Abstract
An ultralow profile, dual-wideband and low passive intermodulation (PIM) in-building ceiling-mount antenna for long term evolution (LTE) distributed antenna system (DAS) application is presented. The proposed antenna was designed based on asymmetrical dipole concept having a ground plane with an inclined feeding edge to achieve wideband characteristic and reduced null radiation pattern in the azimuth plane when oriented horizontally. Various dipole and monopole design approaches are presented to give an insight into the typical elevation dipole-liked radiation pattern in the azimuth plane when oriented horizontally to achieve ultralow profile feature. The proposed antenna improves from a simple rectangular monopole to a newly innovated design with off-center feeding location and radiating elements by implementing new design features, e.g. having variation between edges of the radiator and ground plane, slots within monopole radiator and ground plane and inclination of the feeding edge of the ground plane. These additional features enable the proposed design to have a good compromise between the azimuth plane radiation pattern and impedance matching. A production-quality prototype was fabricated to ensure the best PIM performance is achievable. The performance of the prototype was measured. The antenna offers dual-wideband characteristic covering most of the LTE frequency ranges of 698-960MHz and 1350-3800MHz. The passive intermodulation levels that measured for both 700MHz and 1920MHz bands are better than −150 dBc at carrier input of 2\times20 Watts.