band. The size of the proposed patch is only 0.176λL×0.132λL at its lower operating frequency. The proposed patch antenna has achieved 68% size reduction as compared with the conventional rectangular microstrip antenna with same patch area. An extensive analysis of the reflection coefficient, voltage standing wave ratio, gain, radiation efficiency and radiation pattern of the proposed antenna is presented in this paper. The proposed antenna is suitable for WiMax and HiPERLAN wireless systems.
Dealing with the project of metamaterials scientists often have to design circuit elements at a subwavelength (or ``microscopic'') scale. At that scale, they use the set of Maxwell's equations in free-space, and neither permittivity ε nor permeability μ are formally defined. However, the objective is to use the unit cells in order to build a bulk material with some desired ``macroscopic'' properties. At that scale the set of Maxwell's equations in matter is adopted. To pass from one approach to the other is not obvious. In this paper we analyse the classic definitions of polarization P and magnetization M, highlighting their limits. Then we propose a definition for P and M fully consistent with Maxwell's equations at any scale.
In this article a method of optimizing wireless communication systems using multiple antennas is presented. This method focuses on the synthesis of antenna radiation patterns that are optimized in terms of mutual information, taking into account the specific limitations of the antenna design, such as the available space (for the antenna structure), polarization, number and arrangement of the antennas. The optimization focuses on volume based channel knowledge and on the theory of the intrinsic capacity. Based on this we developed algorithms that allow to determine optimized fixed radiation patterns also for time-variant channels.
This paper presents a new design approach for compact orthogonal broadband printed multiple-input multiple-output (MIMO) antennas based on a coplanar waveguide (CPW)-fed hexagonal-ring monopole antenna (HRMA) element. The design procedure of the basic radiating element is initiated from a stripline (SL)-fed circular monopole antenna (CMA). Then various antennas involved in the design evolution process are introduced to attain a compact CPW-fed HRMA. This basic antenna element has a compact size of 13×10 mm2, 50% smaller than SL-fed CMA, and a prototype of this antenna is built and tested. Based on HRMA element, compact two- and four-element MIMO antenna systems are designed, fabricated and experimentally demonstrated for 5-GHz ISM band operation. The MIMO antenna systems use orthogonally configured of identical closely spaced HRMA elements, with CPW-fed printed on one side of the substrate to achieve good isolation. Design simulation is carried out with the aid of Computer Simulation Technology Microwave Studio (CST MWS) and confirmed with High Frequency Structure Simulator (HFSS). The experimental results are in close agreement with the simulated ones, which validates the design principle. Based on experimental results, the two MIMO antenna systems have an impedance bandwidth of more than 2 GHz, good isolation of less than 15 dB, and a low envelope correlation coefficient of better than -26 dB across the frequency band of (4-6 GHz), which are suitable for 5-GHz MIMO applications.
An octagonal shape patch antenna with switchable inverted L-shaped slotted ground is designed for frequency band reconfigurable and experimentally validated. The antenna is capable of frequency band switching at five different states including an ultra wideband (UWB) state, two narrowband states and a dual-band state by using RF switching element p-i-n diodes. In the case of ultrawide band (UWB) state, the proposed antenna operates over impedance bandwidth of 141% (2.87-16.56 GHz) under simulation and 139% (2.85-15.85 GHz) in measurement with return loss S11 < -10 dB. For two narrowband states, 10 dB impedance bandwidth achieved is 16% (5.05-5.91 GHz) and 11% (8.76-9.80 GHz) under simulation and 14% (5.01-5.79 GHz) and 10% (8.68-9.69 GHz) in measurement, respectively. For the dual band state, 10 dB impedance bandwidth of 2.21-2.52 GHz (13%) & 5.07-5.89 GHz (15%) and 2.18-2.52 GHz (14%) & 8.78-9.71 GHz (10%) under simulation and 2.20-2.50 GHz (12%) & 5.05-5.90 GHz (15%) and 2.19-2.50 GHz (13%) & 8.70-9.60 GHz (9%) in measurement with return loss S11 < -10 dB. The proposed antenna is capable to serve in different wireless communication applications such as WLAN [802.11b/g/n (2.4-2.48 GHz), 802.11a/h/j/n (5.2 GHz), ISM band (2.4-2.5 GHz)], Bluetooth (2400-2484 MHz), WiMAX (2.3-2.4 & 5.15-5.85 GHz), WiFi (2.40-2.48, 5.15-5.85 GHz) and UWB (3.1-10.6 GHz). It also works at 9.2 GHz where airborne radar applications are found. Next, the antenna gain is improved with the help of a circular loop frequency selective surface (FSS) and a PEC (perfect electric conductor) sheet. Measured peak gain represents average improvements about 4 dB-5 dB over the UWB band. Experimental results seem in good agreement with the simulated ones of the proposed antenna with and without the frequency selective surface.
We derive and compare several finite-difference frequency-domain (FD-FD) stencils for points on or near a planar dielectric interface. They are based on interface conditions or from modifying Helmholtz equation. We present a highly accurate formulation based on local plane wave expansion (LPWE). LPWE-based compact stencil is an extension of the analytically obtained LFE-9 stencil as used by the method of connected local fields [Chang and Mu, PIER 109, 399 (2010)]. We report that merely using five points per wavelength spatial sampling, LPWE coefficients achieve better than 0.01% local error near a planar interface. We numerically determine that we have fourth to eighth-order accuracy in the local errors for LPWE stencils.
In this work, characteristics of an arc-monopole loaded with a DRA is analyzed. It is observed that the arc-monopole can be used to effectively couple to multiple DRA modes and generate dual/triple/wideband topologies. The structure is easy to fabricate with no additional substrate or matching slot/vias required to excite the multiple DRA modes. In addition, both broadside and monopole like patterns are obtained for the dual/triple band configurations which are suitable for communication with satellite or airborne targets and for surface-to-surface communication. The enhanced radiation in the source plane for the monopole like pattern can be effectively used to communicate with preferred targets or enhance the range in the direction of interest. In addition, the arc-monopole can be suitably located to couple the source mode to the DRA modes to generate broadband behavior.