The operation of a microwave photonic link is thoroughly investigated both theoretically and experimentally. To this aim, we have developed a simulation tool based on an accurate physical model embedded in a radio frequency (RF) chain simulator. The theoretical predictions are tested on an intensity modulation-direct detection (IMDD) link we have specifically developed to this purpose. Our simulation tool takes into account both optical and electrical characteristics of the link components including the laser dynamics and impedance matching networks. It thus enables an accurate understanding of the different physical and electrical phenomena governing the link's performances even under unusual operation conditions. Specifically, we were able to isolate an unusual behavior and to confirm it experimentally. It is thereby clear that the noise figure of a microwave optical link can be lower than the electrical losses, such as a mismatched output passive electrical network. This state is reached when the optical losses are high enough and when the link's output impedance is mismatched, too.

This article discusses the reduction of nonlinearities in analog-to-digital (A/D) converters using digital signal processing (DSP). Also modeling of certain essential nonlinearities is considered in detail. The main focus is on wideband radio receivers, such as the emerging cognitive radio applications, where a collection of signals at different frequency channels is converted to digital domain as a whole. Therefore, the overall dynamic range can easily be in the order of tens of dBs and thus even mild nonlinear distortion can cause strong carriers to block weaker signal bands. In this article, a mathematical model for clipping distortion due to improper input signal conditioning is derived through Fourier analysis. Additionally, stemming from the analysis an adaptive DSP-based post-processing method for reducing the effects of clipping and integral nonlinearity (INL) in A/D converters is presented with illustrative examples using both computer simulations and laboratory radio signal measurements.

This paper describes some key points in the history and development of the European Microwave Conference, the European Microwave Week, and the European Microwave Association, starting from 1969. It captures the way in which the conference since the earliest days has sought to create a successful blend of scientific and industry interests and has adapted itself to and indeed shaped the many existing technical changes that have characterized and continue to be at the core of the field of microwave engineering.

In this paper, we address the architecture of multistandard simultaneous reception receivers and we aim to reduce the complexity and the power consumption of the analog front-end. To this end, we propose an architecture using the double orthogonal translation technique in order to multiplex two signals received on different frequency bands. A study case concerning the simultaneous reception of 802.11 g and Universal Mobile Telecommunications System (UMTS) signals is developed in this article. Theoretical and simulation results show that this type of multiplexing does not significantly influence the evolution of the signal-to-noise ratio of the signals. In the same time a 30% reduction of the power consumption is expected as well as a significant reduction of the complexity.

The objective is to demonstrate a reproducible carbon nanotube (CNT)-based technology for radio frequency (RF) switch working in the range of 40–60 GHz and fulfilling the specifications: low losses, high isolation, and an operating voltage below 30 V. The first processed component had an operating voltage of 14 V for an ohmic contact in a Nano-Electro Mechanical System (NEMS) tweezer design. This result is confirmed by theory with an operating voltage of 13 V. A capacitive-contact NEMS is also developed using multi-walled CNTs (MWCNTs) coated with a SiO2 dielectric layer deposited by electron beam induced deposition method (EBID). High Frequency Simulation Software (HFSS) RF-simulation on an innovative NEMS geometry shows encouraging results with transmission ratios between “on” state and “off” state up to 34% for ohmic-contact switch and 25% for a capacitive-contact switch.

This article addresses the analysis and digital signal processing (DSP)-based mitigation of phase noise and sampling clock jitter in orthogonal frequency division multiplexing (OFDM) radios. In the phase noise studies, the basic direct-conversion receiver architecture case is assumed with noisy downconverting oscillator. In the sampling jitter case, on the other hand, the so-called direct-radio-frequency-sampling receiver architecture is deployed utilizing bandpass sub-sampling principle. The basis for the DSP-based impairment mitigation techniques is first formed using analytical receiver modeling with incoming OFDM waveform, where the effects of both oscillator phase noise and sampling clock jitter are mapped to certain type subcarrier cross-talk and distortion compared to ideal receiver case. Then iterative detection principles and interpolation techniques are developed to essentially estimate and cancel the subcarrier distortion. Also some related practical aspects, like channel estimation, are addressed. The performance of the proposed mitigation techniques is analyzed and verified with extensive computer simulations. In the simulations, realistic phase-locked-loop-based oscillator models are used for phase noise and sampling clock jitter. In addition, different received signal conditions like plain additive white Gaussian noise channel and extended ITU-R Vehicular A multipath channel are considered for practical purposes. Altogether the obtained results indicate that the effects of oscillator and sampling clock instabilities can be efficiently reduced using the developed signal processing techniques.

