| Since the Federal Communications Commission (FCC) first approved rules forthe commercial use of Ultra-WideBand (UWB) within the band of3.1-10.6GHz in2002, the UWB technology breaks the limitations in the application of militarycommunications and radar remote sensing, and becomes the hot research area ofcommercial and civil wireless communication systems for short distance and high ratetransmission. As a significant component of wireless communication system, antennahas very important influence on the whole system, and so for the development ofUWB systems, the research of UWB antennas has the extremely vital significance.UWB antenna design requires not only small size, wide bandwidth, certainradiation efficiency and omni-directional radiation characteristics, but also providesgood pulse waveform fidelity, simple production process, low cost, easy to integrateto active device and circuit. Due to the existing of Wireless Local Area Network(WLAN, ranging from5.15to5.825GHz) and Worldwide Interoperability forMicrowave Access (WiMAX, ranging from3.1to3.6GHz) in UWB frequency range,the UWB applications are necessary for the rejection of interference with WLAN andWiMAX, namely have notched-band characteristic. Although there are many ways toachieve the notched characteristic, the notches are realized just in single or dualfrequencies, there are strong demands of the realizations of notched-band functionwith controllable bandwidths and high selectivity.For short-range high-speed and low power UWB communication, it is importantto evaluate the capability of UWB antennas for the radiation of pulse signals, and toevaluate the waveform distortion of signals radiated by the UWB antennas during thetransient transmission, propagation and reception. In other words, the time domaincharacteristics also are the significant criteria to estimate the performance of UWBantennas as the frequency domain characteristics. In addition, the introduction ofband-notched structure in UWB antennas shows good band-stop characteristic andsuppresses the interference between the narrowband systems and the UWB systems. It is worthy of further study for the influence of the band-notched structure on the timedomain transmission characteristic and distortion of the UWB signals.The main achievements of this work are as follows:1. The recent developments of small planar UWB antenna and notched-bandstructure are summarized and analyzed, and compared with their advantages anddisadvantages.2. According to UWB antenna design specification, a compact printed dipoleUWB antenna integrated with balun slots and an improved slot UWB antenna areproposed. The two UWB antennas both have wide relative impedance bandwidth,stable gain and omni-directional radiation characteristic.3. Four kinds of methods are introduced to achieve the band-notch function withthe example of a micro-strip fed UWB antenna with U-shaped patch, to explain theimplementation rules of band-notch. And next, a CPW-fed dual band-notched UWBantenna is designed by using the stub-loaded open-loop slot resonator to obtain theband-rejected filtering properties in the WiMAX/WLAN bands. Then two kinds ofCPW-fed and two micro-strip fed UWB antennas are proposed, and all the fourantennas’ band-notched characteristics in WLAN bands are achieved by etchingmultiple resonant slots on the radiator patch, with controllable notched bandwidth andhigh selectivity of the rejection band.4. Four kinds of band-notched UWB antennas as examples are used for theanalysis of the time domain characteristics, and the research emphasis is the influenceof the band-notched structure on the time domain characteristics. Two parameters: thecorrelation factor (ρ) and the pulse width stretch ratio (SR) are resorted to estimate thefidelity of the pulse signals radiated by the band-notched UWB antennas. At last fromthe view of the time domain property with different band-notched technologies, theUWB antenna’s transient response for the co-polarized component is discussed. |
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