Radome Electromagnetic Theory and Design

Chapter 3Frequency Selective Surfaces (FSS) Radomes

Frequency selective surfaces are 2D periodic structures that transmit perfectly in certain frequency bands and reflect perfectly in others in case of incident waves with arbitrary polarization and different incident angles. The unit cell size of the FSS periodic structure is approximately λ/2. Historically, the FSS evolved from the investigation of diffraction gratings in optics. This filtering process, as well as the diffraction grating itself, was discovered by D. Rittenhouse, as documented by a scientific exchange between Hopkinson and Rittenhouse published in 1786 [1]. In this paper, Hopkinson reports about a street lamp he could see through his handkerchief stretched through his hands. There are many applications to FSS planar structures. Among them, the most common is for hybrid radomes in which conformal pass-band radomes are used to reduce the radar cross section (RCS) of the enclosed antennas in the radome outside their operating frequency band [2] by diverting the incident wave in another direction from the incident wave direction. This concept is shown in Fig. 3.1.

figure 3.1 The concept of using FSS to reduce antenna RCS out of band.

At the operating frequency of the enclosed antenna, the FSS is fully transparent, while for out-of-band frequency, the FSS is fully reflective or absorptive. In case of a fully reflective ...