LAUSR

An uni-directional antenna designed by resonance-based reflector has the merits of compact size, low-profile, and ultra-wide impedance bandwidth. However, its front to back ratio (FBR) bandwidth is narrow owing to the small reflection coefficient values at the high frequencies of the RBR in-phase band. To solve this problem, a ring-shaped director (RD) was placed above a resonance-based reflector-based antenna to guide the high frequencies. Then, the FBR bandwidth was enhanced. The proposed antenna achieves a wide measured impedance bandwidth from 2.17 to 3.76 GHz (53.6%). Its FBR band (FBR >7 dB) covers the whole operational band and the FBR >10-dB band covers 2.17–2.58 GHz (17.3%). The proposed antenna consists of a bow-tie element, a ring-shaped resonance-based reflector under the bow-tie element and an RD above the bow-tie element to form a sandwich configuration. The profile of the proposed antenna is only $0.16~\lambda $ at the lowest frequency of 2.17 GHz. To further evaluate the performances of the proposed antenna, the time-domain characteristics of the antenna were analyzed in terms of group delay, waveform response, correlation coefficient, and pulsewidth stretch ratio. Good time-domain characteristics were observed.