Analysis And Design Of Filtering Antennas Based On Characteristic Mode Theory

With the continuous development of the fifth generation mobile communication technology,the RF front-end needs to meet the development trend of high integration and miniaturization.Antennas and filters play an important role in RF systems.The traditional design idea is to design antennas and filters separately and then cascade them.This method requires additional matching circuits between antennas and filters,which takes up a lot of space resources.To solve this problem,researchers in the RF field have proposed the concept of filter antenna,that is,the antenna and filter are designed as a module.In the existing research,the integrated design of filter antenna and the joint design method of filter antenna based on filter have mature theoretical system,but the fusion design method and theory of filter antenna are not perfect.Therefore,this thesis has conducted in-depth research on the fusion design method of filter antenna,and the specific research contents are as follows:（1）A broadband external suppression filter antenna is proposed.The filter antenna consists of two circular patches,two short pins and a pair of half-mode slots.The addition of laminated circular patch not only greatly improves the impedance bandwidth of the antenna,but also achieves a wide out-of-band suppression effect in the high stopband by using the high order modes of the circular patch,and achieves a low stopband filtering effect by adding pins and half-mode slots without affecting the antenna radiation mode.The whole filter antenna has the characteristics of wide bandwidth and broadband external suppression.（2）A dual-beam radiation filter antenna is proposed.The filter antenna realizes dual-beam radiation based on the rectangular patch antenna TM₂₀ mode,and uses a cross-branch feed structure to excite the antenna.The feed structure not only broadens the impedance bandwidth of the antenna,but also introduces a gain zero in the low stopband,and achieves a wider stopband filter range in the low stopband by adding two pairs of parasitic patches without affecting the antenna radiation mode,By adding symmetrical U-shaped slots on the patch and adding symmetrical defected ground structure on the floor,the filtering effect of the filter antenna in the high stopband is realized.The whole filter antenna has the characteristics of double-beam radiation and high frequency selectivity.（3）A dual-band filter antenna is proposed.The filter antenna changes the shape of rectangular patch to trapezoidal patch,and adds two open branches for current shaping.The open branch also provides two gain zeros.In this design,slot coupling feed is adopted to excite the TM₀₁ mode and TM₀₂ mode of the filter antenna at the same time.By adding a pair of full-mode slots,the filtering effect between the two passbands is increased.