Orlandino Testa

A 24 GHz radar, useful for remote vital signs monitoring, operating in linear/circular polarization (LP/CP), was developed to analyze vital signs detection performance in the presence of environmental clutter. The radar system, equipped with horn antennas with and without suitable LP-CP field polarization converters, is designed for monitoring respiratory and cardiac activity in domestic and hospital environments. A geometric optics (GO) model is introduced to show the advantages of circularly polarized (CP) radar sensors over linearly polarized (LP) ones in discriminating vital signals in scenarios where vibrating metallic panels simulate environmental disturbance (worst case). An analytical model, numerical computations, and experimental investigations highlighted the robustness of CP radar sensors in detecting vital signs in the presence of environmental clutter.

A novel class of lightweight, single and multi-refractive dielectric stacked-disk lens (SDL) designs with excellent electromagnetic performances, exhibiting reduced cost and enhanced simplicity compared to their massive counterparts, is presented. Design guidelines, derived from an accurate frequency-dispersive uniaxial tensor model of periodic dual-layer planar stacks, allow optimization of the key lens parameters—disk number, permittivity, thickness, diameter, and inter-disk spacing. Several SDLs designed at 5 GHz using these guidelines, exhibiting stop-band thresholds between 6.6 GHz and 13 GHz, -3dB fractional gain lens-antenna bandwidths ranging from 46.6% to 81.1% and aperture efficiencies between 44.5% and 58.8%, are illustrated. Full-wave simulations, employing a locally-conformal finite-integration technique (FIT), show inter-disk field propagation, diffraction, field focusing and stop-band behaviors. A novel time-domain metric, the Proportional-Derivative Energy Fidelity Factor (PDEFF), is introduced to quantify received field waveform quality at the lens focus region, achieving 95–99% for ultra-wideband through-the-wall imaging and 92–94% for UWB waveforms (for lenses having stop-band thresholds near and above 10 GHz). An antenna prototype incorporating a SDL design approaches a peak gain of 17 dBi (approximately 10 dB attributable to the lens) and an 87% weight reduction relative to a conventional massive lens, confirming numerical simulation predictions.

A new modulation scheme for frequency-modulated continuous-wave (FMCW) radars with millimeter-level target motion detection capability is presented. The proposed radar scheme is free from the synchronization constraint and exhibits low sensitivity to internal parasitic mutual coupling, thus significantly reducing its design complexity without worsening its performance in terms of accuracy and operating ranges. Alternatively to canonical FMCW radars, which exploit chirp signals with triangular or sawtooth-like frequency variation, a radar based on a sinusoidal frequency modulation, which does not require specific synchronization procedures to achieve accurate motion detection even at a short distance from the radar, was developed. Both numerical and experimental results, performed with a 24 GHz radar, have shown the suitability of the proposed modulation scheme for monitoring very small target movements, consistent with those typically exhibited by the human thorax during basic vital activities (heartbeat and respiration). This makes the proposed radar scheme a suitable solution for contactless heart and breath rate monitoring.

Short-range radars are widely used for automotive applications, through-the-wall imaging and to monitor the elderly activity into their home. Given the relevance of such applications, some imaging algorithms are reformulated using a consistent formalism applied with a very efficient region-of-interest grid step. Moreover, to reduce the computation time, the numerical procedures are structured in such a way to employ fast Fourier transform or inverse fast Fourier transform algorithms whenever it results possible, while to reduce the artifact effects due to antenna and wall reflections, the time domain gating technique is implemented. The adoption of the combined technique (reconstruction algorithms and time gating) allows to remove the artifacts on both simulated and measured data with performances comparable with those of the background subtraction technique. The reported test cases evidence the ability of the considered algorithms to operate with different fractional bandwidth and with very fast execution times.

The technology transfer of terahertz wireless communication from research laboratories to commercial applications is a global strategic achievement currently pursued to match the ever-increasing demand for high-speed communication. The use of commercial integrated electronics for the detection of THz waves is an intriguing challenge which has enticed great interest in the scientific research community. Rapid progress in this field has led to the exploitation of THz direct detection using standard CMOS technology based on the so-called self-mixing effect. Our research, stemming out of a collaboration between Sapienza University of Rome and STMicroelectronics company, is focused on the complete design process of a THz rectifier, realized using 50 nm ST B55 CMOS technology. In this paper, we report the optimization process of a case-study receiver, aimed to demonstrate the feasibility of direct demodulation of the transmitted OOK signal. A relatively limited bandwidth extension is considered since the device will be included in a system adopting a radiation source with a limited band. The design refers to a specific technology, the 60 nm MOS in B55X ST; nevertheless, the proposed optimization procedure can be applied in principle to any MOS device. Several aspects of the rectification process and of the receiver design are investigated by combining different numerical simulation methodologies. The direct representation of the rectification effect through the equivalent circuit of the detector is provided, which allows for the investigation of the detector–amplifier coupling, and the computation of output noise equivalent power. Numerical results are presented and used as the basis for the optimization of the receiver parameters.

