The influence of raindrop channels on the measured rain rate and specific rainfall attenuation in Durban (29 o 52'S, 30 o 58'E), South Africa for six rain rate values: 1.71, 4.46, 22.97, 64.66, 77.70 and 84.76 mm/hr selected from the rain events that occurred on the 27th December 2008 is analyzed in this work. Consecutive and alternate drop channels are removed to study the influence of raindrop diameters on the overall measured rain rate. The three-parameter gamma and lognormal models are used for the purpose of analysis. In general and for the two models considered, the lower channels (channels 1 to 5) do not alter significantly the overall rain rate and equally produce minimal attenuation. The critical raindrop channels contributing the larger percentage to the overall rain rate are created by D 0.771mm. The deviations of the measured and estimated rain rates are very small for all the rainfall rates selected. The estimation of the specific rain attenuation at frequency of 19.5 GHz is also discussed. The error estimation using the two models are also analysed.

Received 24 February 2005DOI:https://doi.org/10.1103/PhysRevE.71.069901©2005 American Physical Society

Experimental characterisation of various on-cl-tip capacitors and resistors on GaAs subsrates is performed, and these capacitor and resistor samples are tested Lip to 20 GHz using a Cascade 9000(TM) analytical RF probe station combined with a de-embedding technique. To accurately extract these passive device parameters, equivalent circuit models are presented for the capacitor and resistor. Excellent agreement is achieved between the measured and simulated data. The chosen circuit models depend on the layout and fabrication technology, and capacitor and resistor geometries.

A complete eigenfunction expansion of the dyadic Green's functions (DGFs) for planar, arbitrary multilayered anisotropic media using cylindrical vector wave functions is presented. These formulations are constructed based on the principle of scattering superposition. For the scattering dyadic Green's function in each layer, the scattering coefficients of TE and TM modes are determined from the boundary conditions matched at the planar interfaces. The explicit representation of the DGFs after reduction to the isotropic case agrees well with the existing results corresponding to the isotropic media. The general DGFs for multilayered anisotropic media are then reduced to those for a four-layered forest where the trunk layer is modeled as anisotropic medium. Application is further made for radio-wave propagation through forests of a four-layered geometry, whereas it is shown how these Green dyadic formulations are used in a practical way and how the field distributions due to a dipole can be obtained.

The discrete complex image method (DCIM) has been used extensively for the calculation of spatial-domain Green functions for one-layer or two-layer media. However, one difficulty in applying DCIM to general multilayered media is the lack of a reliable procedure for the extraction of surface wave components. In the paper, the spectral-domain potential Green functions for a general multilayered medium are reformulated so that their denominators are obtained in an iterative form. A two-stage root-searching procedure is proposed for seeking the roots of these denominators. The residuals associated with the surface wave poles are calculated through contour integration. Special methods for handling the branch cuts close to the surface wave poles are discussed. Numerical examples of different geometries are given to reveal the behaviour of the surface wave poles and verify the method.

A simple, robust but accurate method to extract the thermal resistance of BJT/HBT devices is proposed. It only needs the measured device DC I-V BJT/HBT devices, GaAs HBT, silicon BJT and SiGe HBTs. Compared to the measured results taken from both CW DC measurements and isothermal measurements, the extracted values using our method is in excellent agreement with the conventional method

A general formulation for the entire-domain analysis of arbitrarily oriented coupled circular loops has been presented for the first time. The Eulerian angles are used to unambiguously define the orientation of each loop with respect to another. The formulation gives a solution of the Fourier coefficients of the current on each loop after taking mutual coupling into account. The current coefficients can be used to directly obtain the input impedance and radiation characteristics of a coupled loop array. The formulation has been illustrated by applying it to two scenarios involving a pair of coplanar and coaxial loops. It is seen that the rotation of one loop about each axis could have rather different impacts on the mutual coupling between the loops. Thus the results highlight the necessity for the general formulation presented in this paper for correctly and conveniently analyzing all the various possible orientations in coupled circular loop arrays.

In this paper, we present the interlaced fast Fourier transform (FFT) method to parallelize the adaptive integral method (AIM) algorithm for the radar cross-section (RCS) computation of large scattering objects in free space. It is noted that the function obtained after convolution is smoother as compared to the original functions. Utilizing this concept, it is possible to interlace the grid current and charge sources in AIM and compute the potentials on each set of interlaced grid independently using FFT. Since the potentials on each interlaced grid are smooth functions in space, we can then interpolate the potentials to every other nodes on the original grid. The final solution of the potentials on the original grid is obtained by summing the total contributions of all the computed and interpolated potentials from every individual interlaced grid. Since the potentials of each interlaced grid can be computed independently without much communication overheads between the processes, such an algorithm is suitable for parallelizing the AIM solver to run on distributed parallel computer clusters. It is shown that the overall computation complexity of the newly proposed interlaced FFT scheme is still of O(N log N).

A ground-slot coupling technique is applied to design a novel multilayer active hybrid-ring power divider. The prototype consists of three ground slots to couple signal between circuit layers, and two single-stage HEMT amplifiers to boost the coupled signal. It is tested in C-band with 40% -3 dB bandwidth. At 5 GHz center frequency, it has 8 dB small-signal gain and 10 dBm output P1 dB.

