Modelling And Verifications Of Couplings Existed In Array Antennas

With the rapid of radiofrequency and baseband integrated circuits,the development of multipleinput multiple-output(MIMO)and phased array antenna systems is integration and miniaturization.Under the condition of maintaining the original equivalent isotropic radiated power(EIRP),the miniaturization of array antenna systems will inevitably lead to couplings between array elements.For a dual-polarized array element,it will also result in polarization couplings on the element.Couplings between elements and polarization couplings will cause interference in the array antenna system and deteriorate system performance.Therefore,solving couplings between elements and polarization couplings effectively is vital for the renovation of array antenna technology.In this paper,couplings between elements and polarization couplings are both modelled.The models of couplings between elements are verified by microwave orientations and beam syntheses.The model of polarization coupling is verified by a polarization coupling suppression method.Firstly,a field-circuit hybrid equivalent circuit model of coupled arrays and a phase-only microwave orientation approach are proposed.A forward equation for microwave orientation is established and the complex back propagation algorithm is used to solve the equation.Different from conventional circuit equivalence,the proposed hybrid circuit equivalence integrates the modelling of incident waves,coupled elements and radiofrequency receiving channels.Simulations and experiments based on a strongly coupled array and a visualized microwave orientation system are implemented.The orientation results verify the effectiveness and feasibility of the proposed hybrid equivalent circuit and the microwave orientation approach.Secondly,the hybrid equivalent circuit model of coupled arrays is further improved and the equivalent models of the receiving and transmitting coupled arrays are developed.The deterministic relationship among incident waves,coupling elements and radiofrequency channels and the relationship among transmitting waves,coupling elements and radiofrequency channels are established.Based on these relations,the equation for solving mutual couplings and generalized array factors for beam syntheses are derived.Generalized array factors,instead of the conventional array factor derived under the assumption of a linear array,can realize beam syntheses of strongly or tightly coupled arrays.Simulations and experiments based on a 1-D inhomogeneous tightly coupled array and a 2-D tightly coupled array verify the effectiveness and accuracy of the equivalent circuit models and generalized array factors.Finally,an electric field analysis model of polarization couplings is proposed and the polarization coupling suppression theory based on mirrored subarrays is elaborated.The theory can be used to enhance the cross-polarization discrimination of a dual linear polarization array antenna.By dividing an in-phase feed array into two or four identical subarrays and properly mirroring them with a differential feeding,polarization couplings can be remarkably suppressed,regardless of the scale and the cross-polarization discrimination of the original array.The proposed theory can also be utilized to improve the axial ratio of circular polarization array antenna,and it is a practical and robust solution to polarization coupling problems of low profile and compact dual linear polarization and circular polarization arrays.Simulations and experiments verify the effectiveness of the proposed model and the suppression theory.