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In this work, we show how we can improve the image resolution capabilities of a Phase Conjugating (PC) lens as well as the angular resolution of Luneburg lens antennas by employing signal processing techniques such as the Correlation Method (CM), the Minimum Residual Power Search Method (MRPSM), the sparse reconstruction method, and the Singular-Value-Decomposition (SVD)based basis matrix method. In the first part, we apply these techniques for sub-wavelength imaging in the microwave regime by combining them with the well-known phase conjugation principle. We begin by considering a one-dimensional microwave sub-wavelength imaging problem handled by using three signal processing methods, and then we move on to two- or three-dimensional problems by using the SVD-based basis matrix method. Numerical simulation results show that we can enhance the resolution significantly by using these methods, even if the measurement plane is not located in the very nearfield region of the source. We describe these proposed algorithms in detail and study their abilities to resolve at the sub-wavelength level. Next, we investigate the sparse reconstruction method for a normal Luneburg lens antenna and the Correlation Method and the SVD-based basis matrix method for a flat-base Luneburg lens antenna to estimate the Direction-of-Arrival (DOA). Numerical simulation results show that the signal processing techniques are capable of enhancing the angular resolution of the Luneburg lens antenna enabling the lens to locate multiple targets with different scattering cross-sections and achieving higher angular resolution.

In this letter, we show how we can improve the resolution capability of a phase-conjugating lens by employing a signal processing algorithm, namely the Minimum Residual Power Search Method (MRPSM), and we apply it for subwavelength imaging in the microwave regime by combining it with the well-known phase conjugation (PC) technique, which has been extensively used in the electromagnetics area for imaging purposes. We show that by using such a combination, we can achieve subwavelength resolution on the order of λ/10, even if the phase-conjugating lens or the measurement plane is located in the far-field region of the source. We describe the proposed algorithm in detail and study its ability to resolve at the subwavelength level, as well as its computational efficiency in a comparative manner.

In this paper we present two simulation techniques for modeling periodic structures with three-dimensional elements in general. The flrst of these is based on the Method of Moments (MoM) and is suitable for thin-wire structures, which could be either PEC or plasmonic, e.g., nanowires at optical wavelengths. The second is a Finite Difierence Time Domain (FDTD)-based approach, which is well suited for handling arbitrary, inhomogeneous, three-dimensional periodic structures. Neither of the two approaches make use of the traditional Periodic Boundary Conditions (PBCs), and are free from the di-culties encountered in the application of the PBC, as for instance slowness in convergence (MoM) and instabilities (FDTD).

In this letter, we present an improvement over the conventional thin dielectric sheet (TDS) formulation for the analysis of thin dielectric sheets. Our focus is to address the problem of scattering from thin penetrable scatterers by developing a volumetric formulation based on the use of macro-basis functions. The electric fields produced by the source basis functions are derived directly, bypassing the summation of scalar and vector potentials. The latter results in a considerable time advantage in comparison to the conventional method of moments (MoM) solution of the volume electric field integral equation (V-EFIE), while the accuracy remains comparable. In contrast to the TDS formulation, both tangential and normal currents are employed so that problems with high and low permittivity, as well as those involving grazing incident angles, can be accurately analyzed. Several examples are reported that show excellent agreement with conventional techniques and demonstrate the effectiveness of the new approach.

Plane wave scattering by a perfectly conducting strip grating is considered. A methodology for the computation of the induced currents is proposed, which utilizes the knowledge of the current induced in the center region of a truncated finite grating with only a moderate number of strips.

In this paper, we present a novel procedure for an efficient and accurate electromagnetic simulation of microstrip circuits and printed antennas etched in layered media. The proposed approach, based on a new algorithm referred to herein as the equivalent medium approach (EMA), is applied for a rapid design of the preliminary desired circuit prototype. The illustrated technique yields reliable results and reduces the computational time in comparison with the conventional method of moments (MoM). Some examples that demonstrate the accuracy and the efficiency of the described procedure are included.

