Influence of Dielectric Loss on RF Performance of Microstrip Multi-Resonant Circuits

Abstract

Nowadays, fabric-based antennas, resonators, and sensors are attracting significant attention due to their excellent comfortability and flexibility compared with the rigid commercial printed circuit boards (PCBs). Both the dielectric constant ( ${\epsilon }_r$ ) and dielectric loss tangent ( $\tan \delta$ ) of substrate materials have a great influence on their frequency response characteristics. However, the effect of dielectric loss is usually ignored, since traditional radio frequency (RF) devices are fabricated on commercial PCBs with much lower $\tan \delta$ . As the differences of dielectric loss vary widely with different fabric materials, it is of great significance to explore the influence of dielectric loss on the frequency response characteristics. Therefore, this paper systematically studied the influence of substrate properties on RF performance of microstrip multiresonator. Firstly, the models of microstrip multiresonators with different ${\epsilon }_r$ and $\tan \delta$ were created by HFSS simulation. By parametrically sweeping, it showed that the $\tan \delta$ was the key factor for the notch depth. And the larger the $\tan \delta$ , the bigger the electromagnetic loss of the material, resulting in a smaller notch depth of the resonator. Then, three representative materials with different orders of magnitude of $\tan \delta$ (AD-450: 0.002, FR-4: 0.015, and denim fabric: 0.114) were chosen to verify the simulation. The results showed that the common fabric-based resonator has poor RF characteristics for their big dielectric loss compared with those of commercial PCBs. This study is of great significance for designing wearable electronic devices with flexible substrate materials with large dielectric loss.