| Antennas are essential components in all communication. In recent years, there has been an increasing interest in operating at the UHF band. Traditional antennas have a large size when they operate at this band. However, as the trends of integration and miniaturization, the antennas should have a compact structure, some researches are carried out in thesis. The main contents are listed below:Part1, firstly, it is a brief review of the antenn theory about these UHF antenna, then the investigation about the development of antenna in miniaturization, multiband and wide band are presented.Part2, a compact conformal PIFA array has been designed. Firstly, by adding meandered strip, a PIFA element has been designed. The limitation of this array has been discussed and the design guideline of this array has also been introduced. This Antenna array is formed by1×4subarrays. At last, the planar PIFA array is conformal assembled on the cylinder with0.023λ diameter and0.071λ height. The experiment results show that the antenna realizes the miniaturized structure.Part3:a low-profile capacitive fed air-supported microstrip antenna of dual-band and circularly polarized at UHF has been developed. According to the requirements of the engineering application, we designed three antennas.1. Firstly, traditional design methods are studied and used to design the first antenna. It realizes dual-band working frequencies using two patch antennas and realized circular polarization with two-feed. The antenna realizes miniaturized structure. The profile is low, however, the measured gain is low.2. The second version of the antenna is improved based on the first version. The differences between them are the feeding method and the feeding network. In the feeding method, the first version is fed by microstrip line and the second version is fed by coaxial line. The feeding networks are respectively made into the different forms of microstrip line and stripline. Compared with the first version of the antenna, the performance has obviously improved. The measured gain increased about2dB, but the gain bandwidth was narrow.3. Based on the analysis of the advantages and the disadvantages of the two antennas in the previous chapter. To improve the performance of the antenna, we have done a series works. They include:propose air-supported microstrip antenna to increase the gain; propose folded structure to realize miniaturization; propose L-shaped strip feeder to wider the bandwidth and improve axial ratio through four feed. According to the current distribution characteristics in this new structure, we put forward the additional parasitic patch around the sidewalls of the antenna in order to make the antenna can work in dual-band without changing the volume of the antenna. In this method, three types of antenna have beed carried out, they are low profile line polarization antenna, circular polarization antenna and the dual-band circular polarization antenna, respectively. In design process and the structure, these three structures have the inheritance relationship. Finally, the antenna realizes low profile about0.024λ. |
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