In this work, we describe a hexa-band mobile phone antenna with a metallic backing, designed for SAR reduction. The proposed antenna has a simple structure comprising of two radiating strips and a coupling strip which serves to enhance the bandwidth at high frequency. The antenna has been designed to cover multiple bands, namely LTE Band 13 (747–787 MHz); DCS 1800 (1710–1880MHz); PCS 1900 (1850–1990MHz); WCDMA (1920–2170MHz); LTE Band 40 (2300–2400 MHz); and Band 41 (2496–2690MHz). The designed antenna only occupies a small area of 15×29.5 mm2 on the system circuit board. By adjusting the shape, location and size of the backing, the SAR is effectively reduced over all of the bands, while the efficiency of the antenna is preserved. Thus, the antenna is an excellent candidate for incorporation into smart phones for next generation wireless systems.

This paper describes the performance of a multi-band antenna with a Partially Reflective Surface (PRS) printed underneath the substrate to reduce the level of Specific Absorption Rate (SAR). The frequency band considered ranges from 850 MHz to 977 MHz and from 1.7 GHz to 2.1 GHz. The multi-band antenna placed above an FR4 substrate with the PRS printed below was found to reduce the 1-g average SAR in a specific anthropomorphic mannequin (SAM) model by 16.7–28.9 % as compared to the average SAR level of the no-PRS case, without unduly sacrificing antenna gain and radiation efficiency.

In this paper, signal processing techniques are employed for electromagnetic sub-wavelength imaging. Three signal processing algorithms are investigated, including phase conjugation (PC), correlation method (CM) and maximum search and removal method (MSRM).

Summary form only given. Increasing competition in the communication market has fueled the development of increasingly efficient Computer Aided Design (CAD) tools for simulating the performance of microwave circuits. One approach to accelerating the design process is to use a circuit simulator where the microstrip discontinuities are modeled as lumped elements. However, such a network-theory-type of simulator produces accurate results only at low frequencies, and their accuracy degrades rapidly as the operating frequency is increased to the point where the parasitic coupling effects cannot be neglected. One of the most widely employed full-wave algorithms is the Method of Moments (MoM). Though numerically rigorous and accurate, the MoM requires memory and Central Processing Unit (CPU) resources that are orders of magnitude greater than those associated with conventional circuit simulators. Recently, the Characteristic Basis Function Method (CBFM) has been successfully applied for the analysis of Monolithic Microwave Integrate Circuits (MMICs) and antennas etched on layered media. In the original version of this method, the analyzed geometry is decomposed into smaller regions, called blocks, for which high-level basis functions, the Characteristic Basis Functions (CBFs), are generated. Typically, two types of CBFs are calculated, the Primaries (PCBFs) and the Secondaries (SCBFs). The generation of the PCBFs is started by defining appropriate interfaces, i.e., inner ports, between adjacent blocks and considering each section in isolation. To generate accurate results by using the conventional CBFM, it is important to ensure that the inner ports (see Fig. 1) be defined at locations where the effect of the higher-order modes is negligible and the current distribution can be expressed as a linear combination of a forward and a reflected wave. We have developed a new algorithm for an efficient generation of the Primary CBFs which enables us to generalize the decomposition procedure. The partition scheme is user-independent, and allows the interface locations to be arbitrary (see Fig. 1).

summary form only given. In designing frequency selective surfaces (FSS), one of the desirable design goals is to achieve a wide bandwidth, as well as a sharp transition from pass- to stop-band. There are several techniques used to control the FSS bandwidth, which include: (i) choosing suitable lattice spacing; (ii) using element shapes that provide a sharp frequency transition, e.g., screens with thick apertures; and (iii) cascading multiple layers of FSS screens and dielectrics.

