Ultra-wideband slot antenna for wireless USB dongle applications

Abstract

Introduction: The universal serial-bus wireless (WUSB) combines the benefits of the USB with the convenience of wireless technology leading to data rates of 480 Mbit/s up to 3 m and of 110 Mbit/ su p to 10 m [1]. The WUSB is one of the most promising applications of ultra-wideband (UWB) technology and among the first to be commercially available for short-range and high-speed wireless interfaces. WUSB dongles replace the USB cables and deliver instant UWB connectivity for a wide range of devices such as printers, hubs and external hard drives. The dongles employ an on-board UWB antenna on printed circuit boards (PCBs) typically of 23 � 70 mm 2 sizes. Along with miniaturised size and omnidirectional radiation patterns, dongle antennas should be flexible in design with ground independence [2]. A microstrip-fed monopole antenna with reduced ground plane effects [3] and a bended plate monopole antenna [4] are some of the designs reported for WUSB dongle applications. The proposed antenna employs a near-rectangular slot which along with a tapered tuning stub exhibits a wide impedance bandwidth from 2.9 to 11 GHz. The width of the antenna is only 20 mm and is smaller than most of the slot antennas reported for UWB operations [5, 6]. Also, the antenna performance is observed to be unaffected by the PCB/ground length making the proposed design an ideal candidate for a WUSB dongle antenna. A coplanar waveguide (CPW) feed further ensures easy integration with the rest of the USB circuitry. The proposed antenna is successfully designed and experimentally verified. The antenna has excellent impedance matching, stable radiation patterns, and linear group delay over the entire UWB band along with good impulse response. Antenna design: Fig. 1a shows the geometry of the proposed antenna and its optimised dimensions. The antenna consists of a CPW-fed tapered tuning stub along with a near-rectangular aperture etched out from the ground plane of a PCB. The CPW feed is designed for 50 V on FR4 substrate with 1r ¼ 4.4 and thickness h ¼ 1.6 mm. Since the feed and the ground are on the same plane, a substrate with singlesided metallisation is used, making the antenna easy and cost-effective to manufacture.