Contribution to the uncertainty analysis and calibration of active antenna arrays

Resumen

This Doctoral Thesis introduces novel calibration processes applied to antenna arrays with new architectures and technologies designed to improve the performance of traditional earth stations for satellite communications due to the increasing requirement of data capacity during last decades. Besides, the Radiation Group from the Technical University of Madrid has been working on the development of new antenna arrays based on novel architecture and technologies along many projects as a solution for the ground segment in the early future. Nowadays, the calibration process is an interesting and cutting edge research field in a period of expansion with a lot of work to do for calibration in transmission and also for reception. For comprehensiveness we can introduce the statement that the calibration process can be defined by the prediction, measurement and estimation of a measurand, where the last is the compensation weight and the difference between estimation and prediction arises in the computation of uncertainties. In order to follow the statement of this Doctoral Thesis, a series of milestones were achieved related to objectives presented, and validation results were obtained from tests done to one real prototype of a geodesic antenna array for satellite tracking at L band named GEODA. First, an exhaustive revision of the state of the art has been done within the research framework and motivation of the work, resulting in the knowhow of current systems, challenges and solution given to the field of novel antenna array calibration and uplink arraying. Second, the effect of errors on the antenna array response has been well analyzed based on a proposed signal model for active antenna arrays with Monte Carlo simulation. As outcome of this study, a novel analytical method for uncertainty evaluation in active antenna arrays is proposed and the complete expansion of the analytical model demonstrated. The aim of this analytical method is to analyze the impact on the array response due to errors of amplitude, phase and sensor location. Furthermore, main applications and advantages are: analytical evaluation of uncertainty in the complete array response for design and selection of the proper calibration technique of active antenna arrays, and analysis for the components selection during prototyping and design. This method for evaluation offers a significant reduction in computational complexity and time as compared to Monte Carlo simulations. Third, in the characterization, validation and Off-line calibration problem where the number of sub-system and components symbolizes a challenge in terms of exhaustive, complex and expensive measurements campaign, this Thesis presents significant results and discussion of the measurement campaign done for characterization, validation of sub-systems and calibration of one active antenna array of the GEODA. In the framework of the GRUA project, exhaustive measurements in laboratory and anechoic chamber were done for the analysis of new efficient calibration algorithms capable to compensate errors of active antenna arrays in reception and transmission, focused on cost in time and tests reduction for future prototypes. Thus, a novel proposed procedure based on one automated system for measurements has been implemented. Furthermore, the aim of the proposed procedure for characterization and calibration is to select the proper calibration technique and derive measurement requirements for the calibration of active antenna arrays. Main contributions during the characterization, validation and Off-line calibration process can be listed as the presentation of a efficient procedure for characterization and calibration of active antenna arrays, the design assessment based on measurement and uncertainty analysis, the upgrade of LEHA facilities with the development and implementation of the automated architecture usable for future active antenna designs, and the definition of the Off-line calibration process for the active antenna array under test. Fourth, for calibration a categorization based on operation stage in Off-line, On-site and On-line can be done to assess calibration process. This Thesis deals with the problem of calibration of active antenna arrays at reception and also transmission. The definition of the Off-line calibration process is presented as a part of the experimental procedure for characterization and calibration, but the expansion of equations for it application based on proposed phase center variation estimation method is presented along the achievement of calibration process as a previous statement for the explanation of the proposed On-site calibration algorithm which deals with the compensation of mutual coupling effect and gain and phase errors in reception and transmission. As result, the compensation of errors and mutual coupling effect at transmission is proposed applying one blind trusting calibration based on fully antenna characterization and model estimation for accurate reception to transmission translation of compensation matrices. Finally, main contributions during the analysis of calibration process can be clearly listed as the presentation of the proposed Off-line calibration procedure based on phase center variation, and the On-site calibration procedure based on fully antenna characterization. Fifth, during the study of one uplink array of 4x35-m antennas at X and Ka band, where error analysis identifying main issues of uplink arraying and challenges for calibration process with Monte Carlo simulation have been done. Furthermore, a novel On-SC based uplink calibration algorithm for enhancement of the uplink systems stability is proposed with a brief description for development and implementation of a concept demonstrator for completeness. Besides, test results have been obtained using a simple simulator setup for the uplink scenario. Main contributions during the analysis of possible future architectures for ESA deep space station and uplink calibration process can clearly be presented as the analysis of uncertainty sources and impact over large antenna arraying, the presentation of an error budget for 4x35-m antenna array as a function of the error source amplitude, the proposal of a 35-m antenna efficiency reduction model for gravity effect evaluation which has been contrasted with the gravity distortion model proposed by JPL, and the presentation of the proposed On-SC based uplink calibration. In general, for space applications the proposed analytical method for uncertainty evaluation is helpful to analyze the complete array response pattern and evaluate the side-lobe increase of antenna arrays used to communicate with GEO satellites. As well, the increase in antenna arrays for space communications makes the presented analysis a useful and efficient method to evaluate the uncertainty of future systems. Furthermore, this method aids the system designer to specify the tolerance of array components for a specified acceptable degradation. In addition, the method provides information about the most appropriate calibration technique that must be applied to the antenna array. Thus, this contribution represents an important contribution for the reduction of cost and complexity in the prototyping and manufacturing of antenna arrays.