Material characterization has become increasingly important with the adoption of simulation-based workflow for microwave electronics design. This article focuses on the characterization of printable electronics materials using transmission-line measurements and demonstrates the capability of the multiline characterization method to separate dielectric and conductor losses when line geometry and material properties vary between the lines. The effects of multiline algorithm, number of line standards, and methods for selecting optimal line lengths are demonstrated. Consistent characterization results are obtained from inkjet-printed transmission lines on two different substrate materials. In addition, local conductor thickness variations are demonstrated as an effective way to decrease losses. Finally, the simulation-based procedure for determining the material properties is outlined and applied to printable electronics characterization. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

The modulation of a microwave-scale Mach-Zehnder interferometer coupled to a dielectric resonator (DR) tunes the DR resonance frequency. We report on a theoretical study to develop an understanding of the intrinsic tuning properties of an Mach-Zehnder interferometer ring-DR-microstrip line system and present an experimental verification. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A new all-pass filter (APF) is proposed. The APF is based on a symmetrical ring, consisting of four sections of transmission line, which are identical in electrical length, different in characteristic impedance. Two input/output ports are connected orthogonally to the ring. The APF is analyzed by using the odd-even model, and the all-pass condition is then theoretically obtained. Meeting the condition, the circuit is all-pass in frequency, but nonlinear in transmission phase. The nonlinear transmission phase with frequency may be adjusted by changing the lines' impedances, while remaining the all-pass property. Then the APF is used to design a wideband 90° differential phase shifter with adjustable bandwidth. Samples are designed, fabricated and measured. Good agreements are achieved among the theoretic, numerical and experimental results. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

An equivalent circuit model for the wide-band band-pass filters (BPFs) using modified Minkowski-island-based (MIB) fractal patch are proposed in this article. The BPF is mainly formed by a square patch resonator in which a modified MIB fractal configuration with second-order iteration is embedded in the patch. By the equivalent circuit model with diamond structure, the wide-band responses are analyzed. The design procedure included equivalent circuit model is available for wide-band design. For wide-band characteristics, at 5.0 GHz central frequency, it has good measured characteristics including the wider bandwidth of 3.14–6.89 GHz (3-dB fractional bandwidth of 75%), low insertion loss of 0.39 dB, and high rejection level (−48.5/−44.9 dB). The patch size is 7.4 λ 7.4 mm² (0.25 λ_g × 0.25 λ_g) with 14.1% reduction. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A circular disk patch antenna loaded with a hemi-circular slot is initially proposed for achieving circular polarization (CP). To exhibit broad CP bandwidth that can cover the WLAN 2.4 GHz operating band, the patch antenna is fed by an L-shaped probe. To further attain conical beam radiation with peak gain of ∼8 dBic at ±30 degrees theta angle (θ), a 2 × 2 array type is proposed in this study, in which four circular disk patch array elements are arranged in a sequentially rotated fashion via a corporate feed network. Here, desirable 3-dB axial ratio (AR) bandwidth and 10-dB impedance bandwidth of ∼5% and 21% were measured.

As the areal density rapidly changes, the signal reflection increases. In order to avoid the reflection between a magnetic recording head and a read/write driver on hard disk drive interconnects (HDDIs), the windowing technique is used to keep low insertion loss and it causes the higher crosstalk between lines. In this work, the crosstalk on idealized HDDI with windowing is investigated. The crosstalk represented by the scattering parameters calculated by using the full wave simulation software based on finite integral technique. From the results, the improvement of insertion loss and transmission bandwidth (−3 dB bandwidth) can be found when the window percentage is increased. For the 90% windowed structure, these are improved as 4.27 dB at 1 GHz and 4.53 GHz comparing with the conventional structure, respectively. Besides, the crosstalk increases with the increasing of window percentage. However, it can be suppressed up to 5.68 dB in a range of 0.24–1 GHz when the window percentage is 90%. Furthermore, the 90% of windowed structure with 8 mm window pitch possess the lowest crosstalk about 30.22 dB in a range of 0.32–6.4 GHz. In addition, the placing position of windows in a reference plane with a half of the rest length at both ends should be avoided because it increases both crosstalk and insertion loss. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

We present the design of a six pole Chebyshev filter and a cascaded quadruple dielectric resonator (DR) filter using space mapping technique. Implicit space mapping technique is used throughout and the design emerges within few iterations in both the cases. Finite element method based HFSS is used in constructing the fine model and Agilent ADS is used in constructing the coarse model. Fine details such as tuning screws are included in the fine model. The same technique is also applied to a DR-based diplexer and is explained. In all the cases, the results obtained with the hardware match well with the analyzed results. The same procedure can be applied in designing much more complex structures such as multiplexers. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

In this article, a broadband quasi-Yagi array of rectangular loops using low-temperature co-fired ceramic technology is proposed. The antenna is fed by a simple and compact microstrip-to-coplanar strip transition, which serves as balun and impedance transformer simultaneously. Four rectangular loops are used to direct the antenna propagation toward the end-fire direction. Compared with the planar directors in traditional quasi-Yagi antenna, they can provide better director effect to improve the radiation performance. Furthermore, they act as good impedance matching elements to broaden the bandwidth. The measured results show that the proposed antenna achieves a wide bandwidth of 42% for S₁₁ < −10 dB (from 26.1 to 40 GHz), better than 12 dB front-to-back ratio, smaller than 14 dB cross polarization and an average gain over 6.5 dBi across the operating bandwidth. The antenna occupies a compact size of 8 × 8 × 1 mm³.

