Research On Metamaterials-based Leaky Wave Antennas

Leaky wave antenna is a kind of traveling wave antennas.It is basically a waveguiding structure demonstrating a radiation mechanism that permits it to leak power all along its length..As the frequency increases,the wavelength of the electromagnetic wave becomes smaller and the phase between the two adjacent leakage cells of the leaky wave antenna changes slowly.Hence the phase shift between the two leakage cells is formed between the two leakage cells.According to the calculation formula of the antenna array pattern,the main lobe of the radiation pattern will change with the phase interval between the radiating elements.In this sense,the leakage wave antenna has the characteristics of frequency scanning.However,considering the formation mechanism of the frequency scanning,it is difficult to generate a sufficiently large phase range for a leakage wave antenna with the fixed physical size,and thus the scanning angle is less than±60 degree.Meanwhile,the leakage wave antenna based on the composite left-and right-hand transmission line can realize a wide scanning angle from-90 degree to +90 degree.However,due to its resonant nature,the resultant operation bandwidth is narrow.In addition,the high-order mode is easily excited in the leakage antenna which interferes the performance of the leakage antenna.Although the use of one-dimensional antenna array optimization method can solve this problem to some extent,this method can be used in a a very narrow band.These above problems hamper the further development of the leaky wave antennas.Based on the metamaterials,this thesis has developed two leaky wave antennas which have good performances including wide scanning angle and wide frequency band.The main work and research results of this thesis are as follows: 1.The basic knowledge of the thesis has been discussed,including the purpose of the topic and its social value,the developement of leaky-wave antennas and metamaterials at home and abroad.2.The leaky wave antenna and composite left-and right-hand(CRLH)transmission line are studied and analyzed concisely.It includes the basic characteristics of the leaky wave antenna,the design method of low side-lobe leaky wave antenna,the basic characteristics of CRLH transmission line and the principle for the elimination of the stopband.The method for calculating dispersion diagram by the circuit model has been given.3.A leaky wave antenna based on composite left-and right-hand transmission line has been desigend.With a negative permeability unit cell,the propsoed leaky wave antenna demonstrates good performance of broad band and large scanning angle.Considering the symmetry of the leaky wave antenna structure,a wide scaning angle from-85 degree to +85 degree can be achieved,when two ports are excited in turn.The measured and simulated results of the proposed leaky wave antenna are in good agreement,which shows that the operating frequency band covers from 11 GHz to 17.5GHz with the reflection coefficient lower than-10 dB.4.In this thesis,a dual band low sidelobe leakage-wave antenna based on Fabry-Perot(FP)resonator has been designed.The designed FP resonator consists of frequency selective surface(FSS)and high-impedance surface.Two FSSs are fabricated on both sides of the substrate,and thus dual-band FP resonator is achieved.The simulation results demonstrate that the proposed leakage-wave antenna has dual bands and low sidelobes.5.This thesis proposed a feeding structure based on a stepped waveguide.By suitablly changing the thickness of the inner wall of the waveguide,the feeding structure can operate in two frequency bands,which can be used to feed the proposed dual-band leakage-wave antenna.