A frequency tunable multi-layer low cost microwave absorber is proposed for Ku and X bands of applications. The tunability is obtained with the cavity model design using two metallic layers; a frequency selective surface (FSS) layer and a metal backed substrate layer with the air gap between them. The change in air-gap results in variation of the effective substrate height, and as a consequences the resonant frequency is tuned. The coupling of LC resonance and cavity resonance at an air-gap of 7.5 mm results in a dual-band absorption of the design. The proposed absorber performance has been analyzed for both TE and TM polarizations of incident wave, and the results are found to be same. The studies on surface current distribution and incident angle variation are observed to get physical insight behind absorption. The waveguide measurement method is used to correlate the simulated results with the measured one. With this simple cost efficient design, the absorber appears well suited for EMI/ EMC application at X and Ku bands.
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