Closed-form mixed potential Green's functions (MPGFs) for cylindrically stratified media are derived in terms of quasistatic-wave and surface-wave contributions. In order to avoid possible overflow/underflow problems in the numerical calculations of special cylindrical functions such as Bessel and Hankel functions, a novel form of the spectral-domain MPGFs is developed. Then, a two-level methodology is used for the approximation of the spectral-domain MPGFs. In the first step, the qusistatic components are extracted from the spectral-domain MPGFs, and then transformed into the space domain with the use of the Sommerfeld identity and its derivatives. In the second step, the remaining parts of the spectral-domain MPGFs are approximated in terms of pole-residue expressions via the rational function fitting method (RFFM). The proposed method is efficient and fully automatic, which avoids an analytical cumbersome extraction of the surface wave poles (SWPs), prior to the spectrum fitting. In addition, this method can evaluate the spatial-domain MPGFs accurately and efficiently for both the near- and far-fields. Finally, numerical results for the spatial-domain MPGFs of a two-layer structure are presented and discussed.

In this paper, a new look at the electromagnetic field in a reverberating chamber (RC) is presented. It follows the fractional Brownian motion (fBm) model and exploits the Hurst parameter as the key parameter to discriminate among various RC configurations. Experiments accomplished at the RC of the Università di Napoli Parthenope, formerly Istituto Universitario Navale (IUN), confirm the physical soundness of the proposed model.

Microstrip patch antenna has been designed and developed for Unmanned Aerial Vehicle based Synthetic Aperture Radar (UAVSAR). This antenna operates in C-Band at the frequency of 5.3 GHz with a bandwidth of 80\,MHz. The radiation patterns of the antenna were specified to provide a desired scanned area for UAVSAR. The UAVSAR antenna was designed in the form of combination of 3 subpanels to allow dual operating mode (single antenna or dual antenna) selection. Two feed points are provided to the feeding network of each subpanel to reduce undesired power loss. The developed antenna prototype meets the performance requirements of UAVSAR system. It shows promising results in the UAVSAR flight mission conducted in Mersing area, Malaysia for both operating modes.

This paper presents a new method for computing fields diffracted by a wedge for the MECA formulation, which is valid not only for perfect electric conductors but also for lossy penetrable dielectrics. The method is based on the computation of a wedge correction matrix, which establishes a mapping function between fields incident at and diffracted by the wedge. The MECA method is based, in general, upon the oblique incidence of a plane wave at the interface between free space and lossy dielectric media. MECA reduces to the well-studied physical optics (PO) formulation in case of PEC (perfect electric conductor) scatterers. In this work, we consider a scenario involving diffraction caused by a plane wavefront incident on a wedge with flat faces and straight edge. The version of the stationary phase method for three-dimensional equivalent source distributions is employed to calculate the asymptotic contribution of the integration boundary along the edge of the diffraction wedge. This contribution of the critical boundary points is compared to the GTD (geometrical theory of diffraction) diffracted field in order to obtain the correction matrix by which the incident electric field vector is multiplied in MECA. As required to accomplish this comparison, the three-dimensional incident electric field is previously resolved into an edge-fixed coordinate system. Good agreement is demonstrated between full-wave method-of-moments (MoM) results and the results obtained by modifying MECA with our diffraction correction technique. is demonstrated between full-wave method-of-moments (MoM) results and the results obtained by modifying MECA with our diffraction correction technique.

In this paper, a level set method for shape reconstruction problems is considered. By measuring the scattered field, we tried to retrieve the localisation and permittivity of buried objects. The forward problem is solved by the method of moments. For solving the inverse problem, we adopt an evolution approach. Therefore, we introduce a level set technique witch is flexible in handling complex shape changes. A conjugate gradient-based method is used in order to define iterative updates for the level set functions with the goal to minimize a given least squares data misfit functional. In particular, the proposed method is capable of creating new holes inside the design domain, which makes the final design independent of Experimental results demonstrate the feasibility and effectiveness of the proposed technique.

