Showing papers in "International Journal of Rf and Microwave Computer-aided Engineering in 2009"

The AB-C Doherty power amplifier. Part II: Validation

Abstract: In part I, the complete theoretical (and nonlinear) analysis of a Doherty amplifier employing a Class AB bias condition for the Main Amplifier and a Class C one for the Auxiliary device has been presented. In this article, the experimental validation of the proposed theory is presented, describing the step-by-step procedure to be adopted when designing an AB-C Doherty. The amplifier was realized at 2.14 GHz in hybrid form using two (0.5 μm, 1 mm gate periphery) GaN HEMTs. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Compact U-array MIMO antenna designs using IWO algorithm

Abstract: In this article, design of a novel compact four-channel multiple input multiple output (MIMO) antenna is described. The antenna is composed of four U-shaped patch elements and operates at 5.8 GHz. The single U-shaped patch antenna, to operate at this frequency, is designed using the Invasive Weed optimization algorithm. This algorithm is then applied to design two and four-channel MIMO antenna arrays for high degree of isolation. To measure the array performance under MIMO signaling conditions, a multiport metric is used to characterize the compact array rather than the scattering matrix characterization. The measurement and simulation results of reflection coefficient, mutual coupling, and radiation pattern are presented and discussed. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Design of microwave broadband absorbers using a self-adaptive differential evolution algorithm

Abstract: Microwave broadband absorber design for a desired frequency and angle range is presented. The design technique is based on a self-adaptive Differential Evolution (DE) algorithm. Numerical examples are compared with the existing in the literature and with those found by the other evolutionary algorithms. The results show that the new DE algorithm version outerperforms other global optimizers like Particle swarm optimization (PSO) variants and the classical DE algorithm. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

The AB-C Doherty power amplifier. Part I: Theory

Abstract: In this article, the complete theoretical analysis of a Doherty amplifier employing a Class AB bias condition for the Main and a Class C one for the Auxiliary devices, respectively, is presented. Starting from the simplified model of an active device, the analysis of the AB-C Doherty behavior is carried out as a function of the input signal. In particular, the proposed approach is based on the analysis of the output drain current waveforms generated by the two active devices, while assuming a Tuned Load configuration (i.e., short circuit condition) for higher harmonic terminations. A closed form formulation is derived in order to directly design an AB-C Doherty amplifier, while fully understanding the basis of its physical behavior. Finally, which Doherty parameters can be chosen by the designer or have to be implicitly fixed are discussed and clarified. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

The AB-C Doherty power amplifier. Part I: Theory

Abstract: In this article, the complete theoretical analysis of a Doherty amplifier employing a Class AB bias condition for the Main and a Class C one for the Auxiliary devices, respectively, is presented. S...

Multiobjective optimization for small meander wire dipole antennas in a fixed area using ant colony system

Abstract: Fixed area meander line antennas designed on a 5 × 5 rectangular grid were optimized for efficiency and resonant frequency. The Pareto front was developed using ant colony optimization and the numerical electromagnetic code. The lowest frequency antenna fits an area of 0.11λ0 × 0.05λ0 with an efficiency of 88p. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

A novel technique for the direct determination of multimode equivalent circuit models for substrate integrated waveguide discontinuities

Abstract: A novel technique is presented for the automatic, self-consistent and direct determination of wide-band lumped-element equivalent circuit models of substrate integrated waveguide discontinuities. This technique is based on the full-wave analysis of substrate integrated waveguide components by using the Boundary Integral-Resonant Mode Expansion method, which provides a generalized admittance matrix of the components in the form of a pole expansion in the frequency domain. This expression of the admittance matrix permits to directly identify the topology of a multimodal equivalent circuit and the values of its lumped elements, thus avoiding any initial guess or fitting procedure. The basic theory of the full-wave analysis method and the procedure for determining the equivalent circuit model are reported. The features of the proposed technique are detailed through the modeling of an iris-like discontinuity. Moreover, this technique is validated by modeling substrate integrated waveguide filters, whose frequency response is compared with numerical and experimental results. The proposed method can be adopted to obtain libraries of parametric models of substrate integrated waveguide discontinuities, which can be included in computer aided design tools. The multimodal parametric model of an iris-like discontinuity is presented and discussed. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Complex radial basis function networks trained by QR-decomposition recursive least square algorithms applied in behavioral modeling of nonlinear power amplifiers

