Investigation On Novel Hybrid Couplers

The rapid development of microwave communication technologies put forward new requirements on the design of high-performance couplers in front-end systems.Broad band and reconfigurablility are the two most important features.Broadband couplers can meet the requirements of wideband and multi-band communication while reconfigurable couplers with tunable output power division ratio,output phase difference,and central frequency can meet the applications in more scenes.Meanwhile,the high insertion loss and large circuit size introduced by phase shifters can be avoided.Based on the theories of even-/odd-mode analysis,image impedance and transfer function of a two-port network,and equivalent models of transmission line discontinuities,this dissertation studies the design of broadband couplers and a reconfigurable coupler with multiple degrees of tunabilies.In the design of broadband couplers,the even-/odd-mode analysis theory is applied.The ABCD matrix of the stepped impedance transmission lines and coupled lines is calculated by cascading the ABCD matrix of each transmission line.Then,the even-/odd-mode scattering parameters of the half circuits can be obtained.Therefore,the scattering parameters of the entire coupler can be calculated.Finally,the characteristic impedances and the electrical lengths of the transmission lines and coupled lines of the coupler are obtained by numerical optimization.The broadband couplers are realized in the two forms of stripline and fully planar microstrip line.Good agreement is achieved between the full-wave simulated and measured results.It indicats that the proposed coupler has excellent port matching,isolation,amplitude and phase balances between output ports in about 63% and 50% fractional bandwidths.In the design of reconfigurable coupler,the analytical relationships are theoretically deduced firstly for a basic topology of four-port network.Then,a capacitance-loaded transmission line structure is used as an example,with rigorous formulas concerning the capacitance and adjustable parameters also derived when the characteristic impedances and the electrical lengths of transmission lines are given.There are three kinds of reconfigurations: 1)the output power division ratio;2)the output phase difference;and 3)the central frequency.The full-wave simulated results show that the output phase difference can be electrically adjusted within the range of 40°-140° with equal power division,which validates the the proposed method to some extent.