A 3-D Lumped-Components-Free Absorptive Frequency-Selective Transmission Structure Featuring Very Wide Two-Sided Absorption Bandwidths

A 3-D absorptive frequency-selective transmission (AFST) structure that does not require any lumped components and featuring very wide two-sided absorption bandwidths is proposed in this letter. The fundamental design concept is illustrated and the possibility to design AFST structure without lumped components is discussed. The proposed AFST structure exhibits a passband at 6.3 GHz with two-sided absorption bands from 1.15 to 5.45 GHz (130.3% bandwidth) for the lower absorption band and from 7.1 to 12.9 GHz (58% bandwidth) for the upper absorption band. The proposed structure is modeled and simulated using two different full-wave simulation tools. An equivalent circuit model is constructed based on an approximated unit cell. To verify the simulated results, a prototype is fabricated and measured with the free-space method. A comparison with related designs presented in recent literature is also performed to ascertain the implications of the proposed design regarding the lumped component-free feature and wide absorption bandwidth.