Abstract: In this article, we propose a novel complex radial basis function network approach for dynamic behavioral modeling of nonlinear power amplifier with memory in 3 G systems. The proposed approach utilizes the complex QR-decomposition based recursive least squares (QRD-RLS) algorithm, which is implemented using the complex Givens rotations, to update the weighting matrix of the complex radial basis function (RBF) network. Comparisons with standard least squares algorithms, in batch and recursive process, the QRD-RLS algorithm has the characteristics of good numerical robustness and regular structure, and can significantly improve the complex RBF network modeling accuracy. In this approach, only the signal's complex envelope is used for the model training and validation. The model has been validated using ADS simulated and real measured data. Finally, parallel implementation of the resulting method is briefly discussed. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

A hybrid equivalent dipole moment and adaptive modified characteristic basis function method for electromagnetic scattering by multilayered dielectric bodies

Abstract: In this article, the equivalent dipole moment (EDM) method is extended and applied to analyze the electromagnetic scattering of multilayered dielectric bodies. Besides the advantage of reducing the computation time, the proposed EDM method makes it unnecessary to treat the boundary condition on the surface or the interface of the multilayered dielectric body. However, the EDM method is incapable of saving memory. In this case, the adaptive modified characteristic basis function (AMCBF) method is introduced and combined with the EDM method. Numerical results are given to demonstrate the merits of this EDM-AMCBF method. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

High power GaN-HEMT SPDT switches for microwave applications

Abstract: In this article, the design, fabrication, and on-wafer test of X-Band and 2–18 GHz wideband high-power SPDT MMIC switches in AlGaN-GaN technology are presented. The switches have demonstrated state-of-the-art performance and RF fabrication yield better than 65p. Linear and power measurements for different control voltages have been reported and an explanation of the dependence of the power performances on the control voltage is given. In particular, the X-band switch exhibits a 0.4 dB compression level at 10 GHz when driven by a 38 dBm input signal. The wideband switch shows a compression level of 1 dB at an input drive higher than 38 dBm across the entire bandwidth. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Hybrid MoM-FEM modeling of loaded enclosure with aperture in EMC problems

Abstract: To predict electromagnetic field distribution inside a loaded enclosure with the aperture, we present a hybrid formulation which combines method of moments and finite element method. To predict efficiency of the method, the shielding effectiveness of an empty enclosure is compared with the literature. Then the method is applied to dielectric slab loaded enclosure with the single aperture, and the shielding effectiveness, ratio of stored electrical energy, and dissipated power variations are obtained. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

A hybrid model in analyzing nonlinearly loaded dipole antenna and finite antenna array in the frequency domain

Abstract: In this article, a hybrid model is introduced in which our previous fuzzy inference approach is used for extracting the behavior of receiving antenna and predicting the induced current and mutual coupling effects with an excellent accuracy and then it is combined with Volterra series model to analyze nonlinearly loaded finite antenna array. As it is expected, the computation time of the resulted hybrid model is much faster than the accurate ones, without loss of accuracy. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 2009.

