Laboratoire d'Électronique, Antennes et Télécommunications

Several solutions are presented to reduce the mutual coupling between two planar inverted-F antennas (PIFAs) working in close radiocommunication standards and positioned on a finite-sized ground plane modeling the printed circuit board (PCB) of a typical mobile phone. First, the two PIFAs are designed on separate PCBs to, respectively, operate in the DCS1800 and UMTS bands. In a second step, they are associated on the top edge of the same PCB. Realistic arrangements are then theoretically and experimentally studied. Finally, several solutions are investigated to maximize the isolation. They consist in inserting a suspended line between the PIFAs' feedings and/or shorting points. All along this paper, several prototypes are fabricated and their performances measured to validate the obtained IE3D moment method-based simulation results

This paper refers to quantitative reconstruction of the dielectric and conductive property distributions of biological objects by means of active microwave imaging. An iterative reconstruction algorithm based on the Levenberg-Marquardt method is tested with synthetic data. The influence of the receiver geometry is investigated and two methods for choosing the regularization parameter, an empirical method and generalized cross validation (GCV) method, are examined.

This letter presents a dual-band circularly polarized patch antenna dedicated to satellite communications. The dual-band behavior is obtained by inserting a small X-band microstrip patch antenna into a large L-band one. Both patches are printed on the same substrate and fed by electromagnetic coupling through two perpendicular slots etched in their ground planes. These slots are fed by two different 90/spl deg/ microstrip branch-line couplers printed on a stacked lower substrate. A prototype of the antenna was realized with a 1.5-mm-thick upper layer substrate and a 0.758-mm-thick feed layer substrate, both of the same dielectric material with a relative permittivity of /spl epsiv//sub r/=2.22. Simulation and measurement results are presented, showing this compact dual-band antenna achieves the required Meteosat specifications in terms of frequency bandwidth, circular polarization bandwidth, and isolation between the two communication bands.

Hand gestures are a form of non-verbal communication used by individuals in conjunction with speech to communicate. Nowadays, with the increasing use of technology, hand-gesture recognition is considered to be an important aspect of Human-Machine Interaction (HMI), allowing the machine to capture and interpret the user's intent and to respond accordingly. The ability to discriminate between human gestures can help in several applications, such as assisted living, healthcare, neuro-rehabilitation, and sports. Recently, multi-sensor data fusion mechanisms have been investigated to improve discrimination accuracy. In this paper, we present a sensor fusion framework that integrates complementary systems: the electromyography (EMG) signal from muscles and visual information. This multi-sensor approach, while improving accuracy and robustness, introduces the disadvantage of high computational cost, which grows exponentially with the number of sensors and the number of measurements. Furthermore, this huge amount of data to process can affect the classification latency which can be crucial in real-case scenarios, such as prosthetic control. Neuromorphic technologies can be deployed to overcome these limitations since they allow real-time processing in parallel at low power consumption. In this paper, we present a fully neuromorphic sensor fusion approach for hand-gesture recognition comprised of an event-based vision sensor and three different neuromorphic processors. In particular, we used the event-based camera, called DVS, and two neuromorphic platforms, Loihi and ODIN + MorphIC. The EMG signals were recorded using traditional electrodes and then converted into spikes to be fed into the chips. We collected a dataset of five gestures from sign language where visual and electromyography signals are synchronized. We compared a fully neuromorphic approach to a baseline implemented using traditional machine learning approaches on a portable GPU system. According to the chip's constraints, we designed specific spiking neural networks (SNNs) for sensor fusion that showed classification accuracy comparable to the software baseline. These neuromorphic alternatives have increased inference time, between 20 and 40%, with respect to the GPU system but have a significantly smaller energy-delay product (EDP) which makes them between 30× and 600× more efficient. The proposed work represents a new benchmark that moves neuromorphic computing toward a real-world scenario.

The design of several universal mobile telecommunications system multi-antenna systems with radiators having a high isolation, a high total efficiency and a low envelope correlation is presented. First, two planar inverted-F antennas (PIFAs), closely positioned at the top edge of a small ground plane whose size is representative of the printed circuit board of a mobile phone, are described. A technical solution is then proposed to increase the isolation between the antennas and enhance their total efficiency when still keeping them closely spaced. The technical solution is based on an optimal neutralisation technique, applied between the antennas of the structure. Several optimal systems, based on different parameters, are fabricated and measured. The simulated and measured S-parameters are presented in addition to the gain radiation patterns, the surface currents on the structure and the theoretical and experimental total efficiencies. The envelope correlation coefficients are also computed using two different equations. It is then demonstrated that, with the help of the neutralisation technique, a system composed of two closely spaced PIFAs located at the top edge of a small ground plane can lead to a high total efficiency and a low envelope correlation coefficient. In conclusion, this technique can be easily implemented at the terminal side of a wireless link and may enhance its diversity gain and multiple input multiple output performance.

