Microwave Circuit Design Research Articles

Accurate circuit analysis of resonant-type left handed transmission lines with inter-resonator coupling

In this paper, a circuit model for the description of left handed transmission lines based on complementary split rings resonators (CSRRs) is proposed. As compared to previous models, coupling between adjacent resonators is included in the present work. The conditions that make this coupling significant are discussed. Specifically, it will be shown that it is barely present when circular CSRRs are used to implement the left handed transmission line. However, if the line is loaded with rectangular CSRRs separated by a small distance, inter-resonator coupling is important and it significantly influences the electromagnetic behavior of the structures. It will be also shown that under low or moderate coupling, it is possible to describe the structures by means of a simplified model with modified parameters. Several prototype devices with different CSRR topologies and coupling levels have been fabricated to illustrate the phenomenology associated with these structures and the accuracy of their model descriptions. The results of this work can be of interest for the design of planar microwave circuits based on CSRR left handed lines.

On the electrical characteristics of complementary metamaterial resonators

In this letter, a method to obtain the electrical characteristics of complementary split ring resonators (CSRRs) coupled to planar transmission lines is presented. CSRRs have been recently proposed by some of the authors as new constitutive elements for the synthesis of metamaterials with negative effective permittivity, and they have been applied to the fabrication of metamaterial-based circuits in planar technology. The method provides the electrical characteristics of CSRRs (including the intrinsic resonant frequency and the unloaded Q-factor), as well as the coupling capacitance between line and CSRRs, and the parameters of the host line. Parameter extraction from the proposed method is applied to two different structures corresponding to the basic cells of left handed (LH) and negative permittivity lines. The method is of actual interest for the design of microwave circuits and metamaterials based on these complementary resonant particles

Left‐handed and right‐handed transmission properties of microstrip lines loaded with complementary split rings resonators

AbstractIn this work, microstrip lines loaded with complementary split rings resonators (CSRRs) and series capacitive gaps are modeled by means of a lumped element equivalent circuit. The structures exhibit a left‐handed (or backward wave) behavior at low frequencies, followed by forward transmission at higher frequencies separated by a forbidden band. The equivalent circuit model is able to accurately describe the frequency responses of the structures in the left‐handed transmission band, the forbidden band, and the lower frequency region of the forward allowed band. The limitations of this circuit model to properly predict the behavior of the structures at higher frequencies (mainly related to the Bragg effect caused by periodicity) are pointed out. This work can be of interest for the design of microwave circuits based on CSRR metamaterials. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2508–2511, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22011

Microwave Circuit Design Using Linear and Nanolinear Techniques - [Book Review

Microwave Circuit Design Using Linear and Nanolinear Techniques - [Book Review

A textured barium niobate with enhanced temperature stability of dielectric constant for high-frequency applications

Ba5Nb4O15 has shown excellent microwave dielectric properties and is under consideration as a low-temperature cofired ceramic material for advanced radio frequency (RF) applications. By combining tape casting and liquid phase upon sintering, sintered Ba5Nb4O15 thick films stacked to form laminates were produced with aligned elongated grains. This texture engineering, correlated with crystallographic orientation, provides remarkably high temperature stability of dielectric constant up to microwave frequency. Crystallographic texture arises in Ba5Nb4O15 induced by the primary consolidation process, hot pressing, and pulsed laser deposition. The dielectric anisotropy could be efficiently obtained in the textured samples, thereby enabling significant feasibility of microwave circuit designs.

Fast time-domain simulation of optical waveguide structures with a multilevel dynamically adaptive mesh refinement FDTD approach

The finite-difference time-domain (FDTD) technique has been widely employed for the modeling of both linear and nonlinear optical structures. Its main advantages, however, namely, simplicity and versatility, are offered at the expense of significant computational resources needed for the simulation of realistic geometries. In this paper, a recent approach that incorporated an adaptively refined moving mesh into the FDTD technique for microwave circuit design is applied to two-dimensional optical waveguide problems, resulting in dramatic simulation time savings, compared with FDTD, while maintaining its accuracy. To complement the applicability of the proposed technique as a novel photonics design tool, numerical error studies that facilitate the educated a priori choice of the simulation parameters are provided

Multiple time constant modeling of dispersion dynamics in hetero field-effect transistors

A new approach to the modeling of frequency dispersion effects encountered in the drain current characteristics of state-of-the-art hetero field-effect transistors is presented. The empirical, equivalent-circuit based model is dedicated to efficient microwave circuit design and allows for the inclusion of individual dispersion effects, taking into account their respective time constants. The proposed topology allows for small- and large-signal analysis in both the time and frequency domains. Parameter extraction and verification of the model is carried out using pulsed-I-V and dc measurements as well as microwave frequency S-parameter characterization of both a GaAs pseudomorphic high electron mobility transistor (pHEMT) and an InP pHEMT technology. Finally, the model is employed in the design and realization of a GaAs pHEMT traveling-wave monolithic microwave integrated circuit. Simulation results are compared to measurements with a focus on figures of merit which are affected by frequency dispersion

Q-based design method for T network impedance matching

Impedance matching using passive network is very important in the design of RF and microwave circuits to achieve maximum power transfer, minimum reflection, and adequate harmonic rejection. This paper investigates the T network impedance matching analytically. A practical guide is provided for systematic network design based on the desired harmonic rejection specification. Expressions of the frequency response and harmonic rejection in term of the loaded Q are established. The limits of the network are analytically demonstrated. It is shown that the third harmonic rejection is about 12dB higher than second harmonic rejection provided that the loaded Q is larger than twice the minimum Q.

