Triband Frequency-Selective Surface as Subreflector in Ku-, K-, and Ka-Bands

A novel triband frequency-selective surface (FSS) is designed to be a subreflector for reflector antennas. The element of the proposed FSS structure consists mainly of two identical layers of a square loop combined with a hexagonal ring and a hexagon. The designed FSS reflects electromagnetic waves in Ku-band (12-15.2 GHz), but transmits electromagnetic waves in K-band (18-21.6 GHz) and Ka-band (29.3-32 GHz). Moreover, such an FSS has the merit of stable performance for various incident angles within 50° for both TE and TM polarizations. Simulated results show that the insertion losses in K-band are less than 0.5 dB when the incident angles vary from 0° to 45°, and less than 1 dB for the incident angles from 45° to 50°. In Ka-band, the insertion losses are less than 0.5 dB when the incident angles vary from 0° to 30°, and less than 1 dB when the incident angles are from 30° to 50°. For both TE and TM polarizations, the incident angle is up to 50° with S21 less than -15 dB in Ku-band. Both designed procedure and measured results of the FSS are presented and discussed.