A digital predistorter for wireless transmitters

Abstract: A novel digital baseband predistorter with improved reduction of spectral regrowth is proposed and investigated. The improvements are achieved by using a proposed predistortion technique and extended power amplifier (PA) fundamental-frequency modeling. The digital baseband predistortion (DPD), known for its simplicity of realization, low cost and integrability; however, it suffers from poor linearizing performances. We incorporate baseband iterative injection of in-band distortion components into the baseband DPD to enhance the nonlinearity compensation. General formulas for the fundamental-frequency output of a PA with n-order nonlinearity and recursive formulas for calculating the injected components for different number of iterations are developed. The proposed iterative digital baseband predistorter is verified experimentally with a wireless PA and measured results are presented to demonstrate feasibility of the proposed concept. The spectral regrowth suppression of 20 dB is achieved for a 3.5 MHz digitally modulated signal. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Design equations of arbitrary power split ratio waveguide T-junctions using a curve fitting approach

Abstract: Design equations have been developed for the design of an H-plane rectangular waveguide T-junction with an arbitrary power split. These design equations were derived using curve fitting of data produced from a large number of EM simulation runs. A design procedure has been successfully developed and resulted in scalable, practically manufacturable structures. Various types of discontinuities were judiciously placed in the junction to provide adequate degrees of freedom and concurrently achieve diverse design goals. Added discontinuities included wedges and diaphragms which have been implemented as an integral part of the prescribed structures. For demonstration, T-junction designs at Ku-band have been fabricated and tested, which have adequate bandwidth performance covering the US-DBS 12.2–2.7 GHz frequency range. Both excellent match at the input port and in-phase flat power-split ratio over a relatively wide band at the output ports were successfully achieved—an essential requirement for high-performance antenna feeds. The dimensional tolerance of the developed design was also thoroughly investigated using extensive sensitivity analysis, and the developed structures proved to be appropriate for low-cost high-volume fabrication methods such as casting. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

An efficient combination of digital predistortion and OFDM clipping for power amplifiers

Abstract: This article presents a strategy for enhancing efficiency in power amplifiers (PAs) by combining digital predistortion (DPD) linearization and clipping strategies for orthogonal frequency division multiplexing signals in a WiMAX scenario. On the one hand, by reducing the peak-to-average power ratio of multicarrier signals using the well-known clipping technique, it is possible to perform a more efficient PA amplification. On the other hand, nonlinear and linear distortion introduced by the PA operating close to saturation is compensated by the baseband adaptive DPD linearizer. The DPD has to counteract not only the PA nonlinear behavior, but also its dynamics. A test-bench implementing a WiMAX transmitter was deployed to evaluate the possibilities for enhancing power efficiency while fulfilling the demanded linearity requirements. Experimental results showing the power efficiency and linearity enhancement achieved by the proposed strategy are provided. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

On the characterization of UWB antennas

Abstract: Compared with narrowband antennas, ultra-wideband antennas have particular characteristics which involve complementary and new ways to describe them. This article presents theoretical considerations and a methodology to characterize UWB antennas in the time-frequency domains from simulation and measurement using a vector network analyzer. In particular, the impact UWB antenna from the point of view of their filtering features is emphasized. Experimental considerations are developed from a specific UWB antenna. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Application of wiggly ridge waveguide for design of linear array antennas of centered longitudinal shunt slot

Abstract: A suitable radiating element for design of linear arrays of centered longitudinal shunt slot is proposed, which allows it to largely suppress the second order beams. The proposed radiating slot consists of a centered longitudinal slot, which is cut in the broad wall of a single wiggly ridge waveguide. The wiggly ridge is placed exactly under the slot and the wiggly part is in V-shape. It is shown that by varying the wiggle depth of the proposed slot, the amount of power coupled to the slot can be adjusted. Some Stegen's like design graphs are obtained for the proposed slot. Then, two linear arrays consist of five and six elements are designed using the obtained graphs and by neglecting the mutual coupling between slots. The arrays have Dolph-Chebyshev distribution with 20 and 30 dB of side lobe levels. For a better comparison between the proposed slotted arrays and the conventional longitudinal shunt slot arrays, two other slotted arrays in conventional topology and with the same specifications following the well known Elliott's design procedure are designed and simulated. Comparison of the simulated results shows that the second order beams of the designed array are effectively eliminated, while the other antenna specifications are also achieved. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Quad-ridged conical horn antenna for wideband applications: Quad-Ridged Conical Horn

