Keyvan Forooraghi

• Tarbiat Modares University

This article presents a design procedure for implementing artificial neural networks (ANNs) using conventional microwave components at the hardware level with potential applications in radar and remote sensing. The main objective is to develop structured hardware design methods for implementing artificial neurons, utilizing microwave devices to cre...

Slotted waveguide antennas (SWAs) are widely used in various wireless applications such as space aircrafts, radars, and aircraft tracking systems. A specific type of SWA, which has slots in its narrow wall, has caught great interest due to its ability to produce horizontal polarization. However, due to the typically smaller size of the narrow wall...

In this article, a new architecture is proposed for real-time and low-power inference at microwave frequencies for applications such as autonomous robot control and real-time control. The architecture utilizes a hybrid coupler network that performs dot product operations using microwave components like directional couplers, microwave filters, and p...

This letter proposes an optimal patch based on the Haar function series and a genetic algorithm to design waveguide-fed traveling-wave arrays. A supercell is designed that provides better pattern characteristics. The conductance and susceptance equations are obtained in terms of offset and resonance length from simulation results. Using Elliot's de...

In this paper the extended method of lines (E-MoL) is proposed for the analysis of multilayer graphene-loaded three dimensional structures in cylindrical coordinates. Accordingly, the impedance and admittance matrices are defined as the ratios of the electric and magnetic fields at each plane of the stack. The impedance and admittance parameters ar...

This article proposes an active frequency selective surface (FSS) with application to satellite multi‐band antennas in X and Ka bands. The FSS offers two reflective bands at 20 and 30 GHz (downlink and uplink frequencies of broadband communication satellites in Ka‐band) under one biasing state, whereas the frequency characteristics are switched in...

A semi-analytical method for analyzing inhomogeneous meta-surfaces under oblique incidence based on the polarizabilities of constituent particles and interaction constants is presented. The inhomogeneity is proposed in which a meta-surface is considered as a periodic array of repetitive super-cells. Our proposed method provides effective polarizabi...

In this paper, an analytical method is expanded to analyze asymmetrical metasurfaces under normal plane-wave illuminations. In our proposed method, two key factors of the polarizabilities of individual particles, and the interaction constants between them, are employed to analyze the frequency responses of some asymmetrical metasurfaces. The associ...

-In this paper novel reflect-array antenna elements are proposed using aperture-coupled dielectric resonator antenna structures. Using these new structures, wide phase range and wide frequency bandwidth (up to 28.5%) with parallel and linear phase curves are obtained. In each case, an array consisting of 289 elements was simulated using the finite...

In this paper the method of lines (MoL) is extended to analyze two-dimensional (2-D) multilayer structures loaded with graphene plates in cylindrical coordinates. Accordingly, the admittance transformation matrices through a 2-D interface are derived taking into account the tensor-form conductivity of the magnetized graphene plate. The transformati...

A new method for analyzing multi-spectral inhomogeneous meta-surfaces is presented, which include several types of particles. Our proposed method suggests a new semi-analytical technique to solve the total effective polarizabilities of inhomogeneous arrays. Here, we propose the inhomogeneity in which meta-surface can be regarded as constituting arr...

Due to the increasing interest in emerging applications of graphene or other 2D material-based devices in photonics, a powerful, fast and accurate tool for the analysis of such structures is really in need. In this paper, the semi-analytical method of lines (MoL) is generalized for the diffraction analysis of tunable graphene-based plasmonic device...

In this paper, efficient analysis of the plane wave scattering by periodic arrays of magnetically-biased graphene strips (PAMGS) is performed using the semi-numerical, semi-analytical method of lines (MoL). In MoL, all but one independent variable is discretized to reduce a system of partial differential equations to a system of ordinary differenti...

In this paper, we study the existence of a surface wave on bianisotropic metasurfaces (BMS) by using electric and magnetic polarizabilities. These polarizabilities connect the local electric and magnetic fields on BMSs with electric and magnetic surface polarizations. We have chosen the method based on surface polarizations because applying boundar...

