| As a radio signal transceiver,the antenna has become an indispensable part of the wireless system.For decades,mutual coupling between antennas has been an important research content in the field of antennas and has attracted the attention of researchers.The impact of mutual coupling on the performance of various radars and communication systems cannot be underestimated.The specific manifestation is that:mutual coupling will deteriorate the impedance matching of the antenna,reduce the antenna gain and radiation efficiency,and cause distortion of the far-field radiation pattern,and so on.Therefore,it is of great significance and practical value to carry out the research on the mutual coupling of antennas and explore the methods of reducing coupling.Taking the microstrip antenna as an example,this paper conducts research from antenna decoupling methods.In this paper,the research of antenna decoupling method is mainly carried out,and the decoupling method based on band stop filter,field cancellation and blocking structure is proposed,and the modeling analysis and experimental verification research with microstrip antenna as the main antenna form are carried out.The main work and research results are as follows:(1)A slot-array defective ground structure(DGS is proposed,which can be used to reduce the mutual coupling of two-element antenna with single-linearly,dual-linearly circularly polarization.The slot-array DGS is etched surrounding each antenna element on the ground plane and parallel to the radiating edges of each antenna element.The decoupling mechanism is elucidated via an equivalent circuit model and the coupled current field analysis,which reveals slot-array DGS has the spatial band-stop characteristic and changes the direction of the partially coupled current,respectively.Both characteristics of the slot-array DGS contribute to mutual coupling reduction.The simulation results show that by adjusting the position and size of the slot-array DGS,the mutual coupling is reduced by more than 13 dB in the E-plane and H-plane arrays with the array element spacing of 0.5?0,0.46?0,0.42?0 and 0.8?0.Furthermore,a slot-array DGS that can simultaneously reduce the coupling of 0°/90°dual-polarization microstrip antennas is designed.The simulation data shows that the proposed slot-array DGS can increase the isolation of H-plane by 46 dB and the isolation of E-plane by 15 dB.In a circularly polarized antenna with a center-to-center spacing of 0.35?0,to reduce the size of the DGS,a barbell-array DGS with rings loaded at both ends of the slot-array DGS is proposed.The simulation and measurement results show that the isolation between elements has been improved by more than 50 dB.In addition,to reduce the increased back-lobe due to the leakage effect of DGS,an absorber based on high-loss electromagnetic materials was designed and processed.The absorber has an absorption of over 95%in the frequency range of 1.2-1.35 GHz.Applying this absorber to the above circularly polarized antenna,the back-lobe has been reduced by 12.5 dB and 16.1 dB on the Phi=0°and 90°planes,respectively.(2)A decoupling slot-strip array(DSSA)for decoupling 2×2 linearly polarized microstrip antenna and a split-ring array(SRA)for decoupling 2×2 circularly polarized microstrip antenna is proposed.The DSSA consists of a slot array etched on the ground plane and a strip array printed on the radiation patches plane.The band-stop effect of the slot array decreases the mutual coupling of both H-plane and D-plane.Meanwhile,the coupling current generated by the induced current on strip array can cancel the coupling current generated by excited current,which can significantly improve the E-plane isolation.The experimental results demonstrate that a considerable mutual coupling reduction of 33.2 dB for H-plane,28.5 dB for E-plane,and24.1 dB for D-plane is achieved.In addition,in the entire frequency band,the coupling between any two array elements is less than-30 dB.The SRA is etched from the ground plane which is composed of twelve split-rings.Each element is surrounded by four etched split-rings.In addition to the unique band-stop effect of DGS,SRA can also change the amplitude and phase of the original coupling field,and make the polarization of the adjusted coupling field mismatch with the receiving field.The simulated and experimented results show that the coupling between horizontal/diagonal/vertical elements is reduced by 29.6 dB,5.6 dB and 23.6 dB respectively.In the entire working frequency band,the coupling between adjacent elements is less than-30 dB,and the coupling between diagonal antennas is less than-28 dB.(3)A combined decoupling structure that can reduce the E-plane coupling of one-dimensional eight-element array is proposed.The decoupling structure includes the loaded array-antenna decoupling surface(ADS),cutting off the substrate and ground plane(CSG)and the loaded reflective ground(RG).In the first place,through the equivalent circuit model and vector analysis method,three models of isolated antenna element,passive antenna array and active phased array are discussed.The influence of mutual coupling on the active voltage standing wave ratio of the active phased array antenna under various scanning angles is studied.Furthermore,the difference between the coupling mechanism of the microstrip antenna and the dipole antenna on the H-plane and the E-plane is analyzed through simulation and theoretical derivation.By adjusting the position and size of the ADS,it can generate a reflection field that can be offset with the coupling field of adjacent elements.Meanwhile,the designed CSG can cut off the propagation of surface waves between non-adjacent elements.Therefore,the combined ADS-CSG can reduce the coupling between adjacent and non-adjacent elements.In addition,the loaded RG can facilitate the installation of the antenna and the carrier.The Simulated and measured results show that in the 1.2-1.3 GHz band,the coupling between adjacent elements is reduced by more than 10 dB,the coupling between non-adjacent elements is below-30 dB.The active VSWR at each port of the antenna is less than 2.0 in the range of±60°scanning angle in the 1.23-1.3 GHz frequency band.(4)A two-dimensional linearly polarized antenna decoupling method based on ADS-Decoupling Probe(ADS-DP)and double-layer ADS is proposed.Based on ADS-DP,an E-plane and a H-plane compact and high isolation antenna are designed respectively.The decoupling mechanism is to superimpose the extra reflected wave generated by DP and the reflected wave generated by ADS to further increase the amplitude of the reflected wave to cancel the strong coupling wave generated by the compact environment.The simulated results show that the proposed decoupling structure can reduce E-plane coupling in the frequency band(1.205-1.275GHz)and H-plane coupling in the frequency band(1.18-1.32 GHz)by more than 10 dB when the center-to-center spacing is 0.3?0.Furthermore,a 2×2 single-linearly polarized high isolation antenna is designed based on the ADS-DP.The decoupling mechanism is to cancel the E-plane coupled wave and partially the H-plane coupled wave with ADS,and then to cancel the remaining H-plane coupled wave with DP.The simulated results show that the E-plane coupling has a reduction of more than 10 dB in the 1.22-1.3 GHz band,and the H-plane coupling has a reduction of more than 10 dB in the 1.2-1.29 GHz band.Finally,a 2×2 dual-linearly polarized high isolation antenna is designed based on the double-layer ADS.The decoupling structure includes a primary ADS and a secondary ADS.The primary ADS can cancel the E-plane coupling wave and partially H-plane coupling wave,and the secondary ADS can cancel the remaining H-plane coupling wave.The experimental results show that E-plane coupling can be reduced by more than 10 dB in the 1.2-1.3 GHz band,and H-plane coupling can be reduced by more than 10 dB in the 1.2-1.26 GHz range.In addition,with the loaded decoupling structures,the antenna has a stable far-field radiation pattern,and the antenna gain is increased by about0.5-1.0 dB... |
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