Passive Microwave Devices Research Articles

Two-Level Hierarchical FEM Method for Modeling Passive Microwave Devices

In recent years multigrid methods have been proven to be very efficient for solving large systems of linear equations resulting from the discretization of positive definite differential equations by either the finite difference method or theh-version of the finite element method. In this paper an iterative method of the multiple level type is proposed for solving systems of algebraic equations which arise from thep-version of the finite element analysis applied to indefinite problems. A two-levelV-cycle algorithm has been implemented and studied with a Gauss–Seidel iterative scheme used as a smoother. The convergence of the method has been investigated, and numerical results for a number of numerical examples are presented.

Multiresolution analysis similar to the FDTD method-derivation and application

A three-dimensional (3-D) multiresolution analysis procedure similar to the finite-difference time-domain (FDTD) method is derived using a complete set of three-dimensional orthonormal bases of Haar scaling and wavelet functions. The expansion of the electric and the magnetic fields in these basis functions leads to the time iterative difference approximation of Maxwell's equations that is similar to the FDTD method. This technique effectively models realistic microwave passive components by virtue of its multiresolution property; the computational time is reduced approximately by half compared to the FDTD method. The proposed technique is validated by analyzing several 3-D rectangular resonators with inhomogeneous dielectric loading. It is also applied to the analyses of microwave passive devices with open boundaries such as microstrip low-pass filters and spiral inductors to extract their S-parameters and field distributions. The results of the proposed technique agree well with those of the traditional FDTD method.

Application of the AWE method with the 3-D TVFEM to model spectral responses of passive microwave components

This paper describes an efficient algorithm to evaluate the spectral response of passive microwave devices. The method is based on the combination of the tangential-vector finite-element method (TVFEM) for modeling three-dimensional (3-D) microwave passive components and the asymptotic waveform evaluation (AWE) technique for efficiently computing the spectral responses. Unlike previous AWE approaches, which use direct matrix factorization to solve for the moments, we employ a preconditioned conjugate gradient (PCG) method. It is observed that the iterative PCG solver converges much faster by solving only the additional components of the higher moments outside the span of previous moments. Moreover, this paper discusses the effect of shifting the expansion frequency from the real frequency axis to the lower half of the complex frequency plane. Through several numerical examples, a waveguide with an obstacle inside, mitered 90/spl deg/ E- and H-plane waveguide bend, microstrip low-pass filter, and microstrip patch antenna, we show that shifting reduces the pollution due to dominant resonant modes and, consequently, results in a much wider convergence range for the moment-matching AWE technique.

Progress, properties and prospects of passive high-temperature superconductive microwave devices in Europe

The technology of high-temperature superconductors has become mature. Various methods to analyse and optimize the temperature and microwave field dependent surface impedance have been developed. Promising applications of passive microwave devices have been identified between 0.01 and 10 GHz. This progress profits from improved design and simulation tools, aimed at miniaturizing the circuits at optimum performance and integrating them into realistic systems. Important facets of these developments are sketched in terms of their physical basis and illustrated with selected examples of filters, stable oscillators and MRI antennas.

Effect of outgrowths on the surface microwave resistance of YBa 2Cu 3O 7 thin films

The pulsed laser deposited (PLD) YBa 2Cu 3O 7(YBCO) thin films with surface microwave resistance R s equals to 250 μΏ, 7.565 mΩ and 98 mΩ (measured at 10 GHz and 77K) were studied under the transmission electron microscope (TEM). It was found that the non-superconducting large outgrowths increased the R s exceedingly, and the occurrence of large angle grain boundaries enhanced the R s additionally. For planar passive microwave device application, some steps must be taken during the PLD process to prevent the development of large non-superconducting outgrowths.

Microstructural and microwave characterisation of low temperature processed Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ thin films

Tl/sub 2/Ba/sub 2/Ca/sub 1/Cu/sub 2/O/sub x/ thin films on LaAlO/sub 3/ with excellent alignment suitable for the fabrication of passive microwave devices operating at 77 K are fabricated using an ex-situ anneal step in argon atmospheres at temperatures of 720-740/spl deg/C. In order to understand the factors influencing their microwave and transport properties, the microstructure and compositions of the films have been examined by TEM, HREM and SEM and correlated with R/sub s/ measurements obtained by the partial-end-wall-replacement technique.