Planar antenna modeling requires a constrained solution space and open boundaries and so is highly computationally intensive. One of the methods used to overcome this is by using method of moments simulation. The method of moments is a highly efficient method of solving wire antenna structures and is commonly used in antenna optimization. A method of transforming a wire antenna structure to a planar antenna structure is presented using a 4-element Yagi-Uda antenna designed to resonate at 905 MHz. The wire to planar transformation is based on the circular cross section wire to planar strip, a spacing adjustment based on interelement capacitance, and a length scaling to compensate for the change in effective permittivity. The planar antenna shows slightly improved impedance performance at the resonance [voltage standing wave ratio (VSWR) = 1.39]. This transformation decreased the antenna footprint by 15.11% after conversion for a wire antenna to a planar antenna in air with similar radiation characteristics and on FR4 (1.6 mm thickness), the footprint increased by 52%. The antenna simulation time was reduced from 15 min using finite element method to less than 10 s for one cycle by using the method of moments solver. All antenna properties are essentially unchanged. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A new millimeter-wave antenna structure on a low-cost, production platform integrated passive device technology is presented. The antenna consists of a 2-by-1 array of slot antennas at 60 GHz. An in-house developed on-chip antenna measurement setup was used to characterize the fabricated antenna. The measurement results show an antenna gain of more than 5 dBi with a return loss of 18 dB at 60 GHz. The better-than-10-dB impedance bandwidth of the antenna covers the 60-GHz unlicensed band from 57 to 64 GHz. The 3-dB beamwidths of the antenna are 105° and 76° at E-plane and H-plane at 60 GHz, respectively. The size of the die of the antenna is 2 mm × 4.5 mm. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This article demonstrates the applications of a non-destructive electromagnetic target recognition method, called Wigner distribution-principal component analysis (WD-PCA) method, to dielectric coated conducting spheres. These spheres are chosen to be highly similar having the same overall size but slightly different permittivity and thickness values in coating layers. Four different classifiers are simulated by using the WD-PCA method for varying sizes of object libraries under different noise conditions. High correct decision rates are demonstrated even for challenging classifier libraries containing a large number of coated conductors while the method is also shown to be highly robust against noise both in design and test stages. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A symmetrical two-way Wilkinson power divider with shifted output ports, much wide bandwidth and large frequency-ratio is proposed for dual-band application. The corresponding transcendental design equations are derived by using the even- and odd-mode analysis. Moreover, the closed-form scattering parameter expressions are derived. Transcendental design equations are solved and accurate numerical design parameters along with different frequency ratios are obtained. Finally, the proposed structure and design method are validated by simulated and experimental results of typical microstrip planar power dividers, the performance is clearly observed for the input and output matching, isolation and transmission characteristic very well at the two band frequencies. More specifically, the measured transmission characteristics of the divider are 3.11 dB/3.58 dB at the 1.0 GHz/3.5 GHz, respectively. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A miniature ultra-wide band (UVB) antenna is presented. The size of the antenna is 17 mm × 18 mm × 1.575 mm. The antenna radiates at 3.4–20 GHz. The bandwidth of the antenna almost covers the entire UVB of 3.1–10.6 GHz. The size of the antenna is very small. The proposed antenna is fabricated and measured. The experimental results are in a good agreement with the simulated results. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A b-spline based finite element method parabolic wave propagation model is developed and tested against mode summation inside a parallel plate waveguide. The comprehensive numerical analysis of the solution of parabolic wave equation has been done. The algorithm is compared with mode summation in two dimensions. Excellent agreement is observed among the results. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

An analytical approach to inverse electromagnetic scattering is tested on 2-D experimental data. The closed-form singular value decomposition of the scattering integral operator is the basis for determining the radiating components of the equivalent source density. This equivalent source is used to reconstruct the features of a scatterer. Reconstructions performed on different scattering data show the capabilities of the method and, thanks to the closed-form solution, results are available after a very short time of computation. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A computational model is presented for Monte Carlo simulation of waveguides with ridges, by combining the principles of transformation electromagnetics and the finite methods (such as finite element or finite difference methods). The principle idea is to place a transformation medium around the ridge structure, so that a single and easy-to-generate mesh can be used for each realization of the Monte Carlo simulation. Hence, this approach leads to less computational resources. The technique is validated by means of various finite element simulations in the context of 3D waveguides of uniform cross-section. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

In this article, we introduce a new metamaterial complementary electric LC resonator (CELC) and investigate its operational mechanism, characteristics, and potentialities for application in microwave components and devices, such as filters. We consider the excitation of CELC by the electric and magnetic fields of microstrip lines and its resonance characteristics by the diagrams of effective permittivity (ε_eff) and permeability (μ_eff). A circuit model is obtained by the consideration of its coupling with the loaded microstrip line. We then realize a novel left-handed (LH) cell by the combination of the CELC resonator and a short circuited stub. It is designed by the least mean square method. We finally use the cascade connection of such LH cells for the design of a miniaturized narrow-band band-pass filter with high out of band rejection. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A three-dimensional (3D) finite-difference time-domain (FDTD) simulator is developed for the investigation of network (S-) parameters of rectangular cross-section waveguide filters. The simulator is calibrated against analytical LC equivalent models. Any number of horizontal or vertical windows can be located to act as capacitive or inductive irises, respectively, and two-port filter characteristics can be obtained automatically. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This article aims to demonstrate the effects of using different boundary conditions and different computational volume dimensions in numerical simulations of periodic metamaterial arrays. A double band metamaterial unit cell design will be utilized to show that use of different boundary conditions may result in simulation of dissimilar periodic array topologies with completely different electromagnetic responses. It will also be shown that dimensions of the computational volume may strongly affect the overall response of the metamaterial structure due to varying electromagnetic coupling between the array elements. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

The tolerances of very thin, possibly conductive dielectric coating material parameters measured using the wideband free space transmission loss measurement technique in a high noise environment was investigated. The advanced postprocessing algorithm that improves those tolerances has been developed. This algorithm allows extracting thin coating material parameters with practically acceptable accuracy even when the level of systematic and random measurement noise is much greater than the level of transmission loss and insertion phase delay characteristics of the tested material sample. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Broadband amplifiers that can accommodate commercial communication standards such as GSM, UMTS, Wi-Fi, and Wi-Max are extremely important for radio equipment manufacturers. To achieve this coverage, the amplifier should provide high gain and efficiency over a band from 800 to 5200 MHz. Although there are transistor devices that have cut-off frequencies well over these frequencies, amplifiers covering such a broad-bandwidth are difficult to design due to the requirement of broadband matching networks. In this work, design of broadband tunable matching networks is investigated using Real Frequency Direct Computational Technique (RF-DCT). In order to be able to work on sample structures, impedance transforming filters are chosen and a broadband tunable matching network has been designed. Implementation of tunable inductors is investigated and the performance of a tunable matching network using tunable inductors and capacitors is demonstrated. Eventually a broadband frequency tunable amplifier has been designed using the tunable inductor concept. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

