A balanced-to-balanced directional coupler based on branch-slotline coupled structure

Yaxin Liu,Feng Wei,Xiaowei Shi,Cao Zeng

doi:10.1515/freq-2019-0199

Abstract

Abstract In this paper, a balanced-to-balanced (BTB) branch-slotline directional coupler (DC) is firstly presented, which can realize an arbitrary power division ratios (PDRs). The coupler is composed by microstrip-to-slotline (MS) transition structures and branch-slotline coupled structures. The single-ended to balanced-ended conversion is simplified and easy to implemented by the MS transition structures, which intrinsically leads to the differential-mode (DM) transmission and common-mode (CM) suppression. Moreover, the different PDRs which are controlled by the widths of branch-slotlines can be achieved. In order to verify the feasibility of the proposed design method, two prototype circuits of the proposed coupler with different PDRs are fabricated and measured. The return loss and the isolation of two designs are all better than 10 dB. Moreover, the CM suppressions are greater than 35 dB. A good agreement between the simulation and measurement results is observed.

Highlights

Directional couplers (DCs) are used as power divider, hybrid junction, and most commonly used as a sampling device for measuring forward and backward waves on a transmission line
The coupler is composed by microstrip-toslotline (MS) transition structures and branch-slotline coupled structures
The single-ended to balanced-ended conversion is simplified and easy to implemented by the MS transition structures, which intrinsically leads to the differential-mode (DM) transmission and commonmode (CM) suppression

Summary

Introduction

Directional couplers (DCs) are used as power divider, hybrid junction, and most commonly used as a sampling device for measuring forward and backward waves on a transmission line. A novel wideband BTB branch-slotline DC with an arbitrary PDRs is presented. The power distribution for DM signals and the CM suppression are integrated in one circuit. The couplers could achieve the arbitrary PDRs by employing branch-slotline structures. The circuit size of the BTB couplers is similar to single-ended ones. Two design prototypes with PDR of 1:1 and 2:1 are simulated and measured. The return losses and isolations of two designs are all better than 10 dB, and the CM suppressions are greater than 35 dB. Y. Liu et al.: A balanced-to-balanced directional coupler based on branch-slotline coupled structure performance and proves the applicability of the proposed couplers

Analysis and design

Simulation and measurement results

Design results of the proposed coupler with PDR of 1:1

Design results of the proposed coupler with PDR of 2:1

Conclusion