This article aims to provide readers with a physical understanding of the propagation channel that is complementary to mathematical channel modeling. It presents an analysis of the directional propagation channel based on radiophotos. Radiophotos are graphical objects where directions of arrival are superimposed on three-dimensional (3D) panoramic photographs. The interaction between electro magnetic waves and the environment is immediately identified with these representations. This paper focuses on the direction of arrival at mobile in an urban macrocell environment. The first radiophoto collection illustrates the major propagation phenomena such as reflection, diffraction, or street canyoning. The second collection illustrates typical propagation channel profiles that are classified according to delay, azimuth, and elevation spread values. The paper also describes an original panorama-based method for estimating noise level in the azimuth–elevation domain.

This paper presents two feeding techniques for the radiation characterization of integrated antennas at millimeter-wave frequencies. The first method involves feeding the antenna-under-test (AUT) with a radiofrequency (RF) probe. We compare the measurements obtained with a standard RF probe, an extended probe, and an extended probe with reversed connector orientation. We find that the reversed orientation probe produces the best results in terms of effective measurement angular sector and reduction of ripples due to diffraction. The second method involves feeding the AUT through a flexible transmission line. This method achieves a larger range of measurement angles, but still suffers from parasitic scattering likely due to the mounting bracket and still need further development.

A new design method for multi-access antennas is presented. This method is based on a modal analysis assuming the microstrip antennas as a resonant cavity. Using this cavity approach, the eigenmodes perturbation induced by the cavity deformation (adding slots or short circuits) is studied. As an application, a solution of multi-access antenna with two ports, with operating frequency bands centered approximately on digital cellular system (DCS) and universal mobile telecommunication system (UMTS)/Wi-Fi standards is developed. These two ports are isolated using the previous original design method. In addition to the design method, the innovation of the structure resides on its application in terms of flexibility, reconfigurability, and portability for the future development of a unique system that allows cross services where telephony joined multimedia and online services. The design method and the performances are validated through comparisons between simulations and measurements.

In designing a Foreign Object Debris (FOD) detection system on airport runways, this paper deals with the performance of a 77 GHz reflectarray antenna (RA). Debris may be very small and have low radar cross section (RCS), leading to design a high gain primary-fed offset RA. To minimize the aperture blockage, the main radiation lobe is in the specular direction. The antenna has a maximum gain of 40 dBi and aperture efficiency of 50% over the frequency band 76–77 GHz. First measurements using a 77 GHz radar module were carried out on pavement.

The direct measurement of the radiation pattern of an antenna is often unreachable. A near-field sampling followed by a near-field/far-field (NF/FF) transformation is therefore substituted. This process is, in most cases, applied to antennas placed in free-space or over a perfect electric conductor. On the contrary, few results concern real environment conditions. Nevertheless, it is well known that the nature of the soil can drastically change the radiating characteristic of an antenna. The lack of information about the behavior of the antenna in real conditions can give rise to substantial errors in the evaluation of the performances of electromagnetic devices. The aim of this paper is then to propose a new NF/FF transformation able to reliably supply the field radiated by an antenna placed over a plane, homogeneous, dielectric, and lossy interface. The method is based on the cylindrical-wave expansion of the electric field. The real soil is taken into account by means of its reflection coefficients. First results are given for simple antennas and for both transverse magnetic and transverse electric polarizations.

In this paper, the design of compact diplexers and triplexers with dual-mode cavities is presented. Such devices are composed of coupled resonators without additional waveguide element, leading to a more compact architecture. Two topologies of compact diplexers are implemented and compared to a standard manifold diplexer. A hardware prototype is fabricated and measured for experimental verification. A compact triplexer is finally introduced for extending the concept to more than three ports.

The possibility to characterize infinite and periodic frequency-selective surfaces (FSS) filters that have two orthogonal axes of symmetry inside a waveguide is reported. Thus, preliminary measurements can rapidly be obtained at low cost with few elementary cells instead of using a large FSS panel in free space. This is possible because of the equivalence that exists between the electromagnetic fields of two symmetric and oblique plane waves incident on and reflected from an infinite periodic surface and the incident/reflected fields that exist inside a single-mode rectangular waveguide containing a finite number of elementary cells. Comparisons of the measurements with some full-wave simulations for FSS belonging to the first three groups as they were defined by Munk confirm the good agreement between them. This is an interesting and simple assessment tool concerning the fabrication quality of FSS. The extension of this technique to non-symmetric FSS patterns is also discussed and supported by experimental and simulation results. The limitations of the technique are finally discussed.