An inverse scattering approach based on the field equivalence principle is developed for reconstructing the electrical parameters of a stratified medium using only electric field time-domain data measured at two observation points in presence and absence of the medium. The magnetic field data at the observation points are calculated from the electric field data by solving two equivalent problems for the incident and scattered fields. By noting that the field of an equivalent problem for the total field in the interior region between two observation points is null in the exterior region, the functional of the electrical parameters is introduced. A genetic algorithm is applied for minimization of the functional to estimate the parameters. Numerical simulations demonstrate the effectiveness of the approach. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Based on a classification methodology for multiple reflections' (MR) identification recently published by the authors, this work proposes a filtering technique for GPR data to be integrated within the layer stripping (LS) approach. In LS, the reconstruction of the dielectric stack is obtained by recursively inverting the signals backscattered by each layer, from the top to the bottom. According to the state-of-the-art, to simplify the solution of the problem, MR are commonly neglected. The scope of this article is therefore to first discuss the implementation of the MR filtering procedure within a LS algorithm and evaluate from the quantitative point of view which improvements this will yield to the overall performances. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

The study of high frequency diffraction phenomena mostly associated with geometrical theory of diffraction, uniform theory of diffraction, physical theory of diffraction, and their alternatives is reviewed. Several examples illustrate these theories and their applications in antennas and scattering problems. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

In this article, the design approach, the implementation, and experimental results of multiband branch-line couplers operating at arbitrary frequencies are presented. The conventional branch-line coupler structure is adapted to multiband operation by shunting its four ports with multiband reactive networks. The performance of the proposed multiband couplers is theoretically analyzed and optimized through the even-odd mode circuit analysis. Dual-band (2.4–3.5 GHz), triple-band (1.5–2.4–4.2 GHz), and quad-band (1.5–2.4–3.5 GHz) microstrip branch-line couplers have been realized and tested to verify the design method. The good experimental results (input return loss greater than 15 dB and amplitude imbalance lower than 0.7 dB) show excellent agreement with theoretical and simulated ones, thus validating the proposed approach. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This article presents the studies of time domain inverse scattering for a two-dimensional (2D) inhomogeneous dielectric cylinder buried in a slab medium by the asynchronous particle swarm optimization (APSO) and dynamic differential evolution (DDE) method. The method of finite-difference time-domain is employed for the analysis of the forward scattering part, while the inverse scattering problem is transformed into optimization one. The DDE algorithm and the APSO are applied to reconstruct the permittivities distribution of a 2D inhomogeneous dielectric cylinder. Both techniques have been tested in the case of simulated measurements contaminated by additive white Gaussian noise. Numerical results indicate that the APSO algorithm outperforms the DDE in terms of reconstruction accuracy and convergence speed. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

