A recursive Green's function method for boundary integral analysisof inhomogeneous domains

The recursive Green's function method (RGFM) for computation of fields scattered by two-dimensional (2-D) inhomogeneous dielectric bodies is presented. The algorithm efficiently constructs the Green's function for the inhomogeneous region by recursively combining known Green's functions from smaller subdomains. The fields on the scatterer surface are then computed using a boundary integral formulation. Proper implementation of the RGFM results in computational and storage complexities which scale as N^1.5 and N, respectively, where N is the total number of discrete cells in a domain. Comparisons of results obtained using the RGFM with those computed from moment method and exact solutions show the efficiency and accuracy of the technique     

Implicit 3-D dyadic Green's function using self-adjoint operatorsfor inhomogeneous planar ferrite circulator with vertically layeredexternal material employing mode-matching

Self-adjoint operators are found for the differential equations describing the z-dependent field variation in the medium external to the ferrite microstrip circulator puck. The external medium is, in general, inhomogeneously layered, consisting of media with permittivity properties, magnetic properties, or both. Eigenvalue equations characterizing the radially sectioned medium outside the puck are found, as are the eigenvectors. When the z-dependent parts are multiplied with the radial and azimuthal dependences, the complete three-dimensional (3-D) field expressions are determined. Source-constraint equations (representing microstrip lines) driving the circulator are then combined with the mode-matching technique to obtain in direct space, implicit dyadic Green's function elements. Mode orthogonality is employed to encourage sparsity in matrix system development where appropriate or convenient. The implicit Green's function is particularly useful because field information and s-parameters may be found in real space, completely avoiding typical inverse transformations     

The circular homogeneous-ferrite microwave circulator - an asymptotic Green's function and impedance analysis

A detailed analysis of the circular, homogeneous ferrite microwave circulator is provided. Particular emphasis is on the circulator's Green's function and the impact of the asymptotic term within the Green's function on convergence, data quality, and design methodology. The asymptotic term is shown to be logarithmic, which suggests that the Green's function is weakly singular when the source and observation points occupy the same location. With the Green's function properly understood, two techniques - one analytical and one numerical - are then offered to integrate that function in order to obtain Z-parameter data and, subsequently, S-parameter data. Data are provided to show rapid convergence of all parameters of interest. A small coupling angle approximation is then given for the Z-parameters and, from that approximation, a first-order design equation is obtained that relates the coupling angle to circulator radius. A circulator design example is presented and compared to a design associated with the Wu and Rosenbaum method; the comparison substantiates the small coupling angle approximation and design formula.     

A new type of latching switchable ferrite junction circulator

The letter describes a new type of extremely compact latching switchable ferrite junction circulator that is well suited for application requiring fast (approximately two microseconds), low-energy (tens of microjoules in the microwave region) switching. The letter presents results of an approximate theory and initial experimental data.     

A new Ka-band microstrip Y-junction circulator with a ferrite sphere

A novel microstrip circulator with a magnetized ferrite sphere is proposed for millimetre wave communications. A three-dimensional finite difference time-domain (FDTD) approach for the analysis of this ferrite sphere-based microstrip circulator is presented. The electromagnetic fields inside the ferrite junction are calculated by using special updating equations derived from the equation of motion of the magnetization vector and Maxwell's curl equations in consistency. Frequency-dependent insertion loss, isolation and reflection loss of circulator are calculated over a wide band of frequencies with a single FDTD run. Experimental results at the Ka-band are presented and compared with theoretical simulation. Good agreement is found between them.     

Broad-band circulator models for active microwave circuit analysis

A general method is presented for determining a broad-band equivalent circuit of a lossy, nonideal circulator from the scattering parameters over the frequency range of interest. The equivalent circuit has application to the design and analysis of circulator-coupled circuits such as amplifiers and oscillators. The method is applied to two different circulator forms, in coaxial line and waveguide, to show the close agreement to measured performance that can be attained by the method in practice.     

