We have developed and implemented a selfconsistent density functional method using standard norm-conserving pseudopotentials and a flexible, numerical linear combination of atomic orbitals basis set, which includes multiple-zeta and polarization orbitals. Exchange and correlation are treated with the local spin density or generalized gradient approximations. The basis functions and the electron density are projected on a real-space grid, in order to calculate the Hartree and exchange-correlation potentials and matrix elements, with a number of operations that scales linearly with the size of the system. We use a modified energy functional, whose minimization produces orthogonal wavefunctions and the same energy and density as the Kohn-Sham energy functional, without the need for an explicit orthogonalization. Additionally, using localized Wannier-like electron wavefunctions allows the computation time and memory required to minimize the energy to also scale linearly with the size of the system. Forces and stresses are also calculated efficiently and accurately, thus allowing structural relaxation and molecular dynamics simulations.

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The SIESTA method for ab initio order-N materials simulation

Slots or defects integrated on the ground plane of microwave planar circuits are referred to as Defected Ground Structure. DGS is adopted as an emerging technique for improving the various parameters of microwave circuits, that is, narrow bandwidth, cross-polarization, low gain, and so forth. This paper presents an introduction and evolution of DGS and how DGS is different from former technologies: PBG and EBG. A basic concept behind the DGS technology and several theoretical techniques for analysing the Defected Ground Structure are discussed. Several applications of DGS in the field of filters, planar waveguides, amplifiers, and antennas are presented.

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Defected Ground Structure: Fundamentals, Analysis, and Applications in Modern Wireless Trends

The numerical evaluation of certain integral transforms is required for the interpretation of some geophysical exploration data. Digital linear filter operators are widely used for carrying out such numerical integration.

It is known that the method of Wiener–Hopf minimization of the error can be used to design very efficient, short digital linear filter operators for this purpose. We have found that, with appropriate modifications, this method can also be used to design longer filters. Two filters for the Hankel J0 transform (61-point and 120-point operators), and two for the Hankel J1 transform (47-point and 140-point operators) have been designed. For these transforms, the new filters give much lower errors compared to all other known filters of comparable, or somewhat longer, size. The new filter operators and some results of comparative performance tests with known integral transforms are presented.

These filters would find widespread application in many numerical evaluation problems in geophysics.

New digital linear filters for Hankel J0 and J1 transforms

SUMMARY

This paper presents a method for calculating the electromagnetic field from a dipole source in stratified media with general anisotropy. The formulation can be applied to geophysical applications such as ground-penetrating radar and marine controlled source electromagnetic (CSEM) methods. In stratified media, the propagation of fields can be considered in the frequency–wavenumber domain. The resulting set of ordinary differential equations consists of a field vector, a system matrix, and a source vector. In each piecewise homogeneous region, the system matrix is given by the material properties and the horizontal slownesses. The vertical slownesses are the eigenvalues of the system matrix. A diagonalization of the system matrix transforms the field vector into a mode-field that contains upgoing and downgoing field constituents. For system matrices that account for general anisotropy, it is shown how the electromagnetic field from any of the four basic dipole types can be calculated at any desired position in the stratified medium. It is furthermore shown how the reflection and transmission response from a stack can be calculated by a recursive scheme. Potential numerical instabilities due to using propagators are avoided by using this reflectivity method. Due to an energy-flux normalization of the eigenvector matrices, the reciprocity relations for reflection and transmission of electromagnetic fields in general anisotropic media can be derived. Several other useful relations between the reflection and transmission matrices are obtained as well. The propagator method is dependent on the ability to calculate eigenvalues and eigenvectors of the system matrix for all layers. In simple cases with isotropy or transversal isotropy in the direction of medium variation, the eigenvalue problem can be solved explicitly. These eigenvector matrices have useful properties, e.g. when processing data. The possibility to remove layers above or below the receiver layer follows from the decomposition of a field into upgoing and downgoing polarization modes. The propagator theory was implemented in order to model anisotropy in marine CSEM. A modelling study shows that responses are affected by horizontal, vertical, and dipping anisotropy in different manners. This suggests that when anisotropy is present at a survey site, careful planning and interpretation are required in order to correctly account for the responses.

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Electromagnetic fields in planarly layered anisotropic media

A dual-band, low profile, high gain, and low specific absorption rate (SAR) triangular slotted monopole antenna backed with a $4\times 4$ artificial magnetic conductor (AMC) array is presented for wireless body area network (WBAN) applications. The antenna is printed on a Rogers ULTRALAM 3850 substrate, whereas the AMC array is printed on a RO3003 substrate. The design operates at 3.5 GHz, for WiMAX wireless applications, and at 5.8 GHz for the ISM Band. The proposed antenna preserved the dual-band resonance and exhibited acceptable gain and SAR at a separation of 15 mm from the human body model. To reduce such separation and achieve enhancements to gain and SAR, an AMC array was utilized. In free space, gain enhancements by 6.8 and 3.7 dBi were achieved at both frequencies, respectively. Furthermore, over a gap of 1 mm from the human body, gain enhancements by 23.3 and 13.9 dBi were achieved at both frequencies, respectively. In addition, SAR reductions by almost 99% were attained. The antenna was fabricated and measured where a very good agreement was observed between simulated and measured results, with and without the incorporated AMC array. With such results, the proposed design can be highly recommended for wearable medical applications, specifically for diabetic patients.