Considering the class of bi-isotropic media, a special case called the class of simple skewon (SS) media is defined. The SS medium depends on a single parameter. A plane wave incident on a planar interface of an SS medium is shown to reflect as from a DB boundary with vanishing normal components of D and B field vectors. This offers another possibility to realize the DB boundary conditions in terms of a medium interface. The same property is shown to apply for curved boundaries as well.

A design of multilayer dielectric resonator antenna transmitarray for fixed radio frequency identification (RFID) reader applications is presented at 5.8 GHz. Three layers square dielectric resonator antenna (DRA) elements are mounted on dielectric substrate and used as a unit cell in the transmitarray. A circularly polarized 9 × 9 square DRA transmitarray is designed at 5.8 GHz for far-field RFID applications. The transmitarray produces maximum gain of 20.2 dB. The right-hand circular polarization level is lower than -31 dB at the designed frequency with SLL of -22 dB. A design of 9 × 9 near-field focused DRA transmitarray for fixed RFID at 5.8 GHz is investigated. The properties of the near field-focused transmitarray are compared with that of the far field transmitarray designed at the same operating frequency.

In this paper, our purpose is to develop methods that have high resolution and robustness in the presence of unknown source number, array error, snapshot deficient, and low SNR. The DOA (Direction-Of-Arrival) estimation with unknown source number methods referred as MUSIC-like and SSMUSIC-like methods have shown high resolution in the snapshot deficient and low SNR scenario. However, they need to take several times of fine search on the full space, which bring about high computational complexities. Thus, modified methods are proposed to reduce computational complexities and improve performances further. In the modified methods, we priori use conventional beamforming to get the rough distribution of signals' angle, which helps to reduce computational complexity and connect the technique of projection pretransformation. Then through projection pretransformation, original methods are further simplified and improved. As demonstrated in computer simulations, the modified DOA estimation with unknown source number methods shows not only higher resolution in the snapshot deficient and lower SNR scenario, but also more robustness against array errors. Although the proposed methods cannot replace the array calibration completely, they reduce the requirement of calibration accuracy. Combined with these advantages, it has been shown that the new methods are more suitable in engineering.

Metamaterials are artificially structured electromagnetic materials which can lead to the realization of phenomena that cannot be obtained with natural materials. In the terahertz frequency regime, metamaterials have distinguished performance and open up a new way to design and construct the functional devices. Based on the structure of metamaterials, planar symmetric normal and complementary three-resonance resonators in Terahertz band are proposed in this paper. Simulation and experimental study have been carried out. The results show that the proposed structure has three distinct and strong resonant bands in THz regime and that symmetric normal structure and complementary structure can realize the three stop-resonances and pass-resonances respectively. For the well-separating of different resonances in the terahertz band, these symmetric three-passband and three-stopband resonators will be used in the design of multiband terahertz devices.

This paper presents results of a study to characterise wireless point-to-point channel for wireless sensor networks applications in sport hard court arenas, grass fields and on roads. Antenna height and orientation effects on coverage are also studied and results show that for omni-directional patch antenna, node range is reduced by a factor of 2 when the antenna orientation is changed from vertical to horizontal. The maximum range for a wireless node on a hard court sport arena has been determined to be 70 m for 0 dBm transmission but this reduces to 60 m on a road surface and to 50 m on a grass field. For horizontal antenna orientation the range on the road is longer than on the sport court which shows that scattered signal components from the rougher road surface combine to extend the communication range. The channels investigated showed that packet error ratio (PER) is dominated by large-scale, rather than small-scale, channel fading with an abrupt transition from low PER to 100% PER. Results also show that large-scale received signal power can be modeled with a 2nd order log-distance polynomial equation on the sport court and road, but a 1st order model is sufficient for the grass field. Small-scale signal variations have been found to have a Rice distribution for signal to noise ratio levels greater than 10 dB but the Rice K-factor exhibits significant variations at short distances which can be attributed to the influence of strong ground reflections.