A novel waveguide Y-junction circulator with a ferrite sphere formillimeter waves

A novel waveguide Y-junction circulator with a ferrite sphere is developed for uses at millimeter-wave frequencies. Sphere is preferred because the production cost of a pertinent circulator is lower. Performance of the new circulator is comparable to the conventional one with a cylindrical ferrite. A simple formula is derived for determining the center frequency of a circulator. Good agreement between analytical results and measurements is observed. An extremely fast method is developed to analyze the circulator. Various properties of the circulator can be predicted with reasonable accuracy     

A generation of microwave ferrite devices

The development of microwave ferrite materials and devices over the last thirty years is traced. The status of materials, devices, and theoretical understanding prevalent in the mid-1950s is first reviewed. Developments in materials engineering of garnets and lithium ferrites in the 1960s and 1970s are described, along with the evolution of circulators and phase shifters. Current levels of performance achievable in circulators and phase shifters are described, and future challenges and opportunities are discussed     

Application of successive approximation method to the computationof the Green's function in axisymmetric inhomogeneous media

The successive approximation method (SAM) is applied to the computation of the Green's function in axisymmetric inhomogeneous media, SAM is implemented by using an iterative procedure that produces a series, and the series is proven to be a Taylor series. The condition of the convergence is derived from the theory of functions of several complex variables. In each iteration, the Fourier-Hankel transform and its inverse are applied to the approximation of some order of the Green's function and the result is the approximation one order higher than the original. Fast Fourier-Hankel transform (FFHT) is employed to speed up the computation, and thereby, an algorithm SAM-FFHT is formulated     

A comparison of acceleration procedures for the two-dimensionalperiodic Green's function

Alternate acceleration procedures are evaluated for the two-dimensional free-space periodic Green's function. Two of these techniques yield exponential convergence rates and are preferable if high accuracies are required. Numerical aspects of these procedures are described     

A hybrid (finite difference-surface Green's function) method forcomputing transmission losses in an inhomogeneous atmosphere overirregular terrain

A standard parabolic equation (SPE) is used to approximate the Helmholtz equation for electromagnetic propagation in an inhomogeneous atmosphere. An implicit finite difference (IFD) scheme to solve the SPE is applied between the irregularly shaped ground and an altitude z =z_h, below which all inhomogeneities of the medium are assumed localized. The boundary condition at z=z _h is obtained by matching the IFD solution to a surface Green's function (SGF) solution within the uniform region above z =z_h. For ground slopes above about 1°, the IFD implementation of the impedance boundary condition at the ground is shown to maintain the validity of the approximation only for vertically polarized waves. Predictions using this hybrid finite difference (FD)-SGF method agree well with results obtained using other computational methods     

Thin ferrite devices for microwave integrated circuits

This paper is intended as a review of developments which allow ferrite materials in a planar geometry to be used in the realization of magnetic devices which are compatible in form with other microwave integrated circuits. These devices include phase shifters (reciprocal and nonreciprocal), latching circulators, isolators, and phase and amplitude modulators. The application of some of these devices is demonstrated in the form of electronically steerable array antennas.     

A new wave approach for signal and noise modelling of microwave/mm-wave FET based on Green's function concept

Based on the active coupled line concept, a novel approach for calculating the noise performance of microwave/mm-wave field-effect transistors (FETs) is proposed. The voltage and current Green's functions are introduced to determine the correlation matrix of the FET. Some results using this approach have been presented for a microwave MESFET.     

