Design and Characterization of the Fully Metallic Gap Waveguide based Frequency Selective Radome for Millimeter Wave Fixed Beam Array Antenna

—This paper presents a bandpass frequency selective surface (FSS) radome based on fully metallic gap waveguide (GW) technology. The element of the proposed FSS radome consists of a conventional cross-dipole slot etched on metallic plates and positioned over a groove GW cavity. A design with a single GW cavity layer was initially produced which was later optimised for performance, to comprise a dual GW cavity layer, while considering both functionality and manufacturability. It is shown that the proposed FSS element offers a stable and wide bandpass (from 26 - 30 GHz) performance in the broadside direction for both transverse electric (TE) and transverse magnetic (TM) polarizations. For oblique angle of incidence, the suggested FSS element works up to 30 ◦ with a reduction in usable bandpass bandwidth performance to 26 - 28 GHz for both TE and TM polarizations. A 20 × 20 -element GW-FSS array prototype has been fabricated and measured, which was integrated with a ﬁxed beam array antenna to further validate its functionality as a ﬁltering radome. The ﬁndings show an excellent agreement between simulations and measurements. Hence, the proposed GW-FSS represents a great opportunity to develop a all-metallic FSS with low insertion loss, sharp-roll-off ﬁltering, wideband performance and inexpensive fabrication cost.