Lorenzo Silvestri

Characterization of 3D-printed dielectric substrates with different infill for microwave applications

This paper presents the characterization of a 3D printed material based on Ninjaflex filament, through different techniques: the dielectric properties of the material are preliminary retrieved by a waveguide-based method, where a 3D-printed dielectric sample is inserted into a hollow metallic waveguide: this method allows for an accurate and narrow-band characterization. Subsequently, two microstrip lines with different length, realized on a 3D-printed substrate, are used for the broadband characterization in the frequency band from 2 GHz to 20 GHz. The effect of the infill percentage on the dielectric permittivity and loss tangent of the printed material are rigorously investigated and experimentally demonstrated, showing a large tunability when varying the infill from 25% to 100%. These results pave the road to the implementation of novel microwave components, based on the local variation of the dielectric permittivity, and suggest a technique to effectively reduce dielectric losses.

Substrate-integrated waveguide filters based on mushroom-shaped resonators

This paper presents a new class of quasi-elliptic pass-band filters in substrate-integrated waveguide technology, which exhibits compact size and modular geometry. These filters are based on mushroom-shaped metallic resonators, and they can be easily implemented using a standard dual-layer printed circuit board manufacturing process. The presented filters exploit non-resonating modes to obtain coupling between non-adjacent nodes in the case of in-line geometry. The resulting structure is very compact and capable of transmission zeros. In this work, the singlet configuration is preliminarily investigated, and a parametric study is performed. The design of three-pole, four-pole, and higher-order filters is illustrated with examples and thoroughly discussed. A four-pole filter operating at the frequency of 4 GHz has been manufactured and experimentally verified, to validate the proposed technique.

Modeling and implementation of perforated SIW filters

A novel class of substrate integrated waveguide (SIW) filters is presented in this paper. The filters are based on the perforation of the dielectric substrate, which generates the local modification of the effective dielectric permittivity and, consequently, of the characteristic impedance of the waveguide. In particular, perforations are used to obtain a waveguide section below cutoff in the filter band. The waveguide sections below cutoff are exploited to realize the impedance inverters, which in turn connect resonators obtained by half-wave (not perforated) SIW sections. The impedance inverter has been investigated and a filter has been designed and fabricated to demonstrate the feasibility of the proposed method.

Substrate Integrated Waveguide Filters Based on a Dielectric Layer With Periodic Perforations

This paper presents a novel class of substrate integrated waveguide (SIW) filters, based on periodic perforations of the dielectric layer. The perforations allow to reduce the local effective dielectric permittivity, thus creating waveguide sections below cutoff. This effect is exploited to implement immittance inverters through analytical formulas, providing simple design rules for the direct synthesis of the filters. The proposed solution is demonstrated through the design and testing of several filters with different topologies (including half-mode SIW and folded structures). The comparison with classical iris-type SIW filters demonstrates that the proposed filters exhibit better performance in terms of sensitivity to fabrication inaccuracies and rejection bandwidth, at the cost of a slightly larger size.

Substrate-Integrated-Waveguide E-Plane 3-dB Power-Divider/Combiner Based on Resistive Layers

Several different microwave circuits, including beamforming networks and balanced amplifiers, make use of 3-dB power dividers and combiners. A well-known architecture able to work over large bandwidths, a critical request for many applications, is based on E-plane three-port waveguide structures, where a lossy element is added to overcome the inherently poor isolation given by lossless three-port junctions. While a standard implementation based on normal rectangular waveguides often results in large and heavy structures, an implementation based on substrate-integrated-waveguide (SIW) technology offers advantages in terms of compactness, weight reduction, cost minimization, and integration possibilities with active stages. This paper presents the design, fabrication, and characterization of two SIW E-plane 3-dB power divider/combiners where the lossy element is realized using a resistive layer. The prototypes cover the entire

Innovative SIW components on paper, textile, and 3D-printed substrates for the Internet of Things

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A novel filter based on a dual-mode air-filled substrate integrated waveguide cavity resonator

-band from 8 to 12 GHz, and the resistive layers are realized according to two different manufacturing techniques to investigate the potentials of both approaches. The optimization of the resistive layer geometry and resistivity, a critical aspect for low-profile SIW circuits, is discussed in detail. In particular, an analytical formula is derived, which allows to determine the optimum values for the resistive layers’ principal parameters, namely the length and resistivity, without the use of full-wave numerical solvers.

SIW components for the Internet of Things: Novel topologies, materials, and manufacturing techniques

This paper presents an overview of the recent achievements in the developments of novel components and innovative materials for the future Internet of Things (IoT). The development of substrate integrated waveguide (SIW) components and antennas is discussed, with particular emphasis on the use of paper substrates for eco-friendly wireless systems, textile for wearable components, and 3D-printed substrates for fully-3D cost-effective structures. Several prototypes are presented to validate the proposed fabrication technologies and show the potential of integrated microwave systems for IoT applications.

GRETA approach towards new green material technologies

This paper presents a novel filter based on an air-filled substrate integrated waveguide (SIW) cavity resonator. This structure is inspired by the air-filled SIW, recently proposed to realize integrated interconnects with reduces losses. The proposed resonant cavity allows introducing two poles and two transmission zeros in the frequency response of the filter. The size and position of the air-filled portion of the SIW cavity permits to control the resonance frequency of the first two cavity modes, thus setting the pass-band of the filter. The position of the input/output port allows controlling the position of the transmission zero. A filter operating at 4 GHz, with a relative bandwidth of 1.5% and two transmission zeros, has been designed and experimentally verified.

Substrate-Integrated Waveguide Filters Based on Dual-Mode Air-Filled Resonant Cavities

This paper presents an overview of the recent achievements in the development of novel components and manufacturing technologies for the next generation of wireless components and systems, suitable for the Internet of Things (IoT). The technological requirements of the IoT are discussed in this paper: they include, among others, the need for compact and low-cost wireless systems, the adoption of effective integration solutions, the use of eco-friendly materials and fabrication technologies, and the development of wearable devices. The microwave components presented in this work are based on the substrate integrated waveguide (SIW) technology, which looks to be a suitable candidate for the development of a large variety of microwave components and antennas, as well as for the integration of entire systems. Compact solutions based on folded SIW and quarter-mode SIW structures are presented, and the use of novel materials (like paper and textile) and fabrication technologies (like 3D printing and additive manufacturing) are discussed.