Research On Integrated Design Method Of Filter And Antenna

In muliti-band base-station antenna system and large scale active MIMO antenna system,dozens or even hundreds of RF transceivers(RF channels)and antenna units have to be integrated in limited space.Large numbers of active and passive RF devices are used,such as filters and antennas.On the one hand,the insetion loss and interconnection transmission loss caused by the filter circuits seriously affect the overall efficiency of the RF front-end circuit.On the other hand,more and more antenna sub-arrays are installed in limited space which definetly increases the mutual coupling between them.In view of above problems,this paper presents the theory and method of some filter and antenna fusion designs,and designed a series of filtering antennas which featured high in-band radiation efficieny and out-of-band radiation suppression level.Then based on their filtering radiation characteristic,the mutual coupling between different sub-arrays can be reduced and thus expand the application of filtering antenna in multi-band base-staion antenna array designs.In addition,two multi-port multi-function RF devices with filter and antenna oparations are also designed.Above design methods and their extension can effectively improve the integration of large scale MIMO array and reduce power consumption.Specially,the main research contents are as follows:(1)According to different base-station application scenarios,the fusion designs of singlepolarization,double-polarization,single-frequency and dual-frequency filtering antennas are studied,and a series of filtering antennas based on implanted filtering circuits are designed.That is,regard the antenna radiator as an out-put port,then insert non-radiative resonance unit into the antenna feed network.Draw the equivalent circuit and extract the transmission function of the two-port network based on dual-port network analysis and transmission line theory.Calculate the zeros of the transmission function and control it by constructing specific circuit topology.Adjust two zeros to the lower and upper band edge frequencies to obtain bandpass filter response.Since the signal cannot be transmitted from the input port to the radiator at these two specific frequencies,antenna with good out-of-band radiation suppression is realized.Based on above method,a low-profile omnidirectional electric dipole filtering antenna,a miniaturized dual-ban filtering antenna for LTE MIMO system and a dual-polarized filter ME dipole antenna are designed.(2)A fusion design method of single and dual-band filtering antenna without any filter circuit is proposed.Different from traditional filtering antenna designs,this design does not need any parasitic non-radiative resonance unit or filter circuit.By only using a simply openend transmission line,filtering radiation response is integrated into the antenna.As a result,the filtering antennas has high in-band efficiency level and high out-of –band radiation suppression level.Based on this principle,single-and dual-band filtering patch arrays are designed,and the measurement results agree well with the simulation ones.(3)The method of using filtering antenna to reduce the mutual coupling between multiband base-station antenna arrays is proposed.And a novel dual-band base station antenna array using filtering antenna elements for size miniaturization is designed for the first time.Two filtering antenna elements operating at 1710-1880 MHz and 1920-2170 MHz are developed and then employed as basic elements to form two sub-arrays.Since the elements feature high inband radiation efficiency and out-of-band radiation suppression level,high isolation between different sub-arrays can be obtained even without using diplexers.The experimental results show that,compared to the dual-band array using traditional antenna elements,the port-to-port isolation of the array using filtering antenna elements is increased by 5-7 dB with the same center-to-center element spacing.(4)In the research of integrated multi-function RF devices,two multi-port devices with filter and antenna operations are proposed.Firstly,a dual-port device with a novel feed scheme is designed.The feed structure not only behaves as second-order bandpass filter itself,but also functions as the feed network to efficiently excite a dual-polarized ME-dipole antenna.Besides,a self-coupled hook-shaped stub is developed,ensuring high frequency selectivity for both the filter and dial-polarized antenna functions.Secondly,a six-port device is designed.Four ports are the input ports of a 4-element MIMO array operating at 4.5 GHz.It realizes 27.3 % impedance bandwidth and ±45° beam scanning capacity.The other two ports are the input and output ports of the filter channel.15.6 % impedance bandwidth and bandpass filter response are obtained.