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.
Two types of dual-band resonance antennas based on the epsilon negative (ENG) transmission line are presented in this study. The first antenna has two unit cells with mushroom-like structure in which two notches are cut from their edges. This antenna has two different radiation patterns at its operating frequencies and hence it is a dual-mode antenna. In the second antenna, the structure of unit cells is modified in order to have the same radiation patterns at two operating frequencies. This antenna has two orthogonal polarisations at its operating frequencies and hence it is a dual-polarised antenna. The operating frequencies of the presented antennas correspond to the zeroth-and first-order resonance frequencies of the ENG resonator. Two prototypes of the proposed antennas have been fabricated and tested. The measured return loss and radiation patterns are given and discussed.
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