Abstract In the present study, a characteristic mode analysis (CMA) is proposed for the first time to design a periodic leaky‐wave antenna (LWA). By applying CMA to the unit cell of a periodic travelling wave structure, the open stopband is suppressed and circular polarization (CP) radiation is achieved. Also, some parametric studies are added to c...

This contribution presents a reconfigurable frequency selective surface (FSS) for shared-aperture satellite antennas in X and Ka bands. The FSS has been designed to be reflective at 20 and 30 GHz (transmit and receive frequencies in Ka-band) and to allow switching of transmission and reflection responses in X-band (between 9 and 12 GHz). The FSS un...

Abstract In the present study, a novel periodic planar leaky‐wave antenna (PLWA) was designed, simulated, and fabricated based on the substrate integrated waveguide (SIW) technology. The antenna can scan the main beam from around −60° to +20° continuously with complete suppression of open stopband (OSB) by the sweeping frequency from 9.2 to 14.1 GH...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

This paper introduces analytical solutions to gap waveguide slot antenna structures. The reciprocity method is used for the analysis by exploiting Green’s function of a bed of nails structure employing a homogenized plane-wave spectral-domain approach. Green’s function is found using parallel plate waveguide and surface admittance concepts. The spe...

In this paper, we investigate the dyadic Green's function (DGF) of a perfect electromagnetic conductor sphere (PEMCS) due to electric dipoles, theoretically by employing the scattering superposition principle (SSP) and the Ohm-Rayleigh method. Then the derived DGF is used to calculate the scattered field of a PEMCS due to an arbitrarily oriented in...

For sensing and imaging applications of surface-enhanced Raman scattering (SERS), one needs a substrate with the capability of generating a consistent and uniform response and increased signal enhancement. To this goal, we propose a photonic-crystal (PC) structure capable of supporting large field enhancement due to its high quality-factor resonanc...

A novel tri‐band frequency selective surface (FSS) is proposed for space antenna systems in the X, K, and Ka bands. The FSS structure is based on a two‐layer configuration, where the unit‐cell elements at each layer consist of two pairs of rectangular‐shaped dipoles and a square ring. The FSS has been designed to be transmissive at 11.5 GHz (X band...

A novel dual-polarization, single-layer reflectarray has been designed and manufactured to operate at receive (20 GHz) and transmit (30 GHz) frequencies for Ka-band terminal antennas. The reflectarray unit cell is composed of several types of resonant elements printed on the upper side of a conductor-backed substrate, which are designed to produce...

In this study, the authors propose a new idea to employ mantle cloaking in order to reduce the mutual coupling between electrically small antennas (ESAs) placed on man‐pack radio systems. They determined and numerically optimised the parameters of the mantle cloak on loop and monopole antennas; these antennas are to provide near vertical incidence...

DOWNLOAD LINK: https://utah.instructure.com/courses/558911/files/90896623/download?wrap=1 This paper presents a stochastic scheme called geometrically stochastic FDTD (GS-FDTD) to insert the statistical variation of model geometry directly into the finite difference time domain (FDTD) method. Both 1D and 2D GS-FDTD formulations are presented. The...

Straight long slots have high side-lobes in the far-field amplitude patterns, which reduces their use as high-performance antennas. To reduce these side-lobes, a long slot may be tapered to produce the desired radiation patterns. The theory of control of the aperture distribution to reduce side-lobes has been already reported in some works and well...

To enhance Raman scattering, we propose a multi-layer substrate which behaves similar to a magnetic mirror or what is also known as high-impedance surface (HIS). Due to this property, the electric field of the illuminating light is increased by a factor of two. This field enhancement doubles the amplitude of the Raman signal generated by the molecu...

This paper presents a novel stochastic finite difference frequency domain method (S-FDFD) that incorporates the statistical variations of electrical properties directly into the FDFD algorithm by using the delta method approximation. The method is validated through two examples – a 1D bioelectromagnetic layered model and specific absorption rate (S...

This paper presents the dyadic Green’s function (DGF) of a conical cavity with impedance spherical cap (CCISC) which is derived using the eigenfunction expansion method and the method of scattering superposition. The E-field inside the conical cavity from an arbitrarily oriented infinitesimal dipole and a λ/2 dipole antenna is obtained numerically...