In this article, the design of circular antenna arrays (CAAs) and concentric circular antenna arrays (CCAAs) of isotropic radiators with optimum side lobe level (SLL) reduction is studied. The newly proposed global evolutionary optimization method; namely, the firefly algorithm (FA) is used to determine an optimum set of weights and positions for CAAs, and an optimum set of weights for CCAAs, that provides a radiation pattern with optimum SLL reduction with the constraint of a fixed major lobe beamwidth. The FA represents a new algorithm for optimization problems in electromagnetics. It is shown that the FA results provide a SLL reduction that is better than that obtained using well-known algorithms, like the particle swarm optimization, genetic algorithm (GA), and evolutionary programming. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Two designs of microstrip antenna arrays consisting of eight radiating elements and operating within a broad frequency range having the center frequency of 24 GHz are presented. One of the proposed antenna arrays uses a single laminate layer with a ground plane on one side and radiating elements on the other side, the other one is a double layer structure, where the radiating elements with beam-forming network are placed on the top layer and are fed with the use of the slot coupler. The application of U-slot radiating elements with enlarged inner parasitic patch allows us to achieve reflection coefficient better than 10 dB within the assumed bandwidth of currently developed FMCW radars, which is 23–25 GHz frequency range. The theoretical analysis as well as experimental results of the manufactured 2 × 4 antenna arrays is shown. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This work presents a straightforward approach aimed at modeling the dynamic I–V characteristics of microwave active solid-state devices. The drain-source current generator represents the most significant source of nonlinearity in a transistor and, therefore, its correct modeling is fundamental to predict accurately the current and voltage waveforms under large-signal operation. The proposed approach relies on using a small set of low-frequency time-domain waveform measurements combined with numerical optimization-based estimation of the nonlinear model parameters. The procedure is applied to a gallium nitride HEMT and silicon FinFET. The effectiveness of the modeling procedure in terms of prediction accuracy and generalization capability is demonstrated by validation of the extracted models under operating conditions different than the ones used for the parameters estimation. Good agreement between measurements and model simulations is achieved for both technologies and in both low- and high-frequency range. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Investigation results are presented for a cylindrical dielectric resonator antenna (DRA) with a central airgap, which is excited using a coaxial probe connected to a wire monopole. By selecting the proper values of airgap and monopole heights, a desired impedance bandwidth (S₁₁ ≤ −10 dB) from 40% to 67% can be achieved. The proposed DRA provides monopole like omni-directional radiation patterns with low crosspolarization levels throughout the bandwidth. Prototype DRA was fabricated with equal heights of the airgap and monopole and experimentally verified for both the impedance matching and radiation performance. Simulated and measured bandwidths of 67% and 64%, respectively, were obtained with acceptable peak realized gain. The simulated and measured radiation patterns agree well. Furthermore, this DRA is investigated for beam focusing properties when implemented in a circular array consisting of four-elements on a circular finite ground plane. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This work presents a comprehensive design protocol for a W-band E-plane waveguide-to-microstrip transition covering all aspects, from the probe design, matching, cut-off cavity size estimations, verification analysis with different 3D EM simulators, and the entire fabrication process, with special emphasis on tolerances and yield with optimized costs. In fact, a complete study of the manufacture yield is done without the need to fabricate a large number of units of the microstrip-to-waveguide transition by taking advantage of the Monte Carlo tools embedded in 3D EM simulators. A simple equivalent circuit model of the transition is proposed and validated to be used in W-band system level simulations. These are requirements to enable massive use of W-band products (i.e., concealed weapons detection, imaging, etc.) with reasonable costs. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Waveguide-fed slot arrays in standing wave mode have been employed successfully in space based remote sensing radars because of their high efficiency, ease of deployment and their ability to withstand the radiation environment. Although the bandwidth requirement in such systems is minimal, at Ka band and above manufacturing tolerances in the order of 1 mil (25 μm), achieved in the dip brazing process, may affect their performance. To produce designs that are less sensitive to manufacturing tolerance, genetic algorithm (GA) optimization is employed in conjunction with a full wave analysis utilizing the method-of-moments solution to the pertinent integral equations of slot apertures of a planar array. In this work, a single 8 × 10 sub-array of an interferometric antenna, proposed previously for a planetary mapping application, was investigated. The array was first designed by the Elliott's procedure and subsequently the design parameters were perturbed by GA optimization using the moment method analysis. The fitness parameter is a weighted function of return loss and gain over a number of frequencies in the operating band. A matching waveguide section consisting of inductive irises is also optimized using GA and mode matching technique. Optimum designs producing nearly constant gain and good return loss over 6% bandwidth are found to be less sensitive to manufacturing tolerance than the initial Elliott design. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A point-wise approach that can be used efficiently in the numerical solution of Electric Field Integral Equations is introduced. The algorithm is based on the so-called magic distance concept, which defines exactly the point-to-point equivalent of a four-dimensional integral. Magic distance values are rigorously obtained in the electrostatic case and their usefulness is demonstrated. The concept is generalized to the electrodynamic case, resulting in a family of very simple “magic-distance inspired” algorithms that maintain the overall accuracy of Galerkin formulations without appreciable deterioration in the overall accuracy. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This article presents a microstrip implementation of a manifold multiplexer. The design procedure is based on evaluation, through an efficient synthesis algorithm recently proposed, of the characteristic polynomials of the triplexer, including the channel filters. Both the manifold and channel filters parameters are also available at the end of the synthesis. This approach, based on polynomial modeling of the triplexer, has been experimentally validated for the first time through a practical implementation in planar technology. The fabricated prototype consists of three channel filters of third order centered at 1.84, 1.95, and 2.14 GHz, with bandwidth of 75, 60, and 60 MHz respectively. This work illustrates in detail the design and implementation of the practical triplexer, starting from the initial specifications and obtaining the final physical dimensions of the structure. Following the technique here shown, each filter is synthesized taking into account for the loading effects of the whole manifold; the filters dimensioning can be carried out with the filters separated from the multiplexer. In this way the optimization tasks are greatly simplified as compared with previous techniques for multiplexer design. The measured results of a manufactured prototype show return losses under 17 dB and minimum isolation between channels equal to 25 dB. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This article proposes a novel mutual impedance matrix model for compensating mutual coupling effects in adaptive array with application to adaptive nulling of interference signals. In the new method, extreme care has been taken into account for both self impedance and mutual impedance, relating to the mutual coupling effects. Numerical simulation results demonstrate the robustness and capability of this technique. By using the new method, it is found that both the accuracy of the positioning and depth of the nulls are significantly improved. Performance comparisons of the new methodology and several other previous techniques via a number of simulation are presented. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

In this article, a set of differential equations to model the behavior of the extended composite right/left handed transmission line in time domain is proposed. These equations are solved by an explicit finite difference time domain algorithm. To investigate the numerical stability of the proposed algorithm, the amplification matrix is extracted. The results of the proposed algorithm are confirmed by the results of the Agilent ADS commercial software. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This article investigates parasitic radiating structures for coupling reduction between two 900MHz planar inverted-F antennas (PIFAs) in a hand-held device. Measurement of the initial prototype shows that a maximum isolation enhancement of more than 8 dB is achieved with a single parasitic element. This is followed by optimization of the parasitic structure for compactness, improved bandwidth, and tuning capability. First, different techniques for miniaturization are employed to obtain 60% less footprint with a 22 mm x 15 mm meandered parasitic element. Second, it is demonstrated that the isolation bandwidth can be increased by employing several parasitic radiators with different lengths. Finally, it is presented that the operation of a handheld device, as well as the coupling reduction technique, is compromised in proximity to the human body. For the first time, a miniaturized electronically tunable parasitic radiating element is designed to compensate for the detuning of the coupling reduction technique and adjusting its resonance to achieve maximum isolation between two handset PIFAs. Measurements of the fabricated prototype show 810–960 MHz tuning range. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A computationally efficient method is presented for setting up accurate Bayesian support vector regression (BSVR) models of the highly nonlinear |S₂₁| responses of planar microstrip filters using substantially reduced finely discretized training data (compared to traditional design of experiments techniques). Inexpensive coarse-discretization full-wave simulations are exploited in conjunction with the sparseness property of BSVR to identify the regions of the input space requiring denser sampling. The proposed technique allows for substantial reduction (by up to 51%) of the computational expense necessary to collect the finely discretized training data, with negligible loss in predictive accuracy. The accuracy of the reduced-data BSVR models is confirmed by their use within a space mapping optimization algorithm. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

