All-metal bandpass frequency selective surface filter for C-band

This paper presents the design and analysis of a low-cost all-metal frequency-selective surface (AM-FSS). The proposed structure is manufactured using a laser cutting method on a 0.6 mm thick stainless steel sheet. The unit cell consists of a square ring with four stubs positioned off-center toward the middle of the structure. The AM-FSS functions as a bandpass filter, with measured resonance 5.91 GHz, a fractional bandwidth of $ 38.9\% $ 38.9%, and an insertion loss of less than 1.0 dB. The design is remarkably thin, measuring just $ 0.011\lambda _0 $ 0.011λ0, where $ \lambda _0 $ λ0 is the free-space wavelength and has compact dimensions of $ 0.3\lambda _0 \times 0.3\lambda _0 $ 0.3λ0×0.3λ0, making it suitable for miniaturized microwave applications. The proposed design is polarization-insensitive, exhibiting steady angular performance in both TE and TM modes, with a steady response for incidence angles up to $ 45^{\circ } $ 45∘. An equivalent circuit model was utilized to evaluate the frequency response. A prototype of the design has been fabricated, and experimental results closely match the simulations, confirming the validity of the proposed design. The all-metal construction eliminates the need for commercial laminates, ensuring durability, high power handling capabilities, and cost efficiency. This makes the AM-FSS ideal for applications in microwave filtering and radar systems.