| With the development and progress of the world,people rely more and more on wireless communication system.As the front component of communication system,antenna can be seen everywhere in daily life,and circular polarized antenna has attracted much attention because of its excellency in anti-multipath effect and signal reception even in stormy weather.In the times of big data,broadband antenna better meets the requirement of transmission speed and communication capacity.And the miniaturation of such antenna makes itself suitable for more scenarios.Therefore,it is of great importance to study miniaturized broadband circular-polarized antenna.In this thesis,two kinds of miniaturized broadband circularly polarized antennas are studied and designed,and verified by simulation.The specific summary is as follows:(1)A miniaturized broadband circularly polarized slot antenna is designed in this thesis.With microstirp feeding the antenna,it is coupled by slot so that the bandwidth is expanded.And by using metal branches and etching arc-shaped slot around them,a slot-coupling structure is formed.And such structure stimulates broadband radiation as expected.As a result,a circularly polarized antenna is constructed.To achieve better impedance matching,impedance transformation structure is introduced between the microstrip feeder and the radiator.The final test shows that the impedence bandwidth of the antenna is 77.4%(3.8GHz-8.6GHz)and the 3d B axial ratio bandwidth is 79.4%(3.88GHz-8.96GHz).It can be concluded that the antenna proposed has the advantages of low profile,miniaturization and strong anti-interference ability,and can be widely used in Wi Max of5.5GHz and WLAN of 5.8GHz.(2)A miniaturized broadband circularly polarized monopole antenna based on coplanar wageguide feeding is designed in this thesis.On the basis of the most basic CPW feeding structure,the two adjacent circular polarization modes are coupled together,by setting the metal ground with different hight,digging and cutting the angle of the monopole and the floor,and using the parasitic ring with an opening at the bottom.As a result,the bandwidth of the antenna is effectively expanded and the circular polariztion purity of it greatly improved.The final test shows that the overlapping bandwidth of the antenna impedance and the 3d B axial ratio is 77.4%(2.65GHz-6Ghz),that of the antenna impedance and the2 d B axial ratio is 62.2%(3.1GHz-5.9GHz),and the peak gain in band is 4d Bi,which means the test results are in agreement with the stimulation results.The antenna proposed has the advantages of simple structure,small overall size,wide bandwidth coverage and high circular polarization purity,and can be widely applied to Wi Max in 3.3GHz-3.8GHz and5.5GHz. |
