Broadband 1-bit Reconfigurable Intelligent Surface at Millimeter Waves: Overcoming PIN-Diode Degradation with Slotline Ring Topology.

Abstract

This paper explains the non-idealities that arise when using PIN diodes at millimeter-wave frequencies and the important limitations that they bring in classical configurations of 1-bit slotline reconfigurable unit cells. A robust solution is proposed where a single PIN diode is inserted inside a ring topology. The slotline unit cell is analyzed through a circuit-model approach. Its performance is compared with a unit cell based on a single slotline, which also includes a PIN diode, referred to as classical configuration. For experimental assessment, a circuit prototype is fabricated to verify the phase difference of both PIN diode states in each unit cell configuration. The measured results reveal that the slotline unit cell with ring configuration provides a 180° ± 20° reflection phase difference from 36.3 GHz to 45 GHz (21.4% relative bandwidth). Finally, the proposed slotline unit cell with ring topology is measured in a complete array to assess its performance in periodic and quasi-periodic environments. The measurements confirm the 1-bit behavior for both normal and oblique incidence with losses less than 2 dB. Therefore, this enables the design of wideband 1-bit reconfigurable reflectarrays and RIS in this frequency range.