Abstract
A simple coaxially-fed magneto-electric dipole (ME dipole) antenna is designed and experimentally evaluated. The proposed antenna does not require the conventional quarter-wavelength slot cavity for generating the magnetic dipole mode, and only consists of two simple rectangular horizontal patches, a vertical semi-rigid coaxial cable and a square ground plane. It makes the fabrication easier and can reduce the production cost. Also, as the quarter-wavelength slot cavity is removed in the proposed design, the thickness of the antenna can be reduced to 21 mm, i.e., 16.4% of the free space wavelength at the center frequency. The low-profile antenna shows comparable wide impedance bandwidth of 41.03% (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> ≤ -10 dB), and a more stable and higher realized gain from 7.90 - 9.74 dBi (± 0.92 dB variation) over the operating frequency band from 1.86 GHz to 2.82 GHz (centered at 2.34 GHz). The maximum gain has increased around 9.4% when compare with that of the highest reported. While the gain variation in the passband of the proposed antenna is about 58% lower than that of those ME dipole antennas reported in the literature. The radiation mechanism and the effects of the critical parameters of the antenna are also explained with the assistance of the parametric study presented.
Highlights
E LECTRIC dipoles and magnetic dipoles are two types of well-known basic antenna elements. They have very simple, but complementary radiations features; the radiation pattern of an electric dipole has the shape of an "inverted-8" in the E-plane and an omni-directional radiation pattern in the H-plane, while the radiation patterns of a magnetic dipole is vice versa [1], [2]
Combining these two sources of identical amplitude and phases will produce an antenna with similar radiation patterns in the E- and H-planes [2], [3]
A wideband unidirectional antenna named as magneto-electric dipole antenna has been reported [4], it consists of a horizontal planar dipole and a vertical quarter-wavelength slot cavity
Summary
E LECTRIC dipoles and magnetic dipoles (slot antennas) are two types of well-known basic antenna elements. To the authors’ best knowledge, all the magneto-electric dipole antennas reported so far have the same feature: a vertical quarter-wavelength slot cavity created by a pair of conductor walls are utilized to generate the magnetic dipole mode The fabrication of such vertical walls in the millimeter-wave frequency bands may be challenging. It should be mentioned that the simulated results of the cross-polarization are not shown in the figures for clarity since they are very low (less than −80 dB) This is the result of the assumptions of the perfectly symmetrical structure and precise excitation point in the simulation model, the ideally symmetrical excitation of the wide electric dipole and magnetic dipole will not excite any cross-polarization, but it is impossible to achieve in the fabrication, when soldering the coaxial cable to the excitation points on the sides of the two horizontal patches in the practical case. It is the results of the fringing field which, as shown in Fig. 3(a) and (c), has elongated the effective length of the electric dipole and created a larger radiation aperture, the directivity in the E-plane is higher
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