In this research, the novel concept of a resonance-based reflector (RBR) was proposed,\nand a ring-shaped RBR was utilized to design a unidirectional antenna with low-profile and\nbroadband characteristics. Research found the ring operates as two half-wavelength (Ã?»/2) resonators.\nThen, the resonance effect transforms the reflection phase of the ring RBR, and achieves a reflection\nphase of 0ââ??¦ < Ãâ?¢ < 180ââ??¦ in a wide frequency range above the resonance. Then, the in-phase reflection\ncharacteristic (âË?â??90ââ??¦ < Ãâ?¢ < 90ââ??¦) can be obtained in the wide frequency band by placing an antenna\nabove the RBR with a distance smaller than Ã?»/4. Two unidirectional antennas, named Case 1 and\nCase 2, were designed with the ring-shaped RBRs and bowtie antennas (RBR-BAs). The impedance\nbandwidths of Case 1 and the Case 2 are 2.04ââ?¬â??5.12 GHz (86.3%) and 1.97ââ?¬â??5.01 GHz (87.1%),\nrespectively. The front-to-back ratio (FBR, an important parameter to measure the unidirectional\nradiation) of Case 1 ranges from 5ââ?¬â??9.9 dB for frequencies 2.04ââ?¬â??2.42 GHz, and the FBR of Case 2 ranges\nfrom 5ââ?¬â??16 dB for frequencies 2.16ââ?¬â??3.15 GHz. The proposed concept of RBR is desirable in wideband\nunidirectional antenna design, and the designing antennas can be used at the front end of wireless\nsystemsââ?¬â?such as indoors communication, remote sensing, and wireless sensor systemsââ?¬â?for signal\nreceiving or transmitting.
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