| Application of satellite navigation systems is increasingly widely, and it haspenetrated into many aspects of our daily life. Surge of users, high positioning accuracypresents severe challenges to the multi-mode and multi-system compatibility ofNavigation Terminal System. Thus, researches on multi-frequency or broadbandcircularly polarized antenna for Navigation Terminal System are essential. Thisdissertation introduces the radiation mechanisms and implementations formulti-frequency and broadband circularly polarized antenna, and the circularlypolarized antennas based on broadband feed network are researched and proposed. Themajor work can be divided into the following sections.1. Firstly, this paper illustrates the radiation theory and implementation method ofthe single feed multi-frequency and multi-feed broadband circularly polarized antenna.Then mainly study the electrical properties of feeding networks such as3dB directionalcouplers, phase-shifting balun, power divider and phase shifter. The improved designsof parallel-line coupler and miniaturized branch-line balun at L-band are implemented,both of which exhibit good broadband performance.2. A dual-band GPS antenna in stacked patch is designed. Focusing on the index ofGPS atenna, two stacked patches in corner cutting are implied to achieve circularlypolarized radiation. Its3dB axial ratio bandwidth is16MHz and10.2MHz at1575MHz and1227MHz, while the gain is3.2dBi and0.2dBi. Additionally, wide beameffects and good cross-polarization suppression obtained.3. The broadband feed network based on Schiffman phase shifter is researched anda wideband circularly polarized patch antenna is developed. The designed feeding workcomprises a bisecting Wilkinson power divider and an improved Schiffman phaseshifter, the output ports have stable amplitude and phase characteristics over600MHz.The radiation patch fed with dual probe, and capacitive small patches are used for betterfeeding effect. Ultimately, the antenna obtains a wideband circularly polarizedperformance with the3dB axial ratio bandwidth exceeding30%, and the maximumgain of9.8dBi reached.4. Novel coupled-line power divider, phase shifter and dual-fed crossed circularlypolarized dipoles are reaserched. Based on the even-and odd-mode analysis, rigorous design equations and analytical scattering parameter expression increase the flexibilityof the circuit design. The electrical properties of the designed coupled-line feed networkis improved. Then, a crossed dipole antenna of square patch based on the new feednetwork is designed, a metal horn is imployed for radiation improving, and the antennashow good broadband circular polarization performance. Moreover, an improved designof novel symmetric arrow-shaped crossed dipole antenna is proposed, the air bridge andshort probes are introduced to feeding parts, the antena exhibits an excellent electricalperformance across broadband, which has certain reference value for multi-fed crosseddipole antenna design.5. The crossed dipole antenna sample is measured. Far field testing principle forcircularly polarized antenna is introduced, and test procedures of the crossed dipoles forboth near-field and far-field are presented. Finally, the test results are analyzed.This paper dedicated to design multimode antenna for GPS or other satellitenavigation systems. Implementations of multi-frequency and bandwidth expansion forcircularly polarized antenna are studied, and broadband feed networks for circularlypolarized antenna are discussed in detail. The designed dual-band GPS antenna andthree broadband antennas in L-band meet the application requirements for multiband. Aprototype antenna of novel crossed dipole was fabricated, and the measured resultsverified the excellent broadband circularly polarized performance. |
