Roberto Sorrentino

Computer-aided design of beam forming networks for modern satellite antennas

Multicontoured and reconfigurable beam spacecraft antennas rely on sophisticated beam forming networks (BFNs). Accurate and efficient CAD tools are required to meet the stringent requirements on the power division, while avoiding any tuning or trimming of the BFN. Advanced field theoretical techniques for the analysis and optimization of microwave BFNs realized in both waveguide and square coaxial cable technologies are presented. Such advances consist in new segmentation techniques of the microwave components associated with efficient mode-matching formulations for the modeling of isolated as well as coupled discontinuities. The achieved numerical efficiency allows sophisticated synthesis procedures, based on repeated full-wave analysis in wide frequency bands, to be performed on small machines such as a 386 PC. The design tools developed have been widely validated through a comprehensive test campaign. >

Accurate and efficient circuit simulation with lumped-element FDTD technique

A three-dimensional (3-D) implementation of the lumped-element finite-difference time-domain (FDTD) algorithm has been carried out. To accomplish proper description of device dynamic responses, the code incorporates accurate models of lumped bipolar devices, including nonlinear capacitances associated with pn and Schottky junctions. The nonlinear system arising from discretized lumped-element equations is solved by means of an iterative Newton-Raphson algorithm, the convergence properties of which are sensitive to the value of the simulation time step. The computational efficiency of the algorithm (as well as its robustness) has significantly been enhanced by introducing an adaptive time-step algorithm, which dynamically adjusts the time-step itself to ensure convergence during the simulation. Several simulation examples are compared with conventional analysis techniques and demonstrate the algorithm reliability as well as its increased efficiency.

Modeling and characterization of the bonding-wire interconnection

In this paper, the bonding-wire interconnection has been studied from the points of view of its modeling and electrical characterization. Both singleand double-wire structures have been considered, the latter under the assumption of parallel wires. Two electrical models of the bonding wire are discussed. First, the finite-difference time-domain (FDTD) method is proposed for the rigorous analysis of such structures. This method uses a suitable discretization technique, which accounts for the wire curvature by means of a polygonal approximation. A quasi-static model of the bonding wire, suitable for commercial microwave computer-aided-design tools is then proposed. This model is based on the representation of the structure with four sections of a uniform transmission line and the model parameters are evaluated analytically from the dimensions of the interconnection. Accuracy and applicability of the quasi-static model have been assessed by analyzing several test structures, the reference results being obtained with the FDTD method. Finally, the quasi-static model has been used to provide an extensive electrical characterization of the bonding wire versus its main geometrical parameters. This characterization is given in terms of an equivalent series inductance and two equivalent shunt capacitances forming a /spl pi/ low-pass network. This representation is particularly useful in the matching of the bonding-wire discontinuity.

Electromagnetic Energy Harvesting and Wireless Power Transmission: A Unified Approach

In this paper, a rigorous procedure for the circuit-level analysis and design of entire systems, developed to provide power wirelessly, is presented. A unified theoretical approach is first introduced, based on a two-port-equivalent circuit representation, to describe the wireless power transfer link when the transmitter and the receiver are either in the near-field or in the far-field region reciprocally. This approach allows one to compute in a straightforward manner the system figure of merit, namely the power transfer efficiency. Specific guidelines for the two configurations are then intensively discussed together with the adopted software tools based on the combination of full-wave analysis and nonlinear harmonic balance techniques. Several practical examples based on this design procedure are presented, demonstrating predicted and experimental behavior of unconventional devices for both near-field and far-field power transfer usage.

A new algorithm for the incorporation of arbitrary linear lumped networks into FDTD simulators

The inclusion of lumped elements, both linear and nonlinear, into the finite-difference time-domain (FDTD) algorithm has been recently made possible by the introduction of the lumped element FDTD method. Such a method, however, cannot efficiently and accurately account for two-terminal networks made of several lumped elements, arbitrarily connected together. This limitation can be removed as proposed in this paper by describing the network in terms of its impedance in the Laplace domain and by using appropriate digital signal-processing methodologies to fit the resulting description to Yees algorithm. The resulting difference equations allow an arbitrary two-terminal network to be inserted into one FDTD cell, preserving the full explicit nature of the conventional FDTD scheme and requiring a minimum number of additional storage variables. The new approach has been validated by comparison with the exact solution of a parallel-plate waveguide loaded with lumped networks in the transverse plane.

A technique for the fullwave automatic synthesis of waveguide components: application to fixed phase shifters

An efficient computer synthesis technique for waveguide components, based on rigorous field-theoretical models, has been developed. A computer code has been specifically set up for the automatic design of fixed phase shifters in rectangular waveguide technology. Only the electrical specifications are required to generate, normally in 15 to 20 min on a 386/16-MHz IBM PC, the geometrical structure of the components. The agreement with the experiments is shown to be so accurate as to avoid any tuning of the circuits realized. The efficiency and accuracy of the code is based on (i) a suitable segmentation technique of the microwave structure to obtain a very simple but rigorous network model; (ii) the efficient representation of the modal series for the electromagnetic fields; and (iii) a synthesis procedure based on a simplified model to obtain a good initial guess for the final full-wave optimization routine. >

New efficient full wave optimization of microwave circuits by the adjoint network method

For the first time, the adjoint network method, which is well known in the area of circuit theory, is applied directly to the full wave model of microwave circuits. In this manner, the gradient of the objective function, which depends on all geometrical parameters of the microwave structure, is computed by just one full wave analysis, thus reducing dramatically the computational effort required by the optimization.<<ETX>>

Method of Analysis and Filtering Properties of Microwave Planar Networks

A method of analysis of planar microwave structures, based on a field expansion in term of resonant modes, is presented. A first advantage of the method consists in the possibility of taking into account fringe effects by introducing, for each resonant mode, an equivalent model of the structure. Moreover, the electromagnetic interpretation of the filtering properties of two-port networks, particularly of the transmission zeros, whose nature has been the subject of several discussions, is easily obtained. The existence of two types of transmission zeros, modal and interaction zeros is pointed out. The first ones are due to the structures resonances, while the second ones are due to the interaction between resonant modes. Several experiments performed on circular and rectanguIar microstrips in the frequency range 2-18 GHz have shown a good agreement with the theory.

A simple way to model curved metal boundaries in FDTD algorithm avoiding staircase approximation

The conventional FDTD algorithm in Cartesian coordinates uses staircase approximation to treat curvilinear surfaces. This approximation causes loss of accuracy often unacceptable. An extremely simple and more accurate polygonal approximation of curved surfaces is proposed in this paper. The method improves significantly the accuracy of the original FDTD algorithm, without increasing its complexity. >

A New Class of Waveguide Dual-Mode Filters Using TM and Nonresonating Modes

An innovative class of very compact and selective waveguide dual-mode filters is presented in this paper. The basic structure is the TM dual-mode cavity. Such a cavity employs both resonant and nonresonating modes so as to provide two reflection and two transmission zeros. The high design flexibility in terms of transmission zero positioning and response bandwidth has been demonstrated by means of several single cavity designs. The design of Nth-order multiple cavity filters with N transmission zeros is presented and discussed. Different filter topologies are obtained depending on the waveguide structure used to connect adjacent cavities. An efficient mode-matching analysis method is proposed and verified for fast filter optimization. An eighth-order filter with eight transmission zeros has been designed, manufactured, and tested to demonstrate the potentialities of the filter class proposed.