Desertification Monitoring in Biskra, Algeria with Landsat Imagery by means of Supervised Classification and Change Detection Methods

[EN] Desertification is one of the most important problems driven by global climatic change. There are many factors that contribute to the environmental degradation of the Sahara desert surroundings. The first one is related to human activities like the change of land use. Other factors include natural degradation due to change in temperature, humidity and wind. All these complex causes may lead to the movement of sand from the desert to other places like cities and roads, affecting everyday life. For that reason, desertification is being analyzed by governmental agencies in the affected countries. The present work studies this phenomenon in the city of Biskra (Algeria) using optical satellite images taken from the freely available Landsat program. It presents a methodology that could help in the temporal evaluation of the desertification process. Land Use and Land Cover (LULC) change detection in a period of twentyfive years has been carried out using Support Vector Machine (SVM) per object classification. Change indices have been also employed for assessing the degradation. Excellent results using low human operator cost have been fully validated by visual inspection.Azzouzi, SA.; Vidal Pantaleoni, A.; Bentounes, HA. (2017). Desertification Monitoring in Biskra, Algeria with Landsat Imagery by means of Supervised Classification and Change Detection Methods. IEEE Access. 5:9065-9072. doi:10.1109/ACCESS.2017.2700405S90659072

Monitoring desertification in Biskra, Algeria using Landsat 8 and Sentinel-1A images

[EN] Desertification is the persistent degradation of ecosystems caused by environmental changes and human activities. This is a global problem closely related to climate change with severe consequences in urban locations. For that reason, monitoring those locations with low cost and freely available satellite images could be useful for local agencies. This work studies a strategy for the observation of desertification in Biskra (Algeria) with Landsat 8 images and Synthetic Aperture Radar (SAR) images from Sentinel-1A satellite. Radar images are now available from a growing number of missions. These microwave images add valuable additional information to the existing optical products involving soil roughness and moisture content. They are also a very valuable tool to detect man made objects. However, radar images are still difficult to exploit due to their inherent Speckle noise and their characteristics. This study searches the best methodology for the insertion of radar data to a previously designed approach that uses optical data. Several algorithms are implemented and evaluated and the best technique in terms of overall accuracy and Kappa coefficient is selected for the final change map production. The approach achieves Land Use Land Cover (LULC) change detection using Support Vector Machine (SVM) and segmentation. The most useful change indices are obtained for the best methodology product. The simple improved methodology including radar images provides excellent results and it clearly outperforms the baseline optical technique.Azzouzi, SA.; Vidal Pantaleoni, A.; Bentounes, HA. (2018). Monitoring desertification in Biskra, Algeria using Landsat 8 and Sentinel-1A images. IEEE Access. 6:30844-30854. https://doi.org/10.1109/ACCESS.2018.2837081S3084430854

Efficient coupling integrals computation of waveguide step discontinuities using BI-RME and Nyström methods

This paper describes a novel technique for the very efficient and accurate computation of the coupling integrals of waveguide step discontinuities between arbitrary cross section waveguides. This new technique relies on solving the Integral Equation (IE) that provides the well-known Boundary Integral - Resonant Mode Expansion (Bi-RME) method by the Nystrom approach, instead of using the traditional Galerkin version of the Method of Moments (MoM), thus providing large savings on computational costs. Comparative benchmarks between the results provided by the new technique and the original BI-RME method are successfully presented

Microstrip to Double Ridge Empty Substrate Integrated Waveguide Transitions Based on Exponential and Superelliptical Dielectric Taper

