Research On The Stable Beamwidth Broadening Of Broadband Dipole Antennas

To meet the requirements of broad operating bandwidth and wide coverage area simultaneously,broadband wide-beam antennas are widely applied in modern mobile communication base station systems.The base station usually uses unidirectional dipole antennas as radiation elements.Therefore,this dissertation modifies three kinds of dipole antennas and broadens their beamwidths stably across a wide frequency band.The fluctuations of their beamwidths are less than 10° over the fractional bandwidth of 30%.As to the magnetoelectric dipole antenna,we combine the inclined dipole arms with the inclined sidewalls on the reflector plane to widen the E-plane beamwidth.For the stabilization of the beamwidths in the frequency band,the dipole arms are divided into several symmetrical branches.The measured results indicate that the E-plane beamwidth of the antenna is widened stably to 95°-102° and the H-plane beamwidth is widened stably to 98°-104° over the frequency band ranging from 1.9 to 2.7 GHz.In the antenna array design,we continue to maintain its wide-beam radiation characteristic by adjusting the inclination angles of dipole arms and sidewalls properly.To broaden the E-plane and H-plane beamwidth of the planar dipole antenna,we take the top-loaded posts as parasitic elements and load them on the reflector plane.For the analysis of its resonant characteristic,an equivalent circuit model is proposed for the antenna with parasitic elements.We extract the parameters of the circuit model and compare them with simulated results to verify the correctness.Then the pattern bandwidth is widened by the combination of multiple metallic posts.The measured results indicate that the E-plane beamwidth of the antenna is widened stably to 95°-103° and the H-plane beamwidth is widened stably to 96°-103° over the frequency band ranging from 2 to 2.7 GHz.In the antenna array design,the mutual coupling of antenna elements leads to the deteriorative wide-beam radiation characteristic.By redesigning the parasitic element's structure,the beamwidth of the antenna array in horizontal plane is widened stably to about 98° once more.The proposed parasitic elements are also applied in the dual-polarized dipole antenna.We load them in diagonal to broaden the beamwidth in horizontal plane.In the frequency band from 1.8 to 2.6 GHz,the beamwidth is widened stably to 85°-94°.In the antenna array design,we introduce a metallic wall to enhance the input-port isolation to 26 dB.