Abstract
A metacurl antenna made of C-type metaatoms (forming a C-type metaline), called the C-metacurl antenna, is investigated. The investigation reveals that the gain for a left-handed circularly polarized wave, LHCP gain, has a maximum value at frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LH</sub> and the gain for a right-handed circularly polarized wave, RHCP gain, has a maximum value at different frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RH</sub> , where the maximum LHCP gain is smaller than the maximum RHCP gain. Subsequently, a different metaatom that forms the unit cell of an N-type metaline, called the N-type metaatom, is investigated. It is found that the radiation from the N-type metaatom is LHCP. This infers that the maximum LHCP gain for the C-metacurl antenna will increase when some C-type metaatoms are replaced by N-type metaatoms. Based on this inference, a novel metacurl antenna composed of C-type metaatoms and N-type metaatoms, called the compound metacurl antenna, is analyzed. The analysis reveals that replacement with an appropriate number of N-type metaatoms increases the maximum LHCP gain, resulting in a balancing of LHCP gain and RHCP gain. The antenna characteristics under such a gain-balanced situation, including the radiation pattern, axial ratio, and input characteristic (VSWR), are also discussed.
Highlights
A helical antenna backed by a conducting ground plane radiates a circularly polarized (CP) wave in the antenna axis direction normal to the ground plane when the circumference of the helical arm is approximately one wavelength [1]–[3]
Analysis has revealed that a low-profile metacurl antenna composed of C-type metaatoms has a maximum left-handed circularly polarized (LHCP) gain that is smaller than the maximum right-handed circularly polarized (RHCP) gain
Analysis has revealed that, as opposed to the C-type metaatom, an N-type metaatom radiates an LHCP wave. This leads to the expectation that the smaller maximum LHCP gain for the C-metacurl antenna can be increased by replacing some C-type metaatoms with N-type metaatoms
Summary
A helical antenna backed by a conducting ground plane radiates a circularly polarized (CP) wave in the antenna axis direction normal to the ground plane when the circumference of the helical arm is approximately one wavelength [1]–[3]. This structure is designated as the C-metacurl antenna. Note that almost in-phase currents appear at points N and N , because the length from point M to point N along the curled arm is close to λg/2 These two current bands are created near a circle whose circumference on the antenna plane is approximately 1λg at a certain frequency of fRH (> fT), and these current bands rotate counterclockwise along a region near the 1λg circle with change in time t, resulting in generation of the maximum RHCP radiation in a direction near the positive z-axis at fRH. It is found that the measured VSWR across both the LHCP and RHCP gain bandwidths is small, with a value of less than 2, as desired for practical usage
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