Research On Radio Frequency Front-End Function Fusion And Electromagnetic Compatibility

Radio frequency(RF)front-end is an important part of the fifth generation mobile communication(5G)and modern radar detection system.In order to solve the problems of many devices,large size and high loss in the traditional communication system,the key devices of RF front-end are developing rapidly in the direction of functional integration.In addition,improving the electromagnetic compatibility(EMC)becomes the cornerstone of optimizing system and ensuring system stability.Therefore,this paper focuses on the design of RF front-end functional fusion devices,and explores the EMC problems such as system stealth and multi-input multi-output(MIMO)antenna decoupling.The specific work includes:(1)Two circularly polarized(CP)receiving antennas are designed for multi-system compatible satellite navigation system.A multi-mode integrated wideband quadrifilar helix antenna(QHA)is proposed.The distance between the two resonance points can be changed directly by changing the position of the slots on the radiation arm without introducing additional branches or parasitic radiation arms.Finally,design a QHA with wideband,wide half power beam width(HPBW),adjustable resonant frequency,and circular polarization performance;A low profile microstrip CP satellite antenna is designed,and a wideband feeding network is designed by using rotating sequence feeding technology to improve the impedance bandwidth and axial ratio bandwidth of antenna.In addition,a new type of feeding strip is introduced to excite the annular patch of the antenna,so that the electric field distribution of the radiation patch is more uniform and the radiation efficiency is higher.(2)Loading new electromagnetic materials has become an alternative direction for antennas to achieve function fusion characteristics.By introducing metasurface on the basis of the microstrip slot differential antenna,an additional and tunable resonant point is obtained,and the operating bandwidth of the antenna is thus increased.By introducing three-line coupled lines,the antenna also has filtering effect;We complement the traditional Pancharatnam-Berry(PB)phase principle,design a focused metasurface with arbitrary focus,and put forward the constraints of the minimum period of the metasurface.Placing the circularly polarized feeding source at the oblique focus of the metasurface,the structure of feed source will not interfere with the reflected electromagnetic waves,and the gain of feeding source can be greatly increased;The phase distribution information derived from the generalized snell reflection law is added into that of the traditional axicon.Based on the new phase distribution,a planar axicon is designed using the PB phase unit to replace the traditional three-dimensional axicon and generate a diffraction-free beam that can tilt to any direction.(3)For spatial filtering,a metasurface frequency selective surface(FSS),radome and rasorber are designed,respectively.Using metasurface unit-cell,the unit size of each FSS is less than one tenth of the working wavelength,and the angular stability under oblique incidence can be thus improved.The equivalent circuit theory proves that two transmission zeros in the FSS stop band can be adjusted independently;the graphene-based radome is designed using the dynamically adjustable characteristic of graphene's complex conductivity.Reasonably control the chemical potential of different columns in the radome,and the dipole antenna placed in the radome can obtain directional radiation pattern with tunable characteristic;Based on the odd-and even-mode equivalent circuit,a wideband absorber is designed.Then a notch resonator with high quality factor(Q)and a FSS working at the same frequency are introduced into the absorber,which makes the original absorber have the absorptive-transitive-absorptive function.The absorber is evolved into a rasorber.(4)The wideband MIMO antenna and decoupling technology are studied.Firstly,a multi-mode resonator is designed,which consists of a multi-mode slot resonator and a embedded stepped impedance resonator(ESIR).By using coplanar waveguide(CPW)feeding method,a wideband single-layer slot MIMO antenna unit based on multimode resonator is designed.The odd mode resonance of multi-mode slot resonator is close to the lower cut-off frequency,the resonance caused by ESIR forms a higher cut-off frequency.Therefore,the antenna elements can achieve filtering feature without using any extra filtering structure.Then,curved ground,neutralization lines and meander-line resonators are introduced to suppress the electromagnetic coupling between MIMO antenna elements.Therefore,wideband decoupling feature could be achieved.