| As a complementary of narrowband communication technology, ultrawideband communication technology has been widely used in mobile communication systems, radar systems, and remote sensing systems, becoming a very hot competitive technology. Antennas have a great many of different structures and characteristics, but they all have the same function to transmit and receive electromagnetic energy. As people have increasingly demand of the communication services, people have raised many new demands on the antenna, however, at the present, ultrawideband antenna still has the problem of large physical size and narrow band frequency. In this paper, with the aim to broaden operating frequency, improve the characteristics of unidirectional radiation patterns, and achieve band-notched function, a study focused on the planar printed Vivaldi antenna is made. Based on previous researches, some novel technologies are proposed in this paper to improve antenna performance and achieve band-notched function, which satisfy the design requirement, and achieve good results. The thesis mainly consists of following parts:1、Research on improving Vivaldi antenna performance based on eye-shaped slot structureA compact planar printed ultrawideband Vivaldi antenna is proposed, which has good unidirectional radiation patterns, and the whole size of the antenna is very small, which is 36 mm ? 36 mm. Simulated Vivaldi antenna surface current distribution results show that the side lobes and back radiations of the antenna are caused by the surface currents on the outer edges. If the surface currents on the outer edges can be decreased, the side lobe levels and back radiations are reduced, the radiation performance is improved, and good directivity and high gain are achieved. Based on this method, two pairs of eye-shaped slots are inserted into the pins of the Vivaldi antenna, in order to decrease the antenna surface currents. Type-B antenna is fabricated by using PCB printed technology, and measured in the SATIMO system, in the entire operating frequency band, the front-to-back ratio of the Type-B antenna radiation patterns is better than 10 dB, and the measured radiation efficiency percentage is around 80%. Measured results show that Type-B antenna has a wide operating frequency band, which covers 3-12.8 GHz frequency band, the relative bandwidth percentage reaches 124%, the operating frequency band can cover the entire UWB frequency band, and Type-B antenna achieves moderate gain, in the 3-12.8 GHz frequency band, the gain ranges from 3.7 dBi to 8.3 dBi. Type-B antenna has a flat group delay, which is around 1.2 ns in the entire frequency band with a variation less than ? 0.5 ns, which proves that the designed Type-B antenna has good time-domain characteristics.2、Research on UWB Vivaldi antenna with band-notched functionTwo planar printed UWB Vivaldi antennas with band-notched function are proposed, the proposed antennas have wide operating frequency band, which can cover the entire UWB frequency band, and both of them have the ability of filtering the WLAN frequency band, which can overcome interference between UWB systems and WLAN communication system.Firstly, a compact planar printed Vivaldi antenna with band-notched function is proposed, which has a size of 27.5 mm ? 13 mm. By using two pairs of E-shaped slots inserted into the pins of the planar printed Vivaldi antenna, this kind of structure acts as a resonator, which makes surface currents focus around the E-shaped slots. In order to verify the effectiveness of the proposed antenna, the proposed antenna was fabricated by using PCB printed technology, and measured, measured results show that the impedance bandwidth of the proposed antenna, defined by VSWR < 2, is from 2.8 GHz to 12 GHz, and the notched band is from 4.8 GHz to 5.9 GHz, the measured antenna gain increases in the operating frequency band, while declines sharply in the notched band.Afterwards, a compact planar printed Vivaldi antenna is proposed, the size of the antenna is 40 mm ? 40 mm, which has good bandwidth and band-notched characteristics. By using an L-shaped slot inserted into the CPW feeding line of the antenna, the electromagnetic energy is stopped, and the band-notched function is achieved. In order to verify the effectiveness of the proposed antenna, the proposed antenna was fabricated by using PCB printed technology, and measured, measured results show that the impedance bandwidth of the proposed antenna, defined by VSWR < 2, is from 3.1 GHz to 11.8 GHz, and the notched band is from 5 GHz to 5.9 GHz, the measured antenna gain increases in the 3.1-11.8 GHz frequency band, while declines sharply in the notched band. The designed antenna has a flat group delay in the operating frequency band, which is around 1.5 ns in the entire frequency band with a variation less than ? 1 ns, however, in the notched band, group delay declines sharply, which reaches to 2 ns at the middle frequency point. These measured results show that the designed antenna has good time-domain characteristics in the operating frequency band, while in the notched band, the variation of the group delay is very large, and the waveform is seriously distorted. |
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