| Phased array antennas can provide timely information for radar guidance,detection,and tracking,so increasing the scan angle of the phased array antenna means that targets can be found in larger airspace.When a conventional planar phased array scans at a large-angle,problems such as a sharp decrease in effective aperture,an increase in secondary lobes,and mismatch in the active impedance of the array may occur,so that the scanning range is usually limited to within ±60°.Employing beam-deflectable antenna elements can increase the gain of the array at low elevation angles,thereby broadening the scanning range of the array.Currently,the beam-deflectable antenna elements are mostly based on pattern reconfigurable technologies,and their structures are usually complicated which is difficult to apply.In this dissertation,a new design method with adaptive element beam deflection is proposed.When the antenna element is applied to a phased array antenna,the radiation beam of the antenna element can be adaptively deflected with different array scanning angles,thereby obtaining a larger scanning angle.Firstly,according to the direction product theorem,the adaptive antenna with multi-phase centers is proposed in this thesis,and each phase center is independently fed.By adjusting the feed amplitude and phase of each feed point,the element beam pointing direction can be controlled.The feed phase difference of each feeding point of element is set to be equal to the feed phase difference of adjacent array elements,which offers two advantages:first,it can achieve the adaptive deflection of the element beam without increasing the number of phase shifters and changing the conventional array antenna feed structure;second,the element beam deflection can be directly controlled by the phase difference of the array elements.Secondly,a 1 x 7 large-angle scanning array antenna is designed according to the principle of adaptive element and array.An adaptive element with bi-phase centers is designed based on the microstrip magnetic dipole.The distance between the two phase centers is small which can cause strong coupling between the two ports,so the circuit decoupling method is used to decline the coupling between the ports,which can provides additional 20 dB coupling reduction at the center frequency.An adaptive antenna prototype is manufactured,and the experimental results meet well with the simulation results.Further,a 1×7 array antenna is designed based on the adaptive element.The adjacent ports of the array antenna are connected to a power divider,and the backend of the array is directly connected to the feeding network of the traditional array antenna.Both the simulation and the measured results of the array antenna show that ±70° HPBW scanning can be achieved.Finally,a two-dimensional large-angle scanning array antenna is designed according to the principle of adaptive element in an array.A two-dimensional adaptive antenna element with four-phase centers is designed,the relationship between the feed amplitude and phase of each feeding point and the beam deflection is analyzed.Further,the design principle and method of two dimensional array antenna based on adaptive element is introduced in details,especially the feeding structure.Considering that the element structure designed in this paper is rotationally symmetrical,a one-dimensional array(1×8)and a two-dimensional array(8×8)are designed and simulated.The 3dB beam widths are ±73° and ±67°respectively,which are better than the scanning angle of traditional antenna array. |
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