Aircraft down-range profiles formed from simulated and compact-range radar backscatter

Compact-range radar backscatter measurements are taken of aircraft scale models. In addition, computer software is used to predict the RCS of the aircraft. Synthetic down-range profiles formed from the two sources of backscatter data are compared and visualized in an innovative manner. Similar discrimination rates between the two aircraft are obtained on data from both source

An Efficient Hybrid GO-PWS Algorithm to Analyze Conformal Serrated-Edge Reflectors for Millimeter-Wave Compact Range

A method to analyze parabolic reflectors with arbitrary piecewise rim is presented in this communication. This kind of reflectors, when operating as collimators in compact range facilities, needs to be large in terms of wavelength. Their analysis is very inefficient, when it is carried out with fullwave/MoM techniques, and it is not very appropriate for designing with PO techniques. Also, fast GO formulations do not offer enough accuracy to reach performance results. The proposed algorithm is based on a GO-PWS hybrid scheme, using analytical as well as non-analytical formulations. On one side, an analytical treatment of the polygonal rim reflectors is carried out. On the other side, non-analytical calculi are based on efficient operations, such as M2 order 2-dimensional FFT. A combination of these two techniques in the algorithm ensures real ad-hoc design capabilities, reached through analysis speedup. The purpose of the algorithm is to obtain an optimal conformal serrated-edge reflector design through the analysis of the field quality within the quiet zone that it is able to generate in its forward half space.

Contribution to the Analysis, Design and Assessment of Compact Antenna Test Ranges At Millimeter Wavelengths - Contribución al Análisis, Diseño y Caracterización de Sistemas de Medida de Antenas en Rango Compacto para Frecuencias Milimétricas

This Doctoral Thesis entitled Contribution to the analysis, design and assessment of compact antenna test ranges at millimeter wavelengths aims to deepen the knowledge of a particular antenna measurement system: the compact range, operating in the frequency bands of millimeter wavelengths. The thesis has been developed at Radiation Group (GR), an antenna laboratory which belongs to the Signals, Systems and Radiocommunications department (SSR), from Technical University of Madrid (UPM). The Radiation Group owns an extensive experience on antenna measurements, running at present four facilities which operate in different configurations: Gregorian compact antenna test range, spherical near field, planar near field and semianechoic arch system. The research work performed in line with this thesis contributes the knowledge of the first measurement configuration at higher frequencies, beyond the microwaves region where Radiation Group features customer-level performance. To reach this high level purpose, a set of scientific tasks were sequentially carried out. Those are succinctly described in the subsequent paragraphs. A first step dealed with the State of Art review. The study of scientific literature dealed with the analysis of measurement practices in compact antenna test ranges in addition with the particularities of millimeter wavelength technologies. Joint study of both fields of knowledge converged, when this measurement facilities are of interest, in a series of technological challenges which become serious bottlenecks at different stages: analysis, design and assessment. Thirdly after the overview study, focus was set on Electromagnetic analysis algorithms. These formulations allow to approach certain electromagnetic features of interest, such as field distribution phase or stray signal analysis of particular structures when they interact with electromagnetic waves sources. Properly operated, a CATR facility features electromagnetic waves collimation optics which are large, in terms of wavelengths. Accordingly, the electromagnetic analysis tasks introduce an extense number of mathematic unknowns which grow with frequency, following different polynomic order laws depending on the used algorithmia. In particular, the optics configuration which was of our interest consisted on the reflection type serrated edge collimator. The analysis of these devices requires a flexible handling of almost arbitrary scattering geometries, becoming this flexibility the nucleus of the algorithmia’s ability to perform the subsequent design tasks. This thesis’ contribution to this field of knowledge consisted on reaching a formulation which was powerful at the same time when dealing with various analysis geometries and computationally speaking. Two algorithmia were developed. While based on the same principle of hybridization, they reached different order Physics performance at the cost of the computational efficiency. Inter-comparison of their CATR design capabilities was performed, reaching both qualitative as well as quantitative conclusions on their scope. In third place, interest was shifted from analysis - design tasks towards range assessment. Millimetre wavelengths imply strict mechanical tolerances and fine setup adjustment. In addition, the large number of unknowns issue already faced in the analysis stage appears as well in the on chamber field probing stage. Natural decrease of dynamic range available by semiconductor millimeter waves sources requires in addition larger integration times at each probing point. These peculiarities increase exponentially the difficulty of performing assessment processes in CATR facilities beyond microwaves. The bottleneck becomes so tight that it compromises the range characterization beyond a certain limit frequency which typically lies on the lowest segment of millimeter wavelength frequencies. However the value of range assessment moves, on the contrary, towards the highest segment. This thesis contributes this technological scenario developing quiet zone probing techniques which achieves substantial data reduction ratii. Collaterally, it increases the robustness of the results to noise, which is a virtual rise of the setup’s available dynamic range. In fourth place, the environmental sensitivity of millimeter wavelengths issue was approached. It is well known the drifts of electromagnetic experiments due to the dependance of the re sults with respect to the surrounding environment. This feature relegates many industrial practices of microwave frequencies to the experimental stage, at millimeter wavelengths. In particular, evolution of the atmosphere within acceptable conditioning bounds redounds in drift phenomena which completely mask the experimental results. The contribution of this thesis on this aspect consists on modeling electrically the indoor atmosphere existing in a CATR, as a function of environmental variables which affect the range’s performance. A simple model was developed, being able to handle high level phenomena, such as feed - probe phase drift as a function of low level magnitudes easy to be sampled: relative humidity and temperature. With this model, environmental compensation can be performed and chamber conditioning is automatically extended towards higher frequencies. Therefore, the purpose of this thesis is to go further into the knowledge of millimetre wavelengths involving compact antenna test ranges. This knowledge is dosified through the sequential stages of a CATR conception, form early low level electromagnetic analysis towards the assessment of an operative facility, stages for each one of which nowadays bottleneck phenomena exist and seriously compromise the antenna measurement practices at millimeter wavelengths.