This letter presents the design of a compact Planar Inverted-F Antenna (PIFA) suitable for cellular telephone applications. The quarter-wavelength antenna combines the use of a slot, shorted parasitic patches and capacitive loads to achieve multiband operation. The commercial electromagnetic software IE3D is used to design and optimize the structure. The resulting antenna can operate from 880 to 960 MHz and 1710 to 2170 MHz covering GSM, DCS, PCS, and UMTS standards with a VSWR better than 2.5. Good agreement is found between simulated and measured results.

The localisation of moving and transceiver-free objects is addressed by processing the Received Signal Strength Indicator (RSSI) available at the nodes of a wireless sensor network. Starting from the RSSI measurements, the probability of the presence of unknown mobile objects is determined by means of a customised classification approach based on a support vector machine. Experimental results assess the feasibility of the proposed approach.

This article deals with microwave tomography for brain stroke imaging using state-of-the-art numerical modeling and massively parallel computing. Iterative microwave tomographic imaging requires the solution of an inverse problem based on a minimization algorithm (e.g., gradient based) with successive solutions of a direct problem such as the accurate modeling of a whole-microwave measurement system. Moreover, a sufficiently high number of unknowns is required to accurately represent the solution. As the system will be used for detecting a brain stroke (ischemic or hemorrhagic) as well as for monitoring during the treatment, the running times for the reconstructions should be reasonable. The method used is based on high-order finite elements, parallel preconditioners from the domain decomposition method and domain-specific language with the opensource FreeFEM++ solver.

A numerical modeling based on the solution of coupled integral equations is used for the characterization of CPW-fed aperture-coupled microstrip antennas. Various shapes of excitation slots, such as open stubs, slot loops, and capacitively and inductively coupled slots, are investigated in terms of return loss and front-to-back radiated power ratio. It is shown that a centered CPW open stub gives a minimum of back radiation while allowing for easy matching. The slot-loop excitation seems to be a convenient feeding mechanism that also allows the insertion of active devices.

The problem of determining the shape and location of an object embedded in a homogeneous dissipative medium from measurements of the field scattered by the object is considered in this paper. The object is assumed to be an infinite cylinder of known cross section illuminated by a TM plane wave and the scattered field is measured on a line segment perpendicular to the direction of incidence. Measurement data are carried out at three different frequencies for a homogeneous cylinder of known dielectric constant. The location and contour shape are determined using two different reconstruction algorithms, a Newton-Kantorovich (NK) method and the modified gradient (MG) method whose effectiveness and robustness are compared. Both methods are based on domain integral representations of the field in the body. They involve an iterative minimization of the defect between an integral representation of the field measured on the line and the actual measured data. The NK method involves a linearization of the nonlinear relation between the field and the contrast, as well as the solution of a direct scattering problem at each iteration. The MG method seeks the simultaneous reconstruction of the field and the characteristic function of the support of the scatterer without solving a direct problem at each step. Both methods employed the same initial guess and the a priori information that the characteristic function is nonnegative.

Original lightweight, low-cost, and compact air-filled planar antennas with short-circuited elements, fed by a coaxial probe, for dual-frequency (S-antenna) and wide-band applications (E-antenna) are investigated. The two-band frequency antenna is formed of two stacked quarter-wavelength elements, short-circuited along diametrically opposed planes. This structure offers two modes with different radiation characteristics. The ratio between the two frequencies can be closely controlled within a range varying from 1.3-2. A bandwidth of 30% for a VSWR <2 is demonstrated using two stacked quarter-wavelength elements short-circuited along the same plane. Numerical simulation results are compared with experiments and a very good agreement is observed. Radiation patterns and input impedance of both structures are measured and the effects of various physical parameters are presented.

This paper presents microwave tomographic reconstructions of the complex permittivity of lossy dielectric objects immersed in water from experimental multiview near-field data obtained with a 2.45-GHz planar active microwave camera. An iterative reconstruction algorithm based on the Levenberg-Marquardt method was used to solve the nonlinear matrix equation which results when applying a moment method to the electric field integral representation. The effects of uncertainties in experimental parameters such as the exterior medium complex permittivity, the imaging system geometry and the incident field at the object location are illustrated by means of reconstructions from synthetic data. It appears that the uncertainties in the incident field have the strongest impact on the reconstructions. A receiver calibration procedure has been implemented and some ways to access to the incident field at the object location have been assessed.

