On the Use of Ridge Gap Waveguide Technology for the Design of Transverse Stub Resonant Antenna Arrays

This paper presents some considerations on the design of a novel antenna consisting of the combination of a transverse stubs (TS) array excited by Ridge Gap Waveguides (RGWs), as well as a discussion of the experimental results obtained from a prototype that was manufactured and measured. A combination of Continuous Transverse Stubs (CTSs) is used as the starting point. Subsequently, the CTSs are modified to include some metallic blockers that split each CTS into a combination (array) of shorter TSs. This is performed in order to excite each individual TS column using a different RGW; thus, ensuring a close to uniform field distribution in the transverse plane of the TS arrays. Hence, the directivity of the antenna is increased. As a series-feed configuration is considered, the antenna keeps a resonant behaviour, having a narrow-band response. A Corporate Feeding Network (CFN) using the aforementioned RGW technology placed in the same layer as the rest of the antenna is included in the design. The radiating area of the antenna is, finally, 5.88×7.12 with a simulated peak gain of 26.2 dBi and a Side Lobe Level (SLL) below -13 dB. A prototype is manufactured and tested. The simulated and measured radiation patterns maintain similar shapes to those of the simulations, with very similar angular widths in both main planes, although the frequency corresponding to the highest directivity changes to 31.8 GHz. A matching bandwidth of 517 MHz and a gain of 24.5 is, finally, achieved at that frequency.This research was funded in part by the Spanish State Research Agency under project PID2019-107688RB-C21

Study of the growth mechanisms of low-pressure chemically vapour deposited silica films

7 pages, 5 figures.-- Issue title: "Proceedings of the Twelfth European Conference on Chemical Vapour Deposition" (Sitges, Barcelona, Spain, Sep 5-10, 1999).We have studied the surface morphology evolution of SiO2 films grown at 20 nm/min in a low-pressure chemical vapour deposition reactor from SiH4/O2 mixtures at low (611 K) and high (723 K) temperatures. Films have been deposited for times ranging from 10 min up to 48 hours. It is shown that the SiO2 growth at high temperature becomes stable, whereas at low temperature it is unstable (i.e., the surface roughness increases continuously with deposition time). This clear difference is explained on the basis of the different growth mechanisms operating under both experimental conditions. These results are compared with the predictions of the few theoretical works on growth evolution by chemical vapour deposition.This work was partially realized within the frame of the CONICET-CSIC research cooperation program, partially supported by Ministerio de Educación y Cultura (Programa de Cooperación Científica con Iberoamérica), by the 7220-ED/082 project from ECSC and by the 07M/0710/97 project from CAM. F. Ojeda gratefully acknowledges the grant financed by the Comunidad de Madrid (683/96, BOCM 22/4/96).Publicad

Modelling of silica film growth by chemical vapour deposition: Influence of the interface properties

12 pages, 6 figures.-- Issue title: "Thirteenth European Conference on Chemical Vapor Deposition" (Glyfada, Athens, Greece, Aug 26-31, 2001).We have studied the main physical mechanisms involved in the growth of Chemical Vapor Deposition (CVD) systems. We have characterized W films by Scanning Tunneling Microscopy, and SiO2 films by Atomic Force Microscopy (AFM) and Infrared and Raman spectroscopies. Tungsten CVD films display an unstable growth mode since the surface roughness increases continuously with deposition time. In order to assess the physical origin of the instability we have grown silica films in a low-pressure CVD reactor from SiH4/O2 mixtures at 0.3 nm/s at low (611 K) and high (723 K) temperatures. Silica films deposited at high temperature are rougher than those grown at low temperature. Moreover, they become asymptotically stable in contrast to those deposited at low temperature which are unstable. These different behaviors are explained within the framework of the dynamic scaling theory by the interplay for each growth condition between surface diffusion relaxation processes, shadowing effects, lateral growth, short-range memory effects and the relative concentration of active sites, mainly SiH and strained siloxane groups, and passive sites. A continuum growth equation taking into account these effects is proposed to explain the observed growth behavior for both sets of films. Computer simulations of this equation reproduce the experimental behavior.This work was partially supported by the 7220-DE/082 project from ECSC, the 07M/0710/97 project from CAM and Ministerio de Educación y Cultura (MEC, programa de Cooperación Científica con Iberoamérica) and the DGES project BFM2000-0006 from MBC. It was pertormed also within the framework of the CSIC/CONICET research cooperation program.Publicad

