Studies On Frequency Tunable Antenna Based On Ferrite Loaded Substrate Integrated Waveguide

At present,the number of antennas in a wireless communication system is increasing,which causes the increased overall cost and weight of communication system,and the electromagnetic interference coupling between antennas.Therefore,people want to be able to realize the function of multi antennas with an antenna.In this background,the concept of reconfigurable antenna or tunable antenna was put forward to.The research on reconfigurable antenna or tunable antenna based on substrate integrated waveguide technology is a new subject.Substrate integrated waveguide(SIW)technology developed in recent years is a kind of planar waveguide structure.Its transmission characteristics are similar to the transmission characteristics of rectangular waveguide,which is formed by the top and bottom metal plates of a low loss tangent dielectric slab and two sidewalls of period metallic via-holes.The substrate integrated waveguide devices have the advantages of low profile,high Q factor,and easily being integrated on planar circuits.At present,the researches of substrate integrated waveguide reconfigurable antenna mainly focus on electrically tunable antenna realized by electronic devices.Another effective method to realize frequency tunable antennas is to use the intrinsic properties of the materials to change the operating frequencies of antennas.This dissertation focuses on the applications of ferrite loaded substrate integrated waveguide in the design of low profile frequency tunable antennas.The transmission characteristics of the ferrite loaded substrate integrated waveguide have been studied compared with substrate integrated waveguide.The tunable characteristics of ferrite loaded substrate integrated waveguide in the bias magnetic field have been studied.We also studied on the working principle of the ferrite loaded substrate integrated waveguide antennas and the feed structures of the ferrite loaded substrate integrated waveguide.Based on these analyses,several novel frequency tunable substrate integrated waveguide antennas through the magnetic field adjusting are designed.The author's major contributions are outlined as follows:(1)Based on the theory of SIW resonant cavity,a ferrite loaded SIW resonant cavity was analyzed and simulated.We proved that the working frequency of magnetically tunable SIW cavity increases when increasing the bias magnetic field.On this basis,a dual ferrite loaded SIW tunable rectangular slot antenna working in X frequency band has been designed,and samples of the antenna were tested and analyzed.The measurement results show that,the tunable frequency range is 10.5%(from 9.95 GHz to 11.06 GHz),antenna gain in the frequency tuning range is more than 5.0dBi,the simulation and test results prove the validity of the proposed method.(2)An improved single ferrite loaded substrate integrated waveguide antenna has been designed.Compared with the double ferrite loaded substrate integrated waveguide antenna,the antenna only uses a ferrite slab,so that the antenna has the advantages of simple structure,and the better antenna performance.The simulation results show that,the antenna has better gain and front to back ratio,when the bias magnetic field changes from 0 to 0.12 T,the antenna frequency tuning range is about 380 MHz,antenna gain is higher than 6 dBi within the tunable range,radiation pattern and gain is almost not affected by the magnetic field.(3)A new type of magnetic tunable dual-band dual-polarized substrate integrated waveguide antenna has been designed.The multimode characteristic of SIW resonant cavity helps to realize multiband characteristic of the antenna,and the crossed radiation slot causes the radiating element to radiate desired polarized radiation.By properly choosing the length of two arms of the crossed slots,the radiations from the slots can be adjusted to having equal magnitude and 90 phase difference at one frequency,i.e.a circularly polarized radiation,while linearly polarized radiation at one other frequency.Further,the measurement results show that,the operation frequency of the antenna can be tuned by means of the applied magnetic field because of loaded ferrite slabs.Low frequency tunable frequency range is 8.1%(from 8.98 GHz to 9.74 GHz)and high frequency tunable frequency range is 5.5%(from 9.98 GHz to 10.54 GHz).By changing the applied magnetic field,not only the operation frequency of the antenna but also its polarization can be changed.(4)A novel approach to realize broadband frequency tunability of ferrite loaded substrate-integrated waveguide antennas has been presented and proved.We realize broadband frequency tunability by simultaneously changing the location of ferrite slabs in the antennas(mechanical tuning)and bias magnetic fields(magnetical tuning).The proposed method is verified by the antenna designed in X-band with experiments.The measurements show that the antenna has frequency tuning range over 14.94%(9.23 GHz-10.69 GHz).The radiation characteristics of the antenna change little in tunings,showing a good property for tunable antennas.The above research and design work for the low profile antenna provides a new approach and antenna prototype;this type of tunable antenna will have a potential application value in areas such as wireless communication engineering.