Research Of Miniaturization Of Microwave Circuits Based On Slow-wave Structure

As the rapid development of modern communication technology,the miniaturization of devices becomes an important trend.In the RF front-end system,the miniaturized design of many microwave passive components,such as coupler and butler matrix,is especially important.Secondly,high-order harmonics could make microwave system performance greatly worse.Therefore,how to realize the miniaturization of system while high-order harmonics are restrained becomes a problem to be solved.For miniaturization,this thesis proposes a new slow-wave structure with a high slow-wave factor.Then,the proposed slow-wave structure is used to the design of miniaturized branch-line coupler and butler matrix.Meanwhile,the proposed slow-wave structure has a low-pass property,which can suppress high-order harmonic to some extent.As to high-order harmonic problem,with the use of defected ground structure(DGS)and LC resonator,a slow-wave structure with second and third harmonic suppression can be realized.The structure is validated by being used in rat-race coupler.The main contents and innovative points of this thesis are as follows:1.This thesis introduces the working principle of slow-wave structure,and analyzes its characteristics firstly.Then we give some matters needing attention during the design procedure of slow-wave structure.Finally,the calculation method of the characteristic impedance and phase of the slow-wave structure by the S parameter matrix is presented,and related formula is given too.2.The equivalent lumped circuits of meandered-line and interdigital structure are analyzed firstly.Then a solw-wave structure with high slow-wave factor is designed based on a two layers of PCB substrate.The results of electromagnetic simulation,equivalent circuit calculation and measurement results show good agreement.A miniaturized branch-line coupler and 4x4 Butler matrix are designed and fabricated based on the proposed slow-wave structure.The proposed miniaturized branch-line coupler only occupies an area of 14 x 20 mm2 and the proposed 4x4 Butler matrix has a size of 76 x 39 mm2.Their sizes are only 9%and 5.8%of the conventional ones,respectively.The tested results shows that they have good bandwith,insertion loss and phase charactristics.3.Two transmission zeros are introduced to the proposed high slow-wave factor slow-wave structure by adding a defected ground structure and a LC resonator.A new novel slow-wave structure with second and third harmonic suppression,good bandwidth and phase characteristics is designed.The new slow-wave structure is then applied to the design of rat-race coupler.The miniaturized rat-race coupler has a size of 43 x 7 m2,which is only 6%of the conventional one.The measured results show that both the second and third harmonic are suppressed below-25dB,4.In order to cut the cost and reduce design complexity,a new slow-wave structure with second and third harmonic suppression characteristic is realized on a single layer substrate.The new slow-wave structure is used to realize a miniaturized rat-race coupler,which only occupies an area of 44.5 x 15.5 mm2 and has an 86.11%size reduction compared with the conventional one.The measured results of the rat-race coupler show good return loss,insertion loss and phase characteristic.At the same time,both the second and third order harmonic are suppressed blow-25dB.