Design and Realization of a Band Pass Filter at D-band Using Gap Waveguide Technology

Gap waveguide technology is particularly attractive for the design of passive elements in mm-wave systems. Recently, the so-called zero-gap implementation has proved to be very robust to manufacturing tolerances, while at the same time keeping the low loss associated to the contactless standard gap waveguide. In this paper, a Chebyshev filter working at 145 GHz based on this idea and intended to be used in a wireless communication system is designed and optimized. A conventional milling technique has been used in its fabrication, and good measured results have been obtained in a single-pass process.This work has been partly funded by EU Commission within the H2020 Ultrawave project, Spanish Government under project TEC-2016-79700-C2-2-R, and by Chairs of Excellence project appointment at the Universidad Carlos III de Madrid, Madrid, Spain

Pattern-wavelength coarsening from topological dynamics in silicon nanofoams

We report the experimental observation of a submicron cellular structure on the surface of silicon targets eroded by an ion plasma. Analysis by atomic force microscopy allows us to assess the time evolution and show that the system can be described quantitatively by the convective Cahn-Hilliard equation, found in the study of domain coarsening for a large class of driven systems. The space-filling trait of the ensuing pattern relates it to evolving foams. Through this connection, we are actually able to derive the coarsening law for the pattern wavelength from the nontrivial topological dynamics of the cellular structure. Thus, the study of the topological properties of patterns in nonvariational spatially extended systems emerges as complementary to morphological approaches to their challenging coarsening properties.This work has been partially supported by MICINN and MEC (Spain) via Grants No. IS2009-12964-C05-01, No. FIS2009-12964-C05-03, No. FIS2012-38866-C05-01, No. IS2012-38866-C05-01-05, No. MAT2011-27470-C02-02, and No. CSD2009-00013.Publicad

Study and Design of a Diferentially Fed Tapered Slot Antenna Array

The results of a parametric study and design of an ultrawideband dual-polarized array of differentially-fed tapered slot antenna elements are presented. We examine arrays of bunny-ear antennas and discuss the capabilities and limitations of differential antenna technology. As we focus on radio astronomical applications, the absence of a balancing-feed circuit not only reduces the first-stage noise contribution associated to losses in the feed, but also leads to a cost reduction. Common-modes are supported by the antenna structure when a third conductor is present, such as a ground plane. We demonstrate that anomalies may occur in the differential-mode scan impedance. Knowledge of both types of scan impedances, differential and common mode, is required to properly design differential LNAs and to achieve optimal receiver sensitivity. A compromise solution is proposed based on the partial suppression of the undesired common-mode currents through a (low loss) balancing-dissipation technique. A fully steerable design up to 45?? in both principal planes is achieved

Observation and modeling of interrupted pattern coarsening: surface nanostructuring by ion erosion

4 pages, 3 figures.-- PACS nrs.: 68.35.Ct, 05.45.-a, 79.20.Rf, 81.16.Rf.We report the experimental observation of interrupted coarsening for surface self-organized nanostructuring by ion erosion. Analysis of the target surface by atomic force microscopy allows us to describe quantitatively this intriguing type of pattern dynamics through a continuum equation put forward in different contexts across a wide range of length scales. The ensuing predictions can thus be consistently extended to other experimental conditions in our system. Our results illustrate the occurrence of nonequilibrium systems in which pattern formation, coarsening, and kinetic roughening appear, each of these behaviors being associated with its own spatiotemporal range.This work has been supported by Grant Nos. CSD2008-0023, CSD2007-00010, and FIS2009-12964- C05-01, -04 (MICINN, Spain), and CCG08-CSIC/MAT- 3457 (CAM, Spain).Publicad