A study of an ultrawideband frequency-modulated continuous-wave radar with an extended frequency sweep from 0.5 to 8 GHz is presented. It has been applied to through-the-wall human detection. This work presents the modeling of wall attenuation followed by real measurements. The radar system is presented, and trials of human being tracking are shown. This radar will enable large stand-off distance capabilities and dasiadasiain-depthpsilapsila building detection.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this letter, a novel port-to-port isolation technique suitable for a two-antenna system positioned at the top corner of a mobile phone is presented. The chosen planar inverted-F antennas (PIFAs) are intended to operate in the UMTS band [1.922.17] GHz and more precisely in the UMTS Rx band for diversity purpose. First, the distance between the PIFAs is severely reduced to 4 mm (0.027 $\lambda_{0}$ ) in order to obtain a very compact system. This proximal placement causes an increase of the insertion loss between the feeding ports of the PIFAs and therefore degrades the overall diversity performance of the two-antenna system. To compensate for this effect, the neutralization technique previously proposed by the same authors is implemented. Then, a novel way to implement this technique is studied to further improve the PIFAs' port-to-port isolation. It consists in achieving the neutralization of the antennas trough folded lines connected to the printed circuit board (PCB). A new prototype is fabricated and measured. The S-parameters and the total efficiency are presented. Additionally, the most important diversity metrics are computed to evaluate the potential of this novel two-antenna system for diversity applications in the UMTS Rx mode. </para>

A novel internal planar inverted-F antenna (PIFA) suitable for handset terminals is presented. The structure combines shorted parasitic patches, capacitive loads and slots to achieve multiband operation. This compact antenna operates in the GSM, DCS, PCS, UMTS, HIPERLAN/2 and IEEE 802.11a bands within 2.5:1 voltage standing wave ratio (VSWR) and with good efficiency.

In this paper, we propose a global power management approach for energy harvesting sensor nodes. Our approach is based on a joint duty-cycle optimization and transmission power control. By simultaneously adapting both parameters, the node can maximize the number of transmitted packets while respecting the limited and time-varying amount of available energy. We obtain a high-packet delivery by using an original predictive transmission power control that can efficiently adapt the transmission power to the wireless channel conditions. To accurately model the wireless channel and the node communication hardware, a waveform-level radio frequency simulator has been developed. Simulation results show 6.5 times improvement in energy efficiency and a packet reception ratio which is 9 times more efficient than a recently published technique. A 15% increase in energy efficiency, with respect to a fixed transmission power configuration, has also been observed. Finally, the global power management strategy has been validated on a real wireless sensor networks platform. Experimental results are very similar to those obtained in simulations, and thus confirm the efficiency of our power management approach.

The authors present the design of a wideband circularly polarised antenna with switchable polarisation sense. The basic antenna is a circularly polarised aperture coupled patch antenna with a slot excitation located along the diagonal of a rectangular patch. A second slot is added along the other diagonal and beam-lead pin diodes are inserted in both slots to allow a dual sense operation for a compact structure in a 4% CP bandwidth.

In this letter, a reconfigurable unit-cell for transmitarray antenna working at X-band is presented. It is designed to provide 1-bit phase quantization using p-i-n diodes. The unit-cell is based on multilayer frequency selective surfaces with the use of two substrates and a combination of a C-patch and a ring slot loaded by a rectangular gap. It is optimized using full-wave electromagnetic simulation and verified by using waveguide simulator. The experimental results show that the unit-cell provides two values of the transmission phase with a step of 180° at 11.5 GHz. Furthermore, the unit-cell has a low thickness of 0.19λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , and is low-cost and easy to fabricate.

In this communication, we present a new circularly-polarized array antenna using 2×2 linearly-polarized sub grid arrays in a low temperature co-fired ceramic technology for highly-integrated 60-GHz radio. The sub grid arrays are sequentially rotated and excited with a 90°-phase increment to radiate circularly-polarized waves. The feeding network of the array antenna is based on stripline quarter-wave matched T-junctions. The array antenna has a size of 15×15×0.9 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . Simulated and measured results confirm wide impedance, axial ratio, pattern, and gain bandwidths.

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