Emerging research in microwave systems and applications

The electromagnetic (EM) spectrum is becoming overcrowded with a variety of wireless signals and other communication and sensing circuits and devices. This has led to an increased interest in the design of RF and microwave systems and subsystems to help decongest the overwhelmed EM spectrum. However, journals currently available for accepting and publishing research outputs in this field are scarce

Wireless propagation modelling inside a business jet

Wireless communication on-board aircraft has recently received increased attention as passengers are demanding for seamless office-like communication environments during their flight. Aircraft manufacturers are also interested in this technology to reduce cable complexity and provide new in-flight services. Various technologies are being considered for this purpose, such as IEEE802.11a/b/g. A radio propagation map is necessary to determine the received signal strengths inside the environment and can be obtained either through accurate modelling or through a measurement campaign. A simulation model is more attractive as it can be used to identify ideal antenna locations that maximize coverage at the design stage. Since the business jet market necessitates customized cabin configurations for each customer this will avoid costly measurement campaigns. This work presents a novel simulation model which has been used to characterize propagation characteristics inside a Dassault Aviation business jet. The developed package is based on geometric optics (GO) and adopts ray tracing techniques. Simulation results were compared with actual measurements performed on-board the aircraft with a good correlation between the two. This study takes into account only a static channel whereby all passengers are seated.peer-reviewe

Broadband Analysis of Microwave Structures by Enhanced Finite-Element Methods

The paper deals with the broadband modeling of microwave structures by finite-element methods. The attention is turned to original enhancements of accuracy, efficiency and stability of finite-element codes. The partial improvements are based on novel approximations both in the spatial domain and in the time one, in the adoption of complex frequency hopping, fast frequency sweep and envelope finite-element techniques. In the paper, a possible hybridization of approaches is discussed. Proposed finite-element schemes are applied to the analysis of canonical longitudinally homogeneous transmission lines in order to demonstrate their advantages

Fast and Robust Characterization of Dielectric Slabs Using Rectangular Waveguides

Waveguide characterization of dielectric materials is a convenient and broadband approach for measuring dielectric constant. In conventional microwave measurements, material samples are usually mechanically shaped to fit the waveguide opening and measured in closed waveguides. This method is not practical for millimeter-wave and sub-millimeter-wave measurements where the waveguide openings become tiny, and it is rather difficult to shape the sample to exactly the same dimensions as the waveguide cross-section. In this paper, we present a method that allows one to measure arbitrarily shaped dielectric slabs that extend outside waveguides. In this method, the measured sample is placed between two waveguide flanges, creating a discontinuity. The measurement system is characterized as an equivalent Pi-circuit, and the circuit elements of the Pi-circuit are extracted from the scattering parameters. We have found that the equivalent shunt impedance of the measured sample is only determined by the material permittivity and is rather insensitive to the sample shape, position, sizes, and other structural details of the discontinuity. This feature can be leveraged for accurate measurements of permittivity. The proposed method is very useful for measuring the permittivity of medium-loss and high-loss dielectrics from microwave to sub-terahertz frequencies

High Gain Ultra-Wideband Parabolic Reflector Antenna Design Using Printed LPDA Antenna Feed

Reflector antennas with log periodic dipole array (LPDA) feeds are ideal for applications that demand high gain, broadband operation. However, when the phase center of the LPDA is not fixed, mismatches at the focal point cause degradation and large ripple in gain. To overcome these issues, a printed LPDA is optimized for minimal phase center variation as a reflector antenna feed. The antenna is designed to operate at 1-19 GHz frequency band with voltage standing wave ratio (VSWR) less than 3.0 and minimum gain of 17 dBi. Reflector size can be increased for further improvement in gain. Designed antenna parameters, radiation patterns, and aperture efficiencies over frequencies are presented and compared to previous studies.

On the origin of the controversial electrostatic field effect in superconductors

In semiconductor electronics, the field-effect refers to the control of electrical conductivity in nanoscale devices, which underpins the field-effect transistor, one of the cornerstones of present-day semiconductor technology. The effect is enabled by the penetration of the electric field far into a weakly doped semiconductor, whose charge density is not sufficient to screen the field. On the contrary, the charge density in metals and superconductors is so large that the field decays exponentially from the surface and can penetrate only a short distance into the material. Hence, the field-effect should not exist in such materials. Nonetheless, recent publications have reported observation of the field-effect in superconductors and proximised normal metal nanodevices. The effect was discovered in gated nanoscale superconducting constrictions as a suppression of the critical current under the application of intense electric field and interpreted in terms of an electric-field induced perturbation propagating inside the superconducting film. Here we show that ours, and previously reported observations, governed by the overheating of the constriction, without recourse to novel physics. The origin of the overheating is a leakage current between the gate and the constriction, which perfectly follows the Fowler-Nordheim model of electron field emission from a metal electrode.c

Modeling and Optimization of the Microwave PCB Interconnects Using Macromodel Techniques

L'abstract è presente nell'allegato / the abstract is in the attachmen

Folded waveguide resonator filter for communication and radar systems

In this thesis, a primary investigation into developing a compact and low-loss bandpass filter, using novel folded waveguide resonators with a footprint reduction, has been addressed. A slot coupling between adjacent resonators is introduced, which is characterized by using full-wave EM simulations and verified experimentally. Two designs of 2-pole folded waveguide resonator filters of this type have been considered, fabricated and tested. In this thesis, an even more compact FWG resonator filter using a novel slot technique is reported. The attainable size reduction is about 50%, and the filter design is based on theoretical and full-wave electromagnetic (EM) simulations. Based on FWG structure, two types of folded waveguide resonators have been studied and considered the half-wavelength resonator and the quarter-wavelength resonator. Moreover, both structures for the realization of microwave cavities with high-Q, with the result of a high spurious free range and reduced footprint, have been evaluated. Furthermore, a novel folded waveguide resonator with about a 75 % reduction of the volume from the conventional size has been described. For comparison, two types of folded waveguide resonators have been studied, i.e. the quarter-wavelength resonator of square shape and the newly proposed triangular shape. In addition, a demonstration of a filter application for miniature triangular folded waveguide resonators has been designed and simulated using an EM simulator. In addition, numbers of experiments have been conducted to develop cavity FWG and Substrate Integrated folded waveguide SIFW resonator filters using a folded structure, which is the main aim of this thesis. Furthermore, this thesis deals with the simulation and implementation for many designs and topologies of FWG and SIFW resonator filters and their frequency response. Simulation and experimental results were presented to validate the design and to show the advantages of these types of filters. In addition, a new type of filter with a compact multi-layer structure and low loss is attractive for implementation with advanced device technologies, such as micromachining, LTCC and LCP technologies

Annual Report 2012 / Institute for Pulsed Power and Microwave Technology = Jahresbericht 2012 / Institut für Hochleistungsimpuls- und Mikrowellentechnik. (KIT Scientific Reports ; 7643)

The Institute for Pulsed Power and Microwave Technology (Institut für Hochleistungsimpuls- und Mikrowellentechnik - IHM) is doing research in the areas of pulsed power and high power microwave technologies. Both, research and development of high power sources as well as related applications are in the focus. Applications for pulsed power technologies are ranging from material processing to bioelectrics. Microwave technologies are focusing on RF sources for electron cyclotron resonance heating and on applications for material processing at microwave frequencies