Real-time dual-wavelength digital holographic microscopy for extended measurement range with enhanced axial resolution

We report on advanced dual-wavelength digital holographic microscopy (DHM) methods, enabling single-acquisition real-time micron-range measurements while maintaining single-wavelength interferometric resolution in the nanometer regime. In top of the unique real-time capability of our technique, it is shown that axial resolution can be further increased compared to single-wavelength operation thanks to the uncorrelated nature of both recorded wavefronts. It is experimentally demonstrated that DHM topographic investigation within 3 decades measurement range can be achieved with our arrangement, opening new applications possibilities for this interferometric technique. ©2008 COPYRIGHT SPIE

Aerosol-induced correlation between visibility and atmospheric electricity.

Atmospheric aerosol acts to both reduce the background concentration of natural cluster ions, and to attenuate optical propagation. Hence, the presence of aerosol has two consequences, the reduction of the air’s electrical conductivity and the visual range. Ion-aerosol theory and Koschmieder’s visibility theory are combined here to derive the related non-linear variation of the atmospheric electric potential gradient with visual range. A substantial sensitivity is found under poor visual range conditions, but, for good visual range conditions the sensitivity diminishes and little influence of local aerosol on the fair weather potential gradient occurs. This allows visual range measurements, made simply and routinely at many meteorological sites, to provide inference about the local air’s electrical properties.

Improving the GNSS positioning stochastic model in the presence of ionospheric scintillation

