Low-Loss All-Metallic Gap Waveguide-Based Bandpass FSS Radome for Broadside mmWave Applications

This paper presents a bandpass frequency selective surface (FSS) radome based on an all-metallic gap-waveguide (GW) operating at broadside (θ = 0°) for the mmWave band. The proposed GW-based FSS uses conventional cross-dipole slots and a dual-GW cavity over three distinct metallic layers. The top and bottom layers consist of cross-dipole slots, whereas the middle layer consists of a dual GW-cavity and cross-dipole slots layer. The proposed GW-based FSS provides a stable broad bandpass, from 26−30 GHz, in the broadside direction for both transverse electric (TE) and transverse magnetic (TM) polarisations. A prototype of the designed 20×20 GW-based FSS finite array was manufactured and measured with an insertion loss of 0.6 dB. A good agreement between simulations and measurements is shown in broadside directions. The proposed GW-based FSS offers an excellent low-insertion-loss and cost-effective solution to fully metallic bandpass FSS radomes.