Design And Implementation Of Broadband Tunable Flexible Microwave Absorber

The density and thickness of traditional absorption material and Salisbury screen structure is large, the electromagnetic absorption is limited. It is not adapted to the actual dynamic electromagnetic environment. Frequency selective surface(FSS) is used to replace the resistance layer in Salisbury screen. We called the FSS loading active devices as active frequency selective surface(AFSS). This structure can realize absorption tunable. The tunable microwave reflectivity and polarization stability of AFSS absorber based on flexible substrate is discussed in this thesis. The main research results are as follows:We fabricate FSS based on flexible substrate in this thesis, including film mulching exposure, development, etching, stripping process. The absorber can be attached to curved surface. Optimization and improvement of the AFSS structure is discussed in this thesis,both the HFSS simulation and experiment results show that by loading the PIN diode can make the reflectivity tunable between 2-18 GHz. The characteristics of absorption is affected by the equivalent resistance, AFSS pattern size, unit cell spacing, thickness of dielectric layer and substrate dielectric constant, Comparing the series and parallel loading PIN diode, it is shown that the parallel loading status with a wider tunable frequency band, including below-6 dB in 2.65-18 GHz and-10 dB in 2.86-14.2 GHz. It is shown that impedance matching of the whole structure change with the equivalent resistance of PIN diodes by using equivalent transmission line theory. Therefore, the absorption performance is tunable. By further analyzing the impedance, surface current, electric distribution and body loss density of the resonance point. The absorber and free space are impedance matched at resonant frequencies.Energy loss form consist of resonant circuit loss, ohmic loss, echo interference loss.To solve the polarization stability problem of broadband tunable absorber. There are some improving schemes of the AFSS absorber by using the law summarized from square ring series pattern, including double rotation. It is shown that the improved AFSS absorber has rotational symmetry current distribution in AFSS pattern and PIN diode, and the new absorber has good horizontal and vertical polarization stability between 2 and 18 GHz.