Ionospheric scintillations are caused by time-varying electron density irregularities in the ionosphere, occurring more often at equatorial and high latitudes. This paper focuses exclusively on experiments undertaken in Europe, at geographic latitudes between similar to 50 degrees N and similar to 80 degrees N, where a network of GPS receivers capable of monitoring Total Electron Content and ionospheric scintillation parameters was deployed. The widely used ionospheric scintillation indices S4 and sigma(phi) represent a practical measure of the intensity of amplitude and phase scintillation affecting GNSS receivers. However, they do not provide sufficient information regarding the actual tracking errors that degrade GNSS receiver performance. Suitable receiver tracking models, sensitive to ionospheric scintillation, allow the computation of the variance of the output error of the receiver PLL (Phase Locked Loop) and DLL (Delay Locked Loop), which expresses the quality of the range measurements used by the receiver to calculate user position. The ability of such models of incorporating phase and amplitude scintillation effects into the variance of these tracking errors underpins our proposed method of applying relative weights to measurements from different satellites. That gives the least squares stochastic model used for position computation a more realistic representation, vis-a-vis the otherwise 'equal weights' model. For pseudorange processing, relative weights were computed, so that a 'scintillation-mitigated' solution could be performed and compared to the (non-mitigated) 'equal weights' solution. An improvement between 17 and 38% in height accuracy was achieved when an epoch by epoch differential solution was computed over baselines ranging from 1 to 750 km. The method was then compared with alternative approaches that can be used to improve the least squares stochastic model such as weighting according to satellite elevation angle and by the inverse of the square of the standard deviation of the code/carrier divergence (sigma CCDiv). The influence of multipath effects on the proposed mitigation approach is also discussed. With the use of high rate scintillation data in addition to the scintillation indices a carrier phase based mitigated solution was also implemented and compared with the conventional solution. During a period of occurrence of high phase scintillation it was observed that problems related to ambiguity resolution can be reduced by the use of the proposed mitigated solution.

Higher order ionospheric effects in GNSS positioning in the European region

After removal of the Selective Availability in 2000, the ionosphere became the dominant error source for Global Navigation Satellite Systems (GNSS), especially for the high-accuracy (cm-mm) demanding applications like the Precise Point Positioning (PPP) and Real Time Kinematic (RTK) positioning.The common practice of eliminating the ionospheric error, e. g. by the ionosphere free (IF) observable, which is a linear combination of observables on two frequencies such as GPS L1 and L2, accounts for about 99% of the total ionospheric effect, known as the first order ionospheric effect (Ion1). The remaining 1% residual range errors (RREs) in the IF observable are due to the higher - second and third, order ionospheric effects, Ion2 and Ion3, respectively. Both terms are related with the electron content along the signal path; moreover Ion2 term is associated with the influence of the geomagnetic field on the ionospheric refractive index and Ion3 with the ray bending effect of the ionosphere, which can cause significant deviation in the ray trajectory (due to strong electron density gradients in the ionosphere) such that the error contribution of Ion3 can exceed that of Ion2 (Kim and Tinin, 2007).The higher order error terms do not cancel out in the (first order) ionospherically corrected observable and as such, when not accounted for, they can degrade the accuracy of GNSS positioning, depending on the level of the solar activity and geomagnetic and ionospheric conditions (Hoque and Jakowski, 2007). Simulation results from early 1990s show that Ion2 and Ion3 would contribute to the ionospheric error budget by less than 1% of the Ion1 term at GPS frequencies (Datta-Barua et al., 2008). Although the IF observable may provide sufficient accuracy for most GNSS applications, Ion2 and Ion3 need to be considered for higher accuracy demanding applications especially at times of higher solar activity.This paper investigates the higher order ionospheric effects (Ion2 and Ion3, however excluding the ray bending effects associated with Ion3) in the European region in the GNSS positioning considering the precise point positioning (PPP) method. For this purpose observations from four European stations were considered. These observations were taken in four time intervals corresponding to various geophysical conditions: the active and quiet periods of the solar cycle, 2001 and 2006, respectively, excluding the effects of disturbances in the geomagnetic field (i.e. geomagnetic storms), as well as the years of 2001 and 2003, this time including the impact of geomagnetic disturbances. The program RINEX_HO (Marques et al., 2011) was used to calculate the magnitudes of Ion2 and Ion3 on the range measurements as well as the total electron content (TEC) observed on each receiver-satellite link. The program also corrects the GPS observation files for Ion2 and Ion3; thereafter it is possible to perform PPP with both the original and corrected GPS observation files to analyze the impact of the higher order ionospheric error terms excluding the ray bending effect which may become significant especially at low elevation angles (Ioannides and Strangeways, 2002) on the estimated station coordinates.