We propose in this paper a 4-channel time-domain test bench for the characterization and linearity enhancement of microwave power amplifiers (PAs). The proposed time-domain measurement system utilizes four track and hold amplifiers (THAs) for direct subsampling of radiofrequency (RF) signals. The use of wideband THAs to replace samplers or mixers enables reducing analog IF circuit complexity. It permits direct digitization of RF signals like CW, two-tone and pulsed modulated signals, bringing more flexibility in the receiver's performance by enhancing the dynamic range and bandwidth. This test bench is capable of completely extracting the phase, amplitude, and transfer characteristics of non-linear devices excited with CW or modulated RF signals. In this work, two-tone transfer characteristics of a 50 W GaN HEMT Nitronex PA were extracted and processed for applying digital pre-distortion linearization to enhance linearity performance. Time-domain envelope and carrier waveforms (voltage and current) along with third-order inter-modulation distortion (IMD) products with and without digital pre-distortion scheme are also presented.

LInear amplification using Non-linear Components (LINC) is an architecture that achieves linear power amplification for radio-frequency (RF) transmitters. This paper describes the impact of RF power amplifiers (PAs) class on the overall system performances. The linearity and efficiency of the LINC transmitter with different PA classes (AB, B, C, D, E, F, F−1, and J) are evaluated and compared, in terms of error vector magnitude (EVM), adjacent channel leakage ratio (ACLR), and power added efficiency (PAE), for a 16QAM modulation having 5.6 dB peak to average power ratio. Simulations are performed using a gallium-nitride high electron mobility transistor (GaN HEMT) for a power amplifier with an output power of 10 W at 900 MHz.

This paper shows the contribution of slow-wave coplanar waveguides on the performance of power amplifiers operating at millimeter-wave frequencies in CMOS-integrated technologies. These transmission lines present a quality factor Q two to three times higher than that of the conventional microstrip lines at the same characteristic impedance. To demonstrate the contribution of the slow-wave transmission lines on integrated millimeter-wave amplifiers performance, two Class-A single-stage power amplifiers (PA) operating at 60 GHz were designed in standard 40 nm CMOS technology. One of the power amplifiers incorporates only the microstrip lines, whereas slow-wave coplanar transmission lines are considered in the other one. Both amplifiers are biased in Class-A operation, drawing, respectively, 22 and 23 mA from 1.2 V supply. Compared to the power amplifier using conventional microstrip transmission lines, the one implemented with slow-wave transmission lines shows improved performances in terms of gain (5.6 dB against 3.3 dB), 1 dB output compression point (OCP1dB: 7 dBm against 5 dBm), saturated output power (Psat: >10 and 8 dBm, respectively), power-added efficiency (PAE: 16% instead of 6%), and die area without pads (Sdie: 0.059 mm2 against 0.069 mm2).

We present the non-linear electrical properties of simple two-terminal switching devices based on vanadium dioxide (VO2) thin films. The current–voltage characteristics of such devices present negative differential resistance (NDR) regions allowing generating electrical self-oscillations across the investigated devices, with frequencies ranging from several kHz up to 1 MHz. We investigate and compare the factors determining the onset of oscillatory phenomenon in both voltage- and current-activated oscillations and explain its origin. For both activation modes, we will correlate the properties of electrical oscillations (amplitude and frequency) with the amplitude of the continuous excitation signal, the physical geometry of the devices or ambient temperature. We conclude by mentioning several possible applications for the oscillation generation in the radiofrequency (RF)/microwave domains (inverters, integrated a.c. signal generators, pressure and temperature sensors, etc.).

This paper presents the research done at LAAS-CNRS and in the context of “NANOCOMM” project. This project aims to demonstrate the potential of nanotechnology for the development of reconfigurable, ultra-sensitive, low consumption, and easy installation sensor networks with high performance in terms of reliability in line with the requirements of aeronautics and space. Each node of the sensor network is composed of nano-sensors, transceiver, and planar antenna. In this project, three-dimensional (3D) heterogeneous integration of these different components, on flexible polyimide substrate, is planned. Two types of sensors are selected for this project: strain gauges are used for the structure health monitoring (SHM) application and electrochemical cells are used to demonstrate the ability to detect frost phenomenon. After processing, sensors data are processed and transmitted to the reader unit using an ultra-wide band (UWB) transceiver. (digital baseband and radiofrequency (RF) head). The design and implementation of reconfigurable wireless communication architectures are provided according to the application requirements using nanoscale 65 nm CMOS technology. It is proposed to integrate on flexible substrate the transceiver using the flip-chip technique. A 60 GHz planar antenna is connected to the transceiver for the wireless data transmission. This paper is focused on the 3D integration techniques and the technological process used for the realization of such communicating nano-objects on polyimide substrate. The first assembly tests were carried out. Tests of interconnections quality and electrical contacts (Daisy Chain, calibration kit, etc.) were also performed with good results. A bumps contact resistance of 15 mΩ is measured.

The design of a high-stability radiometer is presented in this paper. It is used to characterize the stability of a microwave active cold load at L-band. The two-load radiometer takes advantage of a noise injection technique to improve its sensitivity. A temperature-stabilized enclosure is used to minimize gain and noise temperature fluctuations of the receiver. The radiometer sensitivity is 0.031 K and the gain fluctuations are less than 0.005 dB during 1 day. The total gain and the receiver noise temperature of the radiometer exhibit very small variations (<0.03 dB and 1 K, respectively) on the long term.