Sub-wavelength imaging, aka Superlensing, is the so-called “holy grail” of imaging, which has been extensively researched by many investigators, who have attempted to achieve it by using Metamaterials—specifically double negative (DNG) materials—Transformation Optics (TO)-based designs, Phase Conjugation(PC), and a number of other techniques. Unfortunately, however, the success to-date in this enterprise has been rather limited, and the search for achieving super-resolution still continues unabated.

In this paper, we describe a three-dimensional frequency-selective surface (FSS) element that generates a flat bandpass response over a wide band, as well as controllable low-pass angular response. The unit cell, which consists of a waveguide element with two connected cascaded radiating elements, exhibits a flat bandpass response over the frequency range 13 GHz to 24 GHz, i.e. a −3dB bandwidth (BW/f 0 ) of 66.6%. We show that the angular response of the FSS can be controlled by changing its periodicity, which, in turn, determines the angle at which the first higher-order Floquet harmonic begins to propagate.

In this paper we present a comparative study of flat and profiled lenses designed to operate in the GHz frequency range. Special attention is paid to focusing capabilities and bandwidth performance. Our results indicate that compared to the profiled lens, the flat lens with varying material parameters delivers a better performance in terms of scan capability and bandwidth.

In this paper, a novel technique for efficient electromagnetic simulation of microstrip circuits etched in layered media is presented. The proposed approach is useful for rapid prototyping of the desired circuit response and it uses closed-form expressions for the evaluation of the fields radiated by rooftop basis functions, applied in conjunction with an algorithm referred to herein as the Equivalent Medium Approach. Illustrative examples demostrating the reliability and the efficiency of the described procedures are included.

In order to investigate possible effects on cultured cells of Electromagnetic (EM) fields in the frequency range typical of mobile communications, a large variety of in vitro exposure systems have been designed and numerically characterized. Important requirements for in vitro experiments comprise a high homogeneity of the Specific Absorption Rate (SAR) distribution [1] and the possibility of performing experiments at SAR levels in the range of the actual safety standards of 2 W/kg [2] to achieve a low temperature rise in the cell monolayers. In this paper, a numerical dosimetric analysis has been carried out through CST Microwave Studio® 2009. The homogeneity of the SAR distribution and the coupling of EM fields within the liquid in the presence of a glass slide as support for living cells, has been investigated as a function of the incident field polarization.

Although thermal effects of Radio Frequency (RF) electromagnetic fields on biological tissue are well established in the literature, any possible non-thermal effects are currently being investigated. In-vitro exposure in conjunction with an accurate numerical modeling can be used in determining whether this effects exist and to establish a dose response curve. We would require such exposure to produce a uniform Specific Absorption Rate (SAR) throughout the sample, to avoid artifacts due to thermal hot-spots and to provide accurate dosimetry. The in-vitro uniformity exposure of blood tissue in the far field region of a horn antenna has been numerically investigated employing a FDTD code. The electric field distribution in a cylindrical test tube has been derived, furthermore the biological material has been exposed among two metal parallel plates to improve SAR uniformity. Further modifications, as the introduction of a polypropylene septum at its interior have been analyzed.

This paper shows the importance of using realistic cell shapes with the proper geometry and orientation to study the mechanism of direct cellular effects from RF exposure. For this purpose, the electric field distribution is computed, using the FDTD technique, in realistic cell models exposed to a linearly polarized plane wave of frequencies 900 MHz and 2.45 GHz. Furthermore, an insight on the mutual interactions between erythrocyte cell models shows that polarizing effects significantly affect the values of field intensity within the cell.

A frequency selective surface with a new type of three-dimensional element which produces a quasi-elliptic bandpass response is presented. The element exhibits an elliptic bandpass response with a −3 dB bandwidth (BW/f 0) of ∼ 70%, where f 0 is the centre frequency. The design has been adapted to a form that can be conveniently fabricated by utilising printed technology. The measured results for the frequency response show good agreement with those predicted via numerical simulations.