Radial Line Slot Antenna Design with Groove Gap Waveguide Feed for Monopulse Radar Systems

Radial line slot arrays (RLSAs) are well suited to be used in monopulse radar systems. The excitation of the sum and difference patterns can be achieved by the design of simple feeds as shown in this paper. In this work, a feed system based on the use of a cavity made in groove gap waveguide technology (GGW) is presented. The design is made at 24 GHz but can be easily scaled to higher frequencies as the technology is contact-less and fully made in metal. A good isolation between the sum and difference ports together with a good matching of the two of them is obtained. The radiation patterns of the manufactured antenna are also in good agreement with the simulated ones.This work was supported in part by the Spanish Government, Ministry of Economy, National Program of Research, Development and Innovation under the projects TEC2016-79700-C2-2-R and TEC2017-85529-C3-1-R and by the Madrid Regional Government under the project SPADERADAR “Space Debris Radar” (S2013/ICE-3000) and the FPI grant with reference BES-2015-07523

Intrinsic anomalous surface roughening of TiN films deposited by reactive sputtering

7 pages, 7 figures.-- PACS nrs.: 68.55.−a, 81.15.Cd, 81.15.Aa, 68.35.Ct.Final publisher version available Open Access at: http://gisc.uc3m.es/~cuerno/publ_list.htmlWe study surface kinetic roughening of TiN films grown on Si(100) substrates by dc reactive sputtering. The surface morphology of films deposited for different growth times under the same experimental conditions were analyzed by atomic force microscopy. The TiN films exhibit intrinsic anomalous scaling and multiscaling. The film kinetic roughening is characterized by a set of local exponent values α(loc)=1.0 and β(loc)=0.39, and global exponent values α=1.7 and β=0.67, with a coarsening exponent of 1/z=0.39. These properties are correlated to the local height-difference distribution function obeying power-law statistics. We associate this intrinsic anomalous scaling with the instability due to nonlocal shadowing effects that take place during thin-film growth by sputtering.Financial support is acknowledged from Spanish MCyT Grants No. MAT 2002-04037-C03-03 and No. BFM 2003-07749-C05-01, -02, and -05; Comunidad Autónoma de Madrid, Grant No. GR/MAT/0431/2004, European Community Grant No. G5RD-CT-2000-00333, Centre of Excellence CE PI SAS, Contract No. I/2/2005, and Slovak Grant Agency for Science VEGA, Grant No. 2/6030/26.Publicad

Nanopatterning of silicon surfaces by low-energy ion-beam sputtering: dependence on the angle of ion incidence

5 pages, 3 figures.-- PACS nrs.: 81.16.Rf, 81.65.Cf, 68.35.B-, 68.37.Lp, 68.37.Ps, 68.47.Fg.We report on the production of nanoscale patterning on Si substrates by low-energy ion-beam sputtering. The surface morphology and structure of the irradiated surface were studied by atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM). Under ion irradiation at off-normal incidence angle (~50°), AFM images show the formation of both nanoripple and sawtooth-like structures for sputtering times longer than 20 min. The latter feature coarsens appreciably after 60 min of sputtering, inducing a large increase in the surface roughness. This behaviour is attributed to the preferential direction determined on the substrate by the ion beam for this incidence angle, leading to shadowing effects among surface features in the sputtering process. Under irradiation at normal incidence, the formation of an hexagonal array of nanodots is induced for irradiation times longer than 2 min. The shape and crystallinity of the nanodots were determined by HRTEM. At this incidence angle, the surface roughness is very low and remains largely unchanged even after 16 h of sputtering. For the two angle conditions studied, the formation of the corresponding surface structures can be understood as the interplay between an instability due to the sputtering yield dependence on the local surface curvature and surface smoothing processes such as surface diffusion.Publicad