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A dispersive delay structure (DDS) is a device that creates a specified group delay function over frequency bandwidth. In this study, the idea of trapping the electromagnetic waves in a feedback loop is proposed to achieve higher group delay swing. The proposed structure includes two transmission lines and two junctions that act as power divider/combiner. The transmission lines can be either dispersive or non‐dispersive. The group delay in the proposed configuration is proportional to the injected power into the feedback loop. So, an increase in the group delay swing can be done by improving the junctions or by adding more feedback loops to the structure. Based on this configuration, a novel DDS, using the substrate integrated waveguide transmission line, is introduced. According to the experimental results, the proposed device with a relatively compact size creates high group delay swings (9 ns), and its insertion loss is about 7 dB. [ABSTRACT FROM AUTHOR]

This study proposes a new technique for generating dual polarisation in spiral antennas. The proposed antenna is achieved by creating stair discontinuities in spiral antenna arms, entitled stair arm width (SAW) spiral antenna. Commonly, the spiral antenna is activated in direction finding systems, especially in wideband monopulse systems. Capability of generating sum and difference beams over a wide bandwidth is another feature of the proposed antenna. Radiation characteristics and generated modes of a wideband dual polarised four-arm SAW antenna in comparison with the modulated arm width (MAW) and conventional spiral antennas are presented. The cross-polarisation gain of SAW antenna, compared to MAW antenna, is decreased in difference pattern, which improves the antenna circular polarisation purity. Moreover, the input impedance of the proposed antenna with high ns is more stable than MAW antenna over a wide bandwidth due to gradual discontinuities. Finally, a prototype four-arm SAW spiral antenna is built and evaluated with an available beamformer for 5.8-10 GHz frequency bandwidth. Simulated and measured radiation characteristics proved dual circularly polarised and wideband properties of the antenna. [ABSTRACT FROM AUTHOR]

This paper is going to handle an adaptive meshless method by which a wide range of microwave problems in terms of frequency are numerically solved whose accuracy and computational time are acceptable with respect to some other numerical schemes. As the origin, in the process of imposing the conventional radial point interpolation method (CRPIM) to laser problems, a special function was found, which results in a well-behaved basis function for CRPIM. This basis function possesses two fundamental advantages in view of meshless methods. At first, and in contradiction with conventional basis functions, the shape parameters are deterministic, which results in a higher accuracy than conventional basis functions. Second, it will construct the shape functions without any need for the middle matrix inversion step. Also, the adaptive basis function inherits the fundamental properties of fields. Hence, the computational time is reduced, approximately by half, comparing with the conventional basis functions. To investigate the proposed adaptive method named quantum radial point interpolation method in different areas of interest, it has been employed to solve three classes of partial differential equations in computational electromagnetics, i.e., Schrodinger’s equation in a quantum wave laser, Laplace and electromagnetic wave equations. The results are more accurate and faster than the CRPIM and the finite-element method. [ABSTRACT FROM PUBLISHER]

A configuration of wideband bandpass filter (BPF) with multiple notched bands is presented. Proposed BPF is based on stepped-impedance resonator. By utilising dual stepped-impedance resonators in folded topology a rectangular-ring resonator is formed. Two notched bands in the passband are achieved without using asymmetrical coupled lines. In other words, the filter configuration is capable of producing notched bands. It should be noted that additional information on filter performance and design is presented. Measurement results are presented to approve propounded filter characteristics. The measured passband of the second proposed filter is from 3.68 to 10.2 GHz with insertion loss of –1.76 dB in the first passband at the centre frequency of 4.45 GHz. The measured notched band frequencies are about 5.45 and 7.95 GHz with rejection of –21.77 and –20.82 dB, respectively. The return loss in the passband is better than –11.4 dB. [ABSTRACT FROM AUTHOR]

The root of this study, comes from the lack of regularity where exists in shape function selection in meshless methods. Up to now, shape functions in meshless methods were being established by basis functions. In other words, there was no predictable rule by which the shape functions be predetermined, without any need to basis functions. In presented approach, the authors are going to establish a criterion, which is based on both analytical and simulation results; helps select an approximately well‐behaved shape function for which the shape parameters have been predetermined. This work focused on both Laplace and wave equations as the most important equations in electrostatic and electromagnetic problems to show the validation of the proposed approach in computational electromagnetics. Comparing the results with radial point interpolation method as the most common existing meshless method, finite‐element method and finite‐difference method, the criterion shows extremely good accuracy despite a great reduction in time consumption rate for selecting a compatible shape function. [ABSTRACT FROM AUTHOR]

