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

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.

Balanced Microwave Transmission Lines, Circuits, and Sensors

“…The design process is relatively simple in comparison with other alternative implementations of this kind of balanced circuits. Another simple implementation based on branch slotline structures can be found in [232]. The intrinsic differential nature of the slotline is also employed in the design of wideband BTB differential couplers (branch-line and rat-race) [233] making use of the so-called multimode star junction [234].…”