Evaluating the Influence of Thin Film of Water on the Frequency Dependences of Transmission Line S-Parameters at Positive and Negative Temperatures
Authors: Neveznin V. N. , Komnatnov M. E. 
Published: November 2024

Relevance. Provision of reliable and uninterrupted radio communication is critically important under changing climatic conditions of its operation. The combined effect of temperature and humidity can lead to changes in the electrical characteristics of transceiving devices and thereby disrupt the communication channel. In difficult climatic conditions of operation, due to constant temperature changes on the surface of the printed circuit boards, which are part of them, condensation can form, affecting the performance of the entire device. In this regard, the electrical characteristics change, which must be taken into account when designing critical REE. When designing transmission lines on printed circuit boards, it is reasonable to evaluate climatic impacts on it in a wide frequency range, which requires the development of new models and methods that allow taking into account these impacts.

Goal of the work: to evaluate the influence of the temperature of a thin film of water on the surface of a microstrip transmission line on its frequency dependences of S-parameters. Finite element methods and laboratory experiment were used.

Results. A methodology to account for the effects of ambient temperature and humidity on the electrical characteristics of a microstrip transmission line (MTL) is presented, which allows evaluating the variation of the S-parameters of the line over wide ranges of frequencies, air temperature and humidity, as well as the chemical composition of the environment. The S-parameters of water in a container placed inside a coaxial chamber are measured over the frequency and temperature ranges of 10 MHz to 12 GHz and minus 50 to 100℃, respectively. Using the presented model, the frequency dependences of the electrical conductivity of water at different temperatures are calculated. It is shown that at positive temperature, the electrical conductivity can reach 6.5 Sm/m and at negative temperature it can reach 1.3 Sm/m. Using the developed methodology, the influence of different water electrical conductivity on the S-parameters of MTLs is evaluated. The influence of water and ice layer thickness on the S-parameters of MTLs was shown. It is found that models describing the electrical conductivity of water have an excellent influence on the electrical parameters of the transmission line. Novelty. A method of accounting for the influence of ambient temperature and humidity on the S-parameters of the transmission line is presented, which is characterized by the use of a model of water conductivity based on insertion losses calculated from the measured S-parameters of a coaxial chamber with water in the container when its temperature is changed.

Practical significance: a model and a methodology for taking into account the impact of temperature and humidity of the environment on the MTL characteristics are presented, allowing estimating the S-parameters of the line in a wide range of frequencies, air temperature and humidity, as well as the chemical composition of the environment.