Design Of BeiDou Navigation RF Front-end Devices Based On Metamaterials

With the rapid development and wide application of Bei Dou Navigation Satellite System（BDS）,the researches on its applications have become a hot research content at present and in the future.RF front-end devices,such as antennas,diplexers and low-noise amplifiers,are key components in BDS,and the demand is increasing day by day.In recent years,metamaterials,as artificial composites with special properties,have received increasing attention.Metamaterials can not only be used to design new multifunctional antennas,but also can be used to design high integration microwave diplexers with excellent performance,so has high research value.In this thesis,metamaterials,tri-band dual-circularly polarized antennas,tri-band diplexers and broadband low-noise amplifiers for BDS are studied,and the following achievements are achieved:（1）Based on the metamaterial structure,a tri-band dual-circularly polarized antenna for BDS is proposed and designed.The antenna is a square loop based on Composite Right/Left-Handed Transmission Line（CRLH TL）,which consists of four Double Periodic Bridged-CRLH TL（DP B-CRLH TL）units,and is fed by single feed point.The tri-band dual-circularly polarized characteristic of the antenna is realized by using the multi-band operation characteristics and the left/right hand transmission characteristics of the DP B-CRLH TL unit.The measured results show that the antenna receives right-handed circularly polarized（RHCP）navigation signals in B2 band with the center frequency of 1.208 GHz,the bandwidth of axial ratio less than 3 d B is about 10%,the gain is about-0.5 d Bic;it radiates left-handed circularly polarized（LHCP）short message communication signals in L band with the center frequency of 1.615 GHz,the bandwidth of axial ratio less than 3 d B is about 7.4%,the gain is about-2.6 d Bic;it receives RHCP short message communication signals in S band with the center frequency of 2.492 GHz,the bandwidth of axial ratio less than 3 d B is about 2.8%,the gain is about-0.8 d Bic;and in the three operating frequency bands,|S₁₁|are all less than-10d B,all indicators meeting the official performance standard requirements of Bei Dou navigation antenna.（2）Based on the metamaterial structure,a tri-band diplexer for BDS is proposed and designed,which corresponds to the tri-band dual-circularly polarized antenna designed in this thesis.The diplexer has three ports,and the receiving port is a dual-band bandpass filter,which covers the B2 band（the center frequency is 1.208 GHz）and S band（the center frequency is 2.492 GHz）of BDS;the transmitting port is a single-band bandpass filter,which covers the L band（the center frequency is 1.615 GHz）of BDS.In order to realize the miniaturization of the diplexer,the resonant structure of the dual-band bandpass filter at the receiving port is miniaturized by using metamaterials;then the overall structure is integrated by the coupling method,and no public matching network is required,so it has the advantages of compact structure and small size.The simulation results show that the isolation between the receiving port and the transmitting port of the tri-band diplexer is more than 21 d B,the|S₁₁|in the three bands are all less than-10 d B,and the insertion loss is low,with a good work performance.On this basis,the diplexer is processed and tested,and the test results basically meet the design requirements.（3）A two-stage cascaded broadband low-noise amplifier applied in the reception bands of BDS is designed by using Avago’s ATF series p HEMT,which can cover B2 and S bands of BDS.In order to obtain the wideband characteristic,a parallel resistive negative feedback structure is adopted,and the matching network of each stage is designed in a low Q environment.The measured results show that the operating frequency band of the low noise amplifier is 1.06～2.65 GHz,and the in-band gain is around 28.5±1 d B,which meets the design requirements of wide band and high gain.