Metal‐organic CVD of the high‐Tc superconductor YBa2Cu3O7−δ

AbstractThe great bulk of CVD effort on superconducting oxide materials has concerned MOCVD of the 93 K superconductor YBa2Cu3O7−δ. Most current work involves growth of triaxially oriented YBa2Cu3O7−δ films a few hundred nanometers in thickness on monocrystalline metal oxide substrates at 650–8500C. Optimized MOCVD processes now produce YBa2Cu3O7−δ films with crystallographic quality and electrical properties comparable to the best films prepared by physical vapor deposition techniques, and offer especially attractive opportunities for large‐area growth. Nevertheless, the metal δ‐diketonate precursors used in YBa2Cu3O7−δ MOCVD have limited volatility and other drawbacks, which have motivated extensive background research on barium sources in particular. Non‐traditional methods for delivering precursors to the deposition zone of a reactor, such as aerosol injection and flash vaporization techniques, have also been developed in response to these problems. A diverse range of YBa2Cu3O7−δ MOCVD processes, some involving plasma‐ or photo‐assisted deposition, are in current use. These have been optimized by largely empirical means, although thermodynamic analyses and mechanistic studies offer the prospect of controlling film deposition on a more scientific basis. Unique features of MOCVD in comparison with physical vapor deposition methods include the possibility of controlling film orientation through photochemical effects, and exploitation of the high surface mobility of adsorbed molecular precursors to grow YBa2Cu3O7−δ below 600°C. With reference to potential uses for MOCVD films, near‐term applications in passive microwave devices are considered in greatest detail.

Application of High Temperature Superconductors in Passive Microwave Devices

The front end of a microwave communications system is assembled from circuit elements comprising antennae, local oscillator, mixer and filters. Interconnection is by transmission line, into which delay may be incorporated. All of these components can, with advantage, be implemented in superconducting material. Superconductors, when operating below their cross-over frequency, have values of surface resistance lower than those for normal metals such as copper and silver. This results in lower insertion loss for microwave components, allowing the design of smaller, more compact, yet at the same time more complicated, devices. The non-dispersive nature of superconductors can also be an advantage in enabling very high bandwidth signal processing. High temperature superconductors (HTS) allow operating temperatures in the liquid nitrogen range, not too far below the ambient temperature in many communications satellites. The Oxford microwave programme has concentrated on the implementation of all of the above devices in thin-film HTS, mainly Tl-2212, on a variety of substrates. The film fabrication, and performance of delay lines, antenna-mixers, resonators, filters and a voltage-controlled oscillator, are described.

Microwave ceramics for resonators and filters

High-permittivity ceramics make it possible to noticeably miniaturize passive microwave devices. These ceramics must fulfil the requirements of high permittivity, very low dielectric losses and an extremely low temperature dependence of permittivity to yield temperature-stable resonators. Recent progress has been made in understanding the physics of microwave ceramics, particularly the property-structure relationship, in developing new materials with higher permittivity, better temperature stability and considerably lower sintering temperature, and in making co-fired multilayer devices possible, as well as in developing new microwave devices such as oscillators, antennas and band-pass filters.

Epitaxial TI-Ba-Ca-Cu-O films—preparation, properties and applications

TIBaCaCuO (TBCCO) belongs to a class of HTSC materials showing very high critical temperatures up to 127 K and a strong anisotropy of the superconducting properties. This is caused by a layered lattice structure responsible especially for the observed intrinsic Josephson effect. These properties are especially interesting for technological applications like passive microwave devices, microwave oscillators and mixers, voltage standards and switches. High quality epitaxial TBCCO films necessary for these applications are prepared by recrystallization of a TI free precursor film in a TIO x containing atmosphere at temperatures between 800 and 880 °C.