We reformulate the quasi-static SDA applicable to a lossy multilayer CPW that also incorporates two-layer model of a conductor thickness and the concept of effective permeability due to magnetic field penetration in an imperfect conductor. The present static SDA formulation accounts for the effect of conductor thickness and low frequency dispersion on computation of quasi-static effective relative permittivity and characteristic impedance. The paper also presents the single layer reduction (SLR) formulation and circuit model to compute frequency dependent line parameters of a lossy multilayer CPW. The accuracy of formulation is comparable to that of HFSS and CST, without using complex and time consuming full-wave methods. The results of CST for ϵ_eff, Z₀, α_d, α_c of multilayer CPW, in the frequency range 1–100 GHz, deviate from results of HFSS up to 1.26%, 2.78%, 11.75%, and 18.7%, respectively; whereas corresponding deviations of present formulation are up to 1.56%, 2.4%, 3.04%, and 7%. The results of the present formulation and HFSS are also compared against the available experimental results. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013

Composite right/left-handed (CRLH) metamaterial unit cell whose ground-plane is defected with a rectangular dielectric slot is used to develop a single and multi-pole pole bandpass filter. The unit cell comprises of serially connected interdigital capacitors whose junction is connected to a short-circuited inductive stub. By defecting the ground-plane of the unit cell's structure with a dielectric slot, which is located immediately below the unit cell, enables substantial tuning of the filter's center frequency in the order of 26.5%. This is achieved with minimal effect on the unit cell's insertion and return-loss performance including its selectivity. The filters were fabricated on conventional dielectric substrate and their performance measured to verify the design methodology. The proposed technique eases the trade-off constraints and makes possible the realization of challenging filter specifications constituted from CRLH unit cells using distributed transmission-lines. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013

For output multiplexer (OMUX) filters placed in telecommunication satellites, microwave breakdown happens in an involuntary and undesirable way during tests at atmospheric pressure. This avalanche phenomenon is due to exponential growth of the electronic density caused by thermoelectronic emission under strong electromagnetic field magnitude. In this paper, our objective is to model and characterize experimentally multipole OMUX filters composed with coupled cavities. For identifying the element responsible for the breakdown, the electric field is calculated within each cavity and each iris. In order to characterize the breakdown phenomenon, we proposed an experimental test bench and we measured the power, both at the input and at the output of the filter. The article details the theoretical breakdown prediction and the experimental setup for such a structure. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013

Phase velocity compensation technologies using asymmetric coplanar waveguides (ACPW) with or without defected ground structures (DGS) are proposed to enhance the directivity of wideband 3-dB broadside-coupled coplanar waveguide (BC CPW) couplers. First, even- and odd-mode analyses of BC CPW couplers with four shunt capacitors are performed to obtain closed-form design formulas. Then, ACPW instead of the shunt capacitors are inserted to the input and output ports of the coupler to improve the directivity. Lastly, DGS combining with ACPW are applied to further improve the directivity and broaden the bandwidth. The measured results show that only using ACPW, the bandwidth for the directivity of better than 20 dB is 44.2% with a maximum directivity of 42.6 dB. When both ACPW and DGS are used, the bandwidth for the directivity of better than 20 dB is 63.3%, and that for the directivity of better than 30 dB is enhanced to 21.3% with a maximum directivity of 55.9 dB, which is more than 10 dB over the existing BC CPW couplers. © 2013 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013

A novel microwave breast cancer detection system consisting of an Evolutionary Global Optimized Vivaldi antenna and an algorithm inspired by MUltiple SIgnal Classification (MUSIC) is presented. Its performance is assessed by using a simplified numerical breast phantom for a number of critical conditions including the presence of fibroglandular tissues. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

Two novel process variations aware, necessary and sufficient conditions suitable for implementation in CAD optimizers are proposed to check amplifiers stability. Case studies are presented, showing that the new criteria allow robust amplifier design, under variation of active device immittance parameters in pre-specified rectangular regions, due to manufacturing tolerances. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

In this article, we discuss stability issues for mm-wave monolithic integrated power amplifiers using InP double heterojunction bipolar transistor (DHBT) technology targeting E-band applications at 71–76 GHz and 81–86 GHz. Different stability detection methods based on the classical two-port K-Δ_s pair, linear three-port graphical analysis, system identifications, circuit modal analysis, and normalized determinant function are all reviewed. The corresponding techniques are employed to predict the occurrence of instability at 15 GHz observed during measurements on a fabricated monolithic microwave integrated circuit power amplifier. Experimental results from a redesigned power amplifier with improved stability are presented to confirm that the previously detected oscillation loop is removed using odd-mode stabilization resistors with the correct choice of values and locations. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

The inverse problem under consideration is to reconstruct the characteristic of scatterer from the scattering E field. Dynamic differential evolution (DDE) and self-adaptive dynamic differential evolution (SADDE) are stochastic-type optimization approach that aims to minimize a cost function between measurements and computer-simulated data. These algorithms are capable of retrieving the location, shape, and permittivity of the dielectric cylinder in a slab medium made of lossless materials. The finite-difference time-domain (FDTD) is employed for the analysis of the forward scattering. The comparison is carried out under the same conditions of initial population of candidate solutions and number of iterations. Numerical results indicate that SADDE outperforms the DDE a little in terms of reconstruction accuracy. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

In this article, a partial equivalent element circuit (PEEC) method with Rao-Wilton-Glisson (RWG) basis functions and discrete complex image (DCI) is proposed. Circuit model and its formula are derived. With the proposed RWG-DCI-PEEC method, signal integrity (SI) simulations of high speed differential traces on PCB are carried out in time domain, including response of time domain reflectometry (TDR) and eye diagram of worst case analysis, and are compared with experimental measurements and other commercial softwares. The correctness and effectiveness of our proposed method are verified. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

New designs of wide-band rat-race couplers are proposed. The wide-band operation is achieved with the use of the microstrip nonuniform transmission line sections for the branches of the conventional rat-race coupler. The design formulas are developed using ABCD matrix and the even- and odd-mode analysis. The theoretical analysis has been verified by measurements of the two manufactured wideband rat-race couplers, one operate within 0.85–1.92 GHz and other within 1.55–3.55 GHz frequency range with the equal normalized characteristic impedance functions. For both fabricated couplers, the isolation parameter is better than 15 dB over a 77% relative bandwidth. Also, it is shown that the designed wide-band rat-race coupler can be realized in higher frequency bands with the fixed fractional bandwidth. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

