Gianfranco Manes

A 240-W dual-band 870 and 2140 MHz envelope tracking GaN PA designed by a probability distribution conscious approach

In this paper, we present the design of a dual-band power amplifier (PA) for envelope tracking (ET) operation. The design was based on a multi-section transmission line matching technique and has taken into account the actual probability distribution function of the WCDMA 3GPP DL signal. The technique was applied to a concurrent 870 and 2140 MHz ET PA designed around a GaN HEMT. The ET friendly design method has proven capable to meet the performance equal to those of each single band pulsed load pull with minor loss, over a bandwidth of 100 MHz, reporting an average drain efficiency of 69.5% and 51.0%, and peak power levels of 54.86 dBm and 53.96 dBm at the design frequencies. A detailed discussion of the design method and validating experimental results data are reported.

Wireless localization using self-organizing maps

Localization is an essential service for many wireless sensor network applications. While several localization schemes rely on anchor nodes and range measurements to achieve fine-grained positioning, we propose a range-free, anchor- free solution that works using connectivity information only. The approach, suitable for deployments with strict cost constraints, is based on the neural network paradigm of self-organizing maps (SOM). We present a lightweight SOM- based algorithm to compute virtual coordinates that are effective for location-aided routing. This algorithm can also exploit the location information, if available, of few anchor nodes to compute absolute positions. Results of extensive simulations show improvements over the popular multi-dimensional scaling (MDS) scheme, especially for networks with low connectivity, which are intrinsically harder to localize, and in presence of irregular radio pattern or anisotropic deployment. We analytically demonstrate that the proposed scheme has low computation and communication overheads; hence, making it suitable for resource-constrained networks.

Exploiting Low-Cost Directional Antennas in 2.4 GHz IEEE 802.15.4 Wireless Sensor Networks

Motivated by recent interest in directional antennas for WSNs, we propose a four-beam patch antenna (FBPA) designed to meet the size, cost and complexity constraints of sensor nodes. We use in-field experiments with COTS motes to demonstrate substantial benefits to WSN applications. Used outdoors, the FBPA extends the communication range from 140 m to more than 350 m, while indoors it suppresses the interference due to multipath fading by reducing the signal variability of more than 70%. We also show interference suppression from IEEE 802.11 g systems and discuss the use of the antenna as a form of angular diversity useful to cope with the variability of the radio signal. Experimental data are analyzed to derive model parameters intended for use in future network simulations.

A New Design Method for Single-Feed Circular Polarization Microstrip Antenna With an Arbitrary Impedance Matching Condition

This paper introduces a new analytical method suitable for the design of the single-feed circular polarization (CP) microstrip patch antenna. Specifically, the proposed method imposes simultaneously the circular polarization condition as well as an arbitrary input impedance matching condition. The two conditions are enforced by an analytical method derived from an equivalent circuit model of a quasi-symmetrical patch antenna, and manipulated to control the modal detuning. This method can be used as an aid to speed up the design procedure for CP antennas even working with a numeric CAD tool. The validation of this approach is proven designing and fabricating a prototype implementing an original design, which consists of a circular disc slotted by a concentric elliptical cut with coaxial feed and operating at the center frequency of 2.45 GHz. The fabricated prototype exhibited a return loss of about 19 dB, within an impedance bandwidth of 130 MHz, a measured gain of 3.85 dB and a 0 dB axial ratio at 2.45 GHz with a corresponding modal phase difference of 87 degrees.

Analysis and Performance of a Smart Antenna for 2.45-GHz Single-Anchor Indoor Positioning

This paper presents the theoretical analysis and the experimental evaluation of a new switched beam antenna designed to operate at 2.45 GHz. The antenna enables direction of arrival estimation using six directional planar elements arranged to form a platonic solid geometry. It also supports polarization diversity, and it is suitable for single-anchor indoor positioning applications. We adopt the Cramer-Rao bound to study the estimation accuracy of the proposed antenna in absolute 2-D target positioning using received signal strength measurements. First, we describe the design principles for the radiators, we provide an extensive characterization of the switched antenna prototype, and we discuss positioning applications. We then report experimental data that support the results of the theoretical analysis and show consistency between theoretical expectation and the measurements. Finally, we discuss results from proof-of-concept operative indoor positioning example, showing an average localization error as low as 1.7 m.