A new and efficient scheme for adaptive integral method is presented for solving the RCS of large scattering objects. Interlaced grid system is introduced to reduce the memory requirement for the FFT calculation. The total memory resource required for FFT calculation of the new scheme is approximately 5.6 times less than the conventional AIM method. Interactions between the different grid systems are obtained by using interpolation. It is proven that the complexity of the newly proposed scheme is same as the conventional AIM.

A novel distributed small-signal HBT model at millimeter-wave frequencies is proposed. This new approach is based on an electromagnetic simulation on the extrinsic passive part of an HBT. The S-parameters of the HBT intrinsic active part are computed by using the "multi-port connection method" (K.C. Gupta et al, Computer-aided design of microwave circuits, Artech House Inc., 1981). Then, values of all the HBT intrinsic model elements can be obtained by using explicit analytical expressions. Good agreement between the measured and the simulated results has been demonstrated.

In this paper, the radiation characteristics of an open circular waveguide asymmetrically covered by a layered dielectric hemi-spherical radome are analyzed. On the waveguide opening, the dominant TE11 wave of the circular waveguide is assumed. The technique of dyadic Green’s function is applied to obtain the radiated electromagnetic fields due the circular aperture. Huygens’ equivalence principle and the image theory are utilized to simplify the problem. The translational addition theorems of spherical vector wave functions are also employed to make the mathematical representation of the radiated fields compact. Both the exact formulation in the near (radiating-field) zone and the approximate expressions in the far (Fraunhofer) zone of the radiated fields are obtained. Numerical computations are implemented to show the effects of the off-centered source feed asymmetrically covered by the hemi-spherical dielectric radome.

This paper is devoted to the calculation of the capacitance of monolithic microwave integrated-circuit (MMIC) passive components. The method of moments (MoM) is used to solve the integral equation for the electrostatic problem with the help of the spatial-domain multilayered media Green's function that can be obtained using the discrete complex image method (DCIM). As an application, the capacitance of several MMIC passive components, including capacitors and interconnects, is calculated. The numerical experiments show the efficiency and accuracy of the present method. (C) 2002 John Wiley Sons, Inc.

An analysis of the radiation Q of electrically large loop antennas is presented and its characteristics are discussed. The methodology involves the spherical mode expansion for the fields outside the loop. It is found that higher‐order modes need to be considered for a realistic estimate of the radiation Q of large loops. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 377–380, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10467

Standard approach to calculate electrostatic force and capacitance by solving first-kind integral equation will lead to ill-conditioned linear system. The condition number of resultant discretization matrix can be improved by employing the second-kind integral equation. Adaptive integral method (AIM) is applied in this paper to solve the second-kind integral equation that can be used to calculate capacitance coefficients for three-dimensional structures. The uniformity of multipole moment approximation of the second-kind integral equation is revealed theoretically and numerically; it is realized that the present approach can guarantee the accuracy of AIM for computing capacitance of any structure. The numerical experiments demonstrate that the memory requirement and computational complexity of the present method can be reduced to O(N) and O(N log N) for three-dimensional static problems, respectively. Furthermore, the employment of the second-kind integral equation significantly improves the efficiency of AIM by reducing the number of iterations for convergence.

The electric field integral equation is discretized by using the method of moments (MoM) to solve EM scattering problems such as RCS prediction, and antenna radiation with complex objects. The MoM where the complexity is O(N/sup 2/) operations has limitations on electrically large objects so fast algorithms have been proposed in recent years. The fast multipole method (FMM) can reduce the complexity to O(N/sup 1.5/) and the multilevel fast multipole algorithm (MLFMA) up to O(N log N) operations. In this paper, the RCS of a sphere is analyzed using FMM and MLFMA. Furthermore, the monostatic RCS of a double ogive is compared with measured data for the accuracy of the MLFMA.

A new parameter extraction methodology — local ratio evaluation is presented which is well suitable for converting one model to another. An example is given for VBIC model extraction by going through SPICE Gummel–Poon (SGP) model. It is based on the fact that VBIC model is a direct enhancement and extension of SGP model. First, the standard SGP model is extracted in the standard way. Next, SGP model parameters are directly converted to those in VBIC model. Local modifications are subsequently carried out for those parameters that are affected by different equations used in the two models. Finally, new model parameters for enhanced modeling features are introduced by evaluating the difference between measurement and simulation.

The self- and mutual inductance of a spiral will change significantly with an increase in frequency due to the current redistribution on the metal trace. This phenomenon comes from the skin effect and the simultaneous eddy current. The basic formulae for inductance calculation are thus studied and further improved in this paper. Theories are tested with measured data on sample inductors fabricated on silicon substrate.

The direct integral equation is formulated for describing the current on the multiple perfectly conducting strips in cylindrical geometries for an E-polarization plane wave of normal incidence. By using the Galerkin's method, the surface currents on the conducting strips are expanded in the form of a series of Chebyshev polynomials of the first kind, while the unknown expanding coefficients are solved by a set of matrix equations of finite order with a fast convergence rate and a high accuracy. Furthermore, numerical results are presented to demonstrate the variation of the penetrated near-zone field in the presence of one, two, three, four and six cylindrical apertures, and the hybrid effects of both aperture number and aperture angular widths on the penetrated fields are investigated in detail.

Based on Kuhn's earlier study on current crowding, an improved expression incorporating the skin effect for the prediction of series resistance in spiral inductor modeling has been derived. A modified model for the spiral inductor, which accounts for the eddy-current effect, is thus proposed. Relatively good agreements between the measured data and the results generated from the model are obtained.