The objective of this article is to present an accurate model for behavioral modeling and digital predistortion of power amplifiers (PAs) using physical knowledge. Starting with the physically meaningful block model, we present a novel approach to simplify the block model and propose a simplified physical knowledge-based (SPK) model. The SPK model's performance was experimentally assessed by two types of PAs (a LDMOS Doherty PA and a GaN Doherty PA) and two signals (a single carrier 16QAM signal and a 2-carrier WCDMA signal). All experimental results prove the superiority of the SPK model. Compared with the 1st-dynamic deviation reduction (DDR) approach and the 2nd-simplified DDR approach, the SPK approach achieves average ACPR improvements of 4.4 dB and 2.5 dB, respectively. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

A novel miniaturized planar inverted F-L antenna assembly is considered for UWB radio operations. The antenna design utilizes the electromagnetic coupling between an air dielectric planar inverted-F antenna (PIFA) and a parasitic planar inverted-L (PIL) element, with broadband feeding from a rectangular plate. To improve the functionality of the channel, a simple notch filter has been introduced through a local modification to the broadband feed plate, this takes the form of a simple slotted rectangular spiral resonator which is etched directly onto the plate. This allows the proposed antenna to maintain its full band UWB coverage, with the HYPERLAN/2 band centered at 5.35 GHz to be effectively rejected over the sub-band 5.15–5.725 GHz, without the need for substantial re-optimization of its principal structure parameters. The impedance bandwidth operates over the full UWB band, with VSWR better than 2, this performance is not degraded by the presence of the band rejection. The observed gains, radiation patterns, and group delay confirm that the antenna has appropriate characteristics for short range wireless applications. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

A design technique to improve the spurious resonance behavior of dual-band bandstop filters is presented. A compact dual-band bandstop filter with two stop bands that can be controlled independently with improved passband frequency response is designed. The operational bandwidth of the proposed compact dual-band bandstop filter is increased by pushing the first spurious resonance from being about twice the resonance frequency to more than three times the resonance frequency. Stepped impedance open loop resonators with substantially increased outer-edge width are used to improve the spurious resonance response. Both simulation and measured results are presented and good agreement is obtained between the results. The fabricated filter exhibits dual operating frequencies at 1460 MHz and 2640 MHz with 5.5% and 5% stopband fractional bandwidths, respectively. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

The parameter retrieval method based on the causality principle and Kramers-Kronig relations, which has been proposed for extracting effective parameters of metamaterials (MTMs) is extended to extract effective parameters of chiral metamaterials (CMMs) as well. Using Kramers-Kroning relations, the branch selecting problem which is the challenge of effective media parameters retrieval methods could be simply removed. To demonstrate the validity of the method, first, the constitutive parameters of a homogeneous chiral media are retrieved in the excellent agreement with the supposed parameters. Second validation is achieved by extracting the effective parameters of two well-known CMM structures whose effective parameters have been reported in the literature. The results are in excellent agreement with the reports of the previous works. Finally, a new type of CMMs called windmill structure is suggested, and its effective parameters are then extracted using the proposed method. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

We present a circuit model and parameter determination methodology for test fixtures used for on-wafer S-parameter measurements on CMOS devices. The model incorporates the frequency dependence of the series resistances and inductances due to the skin effect occurring in the metal pads. Physically based representations for this effect allow for excellent theory-experiment correlations for different dummy structures, as well as when de-embedding transistor measurements up to 60 GHz. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

Rotman lenses are used to obtain multiple beams from a single array. Although the beams produced by the feed antennas at focal points have no path length errors, the beams produced by feed antennas at off focal points may have large path length errors. These path length errors cause deterioration in the multiple beams. In this article, two novel methods are introduced to obtain feed curves which reduce the path length errors of off focal feed points significantly, compared with the commonly used circular and elliptical feed curves. The first method obtains feed curve points based on having zero path length error at three chosen points of the radiating array for each beam direction. The second method uses the particle swarm optimization method for obtaining optimum feed points for each beam direction. The results show that there is a very significant drop in the level of the maximum path length errors (in the order of about 1:4). © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

This article introduces a new RFID tag antenna designed for operation at 915 MHz. The proposed antenna is electrically small with dimensions (λ₀/15) × (λ₀/15). It features two vivaldi-like apertures flipped with respect to each other around an axis parallel to their slotted edges. Each aperture is loaded with a meander line with multiple loops. The two sides of the proposed antenna are fed via a common slot line that is coupled electromagnetically to a perpendicular microstrip line at the other side of a dielectric substrate. The new antenna are fabricated using printed circuit board technology and the fabricated prototype is experimentally characterized. The optimization and theoretical investigation of the proposed antenna are performed via both HFSS and CST. The two simulators agree very well with each other and with measurements. The characteristics of the new RFID antenna are generally good, such as: small size (22 mm²), low profile (0.8 mm), flexible impedance matching, reasonable impedance bandwidth (8%), omni-directional radiation, low cross-polarization level (−20 dB at broadside), acceptable radiation efficiency (76%), and gain (−0.3 dBi). © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

Behavioral modeling for the concurrent dual-band power amplifier (PA) is a critical problem in practical applications. The nonlinear distortion in the concurrent dual-band PA is quite different from that in the conventional single-band PA. This article analyzes the nonlinearities in the concurrent dual-band PA and reveals that both input signals in the dual bands are important for the behavioral modeling. The 2D Hammerstein model and 2D Wiener model are proposed for the first time for the concurrent dual-band PA. They are extended versions of conventional Hammerstein and Wiener structures used in the single-band PA by including the cross-band intermodulation in the static nonlinearity block. The proposed 2D models require much less coefficients than the original work of the 2D-DPD model. Experiments were carried out for an 880 MHz/1960 MHz concurrent dual-band Doherty PA to demonstrate the effectiveness of the proposed models. The results clearly show that less than −40 dB normalized mean square errors (NMSEs) are obtained in the dual bands in the behavioral modeling. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

