Research On Conformal Arrays Based On End-fire Antenna

With the rapid development of phased array radar technology,the requirements for the antenna performance in the radar system of the airborne is becoming higher and higher,such as wide bandwidth,high gain,wide scanning angles,easy to be installed and conformal with the carrier,and so on.As a special antenna structure with low profile,the end-fire antenna can not only be easily conformed with the carrier,but also have the directional radiation characteristics to obtain an axial radiation about the carrier.It can be used for compensating the area which is difficult to be scanned by the airborne radar,so as to improve the detection performance of the system.Furthermore,the research on conformal antenna makes the carrier have excellent aerodynamic characteristics,which meets the needs of high-speed moving radar system well.Therefore,it is of great significance to study the conformal arrays based on end-fire antenna elements.The main research contents of this thesis are as follows: 1.There is a problem that the maximum radiation direction of the end-fire antenna,which conformed with the cone,deviates from the axis of the cone.This thesis takes the microstrip structured end-fire antenna as the basic antenna element,in which the radiation component broaden the operational bandwidth by cascading two dipoles together.And then,adjusting the polarization direction of each end-fire antenna element makes the main beam of the conformal array point to the axis of the cone.Therefore,the conformal array realizes the axial radiation characteristics.The simulation results show that the conical conformal array has a impedance bandwidth of 7.89 GHz to 12.39 GHz,covering the whole X-band,and the realized gain varies from 11.85 dBi to 14.27 dBi.2.There is a problem that the sidelobe level of conical conformal antenna array is relative high.This thesis studies and analyzes the influence of spacing between elements and arrangement of the array elements on the radiation performance of conformal antenna array.By reducing the spacing of elements and adjusting the amplitude of element's excitation current to taper distribution,the sidelobe level of conformal antenna array is suppressed.And on this basis,we propose a method of physical isolation to improve the impedance matching of antenna array at high frequency,which is loading metal plates between array elements.The simulation results show that the bandwidth of the conical conformal antenna array with low sidelobe level almost covers the whole X-band,and the maximum sidelobe level in the effective scanning plane at the operating frequency of 10 GHz is-15.24 dB.3.There is a requirement for the high gain of conformal array.Based on the theory that the metamaterial with near-zero permeability can improve the gain of antenna in a wide band,a miniaturized Mu-Near-Zero(MNZ)unit cell is designed in this thesis.And then,the MNZ slabs are embedded in the conformal array antenna aperture,which can be regarded as a flat lens to achieve the electric field distribution of planewave-like,resulting in a gain enhancement of the antenna array.And on this basis,we employ strip directors located at the front of antennas conformed with the cylinder,to further improve the gain of the array.The simulation results show that the gain of the cylindrical conformal antenna array varies from 13.30 dBi to 15.14 dBi in X-band.Compared to the conformal antenna array with directors loaded,the proposed conformal antenna array with the same size achieves a gain enhancement by 0.45 dB to 1.38 dB.