Research And Design Of Monoblock Dielectric Filter

With the rapid development of wireless communication technology,higher requirements have been put forward for the performance of filters for small communication equipment.The dielectric filled cavity filters have gradually become the mainstream choice for its advantages of low cost,low loss and better temperature drift performance.In order to improve the out-of-band suppression of the filter,cross coupling is often introduced in the design of the filter.Coupled elements are added between non-adjacent resonators to construct an auxiliary path,so as to introduce the transmission zero.Compared with the traditional method of increasing the order,this method can not only improve the out-of-band inhibition ability,but also has the advantage of miniaturization.However,since the dielectric filled cavity filters are usually filled with solid blocks of media that are coated with silver to act as metal shielding cavities,it is not possible to add coupled elements inside.Based on the dielectric filled cavity filter,this thesis adopts the linear structure and introduces the cross coupling through the metal microstrip patch to generate transmission zero,so as to improve the out-of-band suppression ability.According to the above background,the monoblock dielectric filter is studied and designed in this thesis.The specific work is as follows:1.A four-cavity monoblock dielectric filter is designed,the design size is 9 mm×6.32 mm×3mm,the center frequency is 2.4 GHz,the working frequency band is between 2.38 GHz and 2.41 GHz,and the in-band return loss is more than 20 d B.By introducing cross coupling between resonator1 and resonator 4 through metal microstrip patch,a transmission zero is generated at 2.35 GHz and2.45 GHz out of band,respectively.The low end suppression of out of band is more than 51 d B,and the high end suppression of out of band is more than 58 d B.The simulation structure is processed,and the measured results agree with the theory basically.2.A six-cavity monoblock dielectric filter is designed,the design size is 17.5 mm×6.79 mm×4.5mm,the center frequency is 2.04 GHz,the passband width is between 1.98 GHz and 2.14 GHz,the in-band return loss is more than 20 d B,and the insertion loss is less than 0.7 d B.By introducing cross coupling between resonator 2 and resonator 5 through metal microstrip patch,a transmission zero is generated at low frequency 1.68 GHz and 1.95 GHz respectively,and a transmission zero is generated at high frequency 2.16 GHz and 2.35 GHz outside the band respectively.Compared with the designed four-cavity integrated dielectric filter,the out-of-band suppression is improved,and the simulation structure is processed.The measured center frequency is 2.07 GHz,and the insertion loss is less than1.2 d B,which is basically consistent with the theory.The filter not only has good filtering performance,but also has great advantages in miniaturization,which can meet the needs of industrial production.