A modified low-band sub-arrayed feeding network is designed for a monopulse linear array. Instead of using two separate networks for sum and difference channels, one feeding network is designed using genetic algorithm to meet the required specifications. All ports are matched and isolated, and network is lossless and simple. By dividing a 24-elemen...

This paper presents a novel stochastic numerical method called stochastic finite difference frequency domain (S-FDFD). S-FDFD introduced in this paper directly inserts the statistical variations of electrical properties into the FDFD. Comparison between full-fledged multi run Monte Carlo results and those of single run S-FDFD shows that the S-FDFD...

In this paper, the method of lines is extended to analyze two-dimensional graphene-based multilayered structures. The graphene plates, with tensor conductivity may cover partially or totally the interfaces between two consecutive layers. In this paper, the impedance and admittance transformations through the graphene-contained interfaces are develo...

In this paper, the method of lines is extended to analyze graphene-based multilayered three-dimensional structures. The graphene plates, with tensor conductivity may cover partially or totally the interfaces between two consecutive layers. The impedance and admittance transformation formulas are then derived at the interfaces. Hence the impedance a...

Abstract In this paper novel reflectarray antenna elements are proposed using aperture-coupled dielectric resonator antenna structures. Using these new structures, wide phase range and wide frequency bandwidth (up to 28.5%) with parallel and linear phase curves are obtained. In each case, an array consisting of 289 elements was simulated using the...

In this paper a miniaturized dual wideband bandpass filter is designed by the modified extended composite right/left-handed transmission line (ECRLH-TL) under balanced conditions in each right/left-hand passbands. A novel equivalent circuit is proposed to provide the design and an implementation of ECRLH unit-cell by means of the complementary, spl...

This research focuses on the analysis of microstrip structures with graphene material as the conducting strip using two numerical methods, spectral domain technique and method of lines. The conductivity of graphene sheet is modeled in the analytical method using a tensor matrix. The results obtained from the above mentioned methods are compared wit...

A new single-feed aperture-coupled, X-band microstrip patch antenna array with circular polarization (CP) is designed. CP is achieved using indented microstrip patches fed through the slots on a substrate integrated waveguide. The antenna has the high radiation efficiency more than 90% over the operating frequency. Impedance bandwidth (VSWR < 2) an...

A new design for the multilayer superlens, with the sub-wavelength imaging ability for various 2D objects in the visible range, is introduced and analyzed. The designed superlens will be more versatile for practical applications. A rigorous and efficient approach based on the method of moments is used to study the imaging performance of this struct...

An optimized multilayer superlens is designed, using a rigorous and efficient approach based on the method of moments (MoM) in conjunction with a simulated annealing (SA) algorithm. For the MoM solution, fast evaluation of closed-form Green`s functions (GFs) in the spatial domain is performed by applying the complex-image (CI) technique, which obvi...

In this letter, an efficient method is presented to solve two-dimensional (2D) microwave inverse scattering problem associated with the microwave imaging. In this method, the unknown contrast function of the investigation domain is represented by Fourier-Jacobi (FJ) expansion which is a wellknown expansion in optics. Using FJ expansion, allows us t...

A tri-band frequency selective surface (FSS) is presented for Ku and Ka bands for space communications. The FSS is designed to be transparent in the frequency range 10.7 GHz–12.05 GHz and to provide total reflection at 20 GHz and 30 GHz, Ku- and Ka-band in satellite communications, respectively. A single square ring with two pairs of dipoles are us...

This paper presents the design and implementation of a novel fully planar modified, extended composite right/left-handed transmission lines (E-CRLH-TLs) utilizing a complementary split ring resonator (CSRR) loaded on the ground plane. The multiband behavior of the proposed layout is demonstrated by an equivalent circuit which in this case is distin...

This paper presents a very fast and highly efficient full-wave hybrid method for analyzing an integrated dielectric lens antenna (ILA) fed by multilayered substrate-integrated waveguide (SIW) slot antenna/array. The feeding antenna structure is modeled as a stacked parallel-plate waveguide with metallic posts, coupling, and radiating slots. Physica...

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 e...

