High-Directivity and low-loss directional couplers based on Empty Substrate Integrated Coaxial Line Technology

Abstract

[EN] High-directivity and low-loss directional couplers, based on Empty Substrate Integrated Coaxial Line (ESICL) technology, are presented in this article. The proposed coupled line direcional couplers, are based on combination of a high-isolation section, a tapering transition based on splines between the access lines and high-isolation sections, reduced-width coupled lines, and inclined arms. The design evolution has justified the combination and precise adjustment of these elements, proving to be a solution for enhancing directivity, reducing return losses, and attaining a more stable coupling coefficient. The use of the ESICL technology exhibits significant promise in terms of electrical performance, bandwidth, seamless integration with other planar circuits, and manufacturing simplicity. For comparison purposes, two directional couplers, with the same coupling coefficient but different operation frequencies, have been designed and manufactured. Additionally, a microstrip coupler has been designed and manufactured for comparison. The simulated and measured results clearly indicate that ESICL directional couplers outperform their microstrip counterparts in terms of losses and directivity, without the need for additional lumped elements or complex geometries.