A Wearable Dual-Band Low Profile High Gain Low SAR Antenna AMC-Backed for WBAN Applications

Recently, the mobile handsets support both the mobile and wireless LAN services. Thus, our target is to introduce a new antenna that supports both services. The antenna operates for most of the mobile applications such as the GSM 850, GSM 900, DCS 1800, PCS 1900, UMTS 2100, and most of the LTE bands, especially the low-frequency LTE 700 band. The antenna also supports the WiMAX, wireless local area network (WLAN), and the Industrial, Scientific, and Medical (ISM) bands. The antenna not only has a compact size, but also it supports a low specific absorption rate (SAR) radiation at all the operating frequencies. It consists of a monopole, a meander line, and an electromagnetic band-gap (EBG) structure. In order to cover the low frequency bands, a meander line is utilized due to its compact size, but unfortunately it is a narrowband antenna that is difficult to cover both LTE700 and GSM 900 bands. The solution stems from the use of an EBG structure that widens the band to cover the two low frequency bands and to reduce the maximum SAR. The higher frequency bands are supported by both the monopole and the meander line since they acts as traveling-wave antennas at the high frequency bands. The antenna meets three challenging parameters: the compact size, the multiband operation including the low frequency bands, and the low SAR radiation. Good agreement is found between the experimental and the simulated results.

Low-SAR, Miniaturized Printed Antenna for Mobile, ISM, and WLAN Services

A novel reconfigurable defected ground structure (DGS) resonator fabricated on coplanar waveguide (CPW) technology is presented. The resonator is endowed with an original design which enables the generation of multiple transmission zeros at arbitrary frequencies. The chosen design is indeed based on a slot defect created on the lateral ground planes of the CPW with the double advantage to allow a simple reconfiguration, by means of surface mounted (or fabricated) components, and a very compact solution, by exploiting the transversal dimension of the coplanar wave transmission line (CPW-TL). Four different states of the diodes configuration are investigated, where in each state multiple transmission zeros are produced in the frequency range from 1 GHz to 11 GHz. The equivalent circuit of each state is obtained using a conventional circuit parameter extraction method. Moreover, the slotline design equations are used to identify the transmission zeros and validated using the magnetic field distribution inside the slot. In this work, the reconfigurability is first proven by means of short bridges mounted in specific locations. These bridges are then replaced by PIN diodes. Simulated and measured results are in good agreement.

Novel Reconfigurable Defected Ground Structure Resonator on Coplanar Waveguide

This letter addresses a modified bandpass ring resonator filter providing compact size, low insertion-loss, wide bandwidth, sharp rejection, and suppressed higher order modes. It is demonstrated that the use of internal folded stubs translates into an overall size reduction of more than 70% through the exploitation of the internal ring area. The introduction of defected ground structures enhances the rejection of higher order modes beside offering a further advantage in terms of size reduction. It is furthermore shown that electromagnetic simulations, transmission line model, as well as measurement results are in very good agreement.

Compact Bandpass Ring Resonator Filter With Enhanced Wide-Band Rejection Characteristics Using Defected Ground Structures

A compact ultra-wideband (UWB) antenna with band-notch characteristic of size 28 mm times 29 mm is proposed. This antenna is designed to cover the Federal Communication Commission (FCC) bandwidth for UWB applications (3.1-10.6 GHz) and have a notch- filtering at the IEEE 802.1 Ia frequency band (5.15-5.825 GHz). This notch-filter effect is obtained by introducing a resonant U-shaped slot at this frequency. The design parameters and the performance of the proposed antenna are analyzed by using different techniques to assure the validity of the simulated results. Comparison between measurements and simulation is also presented.

Design of a Compact UWB Planar Antenna with Band-Notch Characterization

The loop radius of the coincident-loop system above a polarizable half-space has a significant effect on the magnitude of the negative response and its time of occurrence. Computations are made to study this phenomenon for various values of the electrical parameters of the ground, which is described by a Cole-Cole model. An optimum loop radius is found to exist, which leads to the largest peak of the negative response. It is found that for values of the frequency parameter (c) larger than 0.5, the largest peak of the negative response occurs at a time nearly equal to the Cole-Cole time constant. Empirical formulas are deduced relating both the optimum loop radius and the largest peak of the negative response to the electrical parameters of the polarizable half-space. The above phenomena may be used as a simple and effective guide for the detection of a polarizable target and estimating its electrical parameters.

Essam A. Hashish

Papers

Low-SAR, Miniaturized Printed Antenna for Mobile, ISM, and WLAN Services

Novel Reconfigurable Defected Ground Structure Resonator on Coplanar Waveguide

Compact Bandpass Ring Resonator Filter With Enhanced Wide-Band Rejection Characteristics Using Defected Ground Structures

Design of a Compact UWB Planar Antenna with Band-Notch Characterization

Optimum negative response of a coincident‐loop electromagnetic system above a polarizable half‐space