Vittorio Rizzoli

Computer-aided optimization of nonlinear microwave circuits with the aid of electromagnetic simulation

This paper discusses some modern trends in nonlinear (NL) microwave circuit optimization based on electromagnetic (EM) simulation. In order to keep the CPU time required for a typical design within acceptable limits, the number of expensive EM analyses must be kept under tight control. This may be obtained by resorting to a systematic implementation of some modern algorithmic concepts such as space mapping, domain partitioning, and neural-network modeling of the passive subnetwork and/or of its most critical parts. Although these techniques are well established for linear microwave circuit design coupled with EM analysis, their extension to the NL case is not trivial, and deserves a specialized treatment. Several examples are presented in order to give a feeling of the state-of-the-art of NL/EM optimization.

Prediction of the End-to-End Performance of a Microwave/RF Link by Means of Nonlinear/Electromagnetic Co-Simulation

This paper describes the simulation of a microwave link from the transmitter to the receiver intermediate-frequency ports, by means of a rigorous circuit-level nonlinear analysis approach coupled with the electromagnetic characterization of the transmitter and receiver front-ends. This includes a full electromagnetic computation of the radiated far field which is used to establish the connection between transmitter and receiver. Digitally modulated radio-frequency drive is treated by a modulation-oriented harmonic-balance method based on Krylov-subspace model-order reduction to allow the handling of large-size front-ends. An artificial neural network model is then developed to allow fast computation of the link driven by long sequences of the order of millions of samples. In this way, a meaningful evaluation of such link performance aspects as the bit-error rate becomes possible at the circuit level

General electromagnetic compatibility analysis for nonlinear microwave integrated circuits

The paper proposes a new solution to the standard electromagnetic compatibility problem for nonlinear RF/microwave integrated circuits. Radiation from the given circuit is first numerically analysed by means of electromagnetic simulation. Under the assumption of a uniform plane wave incident on the circuit, the reciprocity theorem is then used to characterize the linear subnetwork by a Norton equivalent circuit. Finally, a multitone harmonic-balance analysis allows the effects of the incident wave on the circuit electrical regime to be exactly investigated.

Circuit-level nonlinear/electromagnetic co-simulation of an entire microwave link

The simulation of a microwave link is tackled by a rigorous circuit-level nonlinear analysis approach coupled with the electromagnetic (EM) characterization of the transmitting and receiving antennas. The connection between transmitter and receiver is established by a full EM computation of the radiated far field under modulated input drive.

Domain-Decomposition Harmonic Balance with Block-Wise Constant Spectrum

Domain-decomposition techniques provide a powerful approach to the circuit-level simulation of complex RF/microwave transceivers by envelope-oriented harmonic balance. Once the circuit has been suitably subdivided into blocks, a further significant enhancement in analysis performance may be obtained by limiting each blocks spectrum to the set of lines that are relevant to the block electrical function. Besides providing high numerical efficiency, this technique opens the way to an effective co-simulation of the RF and baseband transceiver sections

Nonlinear distortion and instability phenomena in MEMS-reconfigurable microstrip antennas

We propose a rigorous nonlinear/electromagnetic approach to the analysis of reconfigurable integrated antennas operated by MEMS switches. We describe the microstrip pattern as a unique linear multiport system by EM analysis, and the MEMS as lumped nonlinear components by means of their electromechanical equations. The latter are solved together with the ordinary harmonic-balance equations to derive an in-depth description of the antenna nonlinear behaviour.

CAD Procedures for the Nonlinear/Electromagnetic co-Design of Integrated Microwave Transmitters

The paper introduces a new approach to the nonlinear/electromagnetic co-design of microwave transmitters including integrated antennas. Nonlinear analysis techniques and EM simulation are coupled to produce an accurate description of the transmitter performance. The antenna is not treated as a separate component but as an integral part of the linear subnetwork in order to fully account for any coupling effects that the circuit layout may introduce. For optimization purposes the passive circuit layout is described by neural models derived from rigorous EM simulation. A separate artificial neural network (ANN) is used in the neighbourhood of each harmonic of interest in order to overcome the bandwidth problem. Special ANNs are used to model the radiated field, allowing the design goals to be formulated in terms of far-field specifications, and suitable figures of merit encompassing radiation and nonlinear performance are introduced.

Distortion Analysis of RF Links by Means of Circuit-Level Nonlinear/EM Front-end Simulation and Realistic Channel Description

End-to-end analysis of RF/microwave links is addressed for the first time by combining rigorous circuit-level nonlinear analysis of the transmitting and receiving front ends, electromagnetic (EM) characterisation of the antennas, and realistic description of the radio channel. The latter is a multipath model based on a 3D ray tracing (RT) approach. The connection between transmitter and receiver is established by a full EM computation of the radiated far field under modulated input drive

Nonlinear modelling of reconfigurable microwave components based on resistive MEMS switches

We propose a nonlinear model of a resistive MEMS switch. We describe the nonlinear behaviour of the switch by exploiting an extended harmonic balance (HB) technique allowing the efficient calculation of distortion effects due to MEMS nonlinearities. A comparison with the corresponding capacitive model is also given. As an illustrative example, the results of the simulation of a reconfigurable integrated antenna operated by commercial MEMS switches are compared to measurements.

Fast Nonlinear Analysis of Reconfigurable Microwave Systems by a Behavioral Model of MEMS Switches

The simulation of nonlinear distortion and transient effects in MEMS-reconfigurable microwave circuits and systems of large size is efficiently performed by resorting to a novel behavioral model of MEMS switches. The model is organized in such a way as to allow its standalone use as well as its insertion into a general-purpose envelope-transient simulator based on the harmonic balance principle, in much the same way as an ordinary circuit component.