Wah González, Carlos Roberto

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    Design of a compact dual-band radiometer system for an unmanned aircraft system platform
    (2021-12-09) Wah González, Carlos Roberto; Rodríguez Solís, Rafael A.; College of Engineering; Armstrong, Roy; Medina Sanchez, Rafael H.; León Colón, Leyda V.; Department of Electrical and Computer Engineering; Cruzado Vélez, Ivette
    Water is the most important resource of Earth, representing 71% of it. To understand this resource, variables like salinity and soil moisture content, prove to be useful to study its behave. Salinity content helps to understand the water cycle, ocean density, and exchange of water between the ocean and the atmosphere on the planet. Meanwhile, with soil moisture scientists understand the cycle of water in the land and the exchange with the ocean, and can help to predict flooding and severe droughts. A dual-band antenna, using L and Ka bands (1.413 and 31.5 GHz), was designed and validated to be used as an instrument to measure salinity content and soil moisture. These frequency bands were chosen since they are protected to make Earth research. L-band is a well-used frequency since radiometric are very sensitive to brightness temperature. One of the most important design aspects of this sensor is the antenna, which is designed to be compact, low size, and lightweight, to be mounted on a small Unmanned Aircraft Vehicle (UAV). It consists of a microstrip patch antenna designed to operate at 1.413 GHz.The gain and the front-to-back ratio of the microstrip antenna are 9 dB and 17 dB respectively, with an HPBW of 66 deg. The Ka-band antenna, embedded in the patch, consists of a Substrate Integrated Waveguide (SIW) slot array. This higher frequency band was chosen to correct the ocean salinity measurements, due to errors caused by winds, waves, and asymmetrical surfaces. For the slot array the gain, front-to-back ratio, and HPBW are 14 dB, 15 dB, and 8 deg. Both antennas were coaxially fed to obtain a 50 ohm input impedance. The impedance bandwidth is below -15 dB for both of the bands. A salinity change due to rainfall and brightness temperature codes are presented. The salinity code presents a scenario where the salinity ocean surface is below 33 psu, due to different rainfall rates. While the temperature extraction code is made with a tropical scenario where the physical temperature of the ocean is around 28o Celsius obtaining a voltage at the terminals of the antenna around 0.2 V. With this code, the salinity measurement can be also be extracted.