Implementation Of Frequency Selective Surface In Radar Absorbing Materials

Recently, with the rapid advancement of information age, the military forces of differentcountries are paying more and more attentions to the application of cutting-edge wireless andcommunication techniques to military fields, and how to realize a vantage point in theinformation and electromagnetic military conflicts has become the focus of all researchersaround the world. At present, extensive researches are devoted to Radar Absorbing Material(RAM) as it may provide an optimum solution to electromagnetic shielding and protection.Based on electromagnetic performance of the Frequency Selective Surface (FSS), this paperdiscusses the design and application of RAM. The main contents are as follows.Firstly, the fundamental analytical method of FSS is introduced and FSS unit cells withsquare, circular, Jerusalem shape are studied and compared. Then the effect of surfaceelectromagnetic characteristics with different element size and substrate on the FSS isdiscussed, and the stability of several basic FSS designs has been compared. Based on theresearch outcome of FSS, in this paper, PIN diode with high-frequency on-off switchingproperty is implemented to a novel frequency selective surface design to provide effectiveelectromagnetic protection of radar systems, wireless communication devices and networks inthe S-band (2to4GHZ). When the proposed design is under low-power EM illumination, itexhibits a stable band-pass behavior for incident signals with different polarizations andincident angles within operational band; whereas when it is under high-power EMillumination, it mimics the function of an adaptive switch, yielding a total reflection ofimpinging EM waves across the entire operational band.Secondly, by utilizing the equivalent circuit and Smith chart, the working principles ofSalisbury absorbing screen, Jaumann absorbing material and Analog circuit absorbingmaterial are investigated; and the impact of RAM design parameters such as the thickness ofsubstrate and surface impedance on absorbing performance of RAM has been explored. It isshown that by increasing the thickness and relative dielectric constant of the substrate, theabsorption can be shifted towards the lower frequency, but at the same time it will affect theabsorbing bandwidth and absorbing properties of the design. In addition, thequarter-wavelength property of Salisbury screen is emphasized, and the feasibility of usingFSS to improve the absorbing performance of RAM is also discussed.Thirdly, a composite Salisbury screen with a lossy FSS for ultra-wideband performanceis proposed. The results indicate that the proposed Salisbury screen provides a wideimpedance of about15GHz from3.5GHz to18.5GHz with the return loss greater than or equal to10dB and the relative bandwidth is about135%. So by controlling the resonantfrequency of the FSS and the chip resistors, the performance of the Salisbury screen absorbercan be enhanced.Finally, a thin planar EM absorber consisting of two lossy FSS layers is presented.Square rings and crossed dipoles are used to design the unit cells of lossy layers. The resultsreveal that the proposed double-layer absorber can provide effective absorption of EM wavesin the frequency range of3.8GHz to15GHz, resulting in a relative absorbing bandwidth of119%. Furthermore, the proposed design can be extended to absorbers consisting of more thantwo layers of lossy FSS for wider absorption bandwidth.