Abstract
This work presents the design of a dual-band frequency selective surface (FSS) which works as a bandpass filter in the 28 GHz and 38 GHz bands. The proposed FSS is a single layer, easy to fabricate structure and consists of non-uniform unit cells arranged in a 2\times 2 grid. Furthermore, the proposed FSS is compact and can be placed at \lambda/21 distance from the antenna. The design of FSS is validated by using it as a superstrate for two microstrip patch antennas operating at 28 GHz and 39 GHz, and it is demonstrated that the antennas maintain their radiation characteristics, even with the FSS located at sub-wavelength heights over the antennas. With a slim design, the FSS can be employed as a cover for the antenna of 5G mobile terminals operating in the millimeter-wave bands.