Joint Reprocessing of GPS, GLONASS and SLR

A joint reprocessing of GPS, GLONASS and SLR observations has been carried out at TU Dresden, TU Munich, AIUB and ETH Zurich. Common a priori models have been applied for the processing of all types of observation to ensure both consistent parameter estimates and the rigorous combination of microwave and optical measurements. Based on that reprocessing results, we evaluate the impact of adding GLONASS observations to the standard GPS data processing. In particular, changes in station position time series and day boundary overlaps of consecutive satellite arcs are analyzed. In addition, the GNSS orbits derived from microwave measurements are validated using independent SLR range measurements. Our SLR residuals indicate a significant improvement compared to previous results. Furthermore, we evaluate the performance of our high-rate (30s) combined GNSS satellite clocks and discuss associated zero-difference phase residuals.

Deployment of an all-in-one millimetre-wave anechoic chamber

This paper describes the new anechoic chamber available at The University of Kent, UK. This facility includes a spherical near/far field, planar near field, cylindrical near field and a compact range. The facility allows measurement from 600 MHz up to 110 MHz. The spherical, planar and cylindrical ranges covers up to 40 GHz and the compact range is available from 50 GHz up to 110 MHz. Immediate plans are to use the new facility to measure body-centric antennas and sensing nodes together with near field sampling of finite sized Frequency Selective Surfaces.

Satellite laser ranging and the ETALON Geodetic satellites

The technique of Satellite Laser Ranging is today a mature, important tool with applications in many area of geodynamics, geodesy and satellite dynamics. A global network of some 40 stations regularly obtains range observations with sub-cm precision to more than twelve orbiting spacecraft. At such levels of precision it is important to minimise potential sources of range bias in the observations, and part of the thesis is a study of subtle effects caused by the extended nature of the arrays of retro-reflectors on the satellites. We develop models that give a precise correction of the range measurements to the centres of mass of the geodetic satellites Lageos and Etalon, appropriate to a variety of different ranging systems, and use the Etalon values, which were not determined during pre-launch tests, in an extended orbital analysis. We have fitted continuous 2.5 year orbits to range observations of the Etalons from the global network of stations, and analysed the results by mapping the range residuals from these orbits into equivalent corrections to orbital elements over short time intervals. From these residuals we have detected and studied large un-modelled along-track accelerations associated with periods during which the satellites are undergoing eclipse by the Earth's shadow. We also find that the eccentricity residuals are significantly different for the two satellites, with Etalon-2 undergoing a year-long eccentricity anomaly similar in character to that experienced at intervals by Lageos-1. The nodal residuals show that the satellites define a very stable reference frame for Earth rotation determination, with very little drift-off during the 2.5 year period. We show that an analysis of more than about eight years of tracking data would be required to derive a significant value for 2. The reference frame defined by the station coordinates derived from the analyses shows very good agreement with that of ITRF93.

Characterization of Mars rotational dynamics from Doppler tracking of the InSight lander

In the last decades the evolution of radio science has made it possible to infer the atmosphere composition, the surface and the internal structure of the planets. Since the arrival of the first landers on Mars it was possible to make accurate measurements of the dynamics of this planet; in this thesis we will focus on InSight, considering the data disclosed by the JPL relative to the period from November 26th, 2018 to August 15th, 2021. In particular, the Doppler and Range measurements conducted by the RISE (Rotation and Interior Structure Experiment) will be analyzed. Since the accuracy of these measurements was improved significantly the effects due to the atmosphere of Mars might be measured so it should thus be possible to obtain a better estimate of the parameters characterizing the rotational dynamic of Mars. A large part of this study will therefore be dedicated to the study, modeling, implementation and analysis of the atmosphere of Mars, in both its components: troposphere and ionosphere. Once the complete model of Mars had been built, i.e. including the atmosphere, it was then possible to analyze the residuals, obtained between the data of the measurements carried out and the values predicted by the developed model, in order to obtain an estimate of the rotational dynamic of Mars.

