Research On The Frequency-Reconfigurable And Polarization- Reconfigurable Microstrip Antennas

With the rapid development of technology, it is an inevitable trend to have wireless services in different frequency bands provided on the same platform which makes it to be a current research focus to let antennas obtain the function of reconfiguration. A reconfigurable antenna can change the current distribution by adjusting the structure or the electric size of itself in order to realize the r econfiguration of the parameters of resonant frequency, polarization, radiation pattern and so on to work as a conventional multiple antennas system with the same abilities.Ever since the proposal of reconfigurable antennas, although the theoretical analysis and design methods advanced vastly, the systematic analysis theories are still absent which leaves a large exploration space in the particular designing method and engineering application. An intensive research on frequency- reconfigurable antenna and polarization-reconfigurable antenna was conducted and furthermore, a conclusion on the theory of devising was drawn and utilized in devising reconfigurable antennas in this thesis. Besides, a material based and external field modulated reconfigurable antennas were analyzed and devised in this article. The main contents are as follows:1. In the systematic study on frequency-reconfigurable antenna, based on the transmission line model analytical approach of microstrip antennas, firstly, a frequency-reconfigurable antenna using medium with tunable height was devised and secondly, realize the frequency reconfiguration of an antenna by changing the permeability of medium in external modulation method. Researching the deficiencies of the two tuning modes through theoretical analyzing and hardware testing presented the advantage of applying external field modulation based reconfigurable antennas in this sort of appliance. Introducing the electroactive polymers poly(vinylidene fluoridetrifluoroethylene) [P(VDF-TrFE)] thin film, realized a frequency tuning range from 3.72-4.025 GHz through simulating, improving and testing, and obtained a tuning frequency bandwidth up to 7.57%.2. In the intensive study on reconfigurable antennas using external field modulation, this thesis designed a polarization-reconfigurable antenna with two orthogonal feeding ports to feed the rectangle radiation patch of the antenna. Two phase delay lines of different length made on a barium strontium titanate(BST) ferroelectric thin film under ground plane were added to the feeding sides separately. Adjusting the permittivity of the film by controlling the voltage of external field to change the difference between these two phase delay lines, achieving linear polarization, left-handed circular polarization, right-handed circular polarization respectively. The simulation results of this antenna all meet the design requirements.