Impacts of Radar Echoes on Internal Calibration Signals in the TerraSAR-X Instrument

For calibrating and monitoring the required radiometric stability, the radar instrument of TerraSAR-X features an internal calibration facility coupling into an additional port of the TRMs. Calibration pulses are routed through the front-end to characterise critical elements and parameters of the transmit (TX) and receive (RX) path. Changes in the signal path appear due to thermal effects, degradation, or extreme conditions in space. Especially the front-end TRMs controlling the phased array antenna are of crucial significance for the instrument reliability. There are many indications that the interference of the RX-Calibration signals is caused by an echo from a transmitted TerraSAR-X chirp pulse of the same data take. As consequently implemented in the TerraSAR-X system, different approaches solve these effects of signal interference. In orbit, the commanding sequence can be optimised for avoiding interference. At processing level, averaging techniques minimise the noise effects inside the calibration signals. This paper presents the effects of the radar echoes on the whole internal calibration process and how they can be detected and minimised

Multipactor effect analysis and design rules for wedge-shaped hollow waveguides

A numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides is presented in this paper. The computation of electromagnetic fields is based on the boundary integral–resonant mode expansion method, which provides the modal chart of hollow waveguides with any arbitrary cross section. The advantage of using wedge-shaped waveguides with respect to conventional rectangular ones is the deviation of the resonant paths of the electrons toward regions with lower voltages, thus reducing the probability of multipactor threshold for certain input power. To validate this method, our results have been compared with simulations from previous theoretical studies. Once the simulation tool is validated, it is used to predict the multipactor threshold of wedge-shaped waveguides with different symmetric inclination angles of their horizontal plates. Finally, susceptibility curves as the ones already available for rectangular waveguides are presented. These charts are useful for designing innovative waveguide geometries with improved multipactor-free working power ranges.This work was supported by the Ministerio de Ciencia e Innovación, Spain, under Research Project TEC2007-67630-C03-01/TCM

Simulation of electron transport and secondary emission in a photomultiplier tube and experimental validation

[EN] The electron amplification and transport within a photomultiplier tube (PMT) has been investigated by developing an in-house Monte Carlo simulation code. The secondary electron emission in the dynodes is implemented via an effective electron model and the Modified Vaughan¿s model, whereas the transport is computed with the Boris leapfrog algorithm. The PMT gain, rise time and transit time have been studied as a function of supply voltage and external magnetostatic field. A good agreement with experimental measurements using a Hamamatsu R13408-100 PMT was obtained. The simulations have been conducted following different treatments of the underlying geometry: three-dimensional, two-dimensional and intermediate (2.5D). The validity of these approaches is compared. The developed framework will help in understanding the behavior of PMTs under highly intense and irregular illumination or varying external magnetic fields, as in the case of prompt gamma-ray measurements during pencil-beam proton therapy; and aid in optimizing the design of voltage dividers with behavioral circuit models.This work was supported by Conselleria de Educación, Investigación, Cultura y Deporte (Generalitat Valenciana) under grant numbers CDEIGENT/2019/011 and CDEIGENT/2021/012. P. Martín-Luna is supported by the Ministerio de Universidades (Gobierno de España), Spain under Grant Number FPU20/04958. We thank Hamamatsu (V. Sánchez, D. Castrillo) for technical support and guidance; R. Carrasco (IFIC) and P. Wohlfahrt (Siemens Healthineers) for the CT scanning; D. Calvo and D. Real (KM3net-IFIC) for their LED test platform, the electronics and maintenance services at IFIC for excellent support; and K. Albiol, J. V. Casaña-Copado, A. Gallas Torreira, E. Lemos Cid, G. Pausch, A. Pazos Álvarez, E. Pérez Trigo, S. Rit, A. Ros, J. Roser, J. Stein, J. L. Taín and R. Viegas for useful discussions.Martín-Luna, P.; Esperante, D.; Fernández Prieto, A.; Fuster-Martínez, N.; García Rivas, I.; Gimeno, B.; Ginestar Peiro, D.... (2024). Simulation of electron transport and secondary emission in a photomultiplier tube and experimental validation. Sensors and Actuators A Physical. 365:1-10. https://doi.org/10.1016/j.sna.2023.11485911036

