Miniaturized Frequency-Selective Surfaces Based on Monolithically Integrated Components

In this article, a novel approach to design low-profile miniaturized frequency-selective surfaces (FSSs) is proposed. The effective miniaturization of the FSS elements, based on squarering-slot resonators, is accomplished by reactively loading the FSS unit cell with monolithically integrated components. The reactive components, such as capacitors and inductors embedded in the resonant unit cell, are fabricated using a multistep thin-film process based on benzocyclobutene (BCB) resin. The capacitors are built as planar metal-insulator-metal structures using an ultra-thin dielectric layer of BCB, while the multiturn inductors are fabricated as planar spiral structures with two metal layers and BCB as an interlevel dielectric for crossover. The advantages of the proposed approach are the capability to obtain large values of capacitances and inductances within small areas with low parasitics as well as the benefits in cost reduction and easy fabrication by using a planar microfabrication process. A component value variation analysis is performed to study the effect of fabrication tolerances in the reflection and transmission coefficients of the FSS when non-identical small cells are obtained. It has been experimentally validated that a 2.46 mm unit cell resonates at 4.175 GHz with transmission loss of 0.86 dB, achieving a miniaturization level of λ/29.