Design of Wideband Microwave Absorber with Ultra-wide-angle Response

Frequency selective surface (FSS) is a spatial filter that has frequency selection characteristics for electromagnetic waves with different operating frequencies, polarization states and incident angles. At the same time, frequency selective surface has the advantages of simple structure and easy processing compared with the traditional filters. FSS have been investigated for many decades and extensively utilized in various applications. It can used in radar radomes to reduce the radar cross section (RCS) of an array antenna, as a reflector to transmit and reflect electromagnetic waves in different frequency bands. Normally, electromagnetic waves are incident at an oblique Angle onto the target surface. Therefore, the research of FSS absorbers with stable absorbing performance under oblique incidence has tremendous practical application value. This paper proposes a new design scheme for designing a FSS absorber with stable oblique incident response range from 0° to 70°. A single-square-loop array with lumped resistors and square patch printed on the dielectric substrate is proposed, and it exhibits a characteristic impedance matching for wide incident angles from 0° to 70°. The design scheme of the FSS layer under the condition of oblique incidence is introduced in detail, and the equivalent circuit is adopted to make the design clearer and more direct. The results show the absorption bands with oblique incident angles from 0° to 30°, 30° to 50°, and 50° to 70° reflection coefficients below-10 dB are 3.44 to 9.03 GHz, 4.49 to 9.06 GHz, and 4.87 to 8.96 GHz for TE polarization, respectively. The absorber proposed in this paper will contribute much to the development of ultra-wide-angle oblique incidence.