We report on an existence of a highly lossy interface mode (HLIM) in a designed plasmonic nanostructure for perfect absorption of the incident optical waves. Interactions between the single thin-metallic-layer ($TML$) and slits arrays for excitation of the HLIM in the proposed plasmonic absorber are investigated, and eigenfrequency formula for the HLIM is derived. Analytical and numerical results show that the HLIM is frequency-selective, opens a narrow and steep absorption band in photonic stopband of the slits arrays. Due to the HLIM lossy characteristic, surface plasmon polaritons are significantly trapped at the TML interface with absorption close to 100%.

We present a novel technique by which highly-segmented electrostatic configurations can be solved. The Robin Hood method is a matrix-inversion algorithm optimized for solving high density boundary element method (BEM) problems. We illustrate the capabilities of this solver by studying two distinct geometry scales: (a) the electrostatic potential of a large volume beta-detector and (b) the field enhancement present at surface of electrode nano-structures. Geometries with elements numbering in the O(10⁵) are easily modeled and solved without loss of accuracy. The technique has recently been expanded so as to include dielectrics and magnetic materials.

A new approach to obtain frequency and pattern reconfiguration in Dielectric Resonator Antenna (DRA) has been proposed. The design consists of two identical aperture coupled DRAs separated by a distance of λ₀. A switchable feed based frequency reconfiguration is discussed in which the feed acts as an ideal switch. This design operates at two frequencies viz., 3.6 GHz and 5.2 GHz. These frequencies are independently tuned using trimmers. Further, the slot length of both the DRAs can be tuned independently using movable shorting pins driven by miniature motors. The shorting pins form a part of the ground plane. By varying the slot length of the DRA, the resonant frequency is controlled which in turn helps in gaining pattern reconfiguration. The structure has been designed for lower and middle band frequencies of WLAN, operating between 5.15-5.25 GHz and 5.25-5.35 GHz, respectively. These types of antennas can be employed in MIMO systems for increasing the capacity through Pattern diversity.

A 1800 MHz transverse electromagnetic wave (TEM) cell is introduced for experiments investigating effects on biological samples caused by the exposure from mobile communications. To characterize and quantify the exposure environment in the setup for standardized in vitro experiments, we evaluate the dosimetry and the exposure-induced temperature rise in cultured cells. The study is numerically based on the finite-difference time-domain (FDTD) formulation of the Maxwell equations and the finite-difference formulation of the bioheat transfer equation, with all algorithms and models strictly validated for accuracy. Two sample formations of cells are considered including the cell layer and the cell suspension cultured in the 35 mm Petri dish. The TEM cell is designed to establish standing waves with the maximum E field and the maximum H field, respectively, at the position of the Petri dish. The Petri dish is oriented to E, -E, H, k, and -k directions of the incident field, respectively, to receive the exposure. The specific absorption rate (SAR) is calculated in cells for 10 exposure arrangements combined from the maximum fields and Petri dish orientations. A comparison determines the best arrangement with the highest exposure efficiency and the lowest exposure heterogeneity. The dosimetry and the exposure-induced temperature rise in cells are evaluated for the selected arrangement. To avoid thermal reactions caused by overheating, the maximum temperature rises in cells are recorded during the exposure. Based on the records, the temperature control is performed by setting limits to the exposure duration. We introduce a method to further reduce the exposure heterogeneity and evaluate the influence of the Petri dish holder on the dosimetry and temperature rise. The study compares the TEM cell to the waveguide, as well as the standing wave exposure to the propagating wave exposure. The TEM cell and the selected arrangement of the standing wave exposure improve the exposure quality over the traditional methods, with increased efficiency and decreased heterogeneity of the exposure.

In this article, we introduce an improved optimization based technique for the synthesis of circular antenna array. The main objective is to achieve minimum side lobe levels, maximum directivity and null control for the non-uniform, planar circular antenna array. The design procedure utilizes an improved variant of a prominent and efficient metaheuristic algorithm of current interest, namely the Differential Evolution (DE). An efficient classical local search technique called Solis Wet's algorithm is incorporated with the competitive Differential Evolution. While the competitive DE is used for the global exploration, Solis Wet's algorithm is employed for local search. Combining the capability of both techniques the hybrid algorithm exhibits improved performance for circular array design problem. Three examples of circular array design problems are considered to illustrate the effectiveness of the hybrid algorithm cDESW (Competiteve Differential Evolution with Solis Wet's technique). The design results obtained using cDESW has comfortably outperformed the results obtained by other state-of-the-art metaheuristics like CLPSO, JADE.