Side-selective and non-destructive determination of the critical current density of double-sided superconducting thin films

A method is proposed for the side-selective and non-destructive determination of the critical current density ( j c) of high- T c superconducting (HTSC) thin films deposited on both sides of a thin wafer. The method makes use of the alteration of induced voltage in a coil by the superconducting transition in the HTSC thin film. This voltage alteration is measured in dependence on AC current in the coil. In order to obtain the value of the critical current density, the geometry of the induced current density distribution in the HTSC thin film, and from it the induced voltage in the coil, were calculated for T < T c (full superconducting state of the film) as a function of the distance of film to coil. The finite element approach is used for the calculations. This procedure is applied to the semiautomatic routine characterization of j c of double-sided 3-inch diameter HTSC thin films, which are used for optimization of passive microwave devices.

Thin film growth by the pulsed laser assisted deposition technique

Pulsed laser-assisted deposition (PLD) has recently emerged as a most promising film growth technique, at least for basic research, as this has been best demonstrated for highTc superconducting oxides and YBa2Cu3O7−x in particular. This article briefly outlines the specific features of this technique and its potential, illustrated by the example of the growth of YBa2Cu3O7−x thin films aimed at the preparation of microwave passive devices. The perspectives of development of PLD and its ability to become an industrial process are discussed.

Subpicosecond imaging system based on electrooptic effect

This work presents an ultrafast, interferometric electrooptic sampling system that uses a two-dimensional detector array to image the electric field present on a device. Spatial and temporal resolution are comparable to conventional "point" electrooptic sampling systems, <5 /spl mu/m and <1 ps, respectively. Voltage sensitivity is expected to be 270 mV and may achieve less than 4 mV with sensor cooling and a more effective electrooptic material. A coplanar silicon structure with 10-/spl mu/m feature size would have a field sensitivity of 27 kV/m and 400 V/m, respectively. This compares favorably with the reported sensitivity of 10/sup 5/ V/m for prior imagers and 10 V/m for point samplers. Applications for an E-field "imager" include characterization of field distributions in planar passive microwave devices, multiport analog and digital devices, and studying device and materials physics.

Microwave compatible YBa2Cu3O7−x films on ferrimagnetic garnet substrates

High quality epitaxial YBa2Cu3O7−x (YBCO) thin films have been deposited onto ferrimagnetic yttrium iron garnet (100) substrates using a double buffer layer lattice engineering scheme. The YBCO films are c-axis oriented and show superconductive transition temperatures of 88–89 K with transition widths ≤0.5 K. The films also exhibited Jc’s of 2.7×106 A/cm2 in zero field and 1.1 ×106 A/cm2 in 2000 G at 77 K. Dielectric resonator measurements indicated unloaded Q values of 29 000 at 77 K and 24 GHz for unpatterned films. These values correspond to a surface resistance (RS) of 500 μΩ at 77 K, 10 GHz, which is the lowest obtained to date for a YBCO film on a ferrimagnetic substrate. Such films could be used for fabricating miniature-high-temperature superconducting microwave elements such as nonreciprocal and passive microwave devices, making possible, their integration on a single ferrimagnetic wafer.

Inductive measurements of λ(T) of bare YBCO films and the proximity effect in YBCO/normal metal bilayers

Inductive measurements were performed on YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) films and superconducting/normal metal bilayers using Au, PrBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and (Y/sub 0.4/Pr/sub 0.6/)Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// as normal material in order to investigate their screening properties between T/sub c/ and 2.2 K. YBCO films were prepared using high pressure dc and hollow cathode sputtering, laser ablation, MOCVD and reactive thermal coevaporation and the penetration depth, /spl lambda/, and the c-axis lattice parameter measured. Comparison of the temperature dependence of the superfluid density, n/sub s/(T), for the YBCO films showed a significant difference in the shape of n/sub s/(T) depending on the deposition method used. This could have implications for preparing stable passive microwave devices. We have also demonstrate that SN-bilayers, using YBCO as the superconductor, exhibit an enhanced screening over the entire temperature range compared with bare YBCO films. >

