| The demands for wireless communication devices are growing rapidly,so antennas and other RF devices are increasing day by day.Strong coupling is introduced due to the limited size,which deteriorates the function of the antenna or system.In order to solve this problem,the traditional method is to cascade a filter and the antenna,while a large amount of space will be occupied and high insertion loss will be introduced.In recent years,the integrated design of filter and antenna has become a research hotspot.The concept of filtering antenna is proposed.The filter structure is integrated to traditional antenna and make antenna have the functions of radiation and filter at the same time,which saves the cost of the filter and the occupied space of the system,avoids the loss,and greatly reduces the mutual interference between antennas operating in different frequencies.In this thesis,the filtering antenna for base station application is deeply studied.The magnetoelectric dipole’ antenna with broadband characteristics and low-frequency intrinsic radiation null is used as the antenna unit,and three different filtering antenna with high selectivity are designed.1.A high selectivity filtering magnetoelectric(ME)dipole antenna with harmonic suppression is investigated.By etching a complementary split resonant ring(CSRR)on the shorted wall of ME dipole,a radiation null at upper passband edge can be obtained.The intrinsic radiation null at lower passband edge of ME dipole is utilized,together with the radiation null generated by CSRR,to obtain high selectivity.In addition,to suppress the third harmonic of the antenna,a stepped impedance resonator is loaded on the Γ-shaped feeding structure.For verifying,a prototype operating from 1.44-2.79 GHz is designed,fabricated,and measured.Compared with the traditional ME dipole antenna,the roll-off rate of proposed antenna is better than 1.25,and the stopband rejection levels as high as 16.61 and 17.84 dB,respectively.Furthermore,a third harmonic suppression level of 12.78 dB is obtained.Good agreement can be observed between the simulation and measurement.2.A wideband dual polarized filtering antenna with high selectivity is proposed.By symmetrically changing the rectangular radiation patches of traditional magnetoelectric(ME)dipole into double rhombic structure,a radiation null is introduced at higher frequency,together with the intrinsic null of ME dipole at lower frequency to achieve high selectivity.Furthermore,the third radiation null is generated by extending the length of microstrip,which improves the level of stopband suppression.Finally,a loop is placed around the radiators to increase the realized gain in the passband.The measurement results show that the bandwidth of the antenna(|S11|<-10 dB)is 73.9%,covering 5G sub-6GHz band(3.35.2 GHz),and the stopband rejection is greater than 12.7 dB.This wideband design can also be modified to a dual-band filtering antenna.By symmetrically loading four U-shaped parasitic stubs and a crossed E-shaped stub between the radiators,two radiation nulls are generated in the passband to realize the dual-band bandpass filtering response.The measurement results show that the bandwidth of the dual-band antenna(|S11|<-10dB)covers 3.3-3.6 GHz and 4.8-5.2 GHz respectively.Besides,the stopband rejection is more than 11.8 dB.Good performance of the antenna makes it a promising candidate antenna for 5G sub-6 GHz base station systems.3.A magnetoelectric dipole filtering antenna with high out-of-band suppression level and high selectivity is proposed.The intrinsic radiation null of the traditional magnetoelectric dipole antenna is used,which produces a good filtering response at the edge of the lower passsband.A pair of vertical parasitic metal planes are introduced between the shorted walls and fed through slot coupling,which can be equivalent to a magnetic dipole.The radiated electric field of the magnetic dipole is opposite to that of the original antenna at higher frequency,forming a wide stopband radiation null,which greatly improves the highfrequency stopband suppression level of the antenna.Furthermore,a pair of T-shaped coupling stubs are connected with the shorted wall and used to couple and excite parallel radiation patches.The introduction of T-shaped stubs makes the antenna produce another radiation null with high roll-off rate at higher frequency.The measurement results show that the 10 dB impedance bandwidth of the proposed antenna is 49.4%(5.3-3,2GHz).The rolloff rate of low frequency and high frequency is better than 0.17 and 0.26.Its low-frequency stopband suppression level is greater than 19.2 dB and high-frequency stopband suppression level is greater than 24 dB.Moreover,the antenna radiation pattern is stable and symmetrical in the whole operating passband,and the filtering response is desirable. |