Numerical solution of Green's function of potential field ofeccentric point source in axisymmetric inhomogeneous media

An analysis has been performed for a borehole direct-current resistivity boundary value problem in axisymmetric inhomogeneous media. In order to solve the problem of eccentric excitative sources in actual electrical logging, the authors apply an efficient numerical mode matching (NMM) theory to present Green's function of the potential field of an eccentric point source. The basic and higher order modes are described by applying numerical eigenmode expansion, and the local reflection and transmission matrices are used to match the boundary condition of potential field on every planar layer. Some typical examples are calculated and analyzed. The first example is concerned with a 16-in normal tool, which results are in excellent agreement with the data published previously in references. The second example about the micro laterolog-3 point electrodes is calculated to display a range of different eccentric effects. Some interesting and useful results are obtained     

A compact, monolithic microwave demodulator-modulator for 64-QAMdigital radio links

The design, fabrication and performance of a monolithic microwave direct modulation modulator-demodulator are presented. The subsystem is designed to work in a 64-QAM digital radio link. At this level of modulation, it is necessary to have some possibilities of phase and amplitude trimming by external voltages to achieve sufficient accuracy. The circuit includes elementary functions such as quadrature and in-phase splitters, and circuits giving the possibility to adjust phases and amplitudes for 64 QAM and higher level modulation. The design is such that the same chip can be used either as a direct demodulator or as a modulator. This complex circuit of small dimensions (2.7 mm×3.65 mm) exhibits good demodulation and modulation performances. The overall performances of this monolithic circuit are achieved without degrading the DC yield     

一种紧凑型宽带高效微波整流电路

运用终端短路微带线实现无输入低通滤波器的微波整流电路。该结构串联于整流二极管与地之间,抵消了整流二极管在基频时的容性阻抗,并抑制了谐波电流,因此该整流电路移除了输入低通滤波器和匹配电路,结构和尺寸更加紧凑。理论分析和实验测试表明,本设计在较大输入功率、频率范围内实现了高效整流。实验结果表明,在输入功率12~24 dBm和频率1.48~ 2.02 GHz范围内,整流效率超过70%。当输入功率为21.8 dBm,频率为1.8 GHz时,最高整流效率为83.3%。电路尺寸优于15 mm×20 mm。     

一种915MHz紧凑型肖特基二极管微波整流电路

为了提高射频标签(RFID)中基于肖特基二极管微波整流电路的效率,采用微带结构实现了一种915 MHz紧凑型的整流电路。该微波整流电路具有质量轻、尺寸小、整流输入功率动态范围大等特点,设计的仿真和实验结果显示:输入微波功率在13 dBm~22 dBm的情况下,均获得了高于60%的整流效率。通过完善改进电路,可以进一步提高整流的效率,并应用于微波无线能量传输或大型RFID的微波整流天线。     

A simplified expression of the dyadic Green's function for a conducting half-sheet

Simple analytical expressions of the dyadic Green's function for a conducting half-sheet have been derived. These expressions involve some finite integrals which can be easily calculated by a digital computer and are much simpler than those involving the vector mode function expansion. Input impedances of monopole antennas on and near an edge of a conducting half-sheet and the impedance of a notch antenna have been obtained, and the usefulness of these simplified expressions has been proved. The present results can be applied to check the limits of the applicability of the asymptotic theories, e.g., the geometrical theory of diffraction (GTD) and the uniform asymptotic theory of diffraction (UAT).     

Dielectric Green's function for parameters of microstrip

The program generates a data file of the dielectric Green's function in format suitable as input to the program which has been previously deposited in the IEE Program Library for computation of the parameters of microstrip. With the two programs, tables of microstrip parameters can be generated for any value of substrate permittivity. This program also provides the option of including the effect of an upper ground plane. The calculation embodies the quasistatic approximation.     

The dyadic Green's function for the cylindrical chirostrip antenna

Using the eigenfunction expansion of dyadic Green's function in unbounded chiral medium, and the method of scattering superposition, the expressions of dyadic Green's function for the one and two—layer cylindrical chirostrip antennas are derived, when the field sources are placed in any layer of cylindrical chirostrip antenna. Also, using the method of saddle point integration, the asymptotic expression of dyadic Green's function for the wraparound chirostrip antenna is obtained. The results can be directly used to analyse the radiation characteristics of cylindrical chirostrip dipolc antenna, et al.