This article describes a gain enhancement method for a dual polarized SIW cavity backed slot antenna by using a high order cavity resonance to generate arbitrary levels of inclined linear polarization (LP). To do so, the metal posts are embedded in a main cavity to excite TM220 mode of the cavity and control the amount of coupling to generate adjus...

In this paper, the bandwidth of one SIW rat-race (hybrid ring) coupler has been increased up to 30% by four U-shape slot-coupled transitions without disadvantages due to transmission line loss, radiation and design complexity. The SIW coupler structure has been analyzed by the mode matching method that uses the cylindrical vector expansion to minim...

Aperture-coupled dielectric resonator antenna is proposed using a novel reflectarray antenna unit cell structure. It is shown that a bowtie-shaped slot can enhance the bandwidth performance of a reflectarray antenna. The unit cell's reflection phase response was verfified experimentally using the waveguide simulator method. An array comprising of 2...

This study investigated the microwave absorption properties of core-shell composites containing; iron oxide decorated carbon nanotubes and silica (SiO2@Fe3O4/MWCNT) with various thickness of silica shell (7, 20 and 50nm). Fe3O4/MWCNT was coated with different thicknesses of SiO2 using the sol-gel method. The transmission electron microscopy (TEM) a...

As the mutual coupling effects play a major role in synthesizing of array, it needs to be investigated. This paper discusses the process of computing the mutual coupling among rectangular patch antenna elements (RPAE) conformed onto a hemisphere surface. The elements are arranged in two different distributions, mainly E- and H-plane type. The isola...

In this paper, a gain increased method of cavity-backed slot antennas based on excitation of high order substrate integrated waveguide (SIW) 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 a...

This communication presents an effective and accurate method of computing admittance and resonant characteristics of a single longitudinal waveguide slot, radiating into a dielectric layer. The external magnetic field is computed using the spectrum of two dimensional solutions (S2DS) which reduces a three-dimensional (3D) problem to a 2D problem. S...

A frequency switchable printed dipole antenna is proposed for multiband application. The electrical length of the dipole can be changed by controlling the pin diodes states so that the antenna can operate in three different frequency bands. The larger/smaller of the current path, the smaller/larger of the resonance frequency can be obtained. Three...

This paper presents an efficient analysis of a substrate integrated waveguide (SIW) single-layer hybrid ring coupler (rat-race) for millimeter-wave and microwave applications. The scattered field from each circular cylinder is expanded by cylindrical eigenfunctions with unknown coefficients that have been solved by electric and magnetic tangential...

In this letter, design and fabrication of an ultrawideband combined antenna are presented. Actually, this element is a combination of a TEM horn antenna and some magnetic dipoles. The combination of radiation fields due to these elements causes reduction in reactive energy around the antenna, and with this method, the antenna matching in a wide fre...

A dual linear-polarized dielectric resonator antenna (DRA) reflectarray is presented. The rectangular DRA unit cell includes a windmill-shaped slot in its ground-plane. The results of the reflectarray are validated using the transmission-line method. The fabricated unit cell's phase response was measured in WR90. The proposed reflectarray exhibits...

An aperture-coupled dielectric resonator antenna loaded with a rotated strip is proposed as a new circularly polarized reflectarray antenna element. The unit cell is fabricated, and its phase response is validated using the waveguide simulator method, where the finite integration technique is used to analyze the 256-element array. Excellent results...

This study investigated the microwave absorption properties of magnetic modified multiwall carbon nanotubes (MWCNTs) with different alignments to the electric field (E vector) of the incident electromagnetic (EM) waves. MWCNTs were decorated with Fe3O4 nanoparticles using the wet chemical method and the resulting MWCNT/Fe3O4 was then used as a fill...

In this paper, design and fabrication of an L‐band axial mode 2 × 2 tapered dielectric‐ loaded helical antenna array for international maritime satellite organization (INMARSAT)‐M mobile vehicles are presented. This array has compact size and light weight. By adding a tapered cylindrical dielectric resonator, for satellite communications, important...

In this paper two novel left-handed composite metamaterials consisting of SRRs, wire and single sided S-shaped resonators are proposed. One of them is a reduced-size resonator which uses superposition hypothesis to achieve adjacent resonances for a much broader negative refraction passband. The other is a modified planar structure with improved ele...

