Abstract: Addressing the issues of complex structure and difficulty in achieving large-scale engineering applications caused by traditional frequency selective element design methods, a single-frequency bandpass frequency selective surface (FSS) operating at Ku-band (16.14 GHz) and a dual-frequency bandpass FSS across X-band (10.35 GHz) and Ku-band (15.65 GHz) are designed based on equivalent circuit theory. By using an equivalent circuit model, the optimization design of the frequency selective element is achieved, simplifying the structure and reducing design difficulty. The two frequency selective elements are capable of maintaining good resonant stability at incident angles ranging from 0°to 60°and preserving good polarization stability in both transverse electric and transverse magnetic modes. Moreover, the two frequency selective elements are fabricated and tested to validate their filtering performances. The test results show that the full wave and equivalent model simulation results have good consistency with the physical test results. The designed frequency selective elements have simple structures and broad application prospects in fields such as satellite detection and planar radar radome designs.