Multi-Layer Ultra-Wideband Wilkinson Combiner for Arrays

This work investigates an ultra-wideband (UWB), compact, and multilayer Wilkinson power combiners for tightly coupled array (TCA) designs. The Wilkinson topology designs encompass UHF, L-, and S-bands. These combiners integrate into an experimental UWB TCA. The experimental UWB TCA divides into twenty-four columns, with each column containing eight unit cells, and each cell one-inch square. The Wilkinson power combiner contains eight input ports and one output port. Twenty-four combiners mount to the TCA’s back. The combiner condenses the two-dimensional array (8x24) to a one-dimensional or linear array (1x24). The proposed Wilkinson power combiner possesses a multilayer design reducing common mode current problems caused by vias. The Wilkinson combiner covers 500 MHz to 3.28 GHz and provides a 6.56:1 bandwidth. It achieves tight impedance matching through stripline coupling. The proposed design provides minimal phase error, equal power reception, and low power handling. The power combiner interfaces with an experimental UWB TCA antenna through SMP snap connectors. This paper examines signal combining efficiency to provide minimum path loss. This paper also examines interconnecting transmission lines traversing multiple laminate layers. This necessitates proper current handling because interconnects influence impedance, transmission, and isolation. Integrating a via picket fence improves port isolation and reduces propagating parallel plate modes. The proposed combiner design achieved the following important attributes at or better than the minimum required specifications. The measured combiner design successfully demonstrated -7.8dB minimum return loss for input and -18.1dB return loss for the outputs; 10.92dB ± 1.28dB insertion loss; -12.2db minimum isolation; ± 1.38° minimal phase error; ± 0.57dB power reception imbalance. The proposed UWB combiner design condensed the four-stage Wilkinson footprint to consume no more than 0.4in² (258mm²) surface area, weighed only 1.5oz (42.5g), and less than a half-inch thick

Signal diversity for the reduction of signal dropouts and speckle noise in a laser-Doppler extensometer

A recently demonstrated laser-Doppler extensometer is affected by signal dropouts caused by speckle noise, whereby the carrier-to-noise ratio (C/N) falls below the so-called frequency-modulation threshold. In this article, we present a new optical setup with polarization signal diversity for reducing speckle-induced dropouts dramatically. The probability of a signal dropout can be substantially reduced using weighted combination signals from different photodetectors collecting the scattered light at two orthogonal polarizations. Therefore, we prove in this paper that signal diversity enables a laser-Doppler extensometer for industrial applications. Furthermore, a theoretical model based on the speckle statistics for estimating the probability of signal dropout is introduced. The relationship between the occurrence of signal dropouts and the demodulation bandwidth is studied. The experimental results of the occurrence of dropouts highly match the theoretical estimated probability distribution. Finally, strain measurement demonstrates a significant reduction of speckle noise with the implemented technique