Network modelling of periodic patch loaded slotline

A network model of a patch loaded slotline (PLS) is proposed for the efficient design of related microwave circuits. The unit model is established by combining the network model for a slotline-to-microstrip transition with the equivalent circuits for microstrip step-discontinuities and open-ends. Therefore, this model is useful for the analysis of periodic PLS structures only by cascading it with a uniform slotline. To validate it, the computed results are compared with the EM simulated and measured ones, and they are shown to give good agreement in a wide frequency range.

EM-based microwave circuit design using fuzzy logic techniques

The authors illustrate how EM simulators can be combined with fuzzy logic techniques to develop an efficient approach for designing microwave circuits. They demonstrate the approach by considering the design of a microstrip coupler, a microstrip 6-pole filter and an HTS microstrip 3-pole filter. The fuzzy logic system (FLS) is constructed using data pairs generated from an EM simulator. The FLS is employed as a design tool to directly synthesise the coupler and the filter physical dimensions for a required RF response. The results achieved demonstrate the validity of the proposed approach.

A novel tunable transmission line and its application to a phase shifter

This letter describes the design of a novel transmission line, where characteristic impedance can be adjusted electronically, and its application to a phase shifter. A tunable transmission line enables microwave circuit designers to have flexibility and better return loss which can enhance its tuning range. A UHF band distributed analog phase shifter, as well as a tunable transmission line, is presented. The characteristic impedance of a fabricated novel transmission line varies from 10 to 69.5/spl Omega/, which demonstrates its tunability, and the fabricated UHF phase shifter using this novel line shows the possibility of better reflection coefficient and wider tuning range over the conventional capacitively-loaded distributed phase shifter.

Surface-passivated high-resistivity silicon as a true microwave substrate

This paper addresses the properties of a surface-passivated (enhanced) high-resistivity silicon (HRS) substrate for use in monolithic microwave technology. The detrimental effects of conductive surface channels and their variations across the wafer related to the local oxide and silicon/silicon-dioxide interface quality are eliminated through the formation of a thin amorphous layer at the wafer surface. Without passivation, it is found that the surface channels greatly degrade the quality of passive components in HRS by masking the excellent properties of the bulk HRS substrate and by causing a spread in parameters and peak values across the wafer. Moreover, it is seen that the surface passivation leads to excellent agreement of the characteristics of fabricated components and circuits with those predicted by electromagnetic (EM) simulation based on the bulk HRS properties. This is experimentally verified for lumped (inductors and transformers) and distributed (coplanar waveguide, Marchand balun) passive microwave components, as well as for a traveling-wave amplifier, through which also the integration of transistors on HRS and the overall parameter control at circuit level are demonstrated. The results in this paper indicate the economically important possibility to transfer microwave circuit designs based on EM simulations directly to the HRS fabrication process, thus avoiding costly redesigns.

Cavity-resonance dampening

Today, many microwave circuit designers are noticing that their circuits do not perform quite as well as predicted when they enclose their circuit boards within a package. Cavity resonances are generated inside the package that can change the impedances necessary for proper operation of some circuit elements. With frequencies of operation increasing, this is becoming an increasingly prevalent issue in circuit design.

Fast S-domain modeling of rectangular waveguides with radially symmetric metal insets

This paper describes the application of the boundary integral-resonant-mode expansion (BI-RME) method to the modeling of rectangular waveguides with metal insets. It extends to more complicated radially symmetric insets, a method recently introduced by the authors, for the simple case of a cylindric post. In this extension, a self-consistent new theory is presented, which fully exploits the peculiarities of the considered class of structures, thus straightforwardly leading to the system equations. The efficiency of the BI-RME method, already demonstrated in the wide-band modeling of arbitrarily shaped waveguide components, is further enhanced in the particular application considered in this paper because the currents on the waveguide walls are not involved in the calculation. For this reason, the method-of-moments discretization of the field equations leads to a mathematical model of order much smaller than in the general BI-RME approach and in other boundary integral methods. Due to the state-space formulation of this model, a wide-band representation of the generalized admittance matrix of the structure is easily found in the form of a pole expansion in the S-domain by the calculation of a reasonably small number of eigensolutions of a matrix eigenvalue problem. The method is very fast and reliable, and permits the realization of a very efficient software, well suited for inclusion in computer-aided design tools for microwave circuit design. Some examples show the efficiency of the method, including the application to multiple and slanting insets and to the modeling of an evanescent-mode filter.