Single-anchor indoor localization using a switched-beam antenna

We propose an RF-based localization system that works using a single anchor node. The anchor is equipped with a switched-beam directional antenna that is installed on the ceiling of a room and collects signal strength information sufficient for absolute 2D target positioning. Indoor measurements are used to show satisfactory localization results with range-free (proximity), range-based and fingerprinting schemes.

A new approach for concurrent Dual-Band IF Digital PreDistortion: System design and analysis

In this paper we propose a dual band digital predistorter (DB-DPD), suitable for concurrent dual-band power amplifiers. A sub-sampling receiver is at the basis of the feedback path, while the vectorial gain adjuster is achieved at the proper digital intermediate frequency. The proposed method adopts a conventional memory polynomial DPD for linearization. The approach is tested by system-level simulations and it was proven to be able to correct most of the nonlinearity, with only a modest performance loss with respect to single-band architectures.

Physical/electromagnetic pHEMT modeling

An effective technique, which is based only on geometrical and physical data, is presented for the analysis of high-frequency FETs. The intrinsic part of this electron device is described by a quasi-two-dimensional hydrodynamic transport model, coupled to a numerical electromagnetic field time domain solver in three dimensions that analyzes the passive part of the FET. Such an analysis is entirely performed in the time domain, thus allowing linear and nonlinear operations. The obtained data give insights to some parameters affecting the signal distribution through the entire device structure; a comprehensive discussion of these is given for a test device. In order to prove the validity of the approach, the bias-dependent small-signal analysis is compared with the corresponding measurements up to 50 GHz for two 0.3-/spl mu/m gate-length AlGaAs-InGaAs-GaAs pseudomorphic high electron-mobility transistors, each having two gate fingers of 25-/spl mu/m and 100-/spl mu/m width, at bias points ranging from Idss to the pinchoff regime. The accuracy and the efficiency of the approach make it suitable for device optimization.

Design of a Simplified Delay System for Ultrasound Phased Array Imaging

A novel technique for implementing the dynamically vari- able delay system, required for electronic sector scanning in ultrasound phased-array imaging equipments, has been recently introduced. The technique is based on separate and independent processing of the car- rier and of the envelope of the echo pulses. Carrier phasing is accom- plished by electronic phase-shifters, while envelope delay is varied by delay lines. This latter function, however, can be performed using dw Crete delays in increments much larger than those required by previous techniques. Extensive computer simulations of the array directivity pattern have been performed to evaluate the effect of a coarse delay quantization. Based on the simulation results, the design of a delay sys- tem exhibiting a dramatic simplifkation over alternative techniques is described.

Millimeter-wave FET modeling using on-wafer measurements and EM simulation

Electron device modeling is a challenging task at millimeter-wave frequencies. In particular, conventional approaches based on lumped equivalent circuits become inappropriate to describe complex distributed and coupling effects, which may strongly affect the transistor performance. In this paper, an empirical distributed FET model is adopted that can be identified on the basis of conventional S-parameter measurements and electromagnetic simulations of the device layout. The consistency of the proposed approach is confirmed by robust scaling properties, which enable millimeter-wave small-signal S-parameters to be predicted as a function of the device periphery and number of gate fingers. Moreover, it is shown how the model identified on the basis of standard S-parameter measurements up to 50 GHz can be efficiently exploited in order to obtain reasonably accurate small-signal prediction up to 110 GHz. Extensive experimental validation is presented for 0.2-/spl mu/m pseudomorphic high electron-mobility transistors devices.