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A novel windmill‐shaped metasurface (MTS) structure is firstly presented and applied to realise broadband antennas with stable radiation patterns. Different from conventional square MTS structure, the proposed windmill‐shaped MTS structure is formed by etching several triangular sawtooth slots instead of rectangular slots on the radiating square patch. Through the characteristic mode analysis, it can be found that the proposed MTS structure exhibits a much stable broadside radiation within a large bandwidth of 45.9%. Besides, the tapered edges resulted from the sawtooth slots can be regarded as smoother transitions, which would bring a better impedance matching. Based on above analysis, two antennas with different aperture sizes using the proposed windmill‐shaped MTS are well designed accordingly. Both antennas demonstrate the capability to achieve large impedance bandwidths over 40% and stable radiations (2‐dB gain bandwidth >33%). Compared with the conventional MTS‐based antenna, these proposed antennas improve the bandwidth and radiation performances effectively, showing great promises for modern wireless communication systems. [ABSTRACT FROM AUTHOR]

A planar bidirectional circularly polarized (CP) antenna using orthogonal magnetic dipoles (OMDs) without an extra phase shift line is proposed in this work. It consists of a rectangular microstrip magnetic dipole antenna (MMDA) and a loop radiator with two arms directly connected to the open edge of MMDA. The working principle is revealed by the equivalent sources model to provide a clear physical insight at first. The theoretical investigations imply that by controlling the width and the feed locations of the loop antenna on the aperture, the phase and magnitude for CP radiation can be realized in both endfire and backfire directions without introducing an additional phase shift line structure. For demonstration, one antenna prototype is designed and fabricated. The experimental results indicate that an overlapping bandwidth of 5.91% from 2.30 to 2.44 GHz is attained. Compared with the counterpart using OMDs, the proposed antenna exhibits a low design complexity and improved gains of 3.56/1.83 dBic in the endfire/backfire directions. [ABSTRACT FROM AUTHOR]

This article presents an antenna array to produce a circularly polarized (CP) isoflux beam for CubeSat earth coverage applications. Distinguished from conventional arrays formed by identical elements, the proposed one is based on sequential rotation-fed concentric annular aperture elements. By adjusting the excitation phase, magnitude, and polarization of each annular aperture element, the radiation patterns of the array can be shaped to form isoflux beams. Radiation pattern modeling method is developed to obtain array radiation parameters. Besides, to effectively characterize the impedance matching of the radiators of the array with multiple excitations, an overall reflection coefficient is deduced from signal decomposition. A prototype operating at $C$ -band (5 GHz) is designed, fabricated, and measured. It consists of a radiator and a feeding network. The radiator is formed by two annular aperture elements, of which the inner one is realized by a circular patch antenna while the outer one is formed by eight planar inverted-F antennas (PIFAs). The feeding network drives annular aperture elements in the manner of sequential rotation. In this way, a CP isoflux beam array with a low profile ($0.078~{\lambda }_{0})$ , lightweight, and ease-of-integration for CubeSat is realized. The proposed array can also be extended to realize other shaped beams. [ABSTRACT FROM AUTHOR]