In this work, the use of existing multiresolution analysis (MRA) in meshless method is studied to analyze some dielectrics for which the permeability and permittivity are complex at microwave frequencies. It will be shown that the existing MRA has some disadvantages and non meaningful aspects when is used in above dielectric simulation. In general, this type of MRA belongs to other areas of study such as image processing. Specifying these aspects and proposing some modifications to overcome the disadvantages of existing MRA for reaching a strict method of using wavelets in area of high frequency dielectrics, is the aim of this paper. We have selected the meshless method that is one of the newest and most powerful existing numerical methods as an area of using the modified MRA called computational MRA (CMRA). The use of CMRA in meshless methods, not only leaves most of the disadvantages, but also is faster and more accurate in comparison with the most other numerical methods. [ABSTRACT FROM AUTHOR]

Although many numerical methods have been developed to calculate photonic bandgap structure properties, but always improvement in numerical methods is necessary to have more efficient, accurate and flexible techniques. In the present work, novel periodic meshless shape functions including so-called direct and radial shape functions are presented. The meshless approaches, based on these periodic shape functions as real-space methods, can be used for simulation of periodic structures, like photonics bandgap structures, straightforwardly. The results on band structures derived from the proposed methods are then presented, discussed and compared with those available in the literature, and a very good agreement is seen. It shows that the proposed techniques are veiy promising to be robust techniques in the simulation of periodic structures such as photonic problems. [ABSTRACT FROM AUTHOR]

SUMMARY An improved truly meshless method is presented for three-dimensional (3D) electromagnetic problems. In the proposed method, the computational time for the construction of the introduced shape function is lower than the other meshless methods considerably. An efficient and stable nodal integration technique based on the Taylor series extension is also used in the proposed meshless method. Weak-form formulations adopted for creating discretized system equations of electrostatic and electromagnetic 3D problems are also presented. In the proposed fast truly meshless method, unlike in traditional meshless schemes where background mesh is utilized to compute integrals, nodal integration is used to avoid meshing. The numerical solutions for electrostatic and electromagnetic problems show that the presented method is a robust meshfree method and possesses better computational properties compared with traditional meshless methods. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: A new wideband asymmetric microstrip coupled-line coupler with 3dB coupling value and quadrature phase difference is presented. Compared with the conventional edge-coupled couplers, this structure, consisting of two different transmission lines (interdigital and conventional microstrip transmission lines) as coupled lines, achieves wider operating bandwidth and larger coupling level. The coupled-line length of the proposed structure is approximately λ g /4. To characterize the structure, an equivalent circuit model has been established. A 3dB designed and fabricated coupler with 0.2mm spacing between coupled lines exhibits an amplitude balance of 2dB from 2.2GHz to 4.2GHz. Good agreements between the full-wave simulation and equivalent circuit model results has been achieved and verified the effectiveness of the proposed circuit model. Also, measurement results have been presented. [Copyright &y& Elsevier]

Although, the finite element method numerically is efficient it exhibits difficulties whenever the remeshing of the analysis domain must be performed. For such problems, utilizing meshless computation methods is very promising. But, their large computational cost, which arises from following a time-consuming process to find shape functions, is one of the most important factors limiting the use of these methods. In this paper, we introduce a direct approach, based on properties required for any shape function, to prepare the shape function and propose a new meshless method. The proposed method does not need any predetermined basis or weighting functions and can be performed faster and more efficiently. Another advantage of the introduced method is its capability to apply desirable changes to the shape function. Application of the proposed approach for electrostatic field computation and verification of the obtained results using theoretically known solution is also presented. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: We present a new formulation to implement the complex frequency shifted-perfectly matched layer (CFS-PML) for boundary truncation in three-dimensional vector finite-element time-domain method applied to the vector wave equation. It is shown that the proposed method is highly absorptive to evanescent modes, when computing the wave interaction of elongated structures or sharp corners, and can improve the performance of the boundary truncation, significantly. The impact of the CFS-PML parameters on the reflection error is investigated and optimal choices of these parameters are derived. [Copyright &y& Elsevier]

In this paper, two implicit finite-element time-domain (FETD) solutions of the Maxwell equations are presented. The first time-dependent formulation employs a time-integration method based on the alternating-direction implicit (ADI) method. The ADI method is directly applied to the time-dependent Maxwell curl equations in order to obtain an unconditionally stable FETD approach, unlike the conventional FETD method, which is conditionally stable. A numerical formulation for the 3-D ADI-FETD method is presented. For stability analysis of the proposed method, the amplification matrix is derived. Investigation of the proposed method formulation shows that it does not generally lead to a tri-diagonal system of equations. Therefore, the Crank—Nicolson FETD method is introduced as another alternative in order to obtain an unconditionally stable method. Numerical results are presented to demonstrate the effectiveness of the proposed methods and are compared to those obtained using the conventional FETD method. [ABSTRACT FROM AUTHOR]

