A Low-Profile and Wideband Unidirectional Antenna Using Bandwidth Enhanced Resonance-Based Reflector for Fifth Generation (5G) Systems Applications

The previously proposed resonance-based reflector (RBR) antennas have the merits of wide impedance bandwidth, low-profile, and unidirectional pattern; however, their front-to-back ratio (FBR) bandwidths are narrow. In this paper, a wideband RBR is proposed for FBR bandwidth enhancing antenna with a low profile. The proposed RBR consists of a metallic ring with three stubs printed on a substrate. It has a +/- 90 degrees in-phase bandwidth of 63.57% (3.23-6.24 GHz) and its reflection magnitude values range from -0.02 to -11.5 dB within the in-phase band (-90 degrees < phi < 90 degrees). Compared with the existent RBRs, the proposed RBR achieves a greater reflection magnitude within the in-phase band, which would be critical for FBR enhancement of an antenna. The proposed RBR is applied to a ring-loaded teardrop-shaped bowtie antenna to form unidirectional radiation pattern. The measured -10-dB impedance bandwidth of the proposed antenna is 3.48-6.12 GHz (55.00%), while FBR values are larger than 10 dB within the whole impedance band and the maximum FBR value is up to 20.4 dB. The peak gain is bigger than 7.3 dBi within the whole impedance band. There is a reasonable agreement between the simulated and measured results. The profile of the overall unidirectional antenna is 0.15 lambda L at the lowest operating frequency, and the RBR has the same size as the bowtie antenna. Compared to the previous RBR antennas, the proposed RBR antenna has wider FBR bandwidth. The operating band of the antenna is suitable for 5G system applications.