Study On Super-wideband Antennas For Multi-band Wireless Communication Systems

With the advancement of wireless communication technology, many systems such as mobile portable devices, wireless LANs, UWB systems and so on now have been operated in more than one frequency band . The antenna, as one of the most significant components, its performance eventually determines the capability of a system operating in multiple frequency bands. Therefore, a single compact antenna that has an impedance bandwidth wide enough to cover the operating frequency bands of the multi-band wireless communication system is more desirable. This dessertation investigates several advanced super-wideband (SWB) antennas with the ratio bandwith of more than 10:1. The main research achievements are summarized as follows:(1) A novel SWB monopole antenna is presented,which is composed of an elliptical monopole patch and a trapezoid ground plane with a modified tapered co-planar waveguide (CPW) feeder. The measurement indicates that it has an impedance bandwidth (VSWR≤2) of 1.02 - 24.1 GHz with the raito bandwidth of 23:1. The antenna can support many existing wireless services, including GPS (1.57-1.58 GHz), GSM1800 (1.71-1.88 GHz), PCS1900 (1.93-1.99 GHz), WLAN (2.5 and 5-6 GHz) and UWB (3.1-10.6 GHz), etc.(2) A multi-piont feeding elliptical monopole antenna and a multi-point feeding rectangular monopole antenna are manufactured. The elliptical monopole antenna can cover a frequency range of 1.08-27.4GHz with a ratio bandwidth of more than 25:1. The proposed multi-ponit feeding rectangular monopole antenna achieves a measured ratio bandwidth of more than 46:1, covering frequency range from 0.76 to 35.2GHz. Its frequency range and ratio bandwidth both keep ahead in the would. The transfer function and the time domine characteristics for the rectangular monopole antenna are also examined. (3) A compact CPW-fed UWB antenna based on a Liquid Crystal Polymer (LCP) substrate is proposed. The simulated results show that the antenna cover a frequency range of 2.4-16GHz with a ratio bandwidth wider than that of the same antenna on an ordinary RF substrate. Based on the antenna, a band-notched antenna is designed to avoid the interference with the 802.11a wireless local-area networks (WLAN). Futhermore, based on a peach-shaped SWB antenna, three notch-bands are generated.The measurements confirm that the peach-shaped antenna covers a frequency range from 0.72 GHz to more than 25 GHz. By introducing a tuning stub and a pair of open arc-shaped slots, the band-notch function is created to prevent interference from WLAN (2.5 GHz and 5.5 GHz) systems and some C-band satellite communication systems.(4)A miniaturized half-elliptical microstrip monopole antenna is presented ,whose size is reduced with 57% by means of optimizing ground plane and radiation patch. The simulated results show that the proposed antenna can cover the frequency range from 0.47 to 25GHz with a ratio impedance bandwidth of more than 50:1. To promote the omnidirectional radiation characteristic of the miniaturized antenna ,an asymmetric monopole antenna with L-shaped feeding branch is manufactured . A 52% reduction in antenna area has been achieved with the asymmetric structure. Its measured ratio bandwidth for VSWR≤2 reaches 31:1 with a frequency range from 1.05 GHz to 32.7 GHz.