We present an overview on epitaxial growth, processing technology, device performance, and reliability of our GaN high electron mobility transistors (HEMTs) manufactured on 3- and 4-in. SiC substrates. Epitaxy and processing are optimized for both performance and reliability. We use three different gate lengths, namely 500 nm for 1–6 GHz applications, 250 nm for devices between 6 and 18 GHz, and 150 nm for higher frequencies. The developed HEMTs demonstrate excellent high-voltage stability, high power performance, and large DC to RF conversion efficiencies for all gate lengths. On large gate width devices for base station applications, an output power beyond 125 W is achieved with a power added efficiency around 60% and a linear gain around 16 dB. Reliability is tested both under DC and RF conditions with supply voltage of 50 and 30 V for 500 and 250 nm gates, respectively. DC tests on HEMT devices return a drain current change of just about 10% under IDQ conditions. Under RF stress the observed change in output power density is below 0.2 dB after more than 1000 h for both gate length technologies.

We report investigations on the fabrication and characterization of graphene nanoribbon (GNR) field-effect transistors. Graphene layers are obtained from the thermal decomposition of a Si-face 4H-SiC substrate. To achieve high dynamic performance, a structure with an array of GNR connected in parallel was fabricated by e-beam lithography. The best intrinsic current gain cut-off frequency of 60 GHz and maximum oscillation frequency of 28 GHz were achieved. This study demonstrates the exciting potential of GNR in high-frequency electronics.

The present paper presents a very efficient technique for enhancing the pointing accuracy in beam-waveguide (BWG) antennas and its application to the deep space antenna DSA2 of the European Space Agency. The proposed technique permits to achieve a twofold result: on the one hand, it provides a solution to the beam aberration issue, arising when the antenna simultaneously receives from and transmits to a spacecraft moving in the transversal direction. On the other hand, it allows to perform a fast conical scan to enhance the pointing accuracy of the antenna. Both results are achieved by simple linear displacements of feeds and mirrors located in the lower part of the BWG, with a very limited deterioration of the antenna gain. The required displacements of feeds and mirrors are determined through a fast optimization algorithm, based on a top-down approach, which requires repeated physical–optics analyses of the lower part of the beam waveguide only, with a significant reduction in the computing time.

This paper proposes the design of tunable dual-band resonators for multi-band multi-standard systems. The main objective is to provide frequency tunability in the second resonance while maintaining the first resonance fixed. To this end, two tunable resonators are proposed: the capacitive-loaded stepped-impedance resonator and the capacitive-loaded hole resonator. The work is divided into two main parts. In the first part, an in-depth analysis of the capacitive-loaded stepped-impedance resonator (SIR) structure is done; it provides analytical closed-form design equations that ease the resonator design in contrast to the several approaches available in the literature to date. The analysis is also particularized to the case of the capacitive-loaded constant-section resonator and extended to the capacitive-loaded hole resonator. In addition, a study of the quality factor in capacitively tuned SIRs is also provided. In the second part, resonators are integrated in three dual-band tunable filters, one based on the capacitive-loaded constant-section resonator, another one on the capacitive-loaded SIR, and finally on the capacitive-loaded hole resonator. Two of these filters demonstrate operation in wireless local-area network frequency bands, with a fixed first band at 2.45 GHz and a second band which can be tuned between 5.75 and 5.25 GHz.