[EN] The Empty Substrate IntegratedWaveguides (ESIW) maintain the advantages of the Substrate Integrated waveguide (SIW) (i.e. low-volume, low profile, lightweight, easy manufacturing, and integration in a planar circuit board), and present lower losses and higher quality factors in resonators due to the propagation of the fields through air, instead of through lossy dielectric as in SIW. The operational (monomode) bandwidth of the ESIW can be increased with the Single Ridge ESIW (SRESIW). However, the bandwidth can be further increased with the Double Ridge ESIW (DRESIW). In this paper, a brief study of possible DRESIW geometries has been performed, and two transitions from microstrip line (MS) to DRESIW with a dielectric taper geometry based on different equations are proposed. The new wideband transitions present simulated return losses in back-to-back configurations greater than 20 dB in more than a 95% fractional bandwidth. The transition that presents a better compromise between return losses, bandwidth and ease of fabrication is manufactured. The measured return and insertion losses are better than 19.7 dB and 1.5 dB, respectively, in a 96.4% fractional bandwidth.This work was supported by the Ministerio de Ciencia e Innovacion, Spanish Government, under Project PID2019-103982RB-C44 and Project PID2019-103982RB-C41.Herraiz Zanón, D.; Esteban González, H.; Herraiz, D.; Vidal Pantaleoni, A.; Belenguer, Á.; Boria Esbert, VE. (2021). Microstrip to Double Ridge Empty Substrate Integrated Waveguide Transitions Based on Exponential and Superelliptical Dielectric Taper. IEEE Access. 9:165745-165753. https://doi.org/10.1109/ACCESS.2021.3134089165745165753

Wavelet-like efficient analysis of two dimensional arbitrarily shaped radomes using a surface formulation

Radomes are usually made of lossy dielectric materials, and their accurate analysis is often cumbersome because of their typical large electrical size and geometrical complexity. In real reflector antenna structures, there are always complex interactions between the radome, the reflector surfaces and the directional feeds, which are typically neglected for the sake of simplicity. In this paper we will consider all such interactions in a very accurate way, thus requiring a high number of unknowns for the numerical solution of the problem. To overcome such drawback, an integral equation formulation based on the Equivalence Principle in combination with the wavelet transform has been employed, obtaining finally a robust and accurate CAD tool for the rigorous analysis of arbitrarily shaped radomes containing continuous and discrete electromagnetic sources. It will be shown that the use of wavelet-like bases substantially improves the numerical efficiency and memory requirements of the original integral equation method. For verification purposes, the results obtained with the new technique are successfully compared with examples taken from the literature. Complex antenna structures are then discussed in order to prove the usefulness of the new method.This work has been supported by Ministerio de Educación y Ciencia, Spanish Government, under the Research Projects Ref. TEC2004/04313-C02-01 and TEC2004/04313-C02-02

Accurate consideration of metal losses at waveguide junctions using admittance and impedance integral equation formulations

[EN] At higher frequencies, metal loss effects in passive waveguide components become more pronounced and hazardous. In this paper, we propose two integral equation techniques, based on the generalized admittance and impedance matrices, for the accurate consideration of losses in the metal walls of waveguide junctions. Both techniques have been evaluated in terms of accuracy and numerical efficiency, and conclusions are drawn regarding the best properties of the admittance parameter formulation. Finally, combining such technique with a classical perturbative method for considering propagation losses, we have successfully predicted all loss effects in two real waveguide filters used for commercial applications.This work has been supported by research projects TIC2000-0591-C03-01 and TIC2000-0591-C03-03 and special action ESP2001-4547-PE.Taroncher Calduch, M.; Hueso, J.; Cogollos, S.; Gimeno. B.; Boria Esbert, VE.; Vidal Pantaleoni, A.; Esteban González, H.... (2005). Accurate consideration of metal losses at waveguide junctions using admittance and impedance integral equation formulations. Radio Science. 40(6):1-12. doi:10.1029/2004RS003225S11240

Efficient analysis of arbitrarily shaped inductive obstacles in rectangular waveguides using a surface integral equation formulation

In this paper we propose to use the Surface Integral Equation technique for the analysis of arbitrarily shaped Hplane obstacles in rectangular waveguides, which can contain both metallic and/or dielectric objects. The Green functions are formulated using both spectral and spatial images series, whose convergence behavior has been improved through several acceleration techniques. Proceeding in this way, the convergence of the series is not attached to the employment of any particular basis or test function, thus consequently increasing the flexibility of the implemented technique. In order to test the accuracy and numerical efficiency of the proposed method, results for practical microwave circuits have been successfully compared with other numerical approaches.The authors would like to thank Alcatel Alenia Space (Madrid, Spain) for having provided data of the lossy dielectric loaded evanescent waveguide filter. They also wish to acknowledge the economic support of MEC, Spanish Government, through the coordinated Research Project TEC2004/04313-C02

