Marco Pasian

On the losses in substrate integrated waveguides

This paper presents a study of losses in substrate integrated waveguide. Three mechanisms of losses are considered and separately investigated: side radiation, ohmic loss, and dielectric loss. A systematic comparison of waveguides with different geometry, operating in the same frequency band, is reported. This study permits to give a physical interpretation of the loss mechanisms and to identify design criteria to minimize losses.

On the losses in substrate-integrated waveguides and cavities

This paper presents a study of losses in substrate-integrated waveguides (SIWs) and cavities. Three mechanisms of losses are considered and separately investigated, namely radiation leakage, ohmic loss, and dielectric loss. A systematic comparison of waveguides with different geometry, operating at different frequencies, is reported. This study permits to give a physical interpretation of the loss mechanisms and to identify design criteria to minimize losses. A similar analysis is also developed in this work for the case of SIW resonant cavities. For these structures, a different variation of losses with respect to frequency is found, which reduces the effectiveness of the design criteria established for SIWs.

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.

Dielectric Properties Characterization From 0.5 to 50 GHz of Breast Cancer Tissues

Knowledge of the dielectric properties of human tissues is important for several biomedical applications, including imaging and hyperthermia treatment, as well as for determining safety thresholds in policy making. Breast tissues, both normal and tumorous, are of particular interest because of the medical and social impact of breast cancers. While experimental data is available up to 20 GHz, for higher frequencies, this information is missing, or has been extrapolated from models based on lower-frequency data. Emerging technologies and applications in the millimeter-wave region would benefit from experimental data that bridge this gap. This paper presents the characterization of dielectric properties of breast tissues for the frequency range from 0.5 to 50 GHz. Cole–Cole models are derived for normal and tumorous tissues based on experimental measurements on more than 220 tissue samples obtained at surgery (ex vivo) from a population exceeding 50 patients, covering a wide span of normal and tumorous tissues, from patients ranging in age from 28 to 85 years, with a time from excision to measurements under 3.5 h. This paper also presents a comprehensive analysis of the differences between normal and tumorous breast tissues at different frequencies in terms of sensitivity and specificity.

Accurate Modeling of Dichroic Mirrors in Beam-Waveguide Antennas

Frequency selective surfaces, also called dichroic mirrors, are usually analyzed assuming a uniform plane-wave excitation. However, when these devices are used within reflector antennas to combine/separate beams at different frequencies, they are often illuminated by corrugated horns, which generate a radiation pattern that cannot be approximated by a uniform plane wave. For this reason, it is important to properly analyze the interaction between the electromagnetic field generated by the horn and the transmission (or reflection) response given by the mirror. To carry out this task, this paper presents an approach based on the plane wave expansion of the field generated by the horn. The effectiveness of the proposed method, which is able to provide the degradation due to the dichroic mirror to the horn radiation pattern for both the co-polar and the cross-polar component, is validated versus measurements.

A Formula for Radiation Loss in Substrate Integrated Waveguide

Substrate integrated waveguide, an emerging technology for microwave and millimeter-wave circuits, is affected by three loss mechanisms: ohmic and dielectric losses, standard waveguides, and radiation leakage. While ohmic and dielectric losses can be accurately determined by the analytical formulas of the equivalent rectangular waveguide, no equations are available for radiation leakage. This paper presents the derivation of a formula to calculate the attenuation constant due to radiation leakage in substrate integrated waveguide interconnects.

Frequency Selective Surfaces for Extended Bandwidth Backing Reflector Functions

This paper deals with the use of frequency selective surfaces (FSS) to increase the efficiency X bandwidth product in wideband antenna arrays, whose efficiency is limited by the front-to-back ratio. If the backing reflector for the antenna is realized through a single metal plane solution, its location will be suitable only on a relatively limited frequency range especially if wide angle scanning is required. In order to extend the frequency range of usability, an FSS can be sandwiched between the antenna and the ground plane, providing an additional reflecting plane for an higher frequency band. The possibility to integrate in the antenna different functionalities, otherwise performed by several antennas, is also discussed in the paper. The proposed backing structure composed by the FSS and the ground plane has been designed to be used in conjunction with a wideband antenna consisting of an array of connected dipoles. A hardware demonstrator of the backing structure has also been manufactured and tested.

Crosstalk in Substrate Integrated Waveguides

Substrate integrated waveguide (SIW) represents an emerging technology for the implementation of waveguide components in planar form, in the frequency range of microwaves and mm-waves. While the SIW is similar to a classical metallic waveguide, the structure is not completely shielded and may be subject to a radiation leakage. This leakage could cause a crosstalk between adjacent SIW interconnects. While for other structures, e.g., microstrip lines, the determination of the crosstalk was widely investigated, no quantitative relationship was previously derived in the case of SIW structures. In order to fill this gap, this paper presents for the first time the derivation of a formula to calculate the crosstalk in SIW structures.

Radiation losses in Substrate Integrated Waveguides: A semi-analytical approach for a quantitative determination

Substrate Integrated Waveguides, an emerging technology for microwave and mm-wave circuits, are affected by three loss mechanisms: Ohmic and dielectric, as standard waveguides, and radiation. While for Ohmic and dielectric losses equations to determine the expected deterioration are available, for radiation loss no quantitative relationship was derived. This paper presents a semi-analytical approach to predict the attenuation constant due to radiation loss in Substrate Integrated Waveguides.

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.