In this paper, we address the architecture of a multi-antenna receiver and we aim at reducing the complexity of the analog front-end. To this end, an innovative architecture is introduced based on code multiplexing. This architecture uses the direct sequence spread spectrum technique in order to multiplex the different antennas contributions through a single In-phase/Quadrature (IQ) demodulator. Simulation and measurement results show that the bit error rate does not increase so much with the multiplexing in both Gaussian and fading environments and with strong radiofrequency (RF) defaults conditions. The complexity evaluation shows that the proposed architecture significantly reduces the chip area and the power consumption of the front-end.

This paper discusses the determination of key electrical parameters of AlInN/(AlN)/GaN heterostructures from capacitance–voltage (CV) measurements. These heterostructures gained recently importance since they allow for high electron mobility transistor (HEMT) devices with several remarkable records: densities of the 2D electron gas (2DEG) of 2.6 × 1013 cm−2 for lattice-matched (LM) heterostructures and barrier thickness of 14 nm, beyond 2 A/mm saturation currents, above 100 GHz operation for heterostructures grown on Si (111) with gate length of 0.1 µm. Despite these striking experimental results, a consistent determination of the most important electrical parameters, namely polarization sheet charge density, surface potential, and dielectric constant of the alloy are still missing. By setting up the correct charge balance equation, these parameters can unambiguously be determined. For instance, in the case of nearly LM Al0.85In0.15N these parameters amount to σAl0.85In0.15N/GaN ~ 3.7 × 1017 m−2, eΦS ~ 3 eV and ɛAl0.85In0.15N ~11.2, for the charge density, the surface barrier potential, and the dielectric constant, respectively.

In this paper the non-ideal and frequency-dependent behavior of the hardware components of the ultra-wideband (UWB) transmitter RF-front end is analyzed. Both digital and analytical methods to compensate for this frequency-dependent behavior are investigated, in order to optimize the radiated wave, so that its spectrum perfectly matches the given mask. An example of spectral system optimization with analog devices is shown and verified through measurement results.

GaN technology has gained a lot of attention in Europe over the last few years for various domains including RF electronics. After a few years of active observation, United Monolithic Semiconductors (UMS) has taken the decision to introduce a GaN technology family in its portfolio. Based on its extensive experience of III–V technology and the intensive support and collaboration with partners and European research institutes, UMS has developed the capability to produce state-of-the-art GaN devices and circuits. The present paper will summarize the current status achieved and illustrate it with a few representative examples. Aspects covering material, devices, and circuits will be addressed.

This paper proposes a practical approach for developing a new class of compact slow-wave coplanar waveguide (CPW) series/shunt stubs, which offer 40% reduction in size relative to a conventional design. It demonstrates that the technique using interdigitated capacitive loading can provide size and cost reductions, while also providing performance enhancements such as better return loss. The experimental prototypes presented in this paper demonstrate the validity of the design method and the ability to print interdigitated capacitors inside the center conductor of the series/shunt stubs. The principle of achieving such high-quality circuits is detailed and is also confirmed by theoretical and experimental results, which are in reasonable agreement up to at least 70 GHz. The paper also presents a family of novel topologies of slow wave bandpass filters based on the proposed capacitively loaded CPW series/shunt stubs.

In this paper, we investigate the scattering properties of an array of finite-length single-walled carbon nanotubes (SWCNTs), up to terahertz frequencies. The problem is cast in terms of a Pocklington-like equation. The current density along the CNT is described by a quasi-classical transport model, recently proposed. The numerical solution is obtained by means of the Galerkin method. Case studies are carried out, either referred to isolated SWCNTs and an array of SWCNTs, aimed at investigating the frequency behavior of the scattered field.

In order to perform an accurate design, in particular in non-linear circuit, the equivalent circuit of inductors must be precisely described in a wide frequency band. Many models have been proposed to describe the behavior of inductors on lossy substrate. They consist of a great number of elements, often suggested by physical phenomena. Most of them cannot be extracted from measurements. In this paper, we propose a model composed only of elements that can be analytically extracted from measurement results.