Hatsuo Yabe

Complete calibration of a six-port reflectometer with one sliding load and one short

A novel method is presented for calibrating a six-port reflectometer using only one sliding load of unknown reflection coefficient and one short as a calibration standard. The calibration procedure is derived from the fact that the Fourier coefficients of the periodic port power ratios corresponding to the sliding load positions are closely related to the six-port system parameters. The unknown reflection coefficient of the sliding load as well as the eleven system parameters at each frequency is determined in the procedure. The validity and utility of the proposed method are confirmed by experiments over the frequency range 8.5-12.0 GHz in 0.5 GHz steps with a rectangular waveguide sliding load and a polished metal standard short. >

Numerical dispersion relation for FDTD method in general curvilinear coordinates

The numerical dispersion relation (NDR) of the finite-difference time-domain method in general curvilinear coordinates (FDTD-GCC) is discussed for a two-dimensional (2-D) uniformly skewed mesh. The analysis shows that the average scheme, which is being used in the FDTD-GCC method, causes an additional numerical dispersion error. When this dispersion error is considered, the FDTD-GCC method holds the same NDR as that of the FDTD discrete surface integral (FDTD-DSI) method. It also indicates that the stable range of the FDTD-GCC method, with respect to the skewing angle in the 2-D case, is narrowed due to the average scheme.

Six-port self-calibration based on active loads synthesis

An automatic method for self-calibrating six-port reflectometers is reported in this paper. It is based on the use of an active impedance synthesis system. This self-calibration method allows a completely autonomous operation, reduces measurement errors caused by the frequent connecting and disconnecting of calibration standards, and is suitable for low and high frequencies, where sliding shorts are difficult to manufacture. In addition, it simplifies operation of six-port reflectometers to nonspecialized users. The experimented impedance synthesis presented relies on an in-phase and quadrature vector modulator, and the entire system is computer controlled.

Accurate modeling for drain breakdown current of GaAs MESFET's

Extensive measurements of a drain breakdown current as a function of device bias are reported in this paper. To represent the measured drain breakdown currents accurately, a new modeling function and an equivalent circuit controlled by two voltages are proposed. This model, when integrated into a large-signal analysis program, improves the accuracy of the simulation.

Six-port based wave-correlator

A novel method for calibrating six-port based wave-correlators is reported in this paper. The calibration procedure uses only one phase shifter and offers simple formulas for determining the calibration parameters. Some experiments using a new six-port junction for the wave-correlator at X-band frequency was carried out and the results confirmed the validity and accuracy of the proposed method.

A large-signal switching MESFET model for intermodulation distortion analysis

This paper describes an improved large-signal model for predicting an intermodulation distortion (IMD) power characteristic of MESFETs in switching applications. The model is capable of modeling the voltage-dependent drain current and its derivatives, including gate-source and gate-drain capacitors. The drain current and its derivatives are described by a function of a voltage-dependent drain conductance. The model parameters are extracted from a measured drain conductance versus gate voltage characteristic of a MESFET. This paper also presents a new fully symmetric equivalent circuit for switching MESFETs. The IMD power characteristics calculated with the use of the proposed method are compared with experimental data taken from a monolithic microwave integrated circuit single-pole double-throw switch. Good agreements over the large gate voltages and input power levels are observed.

Solution of scattering from conducting cylinders using an iterative method

Open-region problems of scattering by conducting cylinders are solved employing finite element method (FEM). The radiation condition for the open-region problem is enforced by the field integral equation solution approach using Greens function through an iterative procedure. At each iteration cycle, the induced currents on the scatterer are evaluated and their scattered fields at the terminating surface are calculated by the field integral equation. Using this iterative procedure, the computational domain ran be terminated very closely to the scatterer, yet keeping the sparseness of the FEM matrices. This iterative method is applied for several TE scattering problems of conducting cylinders. The numerical results are presented and compared with the results of other methods to illustrate the applicability and accuracy of this method.

A hybrid finite element solution of electromagnetic scattering in open region

A novel formulation of finite element-integral equation method is proposed for electromagnetic scattering problem in open region. This approach allows for a surface terminated very closely to the scatterer, resulting in decrease of the resultant matrix size. Moreover, by employing a new integral approach, the numerical efficiency is enhanced. Solutions for scattering of some two-dimensional conducting cylinders by this method are obtained and compared with the solutions of other methods and/or measured data.