FDTD method coupled with FFT: A generalization to open cylindrical devices

The extension of a numerical method, based on an FDTD algorithm coupled with FFT, is presented. It can be widely applied to the analysis of axially symmetric passive microwave devices. By incorporating the proper radiation conditions in the algorithm, its capacity to deal with the study of open systems is shown; this allows the determination of its quality factor, as well as the resonant frequency and the spatial distribution of the modes. On the other hand, the proper performance of the technique has been verified (stability of the algorithm, accuracy of results) for modes of high angular dependence. >

A comparison of the magnetic and electric field formulations and their postprocessing functionals in the finite element analysis of passive microwave devices

Using a waveguide T junction and an orthogonal mode transducer as illustrative examples, the admittance matrix elements for a passive microwave device are computed by three‐dimensional finite element analysis from the magnetic field formulation having natural Neumann boundary conditions and from the electric field formulation having enforced Dirichlet boundary conditions. The results from these two formulations are compared using both linear and bilinear postprocessing functionals.

Surface resistance and magnetic penetration depth of structured YBa2Cu3O7-δ-thin films

Abstract We have determined the high-frequency properties of epitaxial YBa2Cu3O7−δ-thin films that are crucial for applications of this high-temperature superconducting material for passive microwave devices. From the quality factor and resonance frequency of integrated coplanar halfwave resonators the surface resistance and the magnetic penetration depth as a function of temperature and rf-power are deduced. Notably this quantities can be obtained for individual thin films and so their microwave performance can comprehensively be characterized. This planar resonator based method not only offers high sensitivity within a wide frequency range but also the ease of integrating resonators as a small-sized test structure with loss mechanisms that would also be present in actual passive devices. As the interpretation of the measured data needs full knowledge of the electric and magnetic field distribution in the cross-section of the resonator line a theoretical field wave analysis is performed employing a “partial wave synthesis” (mode-matching method). Any ambiguity in the determination of the temperature dependence of the magnetic penetration depth is removed by the simultanuous evaluation of pairs of resonator structures of different width. This novel approach yields the magnetic penetration depth as a function of temperature without assuming a specific model. Knowledge of the absolute value of the penetrationg depth also allows the determination of the surface resistance with great accuracy as it is shown in comparison with other methods. Power dependent measurements finally give information about weak-links in the epitaxial films possibly associated with grain- and twin boundaries.

The high temperature superconductivity space experiment (HTSE)

Abstract The High Temperature Superconductivity Space Experiment (HTSSE) program, initiated by the Naval Research Laboratory (NRL) in 1988, is described. The HTSSE program focuses high temperature superconductor (HTS) technology applications on space systems. The program phases, goals and objectives are discussed. The devices developed for this program and their suppliers are enumerated. For HTSSE-I, 15 space-qualified, passive microwave devices were integrated onto a cryogenic cold bus as an experimental payload on a DoD spacecraft. The experiment payload and scientific data measurements systems, designed, developed, and built by NRL, are described.

High-temperature superconducting microwave devices: Fundamental issues in materials, physics, and engineering

High-T c superconductivity has generated a great deal of interest because of the challenges it presents in the fields of material science, condensed matter physics, and electrical engineering, and because of the potential applications which may result from these research efforts. Thin-film passive microwave components may become the first high-temperature superconducting (HTS) devices available for widespread use and commercialization. In this article, we review aspects of material science, physics, and engineering which directly impact high-T c superconducting microwave devices and discuss issues which determine the performance of these devices. Methods of growing HTS thin films on large-area substrates, techniques for fabricating single-level HTS passive microwave components, and the relevant properties of high-T c superconducting films are discussed, with a focus on thin films of the HTS material YBa2Cu3O7−δ. Several known mechanisms for microwave loss in both the superconductor and the dielectric substrate are presented. An overview of the general classes of superconducting passive microwave devices is given, and representative microwave devices which have been recently demonstrated are described in detail. Examples of a select few HTS active microwave components are also presented. Potential microwave applications are illustrated with comparisons to current technology.