Miniaturization And Computer-Aided Tuning Of Butler Matrix

Butler matrix is a common beamforming passive device,which is mainly used in multi-beam antenna and multi-port power amplifier applications.It has the characteristics of simple design,low cost,high flexibility,lossless and good amplitude/phase consistency.With the development of communication technology,the requirements of beamforming devices are becoming higher and higher,and the miniaturization,reconfigurable,wideband,high balance and low insertion loss of Butler matrix are also put forward.However,due to the limitation of Butler's own structure,the number of couplings in Butler will increase rapidly and the structure will become more complex as the number of ports increases.This poses a serious challenge to the performance of the Butler matrix.Based on the requirements of Butler matrix for miniaturization,wideband and high balance,this paper studies and analyzes miniaturization and computer-aided tuning of Butler matrix.Firstly,the miniaturization design of Butler matrix is studied.The miniaturization of the Butler matrix mainly depends on the miniaturization of its internal directional coupler.In this paper,a general model for loaded stub branch-line coupler is proposed,which treats the original transmission line as a three-port network and equivalent transformation of the transmission line with loaded stubs.The size of the coupler is effectively reduced by the equivalence of branch lines and main lines of the coupler,furthermore,a broadband coupler and an electronic tuning of power ratio coupler is miniaturized.The crossovers in Butler matrices are eliminated by flexible layout,a miniaturized 8 × 8 Butler matrix and a broadband miniaturized 4 × 4 Butler matrix is designed and fabricated by using the miniaturized couplers and schiffman phase shifter.Next,a tuning method of the imbalance of Butler matrix is proposed.The imbalance of Butler matrix includes amplitude imbalance and phase imbalance,which refers to the amplitude error and phase error of each output signal.The current industry solution is to improve the design standard of the Butler matrix and improve the machining accuracy to reduce the imbalance,which can only be completed before the production of the Butler matrix.There are also ways to compensate for the phase/amplitude imbalance by adding compensation devices,namely attenuators and phase shifters.In this paper,it is proposed for the first time to compensate the imbalance of Butler matrix by fine-tuning the Butler matrix itself without adding external devices.This paper proposes a derivation method for the transfer matrix of Butler matrix,through which imbalance variables can be introduced into the transfer matrix,so as to obtain the imbalance of each tuning structures matrix only by the external S parameter of Butler matrix.In addition,phase and amplitude compensation structures are considered in the design,and the Butler matrix can be simply tuned after the imbalance variables is extracted.In the research process,a computer-aided tuning method is realized by Matlab,and the two fabricated Butler matrices are tested.The test results verified the theory proposed in this paper.