Broadband Antenna Design Based On The Analysis Of Equivalent Resonant Circuits

Antenna assumes the function of transmitting and receiving radio signals in wireless communication system.With the rapid development of wireless technology,the large amount of information transmission is further demanded in the field of mobile communication.Larger bandwidth is requested to guarantee the quality of mobile communication and it leads to the increasing demand for broadband antenna.Designing antennas with multi-resonance abilities is a common way to expand the impedance bandwidth.The resonant peaks locating at different frequencies can gain the antenna a good impedance matching performance in a wide frequency band.However,the antenna with multiple resonant structures may not realize multiple resonances.It means the generation of multiple resonances is conditional,which we can study to design the antenna with broadband performance successfully.Resonant phenomena can be studied by analyzing resonant circuit,which is basically divided into series resonant circuit and parallel resonant circuit.In this paper,two basic resonant circuits are combined in different ways,which can be classified into three categories by the variation characteristics of S11 parameters with frequency.On the basis of above analysis,the feasibility and the achieving conditions of double resonances from the three categories of combined resonant circuits are studied.To design multi-resonance antenna,model and components of the equivalent resonant circuit is ought to be determined.Based on the research of Michael Hamid,combining Babinet principle,the equivalent resonant circuit of half-wave dipole antenna and half-wave slot antenna is analyzed to be series resonant circuit and parallel resonant circuit respectively.According to the Eigen-mode theory and the method of moment,a method is analyzed of calculating the equivalent resonant circuit components with dimension parameters of the half-wave dipole antenna.Because of the complementary relation between the half-wave dipole antenna and the half-wave slot antenna,the equivalent resonant circuit component of half-wave slot antenna is calculated based on the relation of component between two equivalent resonant circuits.Combining two half-wave dipole antenna,a half-wave dipole antenna and a half-wave slot antenna,two half-wave slot antenna,to which the three categories of combined resonant circuits are related respectively.By designing appropriate dimension parameters,the combinations of antennas can meet the conditions of double resonances and generate double-resonance peaks in S11 curves.In this paper,HFSS is used to verify the condition correctness of achieving double resonances with the first and second category of combined resonant circuits.It is also proved that the third category of combined resonant circuits is failed to achieve double resonances.On the basis of the above analysis,a multi-dipole antenna is designed according to the double resonances condition related to the first category of combined resonant circuits.The antenna has a relative bandwidth of 67%by realizing treble resonances,which proves the feasibility of guiding the design of multi-resonance broadband antenna with analysis of the equivalent resonant circuit.