Optimized Multipactor-Resistant Wedge-Shaped Waveguide Bandpass Filters

[EN] Wedge-shaped waveguides present a certain advantage with respect to rectangular waveguides regarding their resistance to multipactor discharges. In this paper, the optimal configuration for the wedge geometry is investigated based on theoretical results, on a precise multipactor prediction tool, and on previous experience. In addition, design rules are presented, which allow us to achieve for wedge-shaped filters electrical performances comparable to the ones of rectangular waveguide filters, while at the same time improving the multipactor-free power range. As a proof of concept, two three-pole bandpass filters with equivalent electrical characteristic of 150-MHz bandwidth, centered at 12 GHz (Ku band), and the same Q factor have been designed, manufactured, and tested. The first design is based on conventional rectangular waveguide technology, while the second one has non-parallel broadside walls (wedge-shaped cross section). The multipactor power threshold and RF performance of the filters have been measured in order to validate the improvements achievable employing wedge-shaped resonators.This work was supported by the Ministerio de Ciencia e Innovacion, Spain, under Research Project TEC2010-21520-C04-01/TCM.Hueso González, J.; Raboso García-Baquero, D.; Ernst, C.; Schmitt, D.; Boria Esbert, VE.; Gimeno Martinez, B.; Taroncher Calduch, M.... (2013). Optimized Multipactor-Resistant Wedge-Shaped Waveguide Bandpass Filters. IEEE TRANSACTIONS ON PLASMA SCIENCE. 41(8):2135-2144. https://doi.org/10.1109/TPS.2013.2253134S2135214441

Analysis of wedge-shaped waveguides and design of multipactor-resistant microwave bandpass filters. Análisis de guías de onda en forma de cuña y diseño de filtros de microondas paso-banda resistentes al efecto multipactor

