Design of miniaturised frequency selective rasorber using parallel LC resonators

Abstract

This study describes a method for designing miniaturised frequency selective rasorbers (FSRs) with a transmission band located between two adjacent absorption bands. The proposed FSR composes of a bandpass frequency selective surface at the bottom and an absorptive surface (APS) with lumped resistors and parallel LC resonators printed on the top. The absorptive surface is a 2.5-dimensional geometry for the purpose of miniaturisation. The mounted parallel LC resonators mounted in the APS are utilised to implement the transmission characteristics of the proposed FSR while the constructed lumped resistors in the APS are used to realise the absorption performance. A prototype is fabricated and measured in an anechoic chamber under the guidance of a free-space measurement system to verify this method. Experiments show that the proposed FSR has a transmission band at the centre frequency of 7.24 GHz and over the bands from 4.85 to 6.82 GHz and from 8.05 to 9.36 GHz, both reflection and transmission coefficients are less than −10 dB. The performances of the proposed FSR with different incident angles and polarisations are also investigated and results show that it is insensitive to electromagnetic wave polarisations and has a stable performance when the incident angles up to 45°.