Stefano Moscato

Broadband Microwave Attenuator Based on Few Layer Graphene Flakes

This paper presents the design and fabrication of a broadband microstrip attenuator, operating at 1-20 GHz, based on few layer graphene flakes. The RF performance of the attenuator has been analyzed in depth. In particular, the use of graphene as a variable resistor is discussed and experimentally characterized at microwave frequencies. The structure of the graphene-based attenuator integrates a micrometric layer of graphene flakes deposited on an air gap in a microstrip line. As highlighted in the experiments, the graphene film can range from being a discrete conductor to a highly resistive material, depending on the externally applied voltage. As experimental evidence, it is verified that the application of a proper voltage through two bias tees changes the surface resistivity of graphene, and induces a significant change of insertion loss of the microstrip attenuator.

Infill-Dependent 3-D-Printed Material Based on NinjaFlex Filament for Antenna Applications

This letter presents one of the first examples of the exploitation of 3-D printing in the fabrication of microwave components and antennas. Additive manufacturing represents an enabling technology for a wide range of electronic devices, thanks to its inherent features of fast prototyping, the reasonable accuracy, fully 3-D topologies, and the low fabrication cost. A novel 3-D printable flexible filament, based on NinjaFlex, has been adopted for manufacturing the substrate of a 3-D printed patch antenna. NinjaFlex is a recently introduced material with extraordinary features in terms of mechanical strain, flexibility, and printability. Initially, the electrical properties of this material are investigated at 2.4 GHz using the ring resonator technique. The capability of selectively changing the dielectric constant by modifying the printed material density by fine-tuning printing infill percentage is verified experimentally. Subsequently, a square patch antenna is prototyped through 3-D printing and measured to validate the manufacturing technology. Finally, exploiting mechanical flexibility properties of NinjaFlex, the antenna is tested under different bending conditions.

Quarter-Mode Cavity Filters in Substrate Integrated Waveguide Technology

This paper presents a systematic investigation of quarter-mode filters in substrate integrated waveguide (SIW) technology. This class of filters is particularly convenient because it combines the features of SIW structures with the improvement of size reduction. After a thorough analysis of the quarter-mode SIW cavity, this paper presents different coupling mechanisms and feeding techniques for the design of quarter-mode SIW filters: side coupling and corner coupling are considered, highlighting the advantages and disadvantages of the two techniques. Novel filter topologies are introduced, with the design and experimental verification of simple filters and their extension to higher order filter structures. Techniques to introduce transmission zeros are described and demonstrated. Moreover, the combination of quarter-mode SIW cavities and coplanar waveguide resonators leads to increasing the filter order to higher order and allows the implementation of quasi-elliptic filters.

Substrate Integrated Folded Waveguide Filter with Out-of-Band Rejection Controlled by Resonant-Mode Suppression

This letter presents a new filter, based on substrate integrated folded waveguide (SIFW) technology, which exhibits compact size and good out-of-band rejection. The filter is based on a SIFW cavity, which guarantees size reduction, and the out-of-band rejection is controlled by the suppression and tuning of the high-order cavity modes. A detailed investigation of the cavity mode spectrum is presented, to illustrate the operation principle and the design of the filter. The interesting feature of this filter is the possibility to design the pass band and the return band by simply tuning the mode spectrum of the cavity, which is practically unaffected by the connection to the excitation ports. The fabrication and testing of a prototype operating at 4.5 GHz validate the proposed filter topology.

A novel strain sensor based on 3D printing technology and 3D antenna design

The additive manufacturing technique of 3D printing has become increasingly popular for time-consuming and complex designs. Due to the special mechanical properties of commercial NinjaFlex filament [1] and in-house-made electrically conductive adhesives (ECAs) [2], there is great potential for the 3D printed RF applications, such as strain sensors and flexible, wearable RF devices. This paper presents the flexible 3D printed strain sensor, as a 3D dipole antenna of ECA stretchable conductor on 3D printed Ninjaflex filament.

A mm-Wave 2D Ultra-Wideband Imaging Radar for Breast Cancer Detection

This paper presents the preliminary design of a mm-wave ultra-wideband (UWB) radar for breast cancer detection. A mass screening of women for breast cancer is essential, as the early diagnosis of the tumour allows best treatment outcomes. A mm-wave UWB radar could be an innovative solution to achieve the high imaging resolution required without risks for the patient. The 20–40 GHz frequency band used in the system proposed in this work guarantees high cross/range resolution performances. The developed preliminary architecture employs two monomodal truncated double-ridge waveguides that act as antennas; these radiators are shifted by microstep actuators to form a synthetic linear aperture. The minimum antenna-to-antenna distance achievable, the width of the synthetic aperture, and the minimum frequency step determine the performance of the 2D imaging system. Measures are performed with a mm-wave vector network analyzer driven by an automatic routine, which controls also the antennas shifts. The scattering matrix is then calibrated and the delay-multiply-and-sum (DMAS) algorithm is applied to elaborate a high-resolution 2D image of the targets. Experimental results show that 3 mm cross and 8 mm range resolutions were achieved, which is in line with theoretical expectations and promising for future developments.

Chipless RFID for space applications

Recent works reveal a great deal of interest in the subject of wireless passive sensor for space applications. In particular, wireless passive tags can be employed during in-flight operations as well as during ground test campaigns, thanks to their robustness in extreme environments since they do not contain batteries nor any active electronic circuits. Chipless backscatter-based radio frequency identification (RFID) could be a valid alternative to surface acoustic wave (SAW) imple-mentations, especially for short-range applications like sensor monitoring aboard of satellite systems. In this work we present chipless RFIDs based on resonant substrate integrated waveguide (SIW) cavities, showing both the experimental characterization and system simulations, proving the solution feasibility for their usage on space platforms.

Two-Material Ridge Substrate Integrated Waveguide for Ultra-Wideband Applications

A novel ridge substrate integrated waveguide (RSIW) with extended single-mode bandwidth is presented in this paper. The proposed structure is based on a substrate integrated waveguide including two dielectric layers with different permittivity. The ridge is implemented by a row of partial height metal vias, connected at the bottom by a metal strip. An RSIW with cutoff frequency of the fundamental mode at 2.5 GHz and of the second mode at 12 GHz is proposed, thus achieving a bandwidth of almost 5:1. This structure is suitable for applications covering the entire ultra-wideband. The proposed RSIW has been fabricated and tested to verify experimentally the electromagnetic properties of the fundamental and second mode. Finally, the role of the metal strip connecting the bottom of the ridge vias is discussed, showing through numerical and experimental results that the strip plays a fundamental role in avoiding the bandgap in the frequency response of the RSIW.

Innovative technique for substrate integrated waveguide implementation on paper substrate

This paper presents a novel technique for the implementation of substrate integrated waveguide components based on paper substrate. The aim of the work is to develop a new class of microwave devices where the main advantages are the eco-compatibility and the low cost. These aspects match the requirements of microwave components for the new generation wireless sensor networks. The key points of this work are the manufacturing process based on physical etching of a metal layer and the implementation of a substrate integrated waveguide components on paper. In order to verify the reliability of the manufacturing process, two preliminary designs are proposed: a two poles band-pass filter and a cavity backed antenna both operating at 4 GHz.

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

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.