El efecto multipactor de ruptura en RF ha sido objeto de numerosos estudios desde hace más de 80 años, a partir del desarrollo de los primeros aceleradores de partículas en la primera mitad del siglo XX. A mediados de ese siglo, con el desarrollo de fuentes de alta potencia para aplicaciones radar y la llegada de los satélites artificiales, la investigación del multipactor cobró una considerable relevancia, al convertirse este fenómeno en un riesgo determinante para costosos proyectos comerciales. Las guías de onda con secciones rectas canónicas, como las rectangulares o las coaxiales, han sido tradicionalmente las más utilizadas en dispositivos de microondas. Sus principales ventajas son que sus campos electromagnéticos pueden resolverse analíticamente, lo que permite su aplicación directa en diseños complejos, y la simplicidad de su fabricación. Pero las capacidades de computación y las prestaciones de los algoritmos se han multiplicado con los años, lo que ha permitido ampliar el espectro de posibles topologías a geometrías casi arbitrarias, ofreciendo al diseñador una mayor libertad creativa. En todo caso, gran parte de los dispositivos de microondas actuales siguen confiando en la madurez y fiabilidad de las tecnologías de guía de onda tradicionales, que no requieren una inversión adicional en equipos de fabricación. La supresión del efecto multipactor es la motivación para arriesgarse a probar topologías de guía de onda innovadoras, como la guía en forma de cuña. Es en este contexto donde este trabajo de doctorado pretende ofrecer una contribuci'on. En primer lugar, se ha desarrollado un modelo numérico para predecir el efecto multipactor de ruptura en guías de onda huecas en forma de cuña. Esta herramienta ha permitido la identificación de criterios óptimos de diseño. Así mismo, se ha adaptado un método de síntesis de filtros paso-banda en guía rectangular para poder realizar un diseño similar pero basado en la nueva topología. Como culminación, las estructuras diseñadas se han fabricado y medido, con el fin de comprobar sus prestaciones electromagnéticas y su sensibilidad al efecto multipactor. Se ha registrado además una patente para proteger estos nuevos filtros. En resumen, el trabajo ha abarcado el ciclo de actividades relacionadas con el desarrollo industrial completo de un dispositivo pasivo de microondas: investigación básica, análisis, diseño, fabricación y calificación con medidas en el laboratorio. Estas medidas han comprobado la mejora prevista en los umbrales de multipactor de los filtros de microondas con topología en forma de cu¿na, y han confirmado que pueden ofrecer respuestas en frecuencia similares a aquellas de filtros basados en una guía de onda rectangular equivalente. Las implicaciones de los resultados han sido evaluadas a fondo y resumidas en este documento. Como observación final, se ha intentado redactar esta investigación de manera que refleje el proceso natural de aprendizaje, mostrando los aciertos y errores experimentados en el camino, todos los cuales han conducido al resultado final. Este reto no hubiera sido posible sin el apoyo y compromiso de varios profesionales de diferentes centros de investigación e industrias europeas (Universidad Politécnica de Valencia, Universidad de Valencia, Agencia Espacial Europea, Thales Alenia Espacio Espa¿na, Technische Universit¿at Darmstadt, 'Ecole Polythecnique F'ed'erale de Lausanne, Tesat, Aurora Software and Testing y Val Space Consortium), a los cuales estoy agradecido.The multipactor RF breakdown effect has been object of numerous studies for over 80 years, since the development of the first particle accelerators in the beginning of the 20th century. Around the middle of that century, with the development of high power sources for radar applications and with the emergence of the artificial satellites, a new impulse was given to the multipactor research, since it became a risk for expensive commercial projects. Traditionally, waveguides with canonical cross sections, like rectangular or coaxial ones, have been the building blocks of most microwave devices. Their main advantages are that their electromagnetic fields can be solved analytically, enabling their direct application in complex designs, as well as their manufacturing simplicity. But over the years the computation capabilities and algorithms have continuously evolved, which has broadened the spectrum of possible topologies to almost arbitrary geometries, offering the designer more room for creativity. However, most of the current microwave devices still trust on the mature canonical waveguide technologies, which do not require an additional investment in manufacturing equipment. The suppression of the multipactor effect is the motivation for considering an innovative waveguide topology, like the wedge-shaped waveguide. It is within this context where this PhD work aims to offer a contribution. On the one hand, a numerical model for predicting the multipactor breakdown effect in wedge-shaped hollow waveguides has been developed. This tool has aided in the derivation of optimised design criteria. On the other hand, a bandpass filter synthesis method for rectangular waveguide has been adapted in order to calculate a similar design based on the new topology. As a culmination, the designed structures have been manufactured and tested, in order to verify their electromagnetic performance and their multipactor sensibility. A patent was also filed to protect these new filters. In short, this work has comprised the cycle of activities related to the whole industrial development of a passive microwave device: basic research, analysis, design, manufacturing and qualification through testing. These measurements have verified the predicted improvement in the multipactor thresholds of microwave filters with wedge-shaped topology, and have confirmed that they can offer similar frequency responses to the equivalent rectangular waveguide ones. The implications of the results have been thoroughly evaluated and summarised in this document. As a final remark, this research document has been drafted to reflect the natural learning process, and to show the rights and wrongs experienced in the way, which all have led to the final result. Such an endeavour would not have been possible without the support and commitment of several professionals from different European research centres and industries (Universidad Polit'ecnica de Valencia, Universidad de Valencia, European Space Agency, Thales Alenia Espacio Spain, Technische Universit¿at Darmstadt, 'Ecole Polythecnique F'ed'erale de Lausanne, Tesat, Aurora Software and Testing and Val Space Consortium), for which I am grateful.Hueso González, J. (2013). Analysis of wedge-shaped waveguides and design of multipactor-resistant microwave bandpass filters. Análisis de guías de onda en forma de cuña y diseño de filtros de microondas paso-banda resistentes al efecto multipactor [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/33750TESI

