Walter Ciccognani

Time domain propagation measurements of the UWB indoor channel using PN-sequence in the FCC-compliant band 3.6-6 GHz

We have performed a propagation measurement campaign at the University of Rome Tor Vergata, Rome, Italy. We have sounded the channel by a probing signal at a carrier frequency of 4.78 GHz modulated by a train of pulses having a duration of 0.4 ns shaped by a pseudonoise (PN) sequence. The measurement band falls (3.6-6 GHz) in the frequency range allowed by the FCC ruling for ultrawide-band (UWB) operations. To characterize the channel behavior over the large and the small scale, the transmitter is moved in six different positions on the floor, while the receiver is moved in 625 different locations within each room. The receiver locations are arranged in a square grid of 25/spl times/25 points with 2 cm spacing, i.e., less than half of the minimum wavelength of the transmitted signal. A total of 625/spl times/16 impulse responses are recorded in nonline-of-sight (NLOS) conditions, 625 in line-of-sight (LOS) conditions within the rooms and 11 LOS measurements are made in the corridor at incremental spacing of 1 m. We describe the measurement technique as well as the procedure by which we process the experimental data to extract the amplitude, phase and delay associated to each component of the multipath profiles. We also derive path-loss and shadowing models for the UWB indoor channel in both LOS and NLOS conditions. Finally, we present an accurate analysis of the time dispersion of the UWB channel.

GaN-Based Robust Low-Noise Amplifiers

In this paper, an overview of recently reported low-noise amplifiers (LNAs), designed, and fabricated in GaN technology is provided, highlighting their noise performance together with high-linearity and high-robustness capabilities. Several SELEX-ES GaN monolithic technologies are detailed, providing the results of the noise characterization and modeling on sample devices. An in-depth review of three LNAs based on the 0.25- μm GaN HEMT process, marginally described in previous publications, is then presented. In particular, two robust and broadband 2-18-GHz monolithic microwave integrated circuit (MMIC) LNAs are designed, fabricated, and tested, exhibiting robustness to over 40-dBm input power levels; an X-band MMIC LNA, suitable for synthetic aperture radar systems, is also designed and realized, for which measurement results show a noise figure ~ 2.2 dB with an associated gain and robustness up to 41-dBm input power level.

UWB propagation measurements by PN-sequence channel sounding

An extensive measurement campaign is carried out in a modern office building. The channel is sounded by a carrier at 4.78 GHz modulated by a train of pulses, each having a duration of 0.4 ns, shaped by a pseudo noise (PN) sequence, covering the band 3.6-6 GHz. The transmitter is moved in six different positions on the floor, while the receiver is moved within each room by a digitally controlled positioner in 625 different locations arranged in a square grid of 25 /spl times/ 25 points with 2 cm spacing. A total of 625 /spl times/ 16 profiles in nonline-of-sight (NLOS) and 625 in line-of-sight (LOS) conditions are recorded within the rooms. LOS measurements are made in the corridor in 11 locations at incremental spacing of 1 m. We describe the measurement technique as well as the procedure by which we process the experimental data to extract the amplitude, phase and delay associated to each path of the channel impulse responses. Finally, we derive LOS and NLOS path-loss models.

The role of path loss on the selection of the operating bands of UWB systems

We performed a propagation experiment in a modern office building in Rome, Italy. The propagation measurements are based on the use of a vector network analyzer (VNA) over the band 2-12 GHz, with a frequency resolution of 5 MHz. We propose a novel analysis of the dependence of path loss laws on the carrier frequency and bandwidth. Our experimental results show that the path loss exponent strongly depends on the carrier frequency. The path loss exponents increase with the increasing carrier frequency for the line-of-sight (LOS) scenarios, while exhibit an opposite behavior for the non-line-of-sight (NLOS) data. We explain this behavior by the frequency dependence of the reflection coefficient of the walls surrounding the transmitter. Indeed, the lowest frequencies (2-5 GHz) are reflected, while the highest frequencies (up to 12 GHz) pass through the walls.

