Design of quasi-optical filter for geostationary orbit microwave radiometer

We in detail describe the design procedure of a Frequency Selective Surface (FSS) filter used on the FengYun-4(FY-4) microwave satellite, which generates transmission of 112125GHz radiation with insertion loss less than 0.4 dB and achieves more than 20 dB isolation from 175-192 GHz when the FSS filter is operated in the TM polarization at 45 degree of incidence. Firstly, we give the principle of selection of the periodic structure arrangement. Secondly, resonant characteristic of the shorted ring slot unit is demonstrated in detail and its equivalent circuit is proposed as guidance for better understanding the characteristic of the resonant cell. To minimize the insertion loss, the FSS filter formed of two closely spaced freestanding arrays containing resonant shorted ring slot elements is adopted. Software CST is used to obtain the specified transmission response. Simulated transmission coefficients are in close agreement with the required specification, all criteria being satisfied simultaneously, even exceeding the requirement performance specifications, it is concluded that the FSS filter have lower transmission loss in millimeter and sub-millimeter wavelengths. Finally, we give the error analysis of structural parameters to define the fabrication tolerances.