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This paper describes a new low-pass filter topology based on tapered periodic structures. These filters exhibit interesting characteristics in terms of compactness, return loss, insertion loss, selectivity, and the suppression of spurious frequency bands. Hybrid prototypes with a 1-GHz cutoff frequency, based on a coplanar-waveguide technology, and using both low-cost and high-performance substrates, have been fabricated and measured. Spurious frequency bands can be suppressed to below -22 dB at frequencies up to 20 GHz. Passband ripples are negligible, and the return loss is better than 20 dB. A two-section filter has a length of 0.2 [lambda] and exhibits a--120-dB/dec selectivity, while a six-section filter is 0.51 [lambda] long and has a -560-dB/dec selectivity. A design procedure has been established. These filters are compatible with monolithic microwave integrated circuit technologies in which the capacitors can be realized as metal-insulator-metal structures. Index Terms--Bragg cutoff frequency, low-pass filters, periodic structures, spurious frequency suppression, tapered structures.

This paper deals with a microwave microstrip line that is terminated by a laser illumination, which alters the behavior of this microwave device. The first result is the numerical simulation of the microstrip line ended by a photoinduced load with the finite element method (FEM) and with hexahedral edge elements. The main difficulties of this kind of simulation remains in the fact that we deal with an open structure and that the photoinduced load is complex and inhomogeneous. Index Terms--Anisotropic and inhomogeneous complex medium, finite element method, optical control, photoinduced load.