To sustain the ever-increasing use of coupled-line structures in RF/microwave systems, efficient design tools should be developed. In this article, an original approach combining accuracy and speediness is proposed to shorten time-to-market design cycles when such structures are involved. By introducing the quasi-symmetric approach, CPU-time required to analyze asymmetric coupled-lines can be significantly reduced, leading to faster models without sacrificing the overall design accuracy. To achieve this aim, a rigorous formulation was developed and, for the first time, trial functions of C- and π-modes were obtained from the quasi-symmetric case and applied to the asymmetric case. The proposed approach, easily implementable in commercial simulators, was demonstrated through comparisons with published data. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

A new cell element is introduced for broadband reflectarray applications. The presented unit cell exhibits linear phase response which makes it a suitable candidate for broadband X-Ku band applications. This cell element consists of three concentric rectangular loops etched on a two-layer grounded substrate. The dimensions of the cell element have been optimized to achieve linear phase response in the operation band. A square offset-fed reflectarray of 40 cm × 40 cm was designed and fabricated based on this unit cell with wideband performance at X-Ku band. Considering three different feed positions, the whole reflectarray was simulated in CST and good agreement between simulated and measured results was observed. A maximum gain of 32 dBi was obtained which is equivalent to 58% aperture efficiency. Also, a remarkable value of 36%, 1.5-dB gain bandwidth was measured which is higher compared to previously reported designs in the literature. Another investigation that is carried out in this development through theory and simulation is determination of the effect of feed movement along the focal axis on the operating band of the reflectarray. It is shown for the first time that changing the feed location leads to a considerable shift in the operation bandwidth and maximum gain of the designed broadband reflectarray. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

In this work, the signal and noise behaviors of a microwave transistor within its operation domain (voltage drain to source–V_DS, current of drain to source—I_DS, frequency—f) are modeled by data mining techniques (DMT) without using any information on the microwave circuit theory. The device is modeled by a black box whose small signal (S) and noise parameters are evaluated through data mining techniques, based on the fitting of both of these parameters for multiple bias and configuration. It has been shown that DMT have a high potential of faithful and efficient device modeling. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

A miniaturized microstrip antenna on a planar layered periodic structure is proposed, designed and fabricated. The proposed structure miniaturizes patch antennas in the microwave band. With varying the parameters of the proposed structure, the achieved miniaturization factor can be adjusted in the range 2.6–4.2. Numerical and experimental results are presented. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

This article proposes a new trust region-based optimization technique for Radio Frequency (RF)/microwave devices. The proposed approach is apt for modeling scenarios, where standard ANN multilayer perceptron (MLP) and Prior Knowledge Input (PKI) models fail to deliver a satisfactory model. This approach feeds output of standard ANN model as knowledge input to PKI model. The ANN model and the PKI model form a symbiotic pair to yield accurate results. In this paper, the dogleg routine is exploited in the process of optimization to obtain valid trust region steps. The proposed method is compared with sensitivity technique via several RF/microwave components. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2012.

New configuration of cylindrical reentrant cavity with modified shape of the metal post is considered. The eigen wavelengths of two lowest modes obtained numerically are compared with analogous parameters of conventional reentrant cavity. Approximate analytical expressions for calculation of resonant wavelengths are derived with the help of statistical package TableCurve3D. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A compact-size asymmetrical linearly tapered slot antenna required for portable ultra-wideband (UWB) imaging systems is presented. The total antenna size is reduced compared with the conventional linearly tapered slot antenna by using a triangular slot on the left-hand side of the tapered-shaped radiator, whereas introducing a corrugated pattern of cuts on the right side. The antenna operates over a wide bandwidth extending from 3.1 to 10.6 GHz with a maximum gain of 8.5 dBi. Stable radiation patterns are observed across the operational bandwidth, with cross-polarization levels below −20 dB. The realized antenna structure occupies a volume of 35 × 36 × 0.8 mm³, and possesses the essential time domain fidelity needed for UWB imaging applications. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

This article presents a method for determining the required number and locations of transmitting antennas (TXs) to optimize wireless propagation coverage in an indoor ultra wideband (UWB) communication system. In the coverage prediction model, we use the three-dimensional ray-tracing technique associated with a particle swarm optimization (PSO), and asynchronous particle swarm optimization (APSO) for optimizing the TXs location in an indoor environment. The three-dimensional ray tracing and optimization algorithm was applied in indoor environment to find the best location of the TXs by maximizing the power in the coverage area. A deployment is proposed to minimize the TXs and maximize the power in the coverage area. Simulation results illustrate the feasibility of using the integrated ray-tracing, and optimization methods to find the optimal transmitter locations in determining the optimized coverage of a wireless network. The APSO has better optimization results compared to the PSO and numerical results also show that the APSO outperforms the PSO in convergence speed. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

In this article, a novel adaptive bias LInear amplification with Nonlinear Components (LINC) transmitter is introduced and analyzed. Predistortion is applied to the baseband signal and the bias of the high-efficiency power amplifier is adaptively changed according to the envelope distribution of the baseband signal and the power amplifier itself. This novel transmitter can simultaneously achieve high average efficiency and linearity even with a high peak to average ratio signal. A comprehensive simulation framework has been developed using EDA software to validate this adaptive bias scheme with 16, 32, and 64 quadrature amplitude modulation signals. The simulation results show that this novel scheme can help in improving the average overall efficiency of the LINC transmitter by 15% while sustaining expected linearity. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Electromagnetic devices that incorporate volumetric networks of transmission lines with electrically small periodicity and cross-sections are extensively used in various applications. Linear tapers can be employed in these configurations to achieve coupling between a homogeneous background medium and the volumetric transmission-line structure. This is beneficial since various transmission-line structures (homogenizable dense networks of transmission lines) are widely utilized to realize exotic electromagnetic properties commonly related to metamaterials. However, optimizing the dimensions of such multiparametric and electrically large devices could be computationally cumbersome. In this work, a simple semianalytic technique is proposed to reduce substantially the required simulation cost for an optimized design. The tapers are modeled semianalytically as consecutive coplanar components. On the other hand, the transmission-line network is considered as a chain of identical unit cells, the response of which is numerically determined. The semianalytical result of the taper is combined with the numerical result of the unit cell by cascading the respective transfer matrices. The agreement of the obtained results with the corresponding full-wave simulation data of the whole structure is very good. The decreased computational time required for the proposed approach is demonstrated through several numerical examples. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013

