Excitation of Circular Waveguide $\text{TE}_{01}$ Mode of Microwave Communication for Downhole While Drilling

In this paper, circular waveguide TE01 mode is ex-ploited to improve the distance of the single-stage signal trans-mission of microwave communication for downhole while drilling (MCDWD) technology in gas drilling for 5-inch API drill pipe. The excitation of the TE
01
mode which is suitable in the downhole for gas drilling with high velocity gas flow is proposed. Firstly, a rectangular waveguide
$\text{TE}_{10}$
modes is excited by the probe, and then the rectangular waveguide
$\text{TE}_{20}$
mode is generated using the TE20 mode converter with a longitudinal E-plane metal plate which enhances the purity of the TE20 mode. Subsequently, the waveguide height is increased through the stepped waveguide which reduces the effect of the higher order modes. Finally, the
$\text{TE}_{20}$
mode is converted into circular waveguide
$\text{TE}_{01}$
mode through the gradual structure. The simulation shows that the return loss of the proposed structure is less than -15 dB in the frequency range from 6.25 GHz to 6.45 GHz, and the TE
01
mode conversion rate is higher than 93.6%.