Three-dimensional FSS elements with wide frequency and angular response

In this paper, we describe a three-dimensional frequency-selective surface (FSS) element that generates a flat bandpass response over a wide band, as well as controllable low-pass angular response. The unit cell, which consists of a waveguide element with two connected cascaded radiating elements, exhibits a flat bandpass response over the frequency range 13 GHz to 24 GHz, i.e. a -3dB bandwidth (BW/f₀) of 66.6%. We show that the angular response of the FSS can be controlled by changing its periodicity, which, in turn, determines the angle at which the first higher-order Floquet harmonic begins to propagate.