Design and analysis of a dynamically tunable ultra-broadband flexible microwave absorber

We report on the design, fabrication, measurement, and analysis of a dynamically tunable ultra-broadband flexible microwave absorber. The absorber uses an active frequency selective surface based on PIN diode. The results show that the absorber can alter the bias voltage of PIN diode arrays to realize the tunable reflectivity through power control system, including below -6dB between 2.65 and 18GHz and -10dB between 2.86 and 14.2GHz. By analyzing the input impedance of the proposed absorber, it is indicated that the absorber and free space are impedance matched at three resonant frequencies, including 4.4, 11.2, and 16.3GHz. The transmission line equivalent circuit model is built, it turns out that fixed point of impedance matching exists when it's at low frequency.