Abstract:Millimeter/sub-millimeter limb sounder plays an important role in atmospheric science, environmental science and global climate change research. Millimeter/sub-millimeter limb sounding radiometer usually needs to operate in multiple frequency bands, such as multi-band of feed，therefore its bandwidth can not meet the requirements usually. When multiple detection bands share a primary mirror, using quasi-optical technology to achieve the detection of frequency separation can save a lot of space. The combination of quasi-optical polarization wire grid and quasi-optical frequency selector can be used to separate four bands of frequency ranging from 118 GHz to 340 GHz. Quasi-optical polarization wire grid is a quasi-optical power divider/combiner，which separates the four bands signals into 183 GHz/240 GHz and 118 GHz/340 GHz; while quasi-optical frequency selector is a high frequency selective surface, which can transmit high-frequency electromagnetic waves and reflect low frequency electromagnetic waves. Reflected and transmitted electromagnetic waves enter into two receiving modules to achieve signal reception. In this paper, the structural parameters are simulated and optimized in HFSS for the periodic unit. The quasi-optical polarization wire grid and quasi-optical frequency selector technology are implemented according to simulation results. The practically measured results are consistent to the design requirements of millimeter/sub-millimeter limb sounding instrument.