Measurement of ultra wideband channel coefficient through carbon dioxide in a multipath environment

This paper reports an investigation into the effect of carbon dioxide (CO₂) gas on various ultra wideband channel coefficients. Measurements were conducted using apparatus consisting of a rubberized tube (6 mm diameter) connected to a source of CO₂ or nitrogen (N₂). For support, the rubberized tube was wrapped twice around a PVC pipe (160 mm diameter). The rubberized tube was flushed with 100% CO₂ several times before being sealed in the tube at atmospheric pressure. In between measurement trials, removal of CO₂ was achieved by flushing with pure nitrogen. A Vector Network Analyzer (VNA) using two identical directional antennas, with the wrapped section of tubing placed in-between, measured the channel coefficients over ultra wideband frequency spans of (0.3-8) GHz and (1-2) GHz. Significant magnitude differences between the baseline condition and that of CO₂ were observed. We found the same signature of difference curves over the same frequency spans for different measurements. Difference in shape in the frequency band of (1-2) GHz is the same as that of the measured difference over 1-2 GHz in entire frequency band of 300 MHz to 8 GHz for the measured channel coefficients.