Analysis And Design Of A Compact Microstrip Filter Antenna

In coming 5G era,in order to cover more RF transceiver channels for all 2G/3G/4G/5G frequency bands,the integrated,low-power consumed and multi-functional designs become the growing trend of communication systems.Antennas and filters are both essential passive devices at the front end of RF systems.Filters are responsible for filtering out noise or extra signals,while antennas are terminal devices for sending and receiving signals.However,the size of passive circuits is often restricted by its wavelength,the processing technology or other factors,which is difficult to be miniaturized and integrated.Traditionally,antennas and filters work separately and require matching circuits or devices for connection,resulting increased system losses and additional physical spaces.In order to optimize the overall performance of the RF front end,researchers proposed the design of filtering antenna(or filtenna): combine both filtering and radiating functions into a single passive device,which not only minimize the physical size of the system,but also reduces insertion losses and improves the overall efficiency.Therefore,the study high-performance filtering antennas is significant and promising.First of all,the paper introduces the development background of RF systems and the research significance of filtering antennas.Then,the current situation of filtering antenna researches both domestic and abroad is summarized with analysis of the design principles,existing problems and technical challenges.This paper,aims to reduce the size and loss of the RF front end,designs a series of compact,integrated filtering antennas: three novel designs of filtering antennas are proposed and analysed respectively,by implanting parasitic structures inside the antenna,the filtering antennas can achieve good filtering performances while ensuring the antenna radiation functions.The main contents of this thesis are as follow:(1)A Wideband Filtering Patch Antenna with Multiple Radiation Nulls Based on Radiation Cancellation.In this part,parasitic structures are introduced in the patch antenna to realize filtering functions based on the principle of radiation cancellation: by loading the U-strip and coupling square rings,etching slots on the patch and floor,two radiation nulls are inserted at the lower/upper stopband respectively.The parasitic structures can also widen the work band.With no additional circuitry added,the filtering structures does not introduce additional losses or take up extra space,which enables a compact,integrated and low-power filtering antenna design.(2)A Simple Compact Filtering Patch Antenna Based on Mode Analysis with Wide Out-of-band Suppression.In this part,mode analysis of the patch antenna is firstly carried out to suppress the undesired higher modes,then two simple parasitic structures are introduced to realize the radiation cancellation at the stopbands.Firstly,the side lengths of the radiating patch are analysed and adjusted to weaken the higher-order modes of the antenna;Then,by loading the U-shaped strip on the probe and etching the open-ring-shaped slot on the patch,two radiation nulls are inserted to form the upper/lower stopband respectively,two additional resonances are added in the passband to widen the bandwidth as well.Compared with other published works,the proposed filtering antenna is particularly simple and compact without extra circuit.Under the premise of ensuring antenna radiation performance,it realizes high selectivity and high out-of-band suppression level with twooctave frequency harmonic suppression.(3)Millimeter-Wave Dual-Polarized Filtering Antenna Array for 5G Applications.This part studies the highly-integrated dual-polarized filtering antenna/array based on the cross-coupling feeding structure.On the basis of the dual-polarized patch antenna differentially fed with L-probes,parasitic bandstop structures are introduced as crosscoupling feeding structures,which realize the filtering response of high selectivity,wide stopband and high stopband suppression level.The antenna and its 4×4 array are designed in LTCC multi-layer packages with symmetric radiation patterns,low cross-polarization and high front-end ratio,which provides a technical reference for the multi-functional design of the 5G millimeter-wave base station antennas.