Excitation of a pure TEmn mode at low terahertz region

This work presents a methodology of generating circular TE_mn mode at low terahertz region through sidewall couplings. These couplings induce magnetic dipoles. With proper arrangement on the circumference of the circular waveguide, they then jointly excite the desired mode. A model is developed to calculate the coupling strength and to analyze the mode purity. Three mode converters, TE₂₁, TE₀₁, and TE₄₁, were designed, built, and tested at W-band. Back-to-back transmission measurements exhibit excellent agreement to the results of computer simulations when the conductor loss is taken into consideration. The measured transmissions are 97%, 98%, and 95% with 3-dB bandwidths of 18.3, 24.0, and 20.2 GHz, respectively. These Y-type converters are structurally simple but machining errors are still critical. The factors affecting the performance will discuss in more details.