Research On Array Antennas Based On Quasi-Conformal Transformation Optics

The emergence of transformation optics(TO)--coordinate transformation theoryprovides the basis for the design of new electromagnetic devices with the interaction of electromagetic waves and materials.The key is the equalization of the transformation of coordinates in two spaces with the transformantion of electromagnetic material parameters.However,the electromagnetic material parameters calculated based on coordinate transformaion theory are usually complicated,which generally can only be designed by metamaterials.The inherent disadvantages of metamaterials limit the performance of these devices and their actual processing.The quasi-conformal transformation optical(QCTO)theory developed based on the coordinate transformation theory can simplify the solved permittivity into isotropy and normalize the permeability,which means that all-dielectrics can be used to construct new devices.The main research content of this paper is the QCTO theory of array antennas,which can achieve the equivalent radiation performance of the linear antenna array and the conformal antenna array,so that array design can break through the structural limitations.Based on QCTO theory,we study the all-dielectric lens L1,covering the conformal array,and the lens L2 covering the linear array in this paper.The lens L1 is mounted on the conformal antenna array to achieve an equivalent radiation pattern of the corresponding linear antenna array,and its symmetrical excitation amplitude distribution and regular excitation phase distribution can simplify the conformal antenna array's feeding network designing.Further,we can use the realization method of planar array multi-beam to design conformal array multi-beam.The lens L2 is loaded on the linear antenna array to gain an equivalent radiation pattern of the corresponding conformal antenna array,and can realize the wide-angle scanning performance of the planar antenna array.The permittivity distribution of the lens is obtained by solving the Laplace equation under certain boundary conditions.Because the boundary conditions in the virtual space of the two lenses are different,the boundary conditions used when solving the permittivity distribution of the two lenses are different.For the lens L1,we approximate the part with the permittivity less than 1.45,and implement it in the form of punching the dielectric block.According to the permittivity,the lens L1 can be divided into 9 areas.At the same time,a multi-beam network—Rotman lens is used as the feeding network of the conformal antenna array loaded with the lens L1.Because of the existence of the lens L1,the reference theory when designing the conformal antenna array is as same as the linear antenna array,including the feeding part.Therefore,the rotman lens designed in this paper can be directly designed according to the design formula proposed by Rotman and Turner,without further modification.We used a microstrip patch antenna as the antenna unit to build an 8-element linear antenna array and an 8-element conformal antenna array.The conformal antenna array,lens L1,confomal floor and rotman lens are combined for simulation and processing tests.The simulation results and test results are consistent.Results indicate that the designed antenna can achieve a scanning range of ±46°in the operating frequency band,and the crossover level between adjacent beams are all lower than-3 d B on the H plane.For the lens L2,we focus on the low sidelobe performance of the antenna array.Simulation results show that the linear antenna array loaded with the lens L2 can better reproduce the pattern of the conformal antenna array at a low scanning angle.Due to time and capability issues,we only conducted a preliminary study on it.The research in this paper shows that combining the QCTO theory with the antenna array design can achieve the equivalent radiation performance of the linear antenna array and the conformal antenna array.This provides a new design idea for the design of array antenna.