A Directivity-Enhanced Directional Coupler Using Epsilon Negative Transmission Line

Abstract

In this paper, a high directivity parallel coupled line coupler using the negative (ENG) transmission line is proposed. With the aid of even-and odd-mode analysis, it is shown that by using ENG transmission lines in a parallel coupled line coupler, the even-and odd-mode phase velocities can become equal at a desired frequency. Hence, the directivity of a coupler can be infinite theoretically. The coupler circuit model and closed-form relations for lumped elements of this model are presented. In addition, a design procedure for microstrip implementation of this coupler is proposed. Based on the proposed procedure, a 10-dB ENG directional coupler is designed at 2 GHz and validated by full-wave simulations. This coupler is fabricated and measurement results are presented. Experimental results show maximum directivity of nearly 40 dB at 1.95 GHz.

Design of Multilayer and Multiline Microstrip Directional Coupler With Closed Form Relations

“…Alternatively, one of the other widely proposed compensation methods includes connecting lumped components at the ends or center of the coupled lines [15,16]. The discussion of impedance mismatch via additional coupled line and epsilon negative transmission line are presented in [17,18]. It has been shown that high directivity for directional couplers can also be obtained using multilayer configuration [19][20][21].…”

High Directivity Microstrip Coupler Using Variable Width Structure

“…The coupled spur line [5], and reflected power canceller approach [6] work within a narrow band. The Epsilon negative transmission line [7] was used but it needs more number of unit cells to improve the accuracy, which leads to fabrication difficulty. Delay lines [8] were used, but the coupler occupies more space than the conventional one.…”

High Directivity Microstrip Coupler with Asymmetric Structure

“…The coupled spur line [5], and reflected power cancel ler approach [6] work within a narrow band. The epsilon negative transmission line [7] was used, but it needs more number of unit cells to improve the accuracy, which leads to fabrication difficulty. Delay lines [8] were used, but the coupler occupies more space than the conventional one.…”

“…The advantages of the coupler are, that the structure is planar, there is no special fabrica tion technique needed, no vias are used, and the con struction is simpler when compared to other methods [7,[9][10][11], and it does not require any iteration design process [3,4].…”