Conical inductors for broadband applications

Inductors are an integral component in radio-frequency (RF) and microwave circuit design and are typically used as either impedance-matching elements or bias chokes. There are a wide variety of inductors designed to meet today's diverse applications. Using an inductor in a given application requires understanding its capabilities and limitations. One of the main limitations of an inductor is its self-resonance frequency or first parallel-resonance frequency (PRF), which affects the usable bandwidth. This application note presents a commercially available, very high performance inductor that can be used for very broadband UHF to millimeter-wave choking or bias feed applications. Conical inductors are capable of extremely broadband, resonance-free inductance in the microhenry range that can be used for low-loss RF choking and bias feeding. The conical shape combined with careful assembly to low capacitance attach pads allows usable bandwidth of these inductors from 10 MHz to 40 GHz. The conical inductor overcomes the limited bandwidth seen in standard SMT inductors by virtue of its conical design and careful assembly.

HEMT noise neural model based on bias conditions

Knowledge of the microwave transistor parameters at various bias conditions is often required in computer‐aided design of complex microwave low‐noise circuit. Since the measurements of noise parameters are very complex and time‐consuming, microwave circuit designers usually use the catalogues' data or noise models. The noise data that can be found in the catalogues are often limited to a few frequencies and to one or few bias points. Further, most of the existing noise models require recalculation of elements/parameters of an equivalent circuit for every bias point. Microwave HEMT transistor noise prediction based on a multilayer perceptron neural network, proposed in this paper, enables noise prediction for all operating points over a wide frequency range. Neural networks are trained to learn noise parameters' dependence on bias conditions and frequency. After network training, noise prediction for a specified bias point requires only a network response calculation without changes in the network structure.

EM-Based Optimization of Microwave Circuits Using Artificial Neural Networks: The State-of-the-Art

This paper reviews the current state-of-the-art in electromagnetic (EM)-based design and optimization of microwave circuits using artificial neural networks (ANNs). Measurement-based design of microwave circuits using ANNs is also reviewed. The conventional microwave neural optimization approach is surveyed, along with typical enhancing techniques, such as segmentation, decomposition, hierarchy, design of experiments, and clusterization. Innovative strategies for ANN-based design exploiting microwave knowledge are reviewed, including neural space-mapping methods. The problem of developing synthesis neural networks is treated. EM-based statistical analysis and yield optimization using neural networks is reviewed. The key issues in transient EM-based design using neural networks are summarized. The use of ANNs to speed up "global modeling" for EM-based design of monolithic microwave integrated circuits is briefly described. Future directions in ANN techniques to microwave design are suggested.

Computer-Aided Optimization of Nonlinear Microwave Circuits With the Aid of Electromagnetic Simulation

This paper discusses some modern trends in nonlinear (NL) microwave circuit optimization based on electromagnetic (EM) simulation. In order to keep the CPU time required for a typical design within acceptable limits, the number of expensive EM analyses must be kept under tight control. This may be obtained by resorting to a systematic implementation of some modern algorithmic concepts such as space mapping, domain partitioning, and neural-network modeling of the passive subnetwork and/or of its most critical parts. Although these techniques are well established for linear microwave circuit design coupled with EM analysis, their extension to the NL case is not trivial, and deserves a specialized treatment. Several examples are presented in order to give a feeling of the state-of-the-art of NL/EM optimization.

Passive parameterized time-domain macromodels for high-speed transmission-line networks

There is a significant need for efficient and accurate macromodels of components during the design of microwave circuits. Increased integration levels in microwave devices and higher signal speeds have produced the need to include effects previously neglected during circuit simulations. Accurate prediction of these effects involve solution of large systems of equations, the direct simulation of which is prohibitively CPU expensive. In this paper, an algorithm is proposed to form passive parametrized macromodels of large linear networks that match the characteristics of the original network in time, as well as other design parameters of the circuit. A novel feature of the algorithm is the ability to incorporate a set of design parameters within the reduced model. The size of the reduced models obtained using the proposed algorithm were less than 5% when compared to the original circuit. A speedup of an order of magnitude was observed for typical high-speed transmission-line networks. The algorithm is general and can be applied to other disciplines such as thermal analysis.

An improved microwave apparatus for phase behaviour measurements in lean gas condensate fluids

An apparatus based on a microwave resonant cavity has been designed and fabricated for phase behaviour measurements in lean gas condensate fluids over a wide range of temperature and pressure. The re-entrant geometry of the resonator is optimised for detecting any liquid phase present in very lean natural gases. The mode structure of the cavity has been thoroughly investigated with both analytic and finite element models. Three modes, excited by an electric field probe, are monitored when measuring a fluid contained within the resonator. The highest mode ( f vac≈6.9 GHz) is used to detect dew points while the lower modes (460 MHz and 4.3 GHz) are employed for liquid volume and dielectric constant measurements. Careful microwave circuit design ensures good signal-to-noise ratios for all modes over the operating temperature range. Simulations of the resonator containing various fluids indicate that the system is over 10 4 times more sensitive than previous microwave systems and can detect liquid volumes as small as 5×10 −6 cm 3. Dew point measurements in a gas condensate fluid support this prediction.