Radar Instrument Calibration of TerraSAR-X

TerraSAR-X is a high resolution synthetic aperture radar (SAR) satellite launched in 2007. Its active phased array X-Band antenna hosts 384 transmit/receive modules (TRMs) controlling the beam steering in azimuth and eleva-tion. A calibration network provides monitoring of internal instrument behaviour by introducing additional calibration pulses. Evaluation of calibration pulses for every image acquisition guarantees high radiometric stability of all SAR products. This paper shows the latest in-orbit results of the radar instrument stability and TRM performance. The novel PN Gating method is verified in a spaceborne environment for the first time ever

DEM Calibration Concept for TanDEM-X

The TanDEM-X mission comprises two fully active synthetic aperture radar satellites operating in X-band. The primary goal of this mission is the derivation of a high-precision global Digital Elevation Model (DEM) according to HRTI level 3 quality. This requires accurate calibration of the interferometric system parameters. Content of this paper is the development of a general concept for this calibration, which comprises the determination of instrument and baseline errors, of an adjustment concept and of the distribution of control points. This concept has a key incidence on mission aspects like the data acquisition plan and the data take adjustment procedure

Comments on 'SPICE Model of Photomultiplier Tube Under Different Bias Conditions'

The paper 'SPICE Model of Photomultiplier Tube Under Different Bias Conditions' is commented. We revisit the mathematical formulation to compensate for some ambiguities in the original manuscript, and point out some inconsistencies in the results and reproducibility of the simulations, as well as in the optimized parameters originally obtained with the PSPICE simulation engine. All simulations are recalculated with the NGSPICE software using the corrected parameters and compared against the original figures. The reproducibility of our simulations is independently verified with PSPICE, as well as by numerically solving the analytical system of non-linear equations using Newton's method within MATLAB

GMES Sentinel-1: SAR Calibration Algorithms, Part A of IN-11

In the frame of the Global Monitoring for Environment and Security programme (GMES), ESA is undertaking the development of the Sentinel-1, an European polar orbit satellite system for the continuation of SAR operational applications in C-Band. This document provides the Sentinel-1 SAR calibration algorithms reflected by the so called Calibration Segment (CS) as part of the Sentinel-1 Payload Data Ground Segment (PDGS). This CS is composed of different sub-segments in order to implement the overall SAR system calibration strategy. The Sentinel-1 SAR calibration algorithms document identifies all requirements, procedures, algorithms as well as internal and external interfaces necessary to meet the SAR system requirements. This document does not include the overall calibration strategy

TerraSAR-X Instrument Calibration Results and Extension for TanDEM-X

Spaceborne remote sensing with synthetic aperture radar (SAR) has become an essential source of high-resolution and continuous earth observation. Modern satellites like the German TerraSAR-X system provide radar images of unprecedented service with respect to operating flexibility and imaging quality. The outstanding performance of TerrSAR-X image products is achieved by an innovative calibration approach that minimizes systematic antenna and instrument characteristics. The active phased array X-Band antenna is fed by 384 transmit/receive modules for electronic beam steering and shaping in azimuth and elevation direction. The flexible radar instrument hosts an internal calibration system which guarantees the high radiometric stability of all SAR products. New techniques for antenna performance control have been successfully implemented setting a high standard for next-generation SAR missions. This paper summarizes all essential calibration results of TerraSAR-X that cover internal instrument behavior. Furthermore, we give an outlook on the required bistatic calibration techniques for the future TanDEM-X mission that faces additional performance challenges when calibrating two TerraSAR-X satellites flying in close formation