| The rapid development in the wireless communication systems has led to the prosperity of antennas and various military requirements also have promoted the renew of antenna designs.Recently the ultra-broadband antenna has been one of the international research frontiers. In this dissertation, a deeper study on ultra-broadband slot antennas and air substrate antennas are presented, in which a few of novel designs are proposed and the experimental verifications are also given. The dissertation will include the following contents.Firstly, a survey on the broadband microstrip antennas and the air substrate antennas is presented. Then the numerical methods such as the Finite-Different Time-Domain Method (FDTD), the Finite Element Method (FEM), the Method of Moments (MoM) and so on are introduced .In addition, their comparison are given.Secondly, a novel printed slot antenna fed by a fan-shaped microstrip feed is proposed, which has wider bandwidth than that of other slot antennas reported in literature, reaching 114%, with the ratio bandwidth of 3.65:1,and also has a stable radiation pattern. By inducing fractal structure in fan-shaped microstrip feed, a wider bandwidth is also achieved.Thirdly, based on the design of the above antenna, a ultra-broadband and high-gain printed slot antenna is presented .By inducting a ground plane and a circular patch, not only the mono-direction radiation but also a 102% impedance bandwidth are achieved with the measured antenna gain of 5.5dB to 7.8dB over the entire bandwidth. Moreover, the antenna is of a wider beam width by extending the dielectric substrate.Fourthly, an ultra-broadband patch antenna using a wedge-shaped air dielectric substrate is introduced .Its experimental ratio bandwidth of S11≤–10dB reaches 8.8:1,covering frequencies from 3.05GHz to 26.87GHz .
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