Analysis the wavelength for off-focus Cassegrain optical antenna with incident Gaussian beam

Cassegrain antenna has excellent transceiver characteristics, it is widely used in inter-satellite communication. Most researchers are only based on the on-focus antenna system. But in fact, some unpredictable factors, like slight impact or thermal deformation may make the primary and secondary mirror cannot be exactly on-focus. Therefore, the off-focus Cassegrain optical antenna system with incident Gaussian beam are researched in the paper. We conclude that the far field transmission gain is more sensitive to the wavelength of the laser than the energy in off-focus system. So in practical application, we must mainly consider the influence of wave length to the transmission gain. If the secondary mirror is set off-focus by 0.05 mm, the gain will change 20.9474 dB with long wave 1550 nm, and 79.8526 dB with short wave 633 nm. So use long wave laser in off-focus system is better.