Miniaturized superconducting filter realized by using dual-mode and stepped resonators

In this paper, the design principles of a new miniaturized superconducting planar filter configuration is presented. The configuration is based on the combined use of dual-mode cross-slotted patch resonators and stepped resonators. Four-pole filters exhibiting a quasi-elliptical response and with operating frequencies in K-, L-, and C-bands have been designed as a test vehicle of the new configuration. The analyzed topology exhibits a high degree of miniaturization, requiring less than 50% of the area occupied by filters based on dual-mode or hairpin resonators. The physical origin of the transmission zeros is discussed, deriving equivalent-circuit descriptions that are capable of reproducing the measured frequency response. In order to confirm the validity of the introduced design principles, experimental performances on an exemplary L-band filter, realized using a YBCO film deposited on an MgO substrate and exhibiting a 3% fractional bandwidth, are presented. The measured frequency response obtained at T = 77 K agrees well with the simulations, presenting an insertion loss of 0.1 dB and a power handling of 34 dBm.

GaN transistor characterization and modeling activities performed within the frame of the KorriGaN project

The present paper presents the transistor modeling work achieved in the GaN European project KorriGaN (“Key Organisation for Research in Integrated Circuits in GaN technology”). The KorriGaN project (2005–09) has released 29 GaN circuits such as high-power amplifiers (HPAs), low-noise amplifiers (LNAs), and switches. Modeling is one of the main key to reach successful designs. Therefore, nonlinear models of European GaN HEMT models have been developed. This work deals with characterization tools such as pulsed IV, pulsed [ S ] parameters, load-pull measurements, and measurement-based methods to perform GaN HEMT compact models parameters extraction. The present paper will describe the transistor modeling activities in KorriGaN for HPA designs (nonlinear models including trapping and/or self-heating effects) and LNA designs (nonlinear models and noise parameters).

Gate-Source Distance Scaling Effects in H-Terminated Diamond MESFETs

In this paper, an analysis of gate-source and gate-drain scaling effects in MESFETs fabricated on hydrogen-terminated single-crystal diamond films is reported. The experimental results show that a decrease in gate-source spacing can improve the device performance by increasing the device output current density and its transconductance. On the contrary, the gate-drain distance produces less pronounced effects on device performance. Breakdown voltage, knee voltage, and threshold voltage variations due to changes in gate-source and drain-source distances have also been investigated. The obtained results can be used as a design guideline for the layout optimization of H-terminated diamond-based MESFETs.

Comparative investigation of surface transfer doping of hydrogen terminated diamond by high electron affinity insulators

We report on a comparative study of transfer doping of hydrogenated single crystal diamond surface by insulators featured by high electron affinity, such as Nb2O5, WO3, V2O5, and MoO3. The low electron affinity Al2O3 was also investigated for comparison. Hole transport properties were evaluated in the passivated hydrogenated diamond films by Hall effect measurements, and were compared to un-passivated diamond films (air-induced doping). A drastic improvement was observed in passivated samples in terms of conductivity, stability with time, and resistance to high temperatures. The efficiency of the investigated insulators, as electron accepting materials in hydrogenated diamond surface, is consistent with their electronic structure. These surface acceptor materials generate a higher hole sheet concentration, up to 6.5 × 1013 cm−2, and a lower sheet resistance, down to 2.6 kΩ/sq, in comparison to the atmosphere-induced values of about 1 × 1013 cm−2 and 10 kΩ/sq, respectively. On the other hand, hole mobiliti...

An ultra-broadband robust LNA for defence applications in AlGaN/GaN technology

The design, fabrication and test of a 2–18 GHz monolithic Low Noise Amplifier utilizing 0.25 µm AlGaN/GaN HEMT technology is reported. The measured noise figure of the amplifier is less than 4.7dB over the 2 – 18 GHz frequency range, exhibiting a minimum of 3.3 dB at 3 GHz. The LNA gain is 23dB. Even being a low-noise amplifier, the MMIC can withstand 10W input CW RF power, demonstrating no apparent degradation: to the authors knowledge this is the best RF LNA survivability reported to date in this frequency range using GaN technology.

Full W-Band High-Gain LNA in mHEMT MMIC Technology

In this contribution the possible applications, technology, design and measurements of a W-Band high gain LNA are given. The main features of the four stage LNA can be summarised as following: a 25 dB average gain with plusmn2 dB ripple from 70 to 105 GHz, where gain is higher than 21 dB on the entire 70-110 GHz range. LNA predicted noise figure is 2.7 dB between 80 and 95GHz and less than 3.2 dB up to 108 GHz while the chips power consumption is 35 mW. The technology used is a 70 nm GaAs mHEMT process from OMMIC.