| With the diversification of application scenarios and fields,the complexity of application environment for the electronic systems,the requirements for volume,weight,reliability and energy consumption are becoming more and more stringent in addition to the basic performance and functional requirements.With the characteristics of miniaturization and high integration,the microsystem provides solutions to the above difficult problems,which is an important way to break through the bottleneck of current electronic system’s development.However,with the miniaturization and integration of the system,the distance between transmission lines decreases and the energy density of electromagnetic field increases dramatically,which will inevitably aggravate the signal crosstalk between different channels,and worsen the signal integrity of the whole system as well as the system performance.Especially in microwave frequency band and ultra-high speed circuit,the problem is more serious because of the increment of signal radiation.Therefore,it is of great significance to improve the isolation of microwave transmission line in the microsystem to ensure the system working properly of and to improve the performance of the system.On the other hand,the RF front-end occupies most of the area of the microsystem.Furthermore,the transmission line is the main part of this system.Thus,the research on the miniaturization of transmission line is the basis to realize the miniaturization of the whole electronic system.Focusing on the above points,aiming at developing the two key characteristics of high isolation and miniaturization of the microwave transmission line in microsystem,a new type of high isolation transmission line is proposed on the premise of integration,and its transmission characteristics and isolation characteristics are systematically studied.Then,the miniaturization method of the existing high isolation transmission structure,substrate integrated waveguide,is studied.The main research contents include:1.New high isolation transmission line.In the view of the limitations of the characteristic impedance for the existing microwave high isolation transmission line,a new type of high isolation microwave transmission,i.e.,the central symmetrical double-slotted line is proposed.In theory,the propagation properties of the transmission line dominant mode and the first high-order mode are analyzed by using the mode matching method of the full wave analysis.Based on conformal transformation,the corresponding analytical formula of characteristic impedance for the quasi-TEM mode is derived,and the average absolute error is less than 6%.Then,in order to ensure the compatibility between the transmission line and the existing microwave circuit,the transitions from the transmission line to the microstrip line and the parallel double wire are designed,and applied to the test of the transmission line in the form of back-to-back structures.The test results show that the return losses of all structures are less than 16 dB in the range of 1 to18 GHz.Furthermore,the coupling mechanism of the transmission line is analyzed quantitatively by establishing the coupling equivalent circuit of the central symmetrical double-slotted line.Then,the isolation performance of the transmission line is compared with that of the traditional microstrip line with isolation vias.The experimental results show that in the frequency range of 1-18 GHz,the near-end crosstalk of the two transmission lines is close,while the far-end crosstalk of the central symmetrical double-sloted line is at most 14 dB lower than that of the microstrip line with isolation vias.Finally,a T-type broadband power divider operated in the frequency from 7.5 GHz to 18GHz is designed exploiting the proposed transmission line.The performance within passband of return loss less than 18 dB,insertion loss less than 4 dB,amplitude difference less than 0.2 dB and phase imbalance less than 3 degrees are achieved.Finally,the simulation results show that the crosstalk between the power divider and the adjacent line is 11 dB lower than that of the microstrip power divider.2.Machine learning techneque based model for the propagation constants of center symmetric double-slotted line.A single frequency point propagation constants model based on Mondrian forest(MF)is proposed to solve the problem of high accuracy modeling of the existing propagation constants(attenuation constant,phase constant)of the central symmetric double-slotted line.Firstly,the original MF model is applied to the attenuation constant modeling of the central symmetrical double-slotted line.Through the cross validation,the modeling accuracy of support vector regression(SVR),a classical machine learning algorithm,is compared.The results show that the mean absolute error of MF model is 33%to 44%lower than that of SVR under different sample numbers and frequency points.Then,based on MF model,the optimal transmission point of each frequency point is obtained(the minimum attenuation constant).Similarly,when MF model is applied to phase constant modeling,it is found that the mean absolute error of MF model is 19%to 50%lower than that of SVR.Then,in the process of MF modeling,the online training method is introduced to improve the efficiency of local/global modeling,and also avoida the defect of blindly scanning parameters in the optimization problem.This method is applied to the study of the optimal transmission point.The results show that after introducing online training method,the model can find the optimal transmission point after 4 iterations,that is,16 training points,while the traditional parameter scanning method needs at least 27 training points.3.Space mapping based model for the attenuation constant of the centeral symmetrical double-slotted.In order to solve the problem that it is difficult to obtain the broadband accurate model of the attenuation constant of the centeral symmetrical double-slotted line,an accurate modeling method based on frequency dependent space mapping is proposed.Since the number of effective elements involved in the mapping matrix of the model is variable,the modeling time can be changed accordingly,and then the purpose of controlling the modeling time by changing the number of effective elements in the mapping matrix is realized,which improves the modeling efficiency.The model uses star distribution and quadratic polynomials to map physical parameters to rough model parameters,which makes the model universal.Finally,the model takes quartic polynomials as rough model,and obtains high accurate model through space mapping.The results show that when the number of effective elements changes from 20 to 10,the modeling time decreases from 53 minutes to 24 minutes,while the modeling error stays almost constant,and increases from 2.6%to 3.4%,.4.Composite right/left-handed transmission lines based substrate integrated waveguide(SIW).To solve the problem that the indactanceof the traditional composite right/left-handed SIW is low and can not be adjusted,a nonel miniaturized composite right/left-handed SIW with high left-handed inductance is proposed.The structure increases the effective left-handed inductance value through the additional inductance provided by the metal short wire between the surface rectangular slots,and further reduces the area of composite right/left-handed SIW.Moreover,it also increases the adjustable parameter dimension,and improves the design flexibility.Through the simulation of the dispersion,the left-handed inductance is extracted.The results show that the left-handed inductance is increased by at least 90%compared to that of a traditional composite right/left-handed SIW.An H-plane coupling filter centered at 2.9GHz is designed and implemented according to the resonance mechanism of this composite right/left-handed SIW.The results show that the insertion loss of this filter is smaller than 2.9 dB,the return loss is better than 19.3 dB,the Q_u reaches 70.1 and the area of the proposed structure is 57%smaller than that with a traditional composite right/left-handed SIW. |
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