TE10

TE10 mode is the dominant mode with a>b, since it has the lowest attenuation of all modes. Either m or n can be zero, but not both.

CMRR is common mode rejection ratio. it is the ratio of Differential gain to common mode gain. CMRR=Ad/Ac

Do you mean CMRR? If so, it means Common Mode Rejection Ratio.

CMRR measures how well a differential input will reject a common mode signal (common mode means the same signal applied to both differential input leads at the same time). The ratio is expressed in decibels (dB).

There is no attenuation due to absorption, but attenuation will occur due to divergence (spreading out) of the wave.