Research On Ultra-wideband Dual-polarized Low-profile Phased Array Antenna

With the evolvement of radar,communication,and electronic warfare,the demand for multi-functionality,systemization,and intensification has become more and more intense,the collaborative combat platform which integrates reconnaissance,interference,detection,and communication has been favored by people because of its natural advantages.But in this grand concept,there are at least two key problems:when hundreds of military electronic devices are turned on at the same time,the electromagnetic interference on the platform will be very serious,the electromagnetic shielding technology traditionally proposed in order to ensure the equipments to work normally is difficult to effectively cope with such large-scale electromagnetic pollution;the rapid development of radar and even anti-stealth technology makes the survival of any equipment relying on electromagnetic wave challenged,so it has become a problem that must be considered to effectively reduce the radar cross-section.Today,with the remarkable achievements of electronic technology,the performance and volume of many electronic components are going to the extreme.Neverthess,the antenna technology progress slowly by contrast which often becomes a knotty problem that restricts the miniaturization of equipments.In face of the above difficulties,the study of new systemic antennas which can cover multiple frequency bands,meet the needs of applications such as Receipt&Transmission,and occupy a small space becomes extremely urgent.In view of this,the paper proposes an ultra-wideband dual-polarized low-profile antenna suitable for phased array radar systems,which uses a tightly coupled octagonal ring element structure.The mutual coupling between this form of elements is the strongest for all kinds of the polygon rings,making it more fitted for Wheeler's continuous current sheet array model,thus resulting in better broadband effects.In order to feed the balanced octagonal ring with a characteristic impedance of about 120?,a truncated balun is designed,which is equivalent to the transition from coaxial line to parallel wire,and it can meet the requirements of balanced feed and impedance transformation simultaneously;for the sake of improving the wide-angle matching,a passive octagonal ring is placed above the radiation layer;in addition,a metal isolating plate is loaded on the diagonally plane of the reflector,which improves the impedance matching,cross polarization and port isolation to a certain extent The unit cell thus realized occupies a three-dimensional size of 620mm × 620mm × 200mm,and its impedance bandwidth is 135-270MHz,where the broadside and spatial active VSWR are respectively less than 2 and 4.The cross polarization is about 10dB,15dB,and 30dB lower than main polarization at 180MHz,210MHz and 250MHz respectively,and the port isolation performs well in band.The impedance transformation performance of bulun is not only related to the number of section of transformations and the transformation ratio of each section,but also subject to the length of each section.The index of profile height is only 0.09?L,making the space for length adjustment of each section of balun limited,so the truncated balun is modified to a bent balun,allowing the length of each segment to be flexibly adjusted for better impedance matching.By optimization,the spatial active VSWR is reduced to be below 3 at the same unit cell size;the cross polarization is lower than the main polarization by 11.6dB,15.4dB,24.3dB at 180MHz,210MHz,250MHz respectively;port isolation of dual polarization is further enhanced,which is less than-10dB throughout the band;and the cross polarization is not deteriorated.