Study on multipath channels model of microwave propagation in a drill pipe

In the process of air drilling, underground monitoring data can be transmitted by a microwave signal in the drill pipe. In this paper, we analyze the characteristics of the microwave transmission channel in a drill pipe, by regarding the drill pipe as an irregular lossy cylindrical waveguide. We use multipath transmission theory and an experimental statistical method to research the characteristics of the microwave channel and the attenuation law. The existing research results only focus on the dielectric loss of the drill stem; however, herein we point out that there are numerous reflective surfaces that can produce a great deal of reflected waves in the joint section of the drill pipe. Hence, the drill pipe has microwave multipath channel characteristics; consequently, multipath fading and delay are the main factors affecting the transmission quality. According to actual measurement results, the microwave channel composed of a drill pipe unit is in accordance with the ultra-wideband channel standard and has dual cluster multipath channel characteristics. The relative time delay between the two clusters is 51 ns, the mean square delay is 22.58 ns, and the maximum data rate in a drill pipe is about 7 Mb/s.