Ultrashort Wave Broadband Spiral Loaded Antennas

The dissertation is mainly on the topics of miniaturization technology and broadband characteristics for antennas, and that mainly researched omni-direction broadband antennas in very high frequency (VHF) with a lot of theoretical and experimental studies. Several design schemes related to the topics are introduced and many attentions are paid to the engineering application.The omni-direction broadband antennas in VHF are not only requested to have a. compact structure but also a given gain. To meet these requests about the electric and structure's parameters of engineering a central thought way is make the most of a limited space to increase the electric length of the antenna. But the bandwidth will be reduced because of increasing of the electric length in the limited space. To satisfied gain as well as bandwidth a series of design of miniaturization and broadband are studied. In this thesis, MOM and FIT are used to design and simulate the broadband helix antenna in VHF. The author's major contributions are as follows:1. A helix or planar bend structure is used to increase the electric length of antenna when the dimension is limited. The height of antenna is reduced effectively.2. Thick monopole and planar antennas have broadband characteristic relatively. When they are fed and coupled with a helix or planar bend structure it will be realized a rather broad bandwidth and electric small performance.3. Dielectric loaded antenna can reduce the height of antenna and the dielectric can also act as a radome simultaneously.4. A broadband matching network are designed and optimized by the genetic algorithm (GA) to realize a VSWR claim over 30-88MHz.To make use of above these ways a broadband monopole with a parasitic helix and a broadband planar antenna with a parasitic planar helix in VHF are designed successfully, and they can realize VSWR<3, Gain>2 and the height <1.2m over 30-88MHz.