Study of the Multipactor Effect in Groove Gap Waveguide Technology

This paper presents a theoretical and experimental comparative study of the different multipactor threshold values obtained in rectangular waveguide (RW) and groove gap waveguide (GGW). To this end, the multipactor effect has been first analysed in a RW with a recently developed theoretical model. Then, the multipactor breakdown power levels in the equivalent GGW have been predicted with an accurate electron tracking code, showing a significant increment compared with the RW case. In order to validate these results, two E-plane WR-90 rectangular waveguide transformers have been designed with a full-wave electromagnetic simulation tool. The central sections of these transformers have been implemented in RW and GGW, respectively, and their multipactor breakdown power levels have also been predicted. The two designed transformers have been fabricated in aluminium, and then measured in terms of electrical response (scattering parameters) and RF multipactor effect (power threshold values). All the experimental results agree well with the set of simulated data, thus fully validating the performed study

Study of the Multipactor Effect in Groove Gap Waveguide Technology

[EN] This article presents a theoretical and experimental comparative study of the different multipactor threshold values obtained in the rectangular waveguide (RW) and the groove gap waveguide (GGW). To this end, the multipactor effect has been first analyzed in an RW with a recently developed theoretical model. Then, the multipactor breakdown power levels in the equivalent GGW have been predicted with an accurate electron tracking code, showing a significant increment compared with the RW case. In order to validate these results, two E-plane WR-90 RW transformers have been designed with a full-wave electromagnetic simulation tool. The central sections of these transformers have been implemented in RW and GGW, respectively, and their multipactor breakdown power levels have also been predicted. The two designed transformers have been fabricated in aluminum and then measured in terms of electrical response (scattering parameters) and RF multipactor effect (power threshold values). All the experimental results agree well with the set of simulated data, thus fully validating the performed study.This work was supported by the Ministerio de Ciencia e Innovacion, Spanish Government, through the Subprojects C41 and C43 of the Coordinated Research and Development Project PID2019103982RB under Grant MCIN/AEI/10.13039/501100011033.Vague Cardona, JJ.; Asensio, I.; Coves, Á.; San Blas, ÁA.; Reglero Mangada, MS.; Vidal Pantaleoni, A.; Raboso, D.... (2022). Study of the Multipactor Effect in Groove Gap Waveguide Technology. IEEE Transactions on Microwave Theory and Techniques. 70(5):2566-2578. https://doi.org/10.1109/TMTT.2022.31575872566257870

Multipactor Threshold Estimation Techniques Based on Circuit Models, Electromagnetic Fields and Particle Simulators

[EN] Multipactor has become a keylimiting factor of the final performance of satellite communication systems, due to the increase in power levels and/or operating frequency bands. As a result, the critical components of these systems must meet demanding multipactor specifications which should be considered during the design process. This paper describes the different techniques available to predict the multipactor threshold power for radio frequency (RF) and microwave passive hardware under continuous wave (CW) excitation, from cumbersome particle simulations to fast approximate methods based on circuit models. All these techniques have been described and compared together for the first time, including also a detailed description of the configuration issues of commercial particle simulators required to obtain accurate multipactor threshold predictions. The techniques are applied to both wideband and narrowband application examples. The predictions have been compared with measured thresholds of manufactured samples obtained with a novel multipactor test bed, thus allowing to highlight the advantages and limitations of each technique and particle simulator. From this paper, it will be possible to choose the most suitable procedure (and an appropriate simulator, if needed) to obtain multipactor threshold prediction of passive hardware.The work of Pablo González was supported by the FPU Fellowship of the Ministerio de Educación, Cultura y Deporte, Spanish Government, with Ref. FPU17/02901. This work was supported in part by the Ministerio de Ciencia e Innovación (MICIN, Spanish Government) under R&D Project PID2019-103982RB-C41 (funded by MICIN/AEI/10.13039/501100011033), and in part by the European Space Agency (ESA) under Project H2020-ESA-007 (funded by the European Union's Horizon 2020 Research and Innovation Program).González-Santatecla, P.; Alcaide, C.; Cervera, R.; Rodríguez, M.; Monerris, Ó.; Petit, J.; Rodríguez Pérez, AM.... (2022). Multipactor Threshold Estimation Techniques Based on Circuit Models, Electromagnetic Fields and Particle Simulators. IEEE Journal of Microwaves. 2(1):57-77. https://doi.org/10.1109/JMW.2021.313228457772