Design Of Broadband And Dual-band Circularly Polarized Printed Antennas

As a crucial component of modern wireless communication system,antenna plays an important role.Its performance will have a direct impact on the whole communication system.With the rapid development,wireless communications need faster transfer rate and larger information capacity,which requires antennas of broadband and multiband.The traditional narrowband antennas have been overwhelmed.A great diversity of application scenarios and complicated electromagnetic wave transmission environment,demand antennas of more excellent properties.So broadband antennas and multiband antennas become a hot topic.Compared to linear polarized antenna,circular polarized(CP)antenna is very effective in combating multi-path interferences,and it needs no strict orientation between transmitting and receiving antennas.CP antennas are widely used in modern wireless communication systems.This thesis focuses on the design of broadband and dual-band circularly polarized printed antenna.Three antennas are proposed in the thesis,including a broadband circularly polarized monopole antenna with deformed ground,a wideband circularly polarized slot antenna with asymmetric ground plane,and a novel design of a dual-band circularly polarized slot antenna with CPW-fed.First,a broadband circularly polarized monopole antenna with deformed ground is proposed.The antenna is fed by an L-shaped microstrip line with stepped section for impedance matching.In this design,lighting-shaped stub in the ground is the crucial section for CP characteristic,and the small stub near the feeding line also contributes to a broader CP band.The proposed antenna is fabricated and then measured.Experimental results show that the 10-dB impedance bandwidth is 64.2%(2.65 GHz,1.8-3.5 GHz),while the 3-dB AR bandwidth is 73.3%(3 GHz,1.9-4.1 GHz).Moreover,the 2-dB AR bandwidth is 54.5%(2.75 GHz,2.0-3.5 GHz),which denotes a good CP performance.Second,we designed a wideband circularly polarized slot antenna with asymmetric ground plane and an irregular radiation patch.Asymmetric ground plane with open slot on the left is the key section to achieve CP feature.The irregular radiation patch with cut corner on the bottom,groove by the side and a stub on the top result in a wider CP band.Experimental results show that the 10-dB impedance bandwidth is 64.2%(2.65 GHz,1.8-3.5 GHz),while the 3dB AR bandwidth is 73.3%(3 GHz,1.9-4.1 GHz),showing a good CP performance.Finally,a novel design of a dual-band circularly-polarized slot antenna with CPW-fed is presented in this thesis.An arc-shaped patch and L-shaped strip with another arc-shaped patch are introduced for the dual-band circularly-polarized radiation at the lower and upper bands,respectively.The total size is70×70×1.6 mm~3.The antenna has a simpler structure with low profile,which is easy for integration.It is shown that the proposed antenna has a good CP characteristic.The antenna is designed,fabricated and measured.The experimental results show that the 3dB axial ratio bandwidths are 6.2%(3.1-3.3 GHz)for the lower band and 29%(4.7-6.3 GHz)for the higher band.Meanwhile,the impedance bandwidths are 6.3%(3.08-3.28 GHz)and 22%(4.8-6.0 GHz),respectively.The measured results agree well with the simulated.