Research On SIW-based Fixed-frequency Beam Switching Leaky-wave Antenna And Array

Due to its structural advantages of low profile,easy integration with planar circuits,and excellent radiation performances of high directivity,natural frequency scanning,leaky-wave antenna(LWA)based on substrate integrated waveguide(SIW)has become a hot spot in the research field of millimeter wave and terahertz antenna.It is widely used in wireless communication systems such as radar detection,vehicle communication and satellite communication.For realizing flexible and efficient radio wave coverage in confined space and short-range mobile communication,this work studies the characteristics of SIW LWA at the aspects of beam switching,high efficiency and circular polarization,and explores the application of the circularly polarized antenna in micro satellite communication.The main innovations of this work are as follows:1.A fixed-frequency dual-beam switching SIW LWA array is proposed,which is composed of five LWAs with different dual-beam directions.By selecting appropriate structural parameters,each LWA works in fundamental wave mode and-1st spatial harmonic mode at the same time,so as to generate dual radiation beams symmetrical about the broadside direction.In addition,the open stopband(OSB)suppression of LWAs is realized by alternately expanding the radius of side wall metal vias;The pattern distortion caused by mutual coupling between array elements is eliminate through embedding electromagnetic band gap structures into array.By selecting the excitations ports of different array elements through RF chip switches integrated on the back of the array,the final designed array can realize dual beam switching between±35~°,±45~°,±55~°,±65~°and±75~°at 28 GHz.2.Two types of arrays with capability of flexible asymmetric dual-beam switching are proposed.Among them,when the first type of asymmetric dual-beam array works at28 GHz,its forward beam can scan from 13~°to 80~°while the backward beam can scan from-75~°to-10~°;When the second type of asymmetric dual-beam array works at 28GHz,its forward beam direction is fixed at 45~°,and the backward beam scans from-10~°to-80~°.At the same time,under each switching excitation state of these two arrays,the frequency beam scanning of the corresponding LWA element can also be achieved.Therefore,the above LWA arrays with flexible dual-beam switchable characteristic can be applied to both systems with requirements of fixed frequency beam switching and frequency-controlled beam switching.3.A LWA array with the capability of beam-formed dual-beam switching is proposed.The array consists of two dual-beam LWAs and a power divider.Among them,the two elements in the array have different dual-beam directions,and their farfield electric amplitudes meet the cosecant distribution.By exciting different ports,the array can realize the functions of bilateral-shaped beam switching and dual-beam superposition shaping,respectively.In detail,when the array operates in the bilateral-shaped beam switching mode,two symmetrical dual beams whose direction is±25°and±45°while their radiation E-field intensity meets the cosecant distribution at28 GHz can be switched and work individually;when the array operates in the ual-beam superposition shaping mode,two sub-beams of array elements generate simultaneously and add into a sum beam whose radiation E-field intensity meets the cosecant distribution in a wide angle range.The above array is suitable for uniform radio wave coverage system of linear confined space with hard boundary.4.In order to improve the radiation efficiency and frequency gain stability of LWA,a design method of Archimedean spiral slotted LWA is proposed.By reasonably designing the structural size of Archimedean spiral slot,the impedance bandwidth of the final achieved Ka-band LWA is 29%,the bandwidths with radiation efficiency greater than 90%and 80%are 13%and 25%respectively.In the whole broadband,the gain fluctuations of the frequency scanning beams are less than 2.6 d Bi.At the same time,this method is further applied to the design of fixed-frequency beam-switchable LWA array with double-layer structure,which realizes that the beam can be switched in four radiation patterns at a fixed frequency of 28 GHz,and still maintains the characteristics of high efficiency and stable gain.The measured results of the above leaky wave-antenna and array verify its characteristics of wide frequency band,high radiation efficiency and stable gain.5.A structure of LWA that can work in left-handed circular polarization or right-handed circular polarization is proposed.Among them,the designed SIW LWA with fan-shaped slot has 31%axial ratio bandwidth.By switching its excitation port,the left-hand circularly polarized frequency beam scanning covering the range of-51°to 0°or the right-hand circularly polarized frequency beam scanning covering the range of 0°to 50°can be realized.In addition,two LWAs with fan-shaped slot are used to form the array whose gain is 2.2 d Bi higher than the gain of the array element,which realizes the high gain characteristics of the circularly polarized LWA.The measured results of fan slotted leaky wave antenna and array verify its characteristics of broadband circular polarization,changeable circular polarization state and high gain.