Riccardo Moro

Textile Microwave Components in Substrate Integrated Waveguide Technology

Although substrate integrated waveguide (SIW) technology is well established for the fabrication of microwave circuits on rigid printed circuit boards, and the first implementations of textile SIW antennas have recently appeared in literature, up to now, no complete set of SIW microwave components has been presented. Therefore, this paper describes the design, manufacturing, and testing of a new class of textile microwave components for wearable applications, implemented in SIW technology. After characterizing the adopted textile fabrics material in terms of electrical properties, it is shown that folded textile SIW components, such as interconnections, filters, and antennas form excellent building blocks for wearable microwave circuits, given their low profile, flexibility, and stable characteristics under bending and in proximity of the human body. Hence, they allow the full exploitation of the large area garments offered for the deployment of wearable electronics. Besides SIW interconnections, a folded textile SIW filter operating at 2.45 GHz is designed and tested. The filter combines excellent performance in the band of interest with good out-of-band rejection, even when accounting for the tolerances in the fabrication process. Finally, a folded SIW cavity-backed patch antenna is fabricated and experimentally verified in realistic operating conditions.

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.

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.

Inkjet-printed paper-based substrate-integrated waveguide (SIW) components and antennas

This paper presents a novel technology for the implementation of substrate-integrated waveguide (SIW) structures, based on a paper substrate and realized by an inkjet-printing fabrication process. The use of paper permits to implement low-cost microwave structures and components, by adopting a completely eco-friendly implementation technology. SIW structures appear particularly suitable for implementation on paper, due to the possibility to easily realize multilayered topologies and conformal geometries. In this paper, SIW passive components, and antennas (including straight interconnects, band-pass filters, and slotted-waveguide antennas) are proposed for the first time. The design of the components, the steps of the fabrication process, and the experimental characterization of the prototypes are reported in this paper.

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.

Graphene-based electronically tunable microstrip attenuator

This paper presents the design of a graphene-based electronically tunable microstrip attenuator operating at the frequency of 5 GHz. The use of graphene as a variable resistor is discussed, and the modeling of its electromagnetic properties at microwave frequencies is fully addressed. The design of the graphene-based attenuator is described. The structure integrates a patch of graphene, whose characteristics can range from fairly good conductor to highly lossy material, depending on the applied voltage. By applying the proper voltage through two high-impedance bias lines, the surface resistivity of graphene can be modified, thus changing the insertion loss of the microstrip attenuator.

Graphene-Based Electronically Tuneable Microstrip Attenuator

This paper presents the design of a graphene-based electronically tuneable microstrip attenuator operating at a frequency of 5 GHz. The use of graphene as a variable resistor is discussed and the modelling of its electromagnetic properties at microwave frequencies is fully addressed. The design of the graphene-based attenuator is described. The structure integrates a patch of graphene, whose characteristics can range from being a fairly good conductor to a highly lossy material, depending on the applied voltage. By applying the proper voltage through two high-impedance bias lines, the surface resistivity of graphene can be modified, thereby changing the insertion loss of the microstrip attenuator.

On the use of electrostatically doped graphene: Analysis of microwave attenuators

In this contribution, the electrostatic tunability of graphene is exploited in order to fabricate compact and effective microwave filters, namely field attenuators. A graphene patch of millimeter size is placed across the air gap of a discontinued microstrip-line, and tuned by means of an electrostatic bias applied by a high impedance line, that is, in turns, de-coupled from the microwave filter at center-band frequency. Results show that the filter response is strongly dependent on the external bias, and this promises not only for unprecedented performances, in terms of mass, volume and power consumption, but also for possible integration of graphene in a wide class of standard microwave devices.

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.

The next generation textile antennas based on substrate integrated waveguide technology

Textile antennas for body-worn applications have some very specific requirements and needs. From an electrical engineers point of view, good radiation characteristics and impedance matching to the active electronics are important. From the wearers perspective, the antenna should be unobtrusively integrated into the clothing, and the smart textile comfortable to wear. New techniques offer the potential to fulfill these different needs. One new approach consists of applying metalized eyelets to implement substrate integrated waveguide technology on textile materials. This results in high-performance on-body antennas with excellent behavior in close proximity of the human body. Two realizations are discussed: a wideband design and a miniaturized half mode substrate integrated waveguide dual-band design. Both yield excellent free-space and on-body performance, and superb antenna-body isolation, automatically resulting in very robust characteristics when deployed on-body.