Abstract: This article presents a quad-ridged conical horn antenna with high gain and low side lobe level for broadband applications. To the best of authors’ knowledge, the proposed structure presented in this article is completely new. The designed antenna introduces a low VSWR, which is lower than 2.2 for the frequency range of 8–18 GHz, and simultaneously achieves high gain as well as dual-polarizations with high isolation between the corresponding excitations. The common impedance exponential tapering is used at the flare section of the horn, and a coax to waveguide transition, namely quadruple-ridged circular waveguide, with a conical cavity is used to improve the VSWR. The proposed antenna structure is designed and simulated by two well established packages, namely the CST microwave studio and the Ansoft HFSS, showing there is a close agreement between the results obtained by the aforementioned softwares. VC 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE 19: 519–528, 2009.

An iterative design procedure for the synthesis of generalized dual-bandpass filters

Abstract: This article presents an iterative design technique to calculate the optimal position of transmission zeros in dual-bandpass filters. In the proposed design technique, the characteristic function of the filter is linearized around the displacement of the transmission zeros. A linear system is then obtained and solved in combination with a damping technique used to guarantee the convergence. Design examples which demonstrate the efficiency of the proposed method are presented and an experimental verification at 4 GHz using open-loop resonators validates the methodology. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Full-wave analysis of azimuthally magnetized ferrite-loaded circular structures using the one-dimensional finite difference frequency domain method

Abstract: Full-wave analysis of circular guiding structures completely filled with ferrite by using the finite difference frequency domain method is presented. The ferrite is assumed to be azimuthally magnetized to remanence. Emphasis is placed on the TE0m modes that are rotationally symmetric. These modes exhibit nonreciprocal behavior that could be exploited to build phase shifters and microwave isolators. Dispersion diagrams for these modes are given for both forward and reverse waves, and the effect of various ferrite parameters is studied. It is shown that the dispersion diagram may exhibit a region of negative slope, which gives rise to backward wave. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

A compact model for dielectric charging in RF MEMS capacitive switches

Abstract: A unified, macroscopic, one-dimensional model is presented for the quantitative description of the process of dielectric charging in radio frequency micro-electro-mechanical systems (RF MEMS) switches. The fidelity of the model relies on the utilization of experimentally obtained data to assign values to model parameters that capture the nonlinear behavior of the dielectric charging process. The proposed model can be easily cast in the form of a simple simulation program with integrated circuit emphasis (SPICE) circuit. Its compact, physics-based form enables its seamless insertion in nonlinear, SPICE-like, circuit simulators and makes it compatible with system-level MEMS computer-aided analysis and design tools. The model enables the efficient simulation of dielectric charging under different, complex control voltage waveforms. In addition, it provides the means for expedient simulation of the impact of dielectric charging on switch performance degradation. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Fuzzy neural-based approaches for efficient RF-microwave transistor modeling

Abstract: In today's RF and microwave circuits, there is an ever-increasing demand for higher level of system integration that leads to massive computational tasks during simulation, optimization, and statistical analyses, requiring efficient modeling methods so that the whole process can be achieved reliably. Since active devices such as transistors are the core of modern RF-microwave systems, the way they are modeled in terms of accuracy and flexibility will critically influence the system design, and thus, the overall system performance. In this article, the authors present neural- and fuzzy neural-based computer-aided design techniques that can efficiently characterize and model RF-microwave transistors such as field-effect transistors and heterojunction bipolar transistors. The proposed techniques based on multilayer perceptrons neural networks and c-means clustering algorithms are demonstrated through examples. © 2008 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

High-isolation multiway power dividing-combining network implemented by broadside-coupling SIW directional couplers

Abstract: One kind of novel microwave planar power dividing-combining network based on substrate-integrated waveguide (SIW) directional couplers is proposed and investigated. The design strategies of the broadside-coupling SIW directional coupler are introduced, the series connection of several directional couplers with different coupling ratio then result in a multiway power dividing-combining network. One three-way power dividing-combining network is designed and fabricated to demonstrate the validity of the proposed work, high isolation among the ports is observed. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.