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In this paper, a new idea of reconfigurable 3/6 dB branch line coupler is proposed. The proposed coupler is tuned through a simple open and short circuit at the coupler’s branches’ edges. At the short edges case, a 3 dB branch line coupler is obtained. In this case, the coupler’s branches are considered as microstrip transmission lines with 0.3 mm slot width which is etched in each coupler’s branch. At the open edges case, the coupler’s branches are considered as asymmetric coupled microstrip lines. In this case, a 6 dB branch line coupler is obtained. Both CST and IE3D simulators are used to optimize the reconfigurable 3/6 dB branch line coupler dimensions. As a prototypes, two BLCs are designed, analyzed and tested at the “on” and “off” states at 2.5 GHz. The measured
*S*-parameters confirm the proposed concept of the reconfigurable 3/6 dB branch line coupler.

Branch line couplers, parallel coupled-line couplers, and rat-race hybrids are very important passive components in many wireless communication and microwave systems. There are lots of applications of 90˚ hybrid and 180˚ hybrid branch-line tight couplers such as −3 dB or −6 dB coupler in modern microwave and millimeter wave communication systems. It is used widely [

In the branch line coupler presented in

at every point on the line of symmetry. This is the equivalent of an open circuit. Similarly, if two signals are of amplitude

For the even mode

For even mode, the ABCD parameters could be written as Equation (2) and ABCD parameters are given by Equation (3).

For odd mode, the ABCD parameters could be written as Equation (4) and the ABCD parameters are given by Equation (5).

Using ABCD to S-parameters transformation [

Matching condition could be met at

Second matching condition states that

Transmission from Port 1 to Port 2 and from Port 1 to Port 3 could be written using vector representation given by Equation (1) as:

Using Equation (6.b) and Equation (9), the following equations could be written and simplified to find the ratio of signals travelling through Ports 2 and 3 which could be formed as

Equation (10) could be evaluated as:

Defining the power division ratio

Using Equation (11) and Equation (13) the following equation could be written as:

This relationship governs the power division between the output ports of the coupler.

The three design Equations (7) (8) and (14) could be used for the design of 3 dB branch line coupler. For the 3 dB branch line coupler,

The conventional 6 dB branch line coupler could be designed using the three design Equations (7) (8) and (14). For the 6 dB,

BLC | K | ||||
---|---|---|---|---|---|

−3 dB | |||||

−6 dB | |||||

−9 dB | |||||

−10 dB |

The proposed branch-line coupler BLC is composed of four quarter-wavelength transmission-line sections with variable impedances at a designated frequency. Each transmission line consists of two adjacent transmission lines which could be connected or separated at it’s edges as shown in

characteristics including resonant frequency and the power division ratio k are determined mostly by its transmission-line length and impedance, varying its geometry mechanically provides an intuitive method to reconfigure its resonant and division ratio. By using photolithography technique, planar BLC in the form of conductive traces can be fabricated. An open or short process changes dynamically the transmission line section width and enables different division ratio applications. Based on the above analysis and for verification, a reconfigurable

where

Calculated | CST | IE3D | |
---|---|---|---|

w_{1} (mm) | 4.08 | 3.91 | 3.91 |

w_{2} (mm) | 2.519 | 2.39 | 2.39 |

that are used by both simulators. Also,

The proposed structure is fabricated on Teflon substrate with relative dielectric constant

the same for both simulated and measured S-parameters. Also,

A reconfigurable

Abouelnaga, T.G. and Mohra, A.S. (2017) Reconfigurable 3/6 dB Novel Branch Line Coupler. Open Jour- nal of Antennas and Propagation, 5, 7-22. https://doi.org/10.4236//ojapr.2017.51002