Research On The Key Technologies Of Microwave Passive Circuits In Communication Systems

The development of communication technology has set higher requirement for the performance of microwave passive circuit and systems.In the meantime,microwave passive circuits,as one of the key components,still face a lot of difficulties and challenges in terms of improving working performance.Therefore,the research of this dissertation focuses on microwave filtering passive circuits.Main specifications of microwave filtering passive circuits include in-band insertion loss,in-band return loss,bandwidth and so forth,and the selectivity of filters is determined by the transition band gradient and out-of-band rejection.Therefore,this dissertation focuses on the research of rectangle coefficient of the filter,the rejection band,and a variety of new filters have been proposed.The main work and innovation are given as follows:1.In order to increase the out-of-band rejection bandwidth of the filter,the paper uses the advantage that the fan-shaped capacitor has a high self-resonant frequency and does not require subsequent soldering,and combines it with a short-circuit parallel coupled line to develop three low-pass filters.The out-of-band rejection is higher than25 dB and the rejection is 45 dB in the 5 GHz to 10 GHz band.In the transition zone region,the slope of S₂₁ is-47 dB/GHz.Based on this,a parallel-coupled fan-shaped structure filter structure is proposed,that is,the fan-shaped capacitor is loaded on both ends of the parallel coupled line.The out-of-band rejection of the filter exceeds 30 dB,and the rejection at 3f₀,4f₀,and 5f₀ is higher than 40 dB,where the degree of rejection is higher than 60 dB at 4f₀.Then,based on the connection of the ends of the quarter-wavelength resonator and the fan-shaped capacitor,a sector-loaded quarter-wavelength resonator structure is proposed,and the third harmonic suppression degree exceeds 20 dB.The periodic capacitance is introduced at the feed of the quarter-wave filter,which suppresses the second and third harmonic parasitic passbands of the filter.The out-of-band rejection is higher than 30 dB.2.In order to increase the out-of-band suppression depth of the filter,the paper analyzes the electromagnetic band gap characteristics of the dumbbell-type ground fault structure,and gives its lumped circuit equivalent model and the corresponding parameter extraction method.In this paper,the compound right and left hand transmission line is combined with the structure of the defect,and a six-sided mushroom-type and interdigital capacitive filter based on the defect structure is proposed.The first additional transmission zero point for the six-sided mushroom filter is at 2.2 GHz and the rejection exceeds 40 dB.The second additional transmission zero is at 5.9 GHz and the rejection exceeds 50 dB.The frequency of the three transmission zeros outside the band-pass capacitive filter is 4.3 GHz,5.9 GHz and 7.3 GHz,and the rejection is greater than 35 dB.Using the parallel resonance characteristics of the defective structure,the structure of the Hilbert defect is improved,and a quarter-mode integrated waveguide filter is proposed.The filter is generated at the right-hand transition band 4.7 GHz.A transmission zero with a rejection above 28 dB.3.In order to improve the ability of the filter to suppress the interference signal,the resonance characteristics of the traditional ladder impedance and the quarter-wave ladder impedance resonator are analyzed in this thesis.A quarter-wave ladder impedance resonance characteristic is used to develop an interdigital filter.This structure moves the filter's first spurious passband to frequencies above 10 GHz,and the filter out-of-band rejection of 4 GHz to 10 GHz exceeds 30 dB.Then,based on the analysis of the interdigital capacitance-grounded inductive compound right-handed resonator filter,the terminal open-circuited branch was introduