The airborne radomes have to cater superior electromagnetic (EM) performance with bandpass characteristics of stealth application. In this regard, a hybrid A-sandwich radome is proposed in this paper. The proposed radome consists of a novel strongly coupled frequency selective surface (FSS) core sandwiched between two dielectric layers (acts as skin) to form an A-sandwich structure. The dielectric layers are cascaded in such a way that the middle layer has less dielectric parameters than the skin dielectric. The core layer comprises a modified FSS array using strongly coupled FSS layers through a series of metallic vias. This strongly-coupled FSS element will have the advantage of eliminating inter-element interference and improves the EM performance characteristics of the structure. The structure exhibits very good band-pass characteristics (>90%) at a normal impinging angle with sharp roll-off characteristics. To show the efficacy of the proposed structure, the transmission loss has been compared with that of conventional A-sandwich radomes at 0°, 50° incidence angle for both TE and TM polarization. Conformal analysis of the unit cell has been carried out, and sector-wise thickness optimization was performed to analyze the structure for the conformal shaped radome application. Finally, a physical prototype has been fabricated and measured its scattering parameters, radiation characteristics in a fully shielded anechoic chamber. The results are encouraging and prove its suitability for radome application.

A power MOSFET-based push–pull configuration nanosecond-pulse generator has been designed, constructed, and characterized to permeabilize cells for biological and medical applications. The generator can deliver pulses with durations ranging from 80 ns up to 1 µs and pulse amplitudes up to 1.4 kV. The unit has been tested for in vitro experiments on a medulloblastoma cell line. Following the exposure of cells to 100, 200, and 300 ns electric field pulses, permeabilization tests were carried out, and viability tests were conducted to verify the performance of the generator. The maximum temperature rise of the biological load was also calculated based on Joule heating energy conservation and experimental validation. Our results indicate that the developed device has good capabilities to achieve well-controlled electro-manipulation in vitro.

In this paper, the patch-type frequency selective surfaces (FSS) based on substrate-integrated waveguide (SIW) technology is proposed to improve the bandwidth (BW) and angular performance. The proposed FSS configuration overcomes the limitations of both conventional 2D and 3D FSS structures. A closely coupled cascaded mechanism is employed to combine two identical FSS elements separated by thin dielectric substrate results in incorporation of SIW technology; hence, named as 2.5D FSS. A derived equivalent circuit model is used to estimate the basic performance of proposed FSS–SIW elements, and the response of analytical expressions has been validated and final design is obtained using full-wave simulations. Two basic FSS elements viz. single square loop and a Jerusalem cross have been investigated to prove the enhancement in their BW and angular stability. The proposed technique evidently improves the BW and angular stability of FSS structures than in its established form. Besides, various important parameters that influence the performance characteristics of reported 2.5D FSSs are also studied. The important observations made on the thickness, as the thickness increases the bandstop FSS, can change to bandpass FSS. Finally, the proposed FSS structure has been fabricated and measured using free space measurement setup, to show the effectiveness of theoretical results. The measured results show good agreement with simulated results at normal and oblique incidence angle.

An impulse response method is carried out to analyze waveguide's information capacity within a coherent communication system. Such capability is typically estimated according to group delay variations (seconds/bandwidth/distance) after carrier-modulated data undergoes a dispersive medium. However, traditional group delay methods often ignore non-linear effects by assuming input data stream only occupies narrow bandwidth such that a propagation constant can be linearized centered at the carrier frequency. Such a constraint can be lifted with a proposed baseband equivalent impulse response method by using frequency domain convolution and multiplication. Once the impulse response in frequency domain is secured, its time domain counterpart can be calculated based on inverse Fourier transformation. Such analysis can fully reveal data pulse's broadening and gauge its inter-symbol interference by simply convolving input data with extracted impulse response, not limited to specific frequency range or type of waveguide.

A novel transmission-line model is used for the analysis of planar structures, including wire-medium (WM) slabs with vertically aligned wires. The network formalism allows for an effective determination of the relevant spectral Green's functions, of the modal dispersion equation via transverse resonance, as well as of the far-field radiation pattern produced by simple sources via reciprocity, as opposed to the more cumbersome field-matching approach. Numerical results, validated also against state-of-the-art simulation software, confirm the accuracy and effectiveness of the proposed approach. In particular, modal and radiation features are presented for a class of leaky-wave antennas based on planar WM loaded configurations covered by partially reflecting screens, for which leaky unimodal regimes are achieved by minimizing spurious radiation from the quasi-transverse electromagnetic (TEM) mode.

An increasing interest is arising in developing miniaturized antennas in the microwave range. However, even when the adopted antennas dimensions are small compared with the wavelength, radiation performances have to be preserved to keep the system-operating conditions. For this purpose, magneto-dielectric materials are currently exploited as promising substrates, which allows us to reduce antenna dimensions by exploiting both relative permittivity and permeability. In this paper, we address generic antennas in resonant conditions and we develop a general theoretical approach, not based on simplified equivalent models, to establish topologies most suitable for exploiting high permeability and/or high-permittivity substrates, for miniaturization purposes. A novel definition of the region pertaining to the antenna near-field and of the associated field strength is proposed. It is then showed that radiation efficiency and bandwidth can be preserved only by a selected combinations of antenna topologies and substrate characteristics. Indeed, by the proposed independent approach, we confirm that non-dispersive magneto-dielectric materials with relative permeability greater than unit, can be efficiently adopted only by antennas that are mainly represented by equivalent magnetic sources. Conversely, if equivalent electric sources are involved, the antenna performances are significantly degraded. The theoretical results are validated by full-wave numerical simulations of reference topologies.

A fast and efficient full-wave hybrid method for the analysis of a multilayered substrate integrated waveguide (SIW) based slot antenna/array radiating into a dielectric slab radome is presented. The antenna structure is modeled as a stacked parallel-plate waveguide hosting metallic posts and coupling and/or radiating slots. To account the radome effects on the SIW antenna, the physical optics method in conjunction with three-dimensional ray trace technique are used to analyze a dielectric slab radome staked on the aperture of the antenna. The field in the SIW structure is expressed by using an expansion in terms of vectorial cylindrical eigenfunctions. Enforcing the boundary conditions on posts yield the scattering amplitude, while slots are modeled as unknown magnetic currents which are found by solving the integral equation derived from the continuity of the field on the slot surface. A double-layered SIW cavity backed slot antenna radiating into a dielectric slab radome is analyzed, and the results compared with high frequency simulation software (HFSS) simulations. It will be shown that the proposed method is fast and efficient and gives results in very good agreement with the most common simulation tools.

In this paper, a gain-increased method of cavity-backed slot antennas based on excitation of high-order substrate-integrated waveguide cavity resonance has been proposed. To this end, the metallic posts are introduced in a main cavity to excite the cavity's TM220 mode. Then the properties of the modified cavity's TM220 mode are used to feed an array of 2 × 2 slot antenna. Moreover, to acquire insight of modified cavity's field distribution, a comprehensive modal study was performed on the modified cavity to fully understand the effects of the dividing walls on the cavity's field distribution. Also, compared with HFSS, the modal solution that is proposed in this paper provide a considerable time and storage saving. To validate the simulated results, two types of the proposed antenna forming two different polarizations (horizontal and vertical) are analyzed, simulated, and fabricated. The proposed antennas exhibit relatively gain of 8.2 dBi at resonant frequency and high front-to-back ratio. In addition, the gain-enhanced method proposed in the present paper can be extended for using even higher-order cavity resonances, such as TM440, TM660 etc., if higher gain is desirable. The proposed antennas are suitable for using in many wireless communication systems and some radar systems.

This paper presents a comparison between three evolutionary algorithms (EAs) for pattern synthesis of offset reflector antenna fed by a planar array of horn antennas. To perform the optimization process, an elliptical-shaped beam in the U–V plane (U = sinθ cosφ and V = sinθ sinφ) is considered as the desired far-field radiation pattern. To attain the appropriate excitation value for array elements, three conditions are considered: (1) variable amplitude (with uniform phase distribution), (2) variable phase (with uniform amplitude distribution), and (3) variable amplitude and phase excitation. Obtaining the appropriate excitation value based on the mathematical methods is always complicated and time-consuming. Therefore, genetic algorithm (GA) and particle swarm optimization (PSO) as two well-known EAs have been used widely for different applications and shown the promise to solve complicated problems. This paper compares these two EAs with invasive weed optimization (IWO) which is robust and has simple and powerful process with few tuning parameters. We found that for pattern synthesis of multi-feed reflector antenna in different conditions, IWO can provide accurate and comparable results with GA and PSO methods at approximately same iteration number. The convergence diagrams as well as the optimized radiation patterns for different conditions are presented and compared for GA, PSO and IWO.

This paper outlines an original shape optimization library backed by a three dimensional (3D) full-wave electromagnetic (EM) simulator, combining several efficient structural optimization techniques and suitable for viable computer-aided design (CAD) of complex microwave components. The microwave components are modeled by finite element method (FEM) and their dimensions and shape are optimized using four techniques: design of experiments (DOE), level-set method (LS), topology gradient (TG) method, and genetic algorithm (GA). The various methods allow determining the optimal geometry, shape or topology of 2D or 3D objects within the microwave device, by minimizing iteratively a cost function related to the desired specifications. Typical demonstration illustrates the versatility of the proposed library based on the design of a dual mode dielectric resonator filter in order to improve its unloaded quality factor by keeping the same frequency isolation, their accuracy and efficiency are verified by the available measured results.

Electrodynamics models and radiophysical properties of carbon nanotube-dipoles (isolated on the substrate lattices), metallic optical antennas and optical antennas, formed from ZnO nanorods coated with metal films were developed and investigated. The models are based on numerically analytical solution of integrodifferential equations describing the diffraction of electromagnetic waves on impedance and dielectric bodies. The use of integral representations of the kernels of integrodifferential equations allowed us to overcome the difficulties of solution, associated with the singularity of kernels and to reduce the computation time by an order of magnitude.

This paper considers and compares the numerical characterization of regular planar antenna arrays from two viewpoints. In the case where the array is sufficiently large, the well-known infinite array idealization applies and a very efficient simulation method is presented which combines array theory with a specialized form of the finite-element method called the transfinite element method (TFEM). Alternatively, a more direct approach is discussed in which the entire antenna array is simulated as a finite structure using recent advances in the domain decomposition method (DDM). Taken together, the two methods provide a comprehensive simulation method for regular arrays from small order to very large order.

In this work, a very efficient mixed-potential integral-equation formulation is implemented for the rigorous analysis of multilayered structures with arbitrarily shaped two-dimensional periodic metallic and/or dielectric inclusions. Original acceleration techniques have been developed for the computation of the components of the scalar and dyadic Green's functions, based on different types of asymptotic extractions according to the potential considered. The theoretical approach and its computational convenience have been validated through different full-wave analyses concerning both scattering problems and complex-mode dispersive behaviors in various frequency-selective structures for microwave applications.