Mauro Mongiardo

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. >

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 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. >

Elliptical cavity resonators for dual-mode narrow-band filters

A novel cavity resonator with elliptical cross-section is proposed in order to realize dual-mode narrowband filters without tuning and coupling elements. No discontinuities are required inside the cavities hence significantly enhancing the unloaded Q, the ability to operate with higher power levels, and the ease of manufacturing. Dual-mode coupling is generated by the step discontinuity between the input rectangular waveguide and an inclined elliptical waveguide; a rigorous full-wave electromagnetic model for this discontinuity has been developed. Proper choice of the ellipticity and of the inclination angle allows us to obtain the desired coupling and tuning actions. Representative prototypes of elliptical cavities exhibiting various degrees of coupling have been carefully measured; the favorable comparison between experimental and theoretical results proves the accuracy of the model and its applicability for narrowband X/Ku band filters.

Rigorous Network and Full-Wave Electromagnetic Modeling of Wireless Power Transfer Links

The proposed approach makes use of full-wave electromagnetic modeling of wireless power transfer links in order to derive the network characterization, e.g., in terms of scattering or impedance matrix. Once the latter is obtained, we show that network theory provides the appropriate matching impedances for achieving either maximum efficiency, maximum power on the load, or conjugate matching. The proposed approach also permits to derive closed-form matching networks and expressions for power and efficiency. An example of full-wave numerical electromagnetic modeling of a wireless power transfer link is presented. The selected example, which is similar to the experiment published by Kurs et al., shows the importance of selecting the appropriate source/load impedance for obtaining significative results.

A neural network model for CAD and optimization of microwave filters

Improvement of the performance/cost ratio for modern microwave filters requires manufacturing-oriented design, hence accommodating full-wave tolerance analyses and yield optimization which are very computer-insensitive. The use of neural networks for reducing the design effort of microwave filters, although still in its infancy, seems to provide a rather promising option. Once properly selected and trained, neural networks can approximate the filter response at a very modest fraction of the computer resources used by the full-wave rigorous model, hence enabling systematic application of manufacturing-oriented design. In this paper we present the solution of the major important choices related to the effective selection of a neural network suitable for approximating the behavior of a typical microwave filter. For illustration we consider the example of a standard four-pole E-plane metal-insert filter operating in X-band.

Full-wave design and optimization of circular waveguide polarizers with elliptical irises

We describe the design and optimization of a new polarizer structure realized in circular waveguide with insertion of elliptical irises. The device is compact, showing a considerable reduction in size and weight when compared to previously known realizations. It requires manufacturing by milling techniques only and, since it is composed entirely by waveguides with separable cross sections, it is also well suited for electromagnetic modeling. Measured and theoretical results for a polarizer with a 90/spl deg//spl plusmn/1/spl deg/ differential phase shift and a return loss better than 35 dB for both polarizations over the operating frequency band confirm the validity of the proposed design.

A fullwave CAD tool of waveguide components using a high speed direct optimizer

Based on the adjoint network method (ANM) and on mode matching technique, an extremely efficient optimization tool has been developed for the CAD of a class of rectangular waveguide components. This includes filters, phase shifters, branch guide couplers, etc., with step in either the E- or H-plane. With respect to the conventional finite difference computation of the derivatives, a speedup factor of more than 10 times is easily achieved.<<ETX>>

E-plane steps in rectangular waveguide

The classical problem of interacting E-plane step discontinuities is reconsidered. New, frequency-independent equivalent circuits are derived by explicitly considering the edge condition in the rigorous Ritz-Galerkin variational approach. A dramatic reduction of the numerical effort has also been achieved; in fact, in no case were more than two basis functions needed. The theoretical results have been compared with those reported by M. Marcuvitz (1951) as well as with experimental tests, always with excellent agreement. The very high accuracy, the reduced numerical effort, and the absence of relative convergence phenomena make this method ideally suited for the full-wave analysis of interacting discontinuities in efficient computer-aided design routines for small desk-top computers. >

Analysis of packaged microwave integrated circuits by FDTD

The behavior of packaged single and coupled MMIC via-hole grounds has been investigated by using a graded mesh FDTD code running on the massive parallel computer DEC 12000 with 4 K processors. Theoretical simulations have been compared with experimental measurements showing excellent agreement. Moreover, since the package introduces resonances, we have also investigated several different possibilities to choke off these resonances. It is shown that the common practice of inserting a damping layer just below the lid is often not effective. In particular, the importance of placing damping layers also on the side walls is demonstrated. >