Design Of Dual-frequency Dual-polarized Base-station Antennas For Mobile Communications

Antenna is one of key components in the mobile communication system. Therapidly development of mobile communications makes the system become more andmore complex. In order to meet the upgrade requirements, we need to effectively solvethe multi-path fading problem, decrease the number of antennas, and reduce the cost ofantennas and site selection. The dual-frequency dual-polarized base-station antennas canbe used to follow these requirements. Therefore, it is extremely necessary to make astudy on this kind of antennas, which is of theoretical and practical values.In this thesis, two different schemes, i.e. abreast and coaxial dual-frequencydual-polarized base-station antennas are studied. Comparison of the VSWRs, theisolations, and the radiation patterns for these two dual-frequency dual-polarizedbase-station antennas has been made. The main contributions of this thesis aresummarized as follows:1. Different dual-polarized base-station antenna elements with high isolation aredesigned. Dual-frequency dual-polarized base-station antenna operates simultaneouslyboth the CDMA/GSM900 (824-960MHz) and the DCS1800/3G (1710-2170MHz)bands. For the abreast dual-frequency/dual-polarized base-station antennas, two types ofdipoles are designed: compression mold and printing dipoles, each with elementsoperating in different frequency bands. In the coaxial scheme, a dual-bandcombined-dipole is devised. In the DCS1800/3G band, we adopt cross printing dipolefed by L-probes. While in the lower frequency band, we use circular metal layers fed byT-probes as its radiation unit. The two portions are nested within each other, and havethe same phase center. In addition, a dual-frequency double-deck rounded patch elementfed by L-probes is simulated.2. Two dual-frequency dual-polarized antenna arrays according to the abreast andcoaxial schemes are designed. First, we determine the antenna element spacings, andselect the appropriate reflector. For the abreast scheme, we analyze the column spacingsbetween arrays with different bands and find out the optimal size. While for the coaxialdual-frequency dual-polarized antenna array, we focus on the effect of element couplingon antenna performance. These two antenna arrays have been fabricated and measured.Their VSWRs, isolations, and radiation patterns are compared. Both the advantages anddisadvantages of the base-station antenna performance in these two cases are alsodiscussed. 3. The base-station arrays with shaped-beam pattern are synthesized. Accordingthe need in practical applications, genetic algorithm for shaping array patternsadopted to optimize the vertical antenna pattern, such as first upper side lobesuppression, first lower zero filling and electrical down-tilt. Aiming at the inaccuracythe optimized results caused by ignoring mutual coupling among array elementstraditional array synthesis, the element patterns calculated by the simulated software,which the mutual coupling and effect of array environment on the elements areconsidered, are used in the process of optimization, to improve the synthesis accuracy.