In this brief, a new blind spectrum sensing method is proposed based on frequency comparison using a phase frequency detector (PFD). The PFD output patterns are utilized in a way to sense the spectrum with no knowledge of incoming signals, noise, or channel parameters. The detection and false alarm error probabilities are analytically calculated fo...

A new planar spiral antenna with integrated impedance transformer is presented which needs no external balun and can be fed by a coplanar waveguide.The proposed structure has a return loss of <−10 dB over a broad bandwidth of 0.5–5 GHz that is suitable for cognitive radio applications. The effects of different spiral and transformer parameters are...

In this paper, First the structure of a rectangular waveguide with a longitudinal slot is presented to show the quasi-TEM wave with uniform distribution in the waveguide width. This Quasi-TEM wave improves the aperture field illumination of the slot and enhances the efficiency in this kind of antennas. Finally, by simulation a slot antenna is excit...

In this paper, the design of an array of wideband combined antenna elements is presented. A TEM horn antenna is combined with magnetic dipoles to obtain a wideband element with a bandwidth from 180 MHz to 30 GHz. The element is then miniaturized in order to be placed in a two by two array, and then the optimized values of the horizontal and vertica...

In this article, a novel method is introduced to design a high efficiency and broadband reflectarray.Several techniques will be introduced for designing wideband reflectarray. First, by using fractal ring unit cell with 700° phase range; second, by smoothing phase tapering on reflectarray surface; and finally, by finding the optimum free reference...

In this paper, a broadband single-layer microstrip reflectarray element composed of a Giuseppe Peano fractal ring and a square ring is presented and investigated. The proposed element has been validated by comparing the simulation results with those obtained by measurement in a waveguide simulator. By using this type of cell element, a wideband sin...

In this article, the design, simulation, and realization of an L-band axial-mode 1 × 2 short helical antenna array are presented. The antenna array has a compact size and is lightweight. To improve array performance, special attention is paid to important parameters, such as gain, impedance matching, axial ratio, and mutual coupling. Impedance matc...

In this paper, design and simulation of a combined antenna for wideband applications with high radiating power is presented. By using the idea of combined antennas, a TEM horn antenna is combined with magnetic dipoles in order to shift the bandwidth to lower frequencies. Furthermore, a feeding structure which is a transition between coaxial cable t...

This paper addresses conformal array synthesis as a constrained multiobjective optimization problem. Simultaneous reduction of side lobe level (SLL) and cross-polarization (XPL) level is aimed with a constraint on main beam direction. A hybrid of weighted alternating reverse projection (WARP) and two local best multiobjective particle swarm optimiz...

A new compact patch antenna with frequency and polarization diversity is presented and experimentally verified. Four double cross-slots are embedded into corners of a square patch, and the length of the slots are changed according to the ON/OFF states of the PIN diodes located on the slots. The compactness of this antenna is more than 36% in compar...

AbstractA very compact printed circular monopole antenna for ultra‐wideband applications is presented. To achieve wide bandwidth performance, the proposed antenna is fed by a coplanar waveguide feedline. The total size of antenna is as small as 12 mm× 22 mm × 0.787 mm. The simulated and measured results demonstrate an impedance bandwidth covering 2...

A novel varactor-tuned substrate-integrated cavity-backed slot antenna with wide tunability range of resonant frequency is presented. Using four varactors mounted on a dumbbell shaped slot etched on the horizontal wall of a substrate-integrated rectangular cavity, operating frequency of the proposed antenna can be tuned from 5.5 GHz to 7.6GHz, pres...

This paper provides design, simulation and characterization of a planar metamaterial absorber with a complete impassibility to the incident wave polarization. This structure consists of a lossy dielectric layer of FR4 and an electric-field-coupled (ELC) structure on its top surface. This absorber structure has shown almost complete absorption at th...

In this paper, aperture coupled dielectric resonator antenna loaded with rotated strip, is used as a CP element for reflectarray antenna. Phase variations are obtained by a symmetric change in the length of the stub. The effect of the various parameters of the structure on the slope of the phase curve is studied. Simulations are carried out with An...

