Offset-fed metamaterial antenna for radiation mode generation with efficiency improvement

In this paper, a new offset-fed metamaterial antenna based on a slot-loaded composite right/left-handed transmission line is proposed. Two antennas, namely a centre-fed metamaterial antenna and an offset-fed one, have been investigated. The offset-fed metamaterial antenna generates additional resonant modes with endfire radiation like a patch antenna, whereas the centre-fed one produces only broadside radiation like a monopole antenna. The one-dimensional equivalent circuit model is applied to analyse the slot-loaded structure and the two-dimensional microstrip cavity model is employed for the offset-fed structure. The measured results are in good agreement with the theoretical analysis, especially in radiation pattern and radiation efficiency. The radiation efficiency is pronouncedly enhanced up to 27.6% at the zeroth-order resonant mode and to 56.8% at the additionally generated mode (quasi-TM₀₁₀) because of the slot effect on the ground plane.