Tunable Frequency Selective Radome with Broadband Absorbing Properties

Radar radome based on frequency selective surface(FSS) can be used not only to protect antenna from physical damage caused by wind or rain, but also to reduce the radar cross section (RCS) by reflecting the incident wave to unimportant direction or absorbing the incident wave. In this paper, a miniaturized and tunable frequency selective structure with wideband absorbing property is designed for the application of radar radome. To avoid the problem that the periodicity of the bandpass FSS should larger than that of resistive FSS, in our design, the varactor diodes are loaded on the band-pass FSS to achieve the operating frequency adjustability and miniaturize the periodicity of FSS. Through proper adjustment, the periodicity of resistive FSS can be equal to that of bandpass FSS. The period of FSS is equal to 10 mm, which is only lambda/30. Moreover, the passband frequency is able to tune from below 0.5 GHz to 1.14 GHz by adjusting the voltage between the diodes. This property allows the designed FSS structure to be able to apply for the frequency hopping communication. The miniaturized elements may improve the angle stability and delay the lowest frequency at which the grating lobe appears. Besides, the double square loops loaded with lumped resistors are used to absorb the incident wave in absorptive band and to achieve the polarization independent property of the designed FSS. The simulation results show that the designed FSS has well absorbing performance from 6.8 GHz to 24 GHz, and the polarization of incident wave has little influence on its transmission and absorbing properties.