We present two new numerical approaches for physical modeling of high-frequency semiconductor devices using filter-bank transforms and the alternating-direction implicit finite-difference time-domain method. In the first proposed approach, a preconditioner based on the filter-bank and wavelet transforms is used to facilitate the iterative solution of Poisson's equation and the other semiconductor equations discretized using implicit schemes. The second approach solves Maxwell's equations which, in conjunction with the semiconductor equations, describe the complete behavior of high-frequency active devices, with larger time-step size. These approaches lead to the significant reduction of the full-wave simulation time. For the first time, we can reach over 95% reduction in the simulation time by using these two techniques while maintaining the same degree of accuracy achieved using the conventional approach. [ABSTRACT FROM AUTHOR]

We have proposed a dispersive formulation of scalar-based meshless method for time-domain analysis of electromagnetic wave propagation through left-handed materials (LHMs). Moreover, we have incorporated Berenger’s perfectly matched layer (PML) absorbing boundary condition (ABC) into the dispersive formulation to truncate open-domain structures. In general, the dispersive formulations of conventional numerical methods are proper tools for analysis of left-handed (LH) media, whenever the LH media can be characterized by considering spatial or frequency dispersion effect for the constitutive parameters. In comparison to the grid-based numerical methods, it is proven that meshless methods not only are strong tools for accurate approximation of derivatives in Maxwell’s equations but also can provide more flexibility in modeling the spatial domain of problems. However, we have not seen any reports on using dispersive forms of meshless methods for simulation of wave propagation in metamaterials and applying any PML ABCs to dispersive formulation of meshless method. The proposed formulation enables us to take advantage of meshless methods in analysis of LH media with frequency-dependent parameters. For modeling the frequency behavior of the medium, we have used auxiliary differential equation (ADE) method based on the relations between electromagnetic fields intensities and current densities. Effectiveness of the proposed formulation is verified by analysis of 2-D and 3-D numerical examples; also, some basic factors which affect the accuracy, stability, and computational cost of the simulations are studied. [ABSTRACT FROM AUTHOR]

This paper presents the design of a wideband single-layer partially reflective surface (PRS) for a circularly-polarized (CP) resonant cavity antenna (RCA). The proposed single layer double-sided PRS structure has complementary design which results in an increase in the 3-dB gain bandwidth of the antenna over a wide bandwidth due to creating both inductive and capacitive features. Indeed, this complementary structure gives opposite phase behavior which leads to a reverse phase gradient over a wide range of frequencies. Instead of using conventional multi-layer PRS structures or PRSs with thick unit cell for broaden the bandwidth, we have used a thin single-layer PRS structure with the capability to enhance the antenna gain over a wide bandwidth. A CP stacked patch antenna (SPA) is used as a main radiating element inside the RCA structure. To verify the significant effect of the proposed PRS on the antenna performance, the entire RCA structure is fabricated and the results show a reasonable agreement between simulations and measurements. The measurement results show an 3-dB axial ration (AR) and impedance bandwidths of 21% and 32%, respectively. The antenna gain is more than 10.5 dBic over the 3-dB gain bandwidth from 5.8 to 7.3 GHz, i.e 22.9%, with a peak gain of 13.2 dBic. [ABSTRACT FROM AUTHOR]

The demand for analog signal processing (ASP) is rising for high‐speed and high‐frequency systems. In some ASP systems, the core is dispersive delay structure (DDS). DDS creates a steady increase or decrease in group delay over frequency bandwidth. One of the popular methods for designing DDSs is the use of coupled C‐sections structure. Analysis of the coupled C‐sections was based on the analysis of N coupled‐lines network. In this paper, we employ a fast approach for analyzing N coupled‐lines network that does not need solving an eigenmodes problem. Moreover, we propose a novel DDS structure based on the coupled composite right/left‐handed (CRLH) transmission lines with interdigital capacitors and short stub inductors. The proposed DDS operates between 3 to 3.5 GHz with relatively high group delay slope (about 5.5 ns). The measurements are presented for scattering parameters and group delay to compare with simulated results. [ABSTRACT FROM AUTHOR]