In this paper, a new theoretical approach for the classification of multiple reflections in time-domain e.m.~inverse scattering of multi-layered media is presented. The existence of multiples limits the capabilities of inversion algorithms, thus suitable identification and suppression techniques should be applied to reduce this undesired effect. Assuming a scenario composed of loss-less and non-dispersive media, and providing an accurate time delay estimation (TDE) of backscattered signals, the proposed method allows not only to evaluate the presence of multiples and discriminate them from primary reflections, but also to determine their propagation paths. Preliminary tests performed on FDTD simulated data have shown its potentialities to effectively handle multiple reflections and therefore to enhance the e.m. signals backscattered by primary reflectors.

This paper presents a new general formula for calculating the magnetic force between inclined circular loops placed in any desired position. This formula has been derived from the Lorentz force equation. All mathematical procedures are completely described to define the coil positions that lead to a relatively easy method for calculating the magnetic force between inclined circular loops in any desired position. The presented method is easy to understand, numerically suitable and easily applicable for engineers and physicists. The obtained formula is given in its simplest form from the already existing formulas for calculating the magnetic force between inclined circular loops. We validated the new formula through a series of examples, which are presented here.

In this paper, a compact, planar ultrawideband (UWB) monopole microstrip antenna is proposed which offers dual band notch characteristics with enhanced rejection at frequency bands centered at 3.4 GHz and 5.5 GHz. To realize enhanced band notched characteristics at 3.4 GHz, a pair of filters is incorporated which includes an inverted `L' shaped slot and a twisted `J' shaped slot in the patch element. Another pair of filters comprises of a spur line filter in the feed line and `U' shaped slot in the patch are used to get a strong frequency band rejection centered at 5.5 GHz. Step by step development of the antenna with its analysis in frequency and time domain is presented. The prototype is fabricated and the measured results are presented which are in close similarity to the simulated results.

Nowadays, applications of Frequency Selective Surfaces (FSS) for radar absorbing materials (RAM) are increasing, but it is still a challenge to select a proper FSS for a particular material as well as the dimensions of FSS for optimized absorption. Therefore, in this paper an attempt has been made to optimize the dimensions of FSS for microwave absorbing application using Genetic Algorithm (GA) approach. The considered frequency selective surfaces are composed of conducting patch elements pasted on the ferrite layer. FSS are used for filtration and microwave absorption. In this work, selection and optimization of FSS with radar absorbing material has been done for obtaining the maximum absorption at 8-12 GHz frequency. An equivalent circuit method has been used for the analysis of different FSS, which is further used to design fitness function of GA for optimizing the dimensions of FSS. Eight different available ferrite materials with frequency dependant permittivities and permeabilities have been used as material database. The GA optimization is proposed to select the proper material out of eight available materials with proper dimensions of FSS. The optimized results suggest the material from database and dimensions of FSS. The selected material is then mixed with epoxy and hardener, and coated over the aluminium sheet. Thereafter, all five FSS were fabricated on ferrite coated Al sheets using photolithographic method followed by wet etching. The absorption was measured for all FSS using absorption testing device (ATD) method at X-band. Absorption results showed that significant amount of absorption enhanced with the addition of proper FSS on radar absorbing coating.

A printed ultra-wideband (UWB) monopole antenna with both tunable and switchable band-notched characteristics is proposed. An embedded resonant slot loaded with a varactor and a pin diode controlled by DC signal through one common bias network is employed to tune and switch the notch band. In the ``all-pass'' state when the two diodes are partially turned on, the power consumption of this active antenna is only 2.4 μW. Measured return loss, radiation pattern, gain and group delay of the introduced antenna are presented in this paper.