Research And Degin Of Composite Right And Left Handed Transmission Line Bandpass Filter

The filter is an important component of the RF circuit,and it is a key part of the communication system.The Composite Right and Left Handed Transmission Line(CRLH TL)has the peculiar characteristics:the direction of the phase velocity is opposite to the group velocity and the scalar is equal.Therefore,the filter based on CRLH TL has the advantage of small size and novel structure,and gradually becomes a research hotspot in the microwave circuit field.This thesis analyzes and designs the filter based on the CRLH TL,and realizes its miniaturization.This thesis focuses on the implementation of CRLH TL and its influence on filter performance.The main work is as follows:1.The filter is Miniaturized based on the non-resonant CRLH TL.The two filters were designed by using a planar interdigitated structure.One of the filters added trapezoid branch to the cross finger structure.By optimizing the length and width of the cross finger and trapezoid branches,the distribution structure of the transmission line was changed,and the left and right hand characteristics of the filter at a specific frequency were realized.Compared with the traditional filter,the designed filter has low resonant frequency and a compact form factor of0.11?_g×0.15?_g.The proposed filter was fabricated and tested found to have a small insertion loss of 1.59dB.Another filter consists of two SIR resonators using symmetrical intersecting interdigital structures,and fan-branches were added to the ends.The analysis of equivalent circuit and the optimization of dispersion curve offan-shaped branch and interdigitated structure are carried out so as to achieve the left and right hand characteristics in the passband.This filter not only has a high selectivity,but also has a compact structure achieving to0.37?_g×0.26?_g.2.The filter is miniaturized based on the resonant CRLH TL.By adding different Complimentary Split-ring Resonator(CSRR)on the upper and lower surfaces of the substrate integrated waveguide structure,the left and right hand characteristics of the substrate integrated waveguide structure were realized,and the out-of-band suppression of the filter was enhanced.The test results show that the measurement results were consistent with the simulation results,and the 20dB out of band rejection reaches 14GHz.After adding two sets of etching slots to the filter,the 20 dB out-of-band suppression was increased to21 GHz.Then,the two sets of etching grooves on the feed port of the filter increase the range of 20dB out of band to 21GHz under the condition of passband and performance parameter unchanged.This filter used the SIW structure to limit the propagation of electromagnetic waves in a certain spatial range;and the center frequency was effectively reduced by complementary open resonator.The designed filter is not only compact achieving to0.24?_g×0.61?_g,but also has a wide out-of-band rejection and high selectivity.The two types of filters designed have the advantages of high selectivity and miniaturization.The above filters were tested,which were consistent with the simulation results,which meets the requirements of miniaturization in communication system,and has certain engineering practical significance.