| Summary: | 碩士 === 國立彰化師範大學 === 電信工程學研究所 === 106 === In this thesis, we will propose two different types of antenna design. The first is the broadband coaxial sleeve antenna, and the second is the novel endfire surface wave antenna.
Although the traditional sleeve type can make the bandwidth of a monopole antenna wider, it still cannot provide enough bandwidth for coaxial monopole antenna. In order to enhance the bandwidth of coaxial monopole antenna, the bare central copper wire of the tail end of the coaxial monopole is clad partially with an additional sleeve structure. Now the coaxial monopole, looking into antenna from the input point, is clad with two sleeve structures on the head side and tail side, respectively. We also use the corrugated structure to produce an additional resonance point in the low frequency band and hence to improve frequency response. The model increase the structure like skirt at the big sleeve. The radiation pattern of this proposed coaxial monopole antenna is omni-directional pattern with a little tilted down because of the additional sleeve structure. The frequency bandwidth of this proposed coaxial monopole antenna is measured from 500 to 960 MHz under the return lose not smaller than 10 dB.
For the second part, we design a novel endfire surface wave antenna on the substrate integrated waveguide (SIW) with air substrate. Several columns of small rectangular slots on the upper metal layer. For each rectangular slot, an additional inverted L-strips is connected on the narrow side of the slot and higher than the slot by 4mm. The size of the inverted L-strip is a little larger than the slot and so the slot can be fully cover by the inverted L-strip. These inverted L-strip structures can make the surface wave radiate in the endfire direction. We use the L-probe as the excitation source and arrange the length of the probe to make the end strip of the L-probe close to the upper metal layer. This novel endfire surface wave antenna is operated from 8 to 10 GHz for return loss larger than 10 dB and the peak gain is about 6 dB.
Index Terms- sleeve antenna, monopole antenna, coaxial cable, broad-band, slot antenna, surface wave antenna
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