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A novel compact planar microstrip-fed quaisi-Yagi antenna is investigated. The feeding structure is directly realised by a microstrip line and has the advantage of avoiding the introduction of a balun, transition, tapered or truncated structures, thereby decreasing design complexity. The proposed antenna shows measured impedance bandwidth from 2.74 to 4.25 GHz for a return loss less than - 10 dB, and exhibits 13 dB front-to-back (F/B) ratio, - 15 dB cross-polarisation, 8.77 dB absolute peak gain, 60° half power beam width (HPBW) in the E-plane and 68° HPBW in the H-plane at the centre frequency (3.5 GHz). Measured results are in good agreement with electromagnetic simulations.
Introduction: Recently,planarquasi-Yagiantennaswithend-fireradiation have been widely used in modern wireless communication systems owing to their light weight, small size, simple fabrication, low cost, and ease of integration with RF front-end circuits [1]. The bandwidth of this kind of antenna has been considered to be largely determined by the feeding network. These antennas were designed with various feeding structures, such as coplanar-waveguide-to-coplanar-strip (CPW-to-CPS) transition (balun) in [2], microstrip-to-coplanar-strip (MS-to-CPS) transition in [3], artificial transmission line based MS-to-CPS transition in [4],tapered line in [5], and truncated ground planes in [6] and [7]. However, the complex feeding structures would not only increase design complexity but also limit the intrinsically frequency bandwidth of the driven element. Additionally, since they use the ground plane as a reflector, the radiation patterns of planar quasi-Yagi antennas are not as good as for conventional Yagi-Uda antennas.
To solve the above-mentioned problems, this work investigates a new design for the compact planar microstrip-fed quasi-Yagi antenna. Theproposedantennadoesnot include anyof thefollowing:a balun,transition, tapered or truncated structures in the feeding structure, and it provides flexibility to design the reflector, instead of using the...