Calibrating a Radio Frequency Electrooptic Sensor for Field-Relevant Temperature Conditions in a Laboratory Setting

Abstract

Legacy high-powered electric field measurement devices, such as flush plate dipoles (D-dots) and waveguides, are the primary diagnostic tools used for free-field experimentation. Unfortunately, these metallic devices perturb the electric field of interest via scattering and require the use of coaxial cables (fluctuate with temperature). Electrooptic (EO) probes offer a potential solution as they minimally perturb the electric field, and fiber-optic cables can be designed to correct or prevent temperature fluctuations. However, to replace the legacy diagnostics, it is critical that the EO probes are calibrated in field-relevant conditions (outdoor temperatures between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.4~^{\circ} \text{C}$ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$49~^{\circ} \text{C}$ </tex-math></inline-formula> ). Characterization of a modern EO sensor is done by using an environmental chamber and a gigahertz transverse electromagnetic (GTEM) cell. The collected data in this article indicates that modern <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text {LiNbO}_{{3}}$ </tex-math></inline-formula> EO sensors have linear changes across both various temperatures and electric fields. This article outlines the process of creating field-relevant conditions in laboratory settings. Because temperature effects are ubiquitous with most devices, the temperature response of the EO probe needed to be isolated from all other temperature effects. Using a novel way of applying the design of experiments (DoE) method, the temperature response of the EO probe can be isolated and a linear trend can be resolved. The data suggest that the EO probe under test can be used to measure RF fields as long as a small correction factor is applied to 0.52% per °C for every °C away from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22.0~^{\circ} \text{C}$ </tex-math></inline-formula> in either direction.