| Accompanied with the development of ultra-wideband system, the need for ultra-wideband antennas and their arrays is growing larger and larger. Among various kinds of ultra-wideband antennas, small-size light-weight ultra-wideband in frequency domain and high-fidelity in time domain are the ultimate goal of many scholars. Ultra-wideband antennas are widely employed in many areas, such as the civilian communication, forest fire-prevention, military radar, stealth-detection, active defense. In this paper, the author study and comprehensively analysis several kinds of antennas both in time domain and frequency domain, including Vivaldi antenna, planar spiral antenna and planar monopole antenna.The structure of Vivaldi antenna is simple and it's convenient to integrate and construct array. This paper proposed a double-exponential-curve antipodal Vivaldi antenna. Also, a typical ultra-wideband balun is designed to improve the return loss. In 0.3~5GHz band, the return loss is less than -10dB, with the largest gain of 8dB. From its time-domain waveform, the signal transmitted is more likely the input signal compared with the non-balun Vivaldi antenna. Take the Vivaldi antenna without balun as example, this paper examined linear array and simulated different elements by CST 2008 software. The linear array is studied and evaluated in several terms: the lowest working frequency, the return loss of each element, peak-to-peak electric-field waveform monitored in far field and so on.According to the discipline of traditional spiral antenna design, this paper also design an Archimedean antenna and test it using E5071C after loading resistor. In 2~7.5GHz, the return loss is less than -10dB. Combined the feature of Archimedean antenna and equiangular spiral antenna, novel spiral antenna is presented, fabricated and tested. The novel spiral antenna has a novel curve equation of spiral arm which is designed to broaden the bandwidth and improve gain. In 2.5~10.6GHz, the return loss of the novel antenna is less than -10dB. The gain of novel antenna is 1~2dB larger in the frequency larger than 8GHz and its electric field waveform has higher fidelity, larger peak-to-peak voltage which can improve the performance in the ultra-wideband system applications.This paper also designed a novel low-profile shovel shape monopole antenna fed by coplanar waveguide with the advantages of easy integration and convenient fabrication. In the size of 26×30mm2, the return loss is measured by E5071C and the result is less than -10dB in 3.1~10.6GHz band with stable far field pattern. The largest gain is 3.4dB. Then, according to the current distribution analysis, this paper designed a novel tree-like monopole by digging a narrow ellipse-shape notch from the radiation patch. The return loss is about 5dB lower than the shovel-like antenna while the far-field pattern and the peak-to-peak electric field waveform remain almost the same.Based on the tree-shape monopole antenna, this paper proposed two novel kinds of band-rejected antennas in shape of circle slot and U-shape slot. In other frequency range of 3~11GHz, the VSWR is less than 1.5 and the 4.8~5.9GHz band is rejected whose largest value of VSWR is 10:1. These two kinds of antennas can work well with WLAN network. From simulation results, stable far-field pattern and good electric field waveform fidelity are also studied.Finally, this paper summarized the main work and innovation points, presenting the work focus on ultra-wideband antenna design in the future. |
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