A Miniaturized Frequency Reconfigurable Anechoic Chamber Based on Omnidirectional Reflectionless Absorption Spatial Kramers-Kronig Medium

Ideal microwave absorbers capable of broadband omnidirectional reflectionless absorption have been an important subject of scientific research for centuries. Recently, theoretical studies have shown that spatial Kramers-Kronig (KK) media can achieve omnidirectional reflectionless absorption without the use of any gain element. In this paper, the concept of spatial KK relation to cylindrical coordinates is extending and a dual-Lorentz-resonance space-frequency KK permittivity profile is implemented in order to achieve impedance matching to free space. To further extend the absorption spectrum, tunable varactors are introduced into the unit cell to change Lorentz-resonance frequency, and thus, the operating frequency can be reconfigured in a wide frequency range. A two-dimensional (2D) 48-cm-diameter doughnut-shaped anechoic chamber is implemented using the designed cylindrical frequency reconfigurable spatial KK medium. The simulated result shows that a reconfigurable frequency range from 4.5 GHz to 5.25 GHz is realized. Our method paves a new way to design ideal microwave absorber, especially demanding wide-angle incidence and broad bandwidth.