Design Of Multi-frequency Antenna For Satellite Navigation System And Mobile Communication Applications

Differential GPS receiver requires the antenna with wide beam and circularpolarization. Also low elevation gain and dual band are needed. Microstrip antennas andquadrifilar helix antenna (QHA) can meet the above requirements. As microstrip antennahas poor performance in low elevation and ground plane resulting in a larger overall area.Atthe same time, QHA has stronger ability to adapt to the environment and wider beamwidthto be more adopted.With the development of communication technology, mobile communication hasentered the fourth generation mobile communication networks era (4G). In the4G mobilecommunication system, multiple systems share is needed to save base station siteinstallation resources and reduce network construction costs inmobile communicationantenna. Due to the increasing number of users and extending communication services,increasing the channel capacity of mobile communications has become increasinglyimportant. Orthogonal polarization and frequency reuse technology are studied to increasethe channel capacity. In recent years,±45°dual-polarized antenna is widely used in mobilecommunication systems to increase channel capacity and to reduce installation costs.However, base station antenna is difficult to simultaneously achieve high isolation,wideband, low cross-polarization ratio, so dual-polarized wideband base station antennasbecome a hot studing topic.In this paper, two antennas for satellite navigation systems and mobile communicationapplications are studied, the main contents are as follows:1. A simple and innovative structure for designing dual-band quadrifilar helix antenna(DQHA) with single feed for GPS applications is presented. The proposed antenna iscomposed of a coaxial slotted baluns and two bifilar helixes with unequal helical armlength and axial height. Comparing to conventional quadrifilar helix antenna (QHA), thisantenna could achieve dual-band behavior without complex feed network. Parametric studyis performed to explore the structure improvements. Based on the study a dual-bandantenna operating at GPS L1(1.575GHz) and L2band (1.227GHz) has been realized withgood gain and right hand circular polarization. Measured results are presented to validatethe concept. Moreover, due to wrapped helix arms on only one coaxial cable, the manufacture of the proposed DQHA is very simple and easy to realize.2. A novel broadband dual-polarized square dipole base-station antenna was presented.The antenna was composed of cylindrical supported structure, modified double inverted-Lfeed strips, quadratic dipoles and baffle-board. The antenna achieved a common impedancebandwidth of1.69-3.16GHz (VSWR<1.5) and1.71-2.69GHz (VSWR<1.4) at both inputports. In1.71-2.69GHz, It had good performance in isolation which was more than-30dBbetween the two input ports. The cross-polarization of the antenna was better than-29dBand the maximum gain is about10.9dBi.The radiation pattern and the gain in the operatingfrequency band is stable. The antenna is suitable for the GSM1800, CDMA1900,IMT-2000, TD-CDMA, WLAN and WiMax base station applications. This improvedantenna was light and the feed strips were adjustability meanwhile.