Low-frequency magnetic microwave absorber using reactive ground for extended bandwidth

A design method to extend the operating bandwidth of a low-frequency magnetic microwave absorber is presented. According to the mapped impedance distribution from the design objective, a synthesized reactive ground consisting of a triple-ring array, instead of the perfect electric conductor (PEC), is conveniently placed at the back of a commercially available magnetic sheet to realize impedance matching. Compared with the conventional PEC, the reactive ground extends the operating bandwidth of reflection coefficient being less than -10 dB by introducing four consecutive absorption peaks so that the optimized structure achieves broadband absorption from 2.3 to 4.3 GHz with a thickness of 0.027 times the free-space wavelength at the lowest operating frequency and a 60.6% fractional bandwidth which is nearly two times that of the conventional structure. The physical mechanism is further investigated through the distributions of current flow and power loss. Finally, a prototype is fabricated and measured. The good agreement between the simulated and measured results verifies the effectiveness of the presented design method.