Compact Wideband Coplanar Stripline-to-Microstrip Line Transition Using a Bended Structure on a Two-Layered Substrate

Kang Wook Kim,Sachin Kumar,Gwan Hui Lee,Wahab Mohyuddin,Hyun Chul Choi

doi:10.3390/electronics10111272

Abstract

A design of a compact coplanar strip (CPS)-to-microstrip line (MSL) transition using a bended structure on a two-layered substrate is presented. The proposed transition consists of a CPS taper and a bended CPS-to-MSL transition on a two-layered substrate. The CPS taper is formed on the lower substrate with low permittivity (εr = 3.38), and the bended CPS-to-MSL transition is formed on the upper substrate with high permittivity (εr= 10.2). The proposed transition is designed with analytical formulas obtained by applying EM-based conformal mapping without parametric tuning trials. The conductor shape of the bended CPS-to-MSL transition is adjusted to form an optimal Klopfenstein impedance taper. The proposed CPS-to-MSL transition optimally connects between a high impedance CPS line (~160 Ω) and a 50 Ω MSL, which typically results in a long transition length for ultra-wideband performance. The implemented transition bended in a sinusoid shape on the two-layered substrate provides good performance from 2 GHz to 17 GHz with the maximum 2 dB insertion loss per transition, and the horizontal length of the bended transition is reduced to 42.9% of the straight transition length. This bended transition is developed for use in mm-wave balanced antenna/detector feeds but can be applied to a variety of wideband balanced circuit modules, where compact circuit size is critical.

Highlights

In order to reduce the horizontal length of the transition, the proposed coplanar strip (CPS)-to-microstrip line (MSL) transition is implemented in a two-layered structure: on the lower substrate, a CPS feed and a CPS impedance taper are formed using the low dielectric constant substrate for the radiation efficiency of the antenna, and on the upper substrate, a bended structure of a sinusoid shape is formed on a high dielectric constant substrate
The CPS taper is formed on the lower substrate with low dielectric constant, and the bended CPS-to-MSL transition is formed on the upper substrate with high dielectric constant, where the bended transition design helps to reduce the horizontal length of the transition
The proposed transition consists of a CPS taper and a bended CPS-to-MSL transition on a two-layered substrate

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. A new design of the compact CPS-to-MSL transition with ultra-wide bandwidth from 2 GHz to 17 GHz using a bended structure on a two-layered substrate is proposed. In order to reduce the horizontal length of the transition, the proposed CPS-to-MSL transition is implemented in a two-layered structure: on the lower substrate, a CPS feed and a CPS impedance taper are formed using the low dielectric constant substrate for the radiation efficiency of the antenna, and on the upper substrate, a bended structure of a sinusoid shape is formed on a high dielectric constant substrate

Design of the Proposed Compact CPS-to-MSL Transition

Electric Field Distribution

Fabricated Back-to-Back Structure

S-Parameters of the Back-to-Back Structure

Findings

Conclusions