CST MW problem in circularwaveguide simulation

hello friend
while i am simulate circular waveguide in frequency domain solver and time domain solver its show me an memory error and meshing error and its stop simulation automatically
my circular waveguide parameter are as below
inside radius 36mm and outer radius 38mm PEC martial and cor is filed with an air for frequency range 100GHz to 200GHz
while i am able to simulate a rectangular waveguide with a core of air and surface of PEC martial
help me to solve this problem
thank you

Seems like that is an electrically large structure~20 wavelengths. Try using I-solver (recommended for electrically large structures) instead. Not sure if that would solve your problem, but worth a shot. Also, a structure this large would require a huge amount of mesh cells. You might need to get a higher RAM for your PC. If possible, do not forget to make use of the symmetry planes for your structure, this will reduce the total mesh by half for one plane of symmetry.