Millimeter Wave Overmoded Circular Waveguide Tapers for ECRH Applications

The design methodology of the overmoded circular waveguide tapers to connect the gyrotron (ø85mm) output power at 42 ± 0.2 GHz/200 kW/3secs with different diameters (ø63.5 and ø31.75 mm) of transmission line components has been carried out. Design parameter of taper is optimized using coupling theory in such a manner that it provides an appropriate match between input and output of transition with lower spurious modes conversion. There are linear and nonlinear applicable methods for designing internal taper profile. These methods are implemented, and the results of linear tapers are compared with the analogous expressions for raised cosine (nonlinear) tapers. The overall loss in circular linear tapers is less than 1% for the length of approximately 107λ. However, raised cosine tapers may provide lower insertion loss, but linear tapers with moderate values of diameter ratio may be attractive because of its simplicity in fabrication. Both the tapers are designed and simulated using computer simulation technology (CST) Microwave Studio software.