Advanced GNSS-R instruments for altimetric and scatterometric applications

This work is the result of more than eight years during a bachelor thesis, a master thesis, and the Ph.D. thesis dedicated to the development of the Microwave Interferometric Reflectometer (MIR) instrument. It summarizes all the knowledge acquired during this time, and describes the MIR instrument as detailed as possible. MIR is a Global Navigation Satellite System - Reflectometer (GNSS-R), that is, an instrument that uses Global Navigation Satellite System (GNSS) signals scattered on the Earth's surface to retrieve geophysical parameters. These signals are received below the noise level, but since they have been spread in the frequency domain using spread-spectrum techniques, and in particular using the so-called Pseudo Random Noise (PRN) codes, it is still possible to retrieve them because of the large correlation gain achieved. In GNSS-R, two main techniques are used for this purpose: the conventional technique cGNSS-R and the interferometric one iGNSS-R, each with its pros and cons. In the former technique, the reflected signal is cross-correlated against a locally generated clean-replica of the transmitted signal. In the latter technique the reflected signal is cross-correlated with the direct one. Nowadays multiple GNSS systems coexist, transmitting narrow and wide, open and private signals. A comparison between systems, signals, and techniques in fair conditions is necessary. The MIR instrument has been designed as an airborne instrument for that purpose: the instrument has two arrays, an up-looking one, and a down-looking one, each with 19 dual-band antennas in a hexagonal distribution. The instrument is able to form 2 beams at each frequency band (L1/E1, and L5/E5A), which are pointing continuously to the desired satellites taking into account their position, as well as the instrument's position and attitude. The data is sampled and stored for later post-processing. Last but not least, MIR is auto-calibrated using similar signals to the ones transmitted by the GNSS satellites. During the instrument development, the Distance Measurement Equipment/TACtical Air Navigation (DME/TACAN) signals from the Barcelona airport threatened to disrupt the interferometric technique. These signals were also studied, and it was concluded that the use of a mitigation systems were as strongly recommended. The interferometric technique was also affected by the unwanted contribution of other satellites. The impact of these contributions was studied using real data gathered during this Ph.D. thesis. During these 8 years, the instrument was designed, built, tested, and calibrated. A field campaign was carried out in Australia between May 2018 and June 2018 to determine the instrument's accuracy in sensing soil moisture and sea altimetry. This work describes each of these steps in detail and aims to be helpful for those who decide to continue the legacy of this instrument.Este trabajo es el resultado de más de 8 años de doctorado dedicados al desarrollo del instrumento Microwave Interferometric Reflectometer (MIR). Esta tesis resume todo el conocimiento adquirido durante este tiempo, y describe el MIR lo más detalladamente posible. El MIR es un Reflectómetro de señales de Sistemas Globales de Navegación por Satélite (GNSS-R), es decir, es un instrumento que usa señales de GNSS reflejadas en la superficie de la tierra para obtener parámetros geofísicos. Estas señales son recibidas bajo el nivel de ruido, pero dado que han sido ensanchadas en el dominio frecuencial usando técnicas de espectro ensanchado, y en particular usando códigos Pseudo Random Noise (PRN), es todavía posible recibirlas debido a la elevada ganancia de correlación. En GNSS-R existen dos técnicas para este propósito: la convencional (cGNSS-R), y la interferométrica (iGNSS-R), cada una con sus pros y sus contras. En la primera se calcula la correlación cruzada de la señal reflejada y de una réplica generada del código transmitido. En la segunda técnica se calcula la correlación cruzada de la señal reflejada y de la señal directa. Hoy en día muchos sistemas GNSS coexisten, transmitiendo señales de distintos anchos de banda, algunas públicas y otras privadas. Una comparación entre sistemas, señales, y técnicas en condiciones justas es necesaria. El MIR es un instrumento aerotransportado diseñado como para ese propósito: el instrumento tiene dos arrays de antenas, uno apuntando al cielo, y otro apuntando al suelo, cada uno con 19 antenas doble banda en una distribución hexagonal. El instrumento puede formar 2 haces en cada banda frecuencial (L1/E1 y L5/E5A) que apuntan continuamente a los satélites deseados teniendo en cuenta su posición, y la posición y actitud del instrumento. Los datos son guardados para ser procesados posteriormente. Por último pero no menos importante, el MIR se calibra usando señales similares a las transmitidas por los satélites de GNSS. Durante el desarrollo del instrumento, señales del sistema Distance Measuremt Equi Distance Measurement Equipment/TACtical Air Navigation (DME/TACAN) del aeropuerto de Barcelona mostraron ser una amenaza para la técnica interferométrica. Estas señales fueron estudiadas y se concluyó que era encarecidamente recomendado el uso de sistemas de mitigación de interferencias. La técnica interferométrica también se ve afectada por las contribuciones no deseadas de otros satélites, llamado cross-talk. El impacto del cross-talk fue estudiado usando datos reales tomados durante esta tesis doctoral. A lo largo de estos 8 años el instrumento ha sido diseñado, construido, testeado y calibrado. Una campaña de medidas fue llevada a cabo en Australia entre Mayo de 2018 y Junio de 2018 para determinar la capacidad del instrumento para estimar la humedad del terreno y la altura del mar. Este documento describe cada uno de estos pasos al detalle y espera resultar útil para aquellos que decidan continuar con el legado de este instrumento.Postprint (published version