Broadband Time-Modulated Absorber beyond the Bode-Fano Limit for Short Pulses by Energy Trapping

Abstract

Wideband absorption is a popular topic in microwave engineering to protect sensitive devices against broadband sources. However, the Bode-Fano criterion defines the trade-off between bandwidth and efficiency for all passive linear time-invariant systems. In this paper, we propose a broadband absorber beyond the Bode-Fano limit by creating an energy trap using time-modulated switches or diodes. This work starts with an ideal-circuit model to prove the concept, followed by two electromagnetic realizations---a frequency-selective-surface approach for general bandwidth broadening and a low-profile printed-circuit-board design. The prototype of the latter is built and measured, demonstrating a Bode-Fano integral larger than 1. This approach paves the way to many practical ultrawideband-absorber designs.