This article generalises a pattern synthesis technique to conformal arrays. An iterative method is used for optimisation of element excitations in an array of rectangular patch elements that are conformed to a hemispheric surface. The embedded-element co-polarisation and cross-polarisation patterns are evaluated using a full-wave method. These patt...

A new type of low-profile frequency selective surface (FSS) with an overall thickness of λ/40 and a second-order band pass frequency response is presented. The proposed FSS is composed of two metal layers, separated by a thin dielectric substrate. Each layer is a two-dimensional periodic structure with sub-wavelength periodic unit cells. By printin...

In this paper, we introduce a highly electric-field-coupled (ELC) metamaterial planar absorber in microwave frequency range. The structure is a one layer dual linear polarization insensitive absorber, which is designed by utilizing properly arranged resonant structure with orthogonal polarization sensitivity. In addition, this metamaterial absorber...

A simplified structure made of periodic array of cross cut-wire pairs (CCWP), printed on only one side of a dielectric substrate, is introduced. This simple negative refractive index (NRI) metamaterial is responsive to arbitrarily linearly polarized incident waves which supports both symmetric and antisymmetric resonance modes, offering a very wide...

Miniaturization of a rectangular microstrip antenna using a magneto-dielectric substrate is discussed theoretically and experimentally. A compact magneto-dielectric substrate is designed using a metamaterial structure that can reduce the antenna dimensions by increasing the constitutive parameters of the substrate. Furthermore, the proposed structu...

A fast and adjustable spectrum sensing method is proposed using a phase frequency detector for cognitive radio applications. Using this method, spectral sensing can be done in a very short time by a low‐cost, low‐power circuit, compared with available implemented methods. Different aspects of sensing procedure in different situations are investigat...

In this article, compact microstrip bandpass filters using dual-mode stub-loaded resonators and capacitive/inductive source-load coupling are presented to realize opposite asymmetric quasi-elliptic responses. Two transmission zeros are generated in each design to sharpen the cutoff slope at the two sides of the passband. Both the coupling matrix an...

In this article, a miniaturized nonbianisotropic left-handed metamaterial composed of spiral-S-shaped resonator and conducting wire is proposed. This symmetrical structure avoids bianisotropy and it shows a controllable low-loss double negative (DNG) band. Its electrical size is less than half of the well-known S-shaped resonator, which makes it to...

This article presents a new miniaturized reconfigurable slotted microstrip patch antenna with defected ground structure. The antenna operates in two different frequency bands with polarization pattern diversity and broad radiation characteristics. The size reduction of this antenna is more than 34% in comparison to a conventional rectangular patch...

A miniature harmonic-suppressed microstrip band pass filter (BPF) with a new triple-mode stub-loaded resonator is presented in this letter. Four distinct mechanisms are utilized to create five transmission zeros (TZs), leading to sharp skirts and wide stopband. Both simulation and measurement results are presented. The simulated/measured minimum pa...

A substrate integrated waveguide (SIW) loaded by embedded split-ring resonators (SRRs) with transversal negative effective permeability is proposed. It is shown that the structure can support propagation of backward waves below cutoff frequency. Therefore, the width of the SIW structure can be considered less than half a wavelength at the cutoff fr...

In this article, a compact butler matrix for wireless communications is designed and implemented at 2.4 GHz using defected ground structures (DGS).The butler matrix consists of a 3-dB coupler, crossover (0-dB coupler), and phase shifter. The 3-dB coupler and crossover are compacted using T-model of transmission line and DGS. The size of proposed bu...

Annular waveguide slot antennas were introduced to form arrays with the possibility to alter the polarization of the antenna between the four major cases of linear horizontal or vertical and right or left hand circular. This important achievement needs the array to be formed in a four-quadrant scheme with three phase shifter units to set the desire...

Fast, accurate and efficient sensing is of important aspects in cognitive radio technology. We propose a simple, practical design for two-dimensional sensing in spectral and spatial domain. In fact detection and localization of signal are done in a wide band elliptical array. Two sets of phase differences help to fast calculation of frequency and a...