Two formation channels of ultra-compact dwarf galaxies in Hickson compact groups

Context. The formation of ultra-compact dwarf galaxies (UCDs) is believed to be driven by interaction, and UCDs are abundant in the cores of galaxy clusters, environments that mark the end-point of galaxy evolution. Nothing is known about the properties of UCDs in compact groups of galaxies, environments where most of galaxy evolution and interaction is believed to occur and where UCDs in an intermediate stage in their evolution may be expected. Aims. The main goal of this study is to detect and characterize, for the first time, the UCD population of compact groups of galaxies. For that, two nearby groups in different evolutionary stages, HCG22 and HCG90, were targeted. Methods. We selected about 40 UCD candidates from pre-existing photometry of both groups, and obtained spectra of these candidates using the VLT FORS2 instrument in MXU mode. Archival HST/ACS imaging was used to measure their structural parameters. Results. We detect 16 and 5 objects belonging to HCG22 and HCG90, respectively, covering the magnitude range -10.0 > M(R) > -11.5 mag. Their integrated colours are consistent with old ages covering a broad range in metallicities (metallicities confirmed by the spectroscopic measurements). Photometric mass estimates put 4 objects in HCG90 and 9 in HCG22 in the mass range of UCDs (> 2 x 10(6) M(circle dot)) for an assumed age of 12Gyr. These UCDs are on average 2-3 times larger than the typical size of Galactic GCs, covering a range of 2 less than or similar to r(h) less than or similar to 21 pc. The UCDs in HCG22 are more concentrated around the central galaxy than in HCG90, at the 99% confidence level. They cover a broad range in [alpha/Fe] abundances from sub-to super-solar. The spectra of 3 UCDs (2 in HCG22, 1 in HCG90) show tentative evidence of intermediate age stellar populations. The clearest example is the largest and most massive UCD (similar to 10(7) M(circle dot)) in our sample, which is detected in HCG22. Its properties are most consistent with a stripped dwarf galaxy nucleus. We calculate the specific frequency (S(N)) of UCDs for both groups, finding that HCG22 has about three times higher S(N) than HCG90. Conclusions. The ensemble properties of the detected UCDs supports two co-existing formation channels: a star cluster origin (low-luminosity, compact sizes, old ages, super-solar alpha/Fe), and an origin as tidally stripped dwarf nuclei (more extended and younger stellar populations). Our results imply that the UCDs detected in both groups do not, in their majority, originate from relatively recent galaxy interactions. Most of the detected UCDs have likely been brought into the group along with their host galaxies.

Self-bound models of compact stars and recent mass-radius measurements

The exact composition of a specific class of compact stars, historically referred to as ""neutron stars,'' is still quite unknown. Possibilities ranging from hadronic to quark degrees of freedom, including self-bound versions of the latter, have been proposed. We specifically address the suitability of strange star models (including pairing interactions) in this work, in the light of new measurements available for four compact stars. The analysis shows that these data might be explained by such an exotic equation of state, actually selecting a small window in parameter space, but still new precise measurements and also further theoretical developments are needed to settle the subject.

Vortex configuration flow cell based on low temperature cofired ceramics as a compact chemiluminescence microsystern

The integration of optical detection methods in continuous flow microsystems can highly extend their range of application, as long as some negative effects derived from their scaling down can be minimized. Downsizing affects to a greater extent the sensitivity of systems based on absorbance measurements than the sensitivity of those based on emission ones. However, a careful design of the instrumental setup is needed to maintain the analytical features in both cases. In this work, we present the construction and evaluation of a simple miniaturized optical system, which integrates a novel flow cell configuration to carry out chemiluminescence (CL) measurements using a simple photodiode. It consists of a micro-mixer based on a vortex structure, which has been constructed by means of the low-temperature cofired ceramics (LTCC) technology. This mixer not only efficiently promotes the CL reaction due to the generated high turbulence but also allows the detection to be carried out in the same area, avoiding intensity signal losses. As a demonstration, a flow injection system has been designed and optimized for the detection of cobalt(H) in water samples. It shows a linear response between 2 and 20 mu M with a correlation of r > 0.993, a limit of detection of 1.1 mu M, a repeatability of RSD = 12.4 %, and an analysis time of 17 s. These results demonstrate the suitability of the proposal to the determination of compounds involved in CL reactions by means of an easily constructed versatile device based on low-cost instrumentation.

A compact shock-assisted free-piston driver for impulse facilities

A free-piston driver that employs entropy-raising shock processes with diaphragm rupture has been constructed, which promises significant theoretical advantages over isentropic compression. Results from a range of conditions with helium and argon driver gases are reported. Significant performance gains were achieved in some test cases. Heat losses are shown to have a strong effect on driver processes. Measurements compare well with predictions from a quasi-one-dimensional numerical code.