Triple-step feed line-based compact ultra-wideband antenna with quadruple band-notch characteristics

Abstract

ABSTRACT An ultra-wideband (UWB) antenna with quadruple-band-rejection characteristics and a size-miniaturised approach for portable wireless applications is designed and experimentally investigated. The proposed antenna consists of a unique trapezoidal-shaped patch, 50 Ω triple-step microstrip feed line and step–truncated ground plane. The patch tapering improves the bandwidth of an antenna to 2.8–12.5 GHz with fractional–bandwidth of 127%, covering an entire UWB (3.1–10.6 GHz). Consequently, it provides a nearly omnidirectional radiation pattern, better gain and excellent radiation efficiency. The three steps of the feed line increase the electrical length of the patch, achieving size reduction of the fabricated antenna to 20 mm × 29 mm. Generally, UWB systems suffer owing to strong narrowband signal interference from unlicensed wireless communication devices. To avoid this, the proposed antenna is designed with quadruple band-notch characteristics. It includes three inverted U-slots (length approaches half the guided wavelength), which are used to reject the 3.5, 4.5 and 5.2/5.8 GHz bands. Moreover, a C-strip pair besides the feed line is used to reject the 8.35 GHz X-band. The simulated results were also compared with the experimental performance of the prototype in terms of reflection coefficient, voltage standing wave ratio, radiation pattern, transfer function, group delay and gain of the antenna.