Pietro Bolli

Passive intermodulation on large reflector antennas

In this work, an analytical model for the study of passive intermodulation (PIM) on large reflector antennas is presented. Passive intermodulation, in the scattered field, arises when the scatterer is nonlinear, or when it presents junctions connecting linear materials. Its presence causes a degradation of some antenna parameters and, especially, the cross-polar level, which may rise by several tens of dB. It would then be useful to develop a technique to predict its influence, in order to take appropriate steps during antenna design. A heuristic model for the junction problem has previously been derived and validated with measurements in a time-domain physical optics (TD-PO) framework. These results are applied here to a TD-PO analysis of reflector antennas, in particular, for a satellite-communication antenna and for a radio-astronomy antenna.

A time-domain physical optics heuristic approach to passive intermodulation scattering

Passive intermodulation (PIM) is a phenomenon which often arises at junctions between different materials. This may be a major issue in tightly packed antenna farms as those typically present on communication satellites. Here, an heuristic nonlinear extension to the time-domain physical optics (TD-PO) is proposed, to take into account electromagnetic scattering at intermodulated frequencies when such a junction is illuminated by two impinging electromagnetic fields at different frequencies. Simulation results are compared with measures to validate the model.

A hybrid perturbative technique to characterize the coupling between a corrugated horn and a reflector dish

In this paper the electromagnetic coupling between a corrugated horn and a reflector dish is analyzed with a new hybrid perturbative technique. This coupling may produce significant modifications especially in the return loss and in the cross-polar pattern of the feed. The hybrid perturbative approach combines three different techniques: a mode matching (MM) technique for the propagation inside the horn, a method of moments (MoM) technique for the radiation of the horn taking into account the external part of the horn itself, and a fast Gaussian beam asymptotic physical optics (FGBAPO) technique for the interactions between the feed and the reflector. Some measurements and the comparison with rigorous numerical results demonstrate the accuracy of the new hybrid technique and the effects of this electromagnetic coupling on the feed performance.

Genetic algorithms for the determination of the nonlinearity model coefficients in passive intermodulation scattering

Zones with nonlinear behavior on an object cause intermodulated components in the scattered electromagnetic field. This problem is relevant both for satellite communications and for radio-astronomical applications. Recently, a heuristic model for the passive intermodulation analysis has been derived in a time domain physical optics framework. The heuristic approach proposed requires the determination of few coefficients. Here, a genetic algorithm is introduced for the computation of the optimum values for these coefficients.

A time domain physical optics approach to passive intermodulation scattering problems

Passive intermodulation (PIM) is a phenomenon which often arises at junctions between different materials. This may be a major issue in tightly packed antenna farms as those typically present on communication satellites. Here an heuristic non-linear extension to the time domain physical optics is proposed, to take into account electromagnetic scattering at intermodulated frequencies when such a junction is illuminated by two impinging electromagnetic fields at different frequencies.

Automatic evaluation of the non-linear model coefficients in passive intermodulation scattering via genetic algorithms

An heuristic model for the passive intermodulation analysis has been recently derived in a time domain physical optics framework. The heuristic approach proposed requires the determination of few coefficients which has been pursued, previously, by a trial-and-error procedure. Here a genetic algorithm is introduced for the automatic evaluation of the optimum values for these coefficients.