Design and development of mode launcher for TM01 mode in circular waveguide in S-band

This paper presents coaxial TEM-to-TM01 mode converter in circular waveguide in S-Band. Many of the High power microwave sources generate power in the form of TM01 mode at 3GHz. The proposed mode launcher is used for calibration purpose at low power. Coaxial line is attached to the axis of circular waveguide to excite TM01 mode and to increase the conversion efficiency stair type of monopole antenna is connected to the inner conductor of coaxial line. Furthermore the dielectric of coaxial line is extended in to the waveguide over inner conductor to achieve maximum possible return loss i.e. 72dB simulated and 50dB measured; since there is a requirement of minimum reflection. Proposed design offered 40% of bandwidth. Radiation pattern of TM01 mode is then investigated to verify propagated mode. The test results are in good agreement with the simulation.