Studies On Low-profile Ultrawideband Antenna

With the rapid development of wireless communication techniques,the communication systems such as modern communication,electronic countermeasures,radar,etc.have a higher requirement for the portability,concealability and miniaturization of communication equipment.Antennas are indispensable key components in communication systems.It is necessary to carry out miniaturization design.In the new generation communication system,UWB antennas can effectively increase the capacity,enhance the resistance to multipath fading,and improve the date rate of the communication system and so on.On the one hand,many low frequency portable systems,such as car system,airborne system and satellite system,require more compact UWB antenna with low profile and stable radiation pattern for which can effectively reduce the load and volume of the system as well as reduce the RCS to some extent.On the other hand,the miniaturization and low-profile design of the UWB antenna are often at the expense of the operating bandwidth and radiation pattern stability of the antenna.Therefore,in the miniaturization and low-profile design of the wideband antenna,it is very meaningful to study on broading the operating bandwidth of the antenna as well as keeping the stable radiation pattern.Firstly,for the radiation pattern distortion problem of the UWB directional antenna,a new UWB directional antenna based on Vivaldi antenna is analyzed.The antenna is characterized by a 3-dimensional folded structure and capacitively loaded at the end of the radiation fins.The antenna has a low profile of 0.216?_max(?_maxax is the wavelength of the minimum frequency of the available band),VSWR<2.5 from 0.9GHz to 10GHz,and a stable directional radiation pattern over the whole frequency band.The measurement results are basically consistent with the simulation results.The measured gain is from 3.6 dBi to 8.2 dBi.The antenna successfully solves the problem of unstable radiation pattern of the low profile UWB directional antenna.Then a low-profile dual-polarized UWB antenna based on high-impedance surface?HIS?is designed.The wide impedance bandwidth of the antenna is owing to combine the two resonant modes of HIS-based dipoles resonance and transverse electric surface wave resonance.The HIS adopts a new low-capacity periodic structure,which can be coupled with a dual-polarized crossed-dipoles to obtain better impedance matching.The structure of the crossed-dipoles are also improved by adding parasite radiation arms and balanced shorting pins,which successfully increase the isolation between the two ports of the antenna,and make the radiation patterns more symmetric.The measurement results are in good agreement with the simulation results.The measured S11<-10 dB bandwidth of the antenna is 41.5%,and the profile of the antenna is 0.06?c?where?c is center frequency of the antenna's operating frequency band?.In summarize,two types of low-profile UWB antennas have been researched and designed in this thesis,good research results have been obtained,which have extensively practical value and reference significance.