This article presents a dual-plane structure high selectivity tri-band bandpass filter (BPF) which consists of a pair of T-shaped microstrip feed lines with capacitive source-load coupling as well as spur lines embedded, and three resonators, i.e., a dual-mode stub-loaded stepped impedance resonator and two nested dual-mode defected ground structure resonators. Using the intrinsic characteristics of the resonators and feed lines, nine transmission zeros near the passband edges and in the stopband can be generated to achieve high selectivity. An experimental tri-band BPF located at 2.4/5.7 GHz [wireless local area networks (WLAN) application] and 3.5 GHz [worldwide interoperability for microwave access (WiMAX) application] has been simulated and fabricated. Good agreement between the simulated and measured results validates the design approach. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A novel low-profile slot-loaded epsilon-negative (ENG) transmission line (TL) is proposed for efficiency-improved zeroth-order resonant antennas. It is demonstrated that the quality factor of the ENG TL-based zeroth-order resonator can be remarkably reduced by enlarging the slot size, therefore, a highly efficient radiating resonator can be designed with higher gain at the zeroth-order frequency. Two one-dimensional zeroth-order resonant antennas with identical unit cell size but different unit cell number are fabricated and measured, each of which can realize a monopole-like radiation pattern at nearly the same frequency. A maximum gain of 1.96 dBi is generated for the electrically small two-unit-cell configuration together with an improved efficiency from 57.0% to 69.1%, while the compact four-unit-cell antenna can realize a maximum gain of 3.86 dBi with an improved efficiency from 71.0% to 82.4%. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A new equivalent circuit model for 3D multilayer on-chip inductors based on physical principles is presented in this article. The model consists of multiple elementary cells, and every cell in the distributed model represents a single stacked inductor. The model also takes into account the distributed effect of the via-hole with feedline which is used to connect the test pad to the lowest mental layer. A parameter-extraction approach for proposed model which combines the analytical approach and empirical optimization procedure is investigated. Good agreement is obtained between simulated and measured results for a six metal layers on-chip inductor on silicon in the frequency range of 50 MHz to 20 GHz. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

A robust technique for microwave design optimization is presented. It is based on variable-fidelity electromagnetic (EM) simulations where the approximate optimum of the “coarser” model becomes an initial design for finding the optimum of the “finer” one. The algorithm automatically switches between the models of different fidelity taking into account the computational budget assumed for the design process. Additional mechanisms enhancing the algorithm include: frequency scaling to reduce the misalignment between the models of different fidelity, as well as the local response surface approximation to reduce the number of EM simulations. The presented technique is particularly suitable for problems where simulation-driven design is the only option, for example, for wideband antennas and dielectric resonator filters. Our method is demonstrated using two filters and one antenna example. In all cases, the optimal design is obtained at a low computational cost corresponding to a few high-fidelity simulations of the structure. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

Taguchi's method is a quality design technique whose applications in numerical single-objective optimization have been recently exploited. In this article, a novel multi-objective (MO) algorithm based on Taguchi's technique is illustrated and its performances assessed. Validation is performed through a comparison between the presented algorithm and a MO genetic algorithm (GA) based optimization, first on different sets of test functions and then on a practical antenna array synthesis problem. Results indicate a generally better behavior of the proposed algorithm in terms of convergence and spreading over the Pareto front with respect to the GA benchmark. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE , 2013.

The nonlinear behavior of power amplifiers (PAs) and the in-phase/quadrature (I/Q) imbalance in I/Q modulators are considered as the main sources of distortions and impairments in radio frequency transmitters. In this article, a compound structure and a single-step identification procedure are proposed for the modulator's I/Q imbalance and DC offset and the PAs nonlinearity modeling and compensation of wireless transmitters. In fact, the performance of the digital predistortion technique used for PA linearization is adversely affected by the I/Q modulator's impairments that result mainly from gain/phase imbalance and DC offset. The measurement results reveal the robustness of the proposed model in modeling and linearization of the PA in the presence of I/Q modulator imperfections and show its superiority as compared to the generalized memory polynomial model and the dual-input polynomial model. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.

The channel capacity of indoor multiple-input multiple-output ultra-wide band (MIMO-UWB) transmission for smart antenna is presented. The genetic algorithm (GA) is used to synthesize the radiation pattern of the directional antenna array to maximize the capacity performance in indoor MIMO-UWB communication system. Three types of antenna arrays such as circular shape, L shape and Y shape arrays are used in the transmitter and their corresponding capacity on several paths in the indoor environment are calculated. The UWB impulse responses of the indoor channel for any transmitter-receiver location are computed by applying shooting and bouncing ray/image (SBR/image) techniques, inverse fast Fourier transform and Hermitian processing. By using the calculated frequency response, the capacity performance of the synthesized antenna pattern on MIMO-UWB system can be computed. Based on the topography of the antenna array and the capacity formula, the array pattern synthesis problem can be reformulated into an optimization problem and solved by the GA algorithm. The GA algorithm optimization is applied to a high order nonlinear optimization problem. The novelties of our approach is not only choosing capacity as the cost function instead of sidelobe level of the antenna pattern, but also considering the antenna feed length effect of each array element. The cost function for the problem is nonsmooth and discontinuous with respect to the antenna pattern. It is difficult to solve by gradient methods, since the derivative is hard to derive. The GA algorithm is employed to optimize the excitation voltages and feed lengths for these antenna arrays to increase the capacity. The strong point of the GA is that it can find out the solution even if the performance index cannot be formulated by simple equations. Numerical results show that the synthesized antenna array pattern is effective to focus maximum gain to the LOS path for these antenna arrays. In other words, the receiver can increase the received signal energy to noise ratio. The synthesized array pattern also can mitigate severe multipath fading in complex propagation environment. As a result, the capacity can be increased substantially in indoor MIMO-UWB communication system. The investigated results can help communication engineers improve their planning and design of indoor wireless communication. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.