(1) Background: An optical simulator able to provide a repeatable signal with desired characteristics as an input to a photoplethysmographic (PPG) device is presented in order to compare the performance of different PPG devices and also to test the devices with PPG signals available in online databases. (2) Methods: The optical simulator consists of an electronic board containing a photodiode and LEDs at different wavelengths in order to simulate light reflected by the body; the PPG signal taken from the chosen database is reproduced by the electronic board, and the board is used to test a wearable PPG medical device in the form of earbuds. (3) Results: The PPG device response to different average and peak-to-peak signal amplitudes is shown in order to assess the device sensitivity, and the fidelity in tracking the actual heart rate is also investigated. (4) Conclusions: The developed optical simulator promises to be an affordable, flexible, and reliable solution to test PPG devices in the lab, allowing the testing of their actual performances thanks to the possibility of using PPG databases, thus gaining useful and significant information before on-the-field clinical trials.

A frequency-modulated continuous-wave radar for short-range target imaging, assembling a transceiver, a PLL, an SP4T switch, and a serial patch antenna array, was realized. A new algorithm based on a double Fourier transform (2D-FT) was developed and compared with the delay and sum (DAS) and multiple signal classification (MUSIC) algorithms proposed in the literature for target detection. The three reconstruction algorithms were applied to simulated canonical cases evidencing radar resolutions close to the theoretical ones. The proposed 2D-FT algorithm exhibits an angle of view greater than 25° and is five times faster than DAS and 20 times faster than the MUSIC one. The realized radar shows a range resolution of 55 cm and an angular resolution of 14° and is able to correctly identify the positions of single and multiple targets in realistic scenarios, with errors lower than 20 cm.

A wideband high-gain circularly polarized (CP) shaped dielectric horn-lens antenna (SDHLA) operating in the frequency band between 6.7 and 18.2 GHz [fractional impedance bandwidth (FIBW) of 92.4%] with a 3-dB axial-ratio in the frequency range from 8.1 to 16.3 GHz [fractional axial-ratio bandwidth (FARBW) of 67.2%], is presented. The antenna, composed of a suitably shaped dielectric horn, integrated with a super-ellipsoidal-axicon dielectric lens made out of stacked thin dielectric disks, is mounted on a printed circuit board (PCB) where a broadband microstrip line terminated with a radial stub is used to excite a S-shaped slot through which the circular polarization is achieved. Parameterized 3D Lamé curves describe the optimal geometries of horn and lens profiles. The antenna features a peak realized gain exceeding 13.1 dBi that is beneficial in a variety of applications, such as digital video broadcasting (DVB), remote sensing, weather monitoring, satellite communications, and air traffic control. The full-wave electromagnetic solver CST Studio Suite™, based on a locally conformal finite integration technique (FIT), was employed to design and characterize the antenna. The antenna characteristics estimated by FIT were found to be in good agreement with the experimental measurements performed on an antenna prototype.

A wideband high-gain dielectric horn-lens antenna (DHLA) for wireless communications and UWB applications, featuring 122% fractional bandwidth, is presented. The antenna, consisting of a dielectric horn equipped with a spherical-axicon dielectric lens that increases and equalizes the gain within the operating band, is placed on a PCB featuring a wideband 8-shaped slot fed by a tapered microstrip line employed to excite the radiating system. The lens, integrated within the body of the dielectric horn, has the property of focusing the RF energy near its vertex on an extended frequency band, thus ensuring compact size, excellent field coupling with the antenna excitation system, and a significant increase of antenna gain. The antenna operates in the 3-12.4 GHz frequency range with relatively flat group delay, making it suitable for operating with narrowband, broadband, and impulsive UWB signals. The antenna can work properly without or with a metal reflector useful to enhance gain (up to 19 dBi), improve the front-to-back ratio, and reduce the impact of the antenna characteristics from the installation site. CST Studio Suite™, implementing a full-wave locally conformal finite integration technique (FIT), was employed to design and characterize the antenna. The antenna characteristics estimated numerically were found to be in good agreement with the experimental results performed on an antenna prototype.

The performances of a multiple-input multiple-output (MIMO) radar, employing 16 equivalent antennas, and multiple-input single-output (MISO) radar, employing 10 antennas, for through-the-wall imaging applications are analyzed. In particular, imaging algorithms based on the Fourier transform (FT) and the multiple signal classification (MUSIC) available in the literature are compared with the FT-MUSIC hybrid algorithm recently developed by the authors. Three different investigations have been performed. The first, performed analytically, refers to a scenario in which a point scatterer is placed in free space, and the second, addressed numerically using the CST full-wave software, refers to a scenario in which two targets are present, while the last was executed in a real scenario where a metal panel is placed behind a tuff wall. All the algorithms and radar configurations were found to be suitable for accurately reconstructing the position of the investigated target. In particular, applying the FT technique, the MISO configuration has a lower cross-range half-power beamwidths (HPBW) than the MIMO one, while the range HPBW is the same for the two radar configurations. Despite the different number of elements present in the two radar configurations, similar range and cross-range HPBW are obtained for both configurations when MUSIC and FT-MUSIC techniques are employed. The field of view for FT and FT-MUSIC is about 45°, while it is less than 15° for the MUSIC algorithm. The HPBWs obtained with the experimental setup are very close to those obtained in the analytical study. Finally, the proposed experimental MISO radar acquires the data in half the time required by the MIMO one. The numerical results, confirmed by the experimental measurements, seem to indicate in the FT-MUSIC technique the one that provides the best performance for the considered radar configurations.