One of the main problems of the conventional meshless methods in the time domain is their conditional stability. Up to now, some algorithms have been introduced to remove the stability condition, like alternating‐direction‐implicit (ADI) and locally one‐dimensional (LOD) schemes. ADI meshless method has been investigated completely, but there is no report to exploit the full efficiency of the LOD meshless method. So, in this study, LOD scheme is employed to a meshless method for solving three‐dimensional transient electromagnetic problems. The initial form of the proposed meshless method solves time‐domain Maxwell's equations in three sub‐steps, so it is called LOD3. LOD3 meshless method has first‐order temporal accuracy. Moreover, LOD5 meshless method is introduced to upgrade temporal accuracy. Also, the results show that LOD5 meshless method is more accurate than ADI and LOD3 meshless methods. The accuracy of the proposed method is due to two main factors; Crank–Nicolson scheme and solving the equation in five sub‐steps instead of one sub‐step. Stability and accuracy of the proposed method are assessed through numerical experiment. Also, the unconditional stability of the proposed method is proved, analytically. [ABSTRACT FROM AUTHOR]

A compact single-radiator circularly polarized (CP) leaky-wave antenna (LWA) based on composite right/left-handed (CRLH) transmission line is presented. The proposed antenna is based on substrate-integrated waveguide (SIW), and its unit cell consists of a T-shaped interdigital slot, which provides a CRLH property, a proper CP, and also effective compactness for the full-length LWA. The proposed LWA provides beam scanning from −19° to +84° over the frequency range of 7.35–10.15 GHz, while maintaining a good CP. By providing the balanced condition for the CRLH unit cell, a continuous backward-to-forward scanning including broadside is achieved. The maximum gain of the LWA is 8.95 dB which is satisfactory, considering the compactness of the antenna. Moreover, the radiation efficiency has an average of 85.7% over the operating frequency band. The measurement results are in good agreement with the simulation ones and show considerable advantages over the SIW-based CP LWAs proposed in the recent literature. [ABSTRACT FROM AUTHOR]

This communication presents a novel transient meshless formulation for analyzing wave propagation through linear dispersive materials. Many real materials are linear dispersive; thus, their constitutive parameters are not constant and change with frequency. However, the conventional numerical techniques are not proper tools for numerical analysis of dispersive materials, considering that they are formulated based on the assuming constant constitutive parameters for the materials. Therefore, until now, a number of numerical techniques have been proposed for modeling frequency behavior of dispersive materials. On the other hand, meshless methods are new and powerful numerical techniques which their capability in simulating the problem domain without using connection information among nodes makes them efficient techniques for modeling problems with complex geometries. In this communication, we have demonstrated that by incorporating some approaches into the meshless methods, we can turn them into suitable tools for modeling dispersive media. In order to obtain a meshless analysis of a dispersive medium, we have considered the scalar radial basis function meshless method, and for taking the frequency behavior of the medium into account, the auxiliary differential equations method has been used. Hence, the proposed dispersive meshless method not only models the frequency behavior of the dispersive materials but also provides more flexibility in simulating problems with complex geometries. In addition, the efficiency and accuracy of our proposed method are investigated by two numerical examples. [ABSTRACT FROM PUBLISHER]

A vector-based meshless method or vector meshless method, which is proven to be divergence-free, was recently proposed for transient electromagnetic analysis. In this method, an explicit finite-difference scheme is used for approximating the time derivatives in Maxwell's equations. Therefore, the stability criterion constraints the maximum time-step. This paper presents the alternating-direction implicit (ADI) formulation of the vector meshless method based on a different form of the ADI algorithm named the leapfrog ADI scheme. The computational cost of the leapfrog ADI scheme is less than the conventional ADI algorithm and algebraically equivalent. In the proposed vector meshless method, Courant-Friedrichs-Lewy limit does not constrain the time-step due to its implicit formulation. Moreover, the stability condition of the conventional vector meshless method and the proposed ADI vector meshless method are investigated through their amplification matrices in this paper. The results show that the proposed method has two features: unconditional stability and divergence-free property. The first one is obtained due to the incorporation of the leapfrog ADI algorithm, and the second one is achieved by the use of vector basis functions. The divergencefree property of the proposed method can lead to obtaining more accurate solutions than the conventional meshless method. In addition, some numerical examples are presented to verify the properties and the efficiency of the proposed method. [ABSTRACT FROM AUTHOR]

In this study, one of the most important destructive effects in end-pumped Nd:YAG laser, that is, thermal lensing is analyzed. Different partial differential equations, supplemented by suitable boundary conditions, are solved and joined to illustrate the fluctuations in laser Transverse Electromagnetic (TEM) mode. Because of no analytic demonstration of this effect, an efficient meshless method known as radial point interpolation meshless method (RPIM) is used to simulate the problem divided into two two-dimensional cases, that is, xz and yz planes so as to be graphically understandable. The results are in good agreement with measurement reports, and the RPIM shows better accuracy than FEM. [ABSTRACT FROM AUTHOR]

In this communication, the design and implementation of a three-band substrate integrated waveguide (SIW) leaky-wave antenna (LWA) based on the composite right/left-handed (CRLH) structure is presented. CRLH unit cell of the proposed antenna is composed of two adjacent interdigital slots with two vias between them. Two CRLH bands along with a new right-handed (RH) band between them are achieved through this structure. The first CRLH band (7.1–10.75 GHz) is balanced and the second one (15.1–21.75 GHz) is unbalanced with 0.25-GHz stop band. Beam scan angle in the first CRLH band is from $- 78^\circ $ to $+ 78^\circ $, in the second one from $- 40^\circ $ to $+ 20^\circ $ and in the new RH band (12.6–13.4 GHz) from $+ 22^\circ $ to $+ 54^\circ $. Antenna radiation efficiency in the first CRLH band is about 90%. Simulated and measured results are compared and there is a good agreement between them. [ABSTRACT FROM PUBLISHER]

SUMMARY In this work, the application of Daubechies' scaling functions (DSFs) in computational engineering, particulary radial point interpolation meshless method (RPIM) in electromagnetic engineering, is studied. This analysis indicates some shortcomings of DSFs in computational engineering. In fact, the DSFs take the role of shape functions in RPIM, but they do not hold some general properties of shape functions. Modifying these shortcomings according to engineering requirements as time consumption rate, new scaling (shape) functions are derived, and testing them into two important classes of electromagnetic problems, that is, incident wave on dielectrics and scatterers, gives good agreement with exact solutions. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Two UWB LNAs based on a new configuration suitable for low-power and low-voltage applications are presented. The proposed configuration saves bias circuit because of sharing only a bias circuit. In designing LNA-1 good phase linearity property achievement is followed for low-power and low-voltage applications, while in LNA-2 the main concerns are high power gain, by keeping low-power consumption, and small chip area. By taking advantages of resistive-feedback and RLC load, wideband input matching is obtained. Based on the proposed configuration, accompany with complete noise analysis, noise of LNA-2 is highly suppressed and flat noise figure is reaped. The 130nm CMOS LNA-1 and LNA-2 dissipate 2.95mW and 6.09mW, respectively, from 0.7V supply voltage, without using of forward-body-bias technology. Input return loss of both LNAs is below than −10.5dB while LNA-1 achieves average power gain of 9dB and LNA-2 17dB. The group-delay variation of LNA-1 is about ±6.1ps over the band of 3.1–10.6GHz. The NF of LNA-2 is 2.4–2.89dB over the whole band of interest. [Copyright &y& Elsevier]

A Gysel power divider/combiner with the second and third harmonic suppression using one resistor is proposed. Three open-circuit stubs are used to suppress the second and third harmonics. To calculate the values of the design parameters, the closed-form design equations are derived. A sample power divider is designed at 1 GHz to verify the design procedure. The measured results are nearly in agreement with the simulation results. The proposed Gysel power divider provides a high power-handling advantage over Wilkinson power divider. Moreover, it has a fractional bandwidth of 30% and harmonic suppression of 25 and 35 dB at the second and third harmonics, respectively. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, an accurate and efficient method for analysis of a GaAs MESFET including frequency-dependent losses of the electrodes in the time domain is presented. The time domain analysis is obtained based on the fully distributed model using finite-difference time-domain (FDTD) technique, with the assumption of the skin effect losses. The time-domain results are verified using the conventional time-domain to frequency-domain (TDFD) solution technique. [Copyright &y& Elsevier]

Ink-jet printing technology is one of the most promising printing techniques enabling fabrication of metamaterial absorber (MMA) in a one-step and direct process. In this study and for the first time the metamaterial microwave absorbing structure is proposed using water-based reactive inks and ink-jet printing technique. The MMA based on Unite-Ring-Swastika Cross Resonator (URSCR) is printed on a copy paper. The printed MMA structure is flexible and includes an ink-jet printed silver unit cell, a dielectric layer (copy paper), and an ink-jet printed silver ground plate was formed underneath the substrate. The working principles of the unit cell of MMA and its parametric simulations are evaluated. The performance of MMA with the full-wave simulation at the microwave frequency band is assessed as well, showing great agreement with the results obtained from the measurements. The experimental results indicate that the amount of measured flexible MMA absorption based on URSCR at resonance frequency on a planar surface at 0° to 40° incident angles and on a cylindrical surface at a 0° incident angle stays over 99%. [ABSTRACT FROM AUTHOR]