Abstract-An ultra-wideband (UWB) U type monopole antenna fed by a coplanar waveguide (CPW) is proposed. It has low profile and very compact size (14.48 mm × 28.74 mm × 0.8 mm). It provides an wide impedance bandwidth ranging from 3.08 GHz to about 12.75 GHz adjustable by variation of its parameters, such as the relative permittivity and thickness of the substrate, width, and feed and ground plane dimensions. Parametric study is presented. Details of the proposed ultra-wideband design are described. Simulation results are presented and discussed in this paper.

Abstract-In this paper, a new compact circular monopole ultrawideband antenna with multiple narrow bands notched is proposed, which is implemented by using the existing techniques, such as loading a L-type band-stop filter, inserting a split ring resonator (SRR), and the method we proposed that connecting L branches on the radiation disk. Four sharp notches at 2.4 GHz, 3.5 GHz, 5.5 GHz, and 7.6 GHz are achieved separately. The measured VSWR shows a good agreement with the simulation results. The radiation patterns are obtained from Ansoft HFSS simulations and verified by CST Microwave Studio. The results prove that this kind of antenna can be applied in the UWB communication systems to avoid interference with other wireless systems, such as the 2.4 GHz WLAN, 3.5 GHz WiMax, and 5.8 GHz WLAN etc. The parameters determining the antenna's band notched characteristic are discussed.

a small variation in the antenna gain is seen for both proposed and reference antennas.In designing UWB antennas, it is insufficient to evaluate the antenna performance solely in traditional well-defined parameters such as VSWR, radiation patterns, and gain. It is crucial to evaluate the system transfer functions as the transmitting and receiving antennas are viewed as a whole system [10][11][12][13][14]. For UWB applications, the magnitude of the transfer function should be as flat as possible in the operating band. The group delay is required to be constant over the entire band as well. A transmitting-receiving antenna system whose transfer functions satisfy these requirements will introduce limited distortions to base band signals.In this article, the system transfer function, which is in essence the transmission scattering parameter S21 of a two-port network, was measured by using an HP8722ES vector network analyzer with a pair of proposed antennas serving as the transmitting and receiving antennas.The transmitter and receiver are positioned face to face and side by side, respectively, with a distance of 15 cm, as plotted in Figure 7. It should be noted that the measurement was carried out in a real environment with reflecting objects in the surrounding area.Measured magnitude of the transfer function is shown in Figure 8. From the measured results, it can be seen that at the notched band the attenuation is more than 20 dB, and the magnitude outside of the notch band in 3.1-10.6 GHz is relative flat. Then it reveals that stable band-notched characteristic of the proposed UWB antenna has been obtained. The two magnitude curves for both scenarios, that is, face to face and side by side, are almost identical.The measured group delay is given in Figure 9. The variation of the group delay for both scenarios, that is, face to face and side by side, is within 1.5 ns across the whole UWB except the notched band in which the maximum group delay is nearly 3 ns. The group delay of the antenna systems corresponds well to the magnitude of the transfer function. Therefore, it proves that the antenna has a good time-domain characteristic and a small pulse distortion as well. CONCLUSIONSA printed circular-ring monopole antenna for UWB application has been investigated, which presents a band-notched characteristic in WLAN band by attaching a C-shaped short-circuited stub. The transfer functions of the antenna system correspond well to the VSWR. With the proposed antenna design, band notching can be easily obtained without the use of external filters, which can greatly simplify the circuit design of a communication system. filter has a compact structure with overall dimensions of 20 mm by 17.05 mm, a 3-dB bandwidth of 25.2% at 1.19 GHz, insertion loss of À3 dB, attenuation greater that 60 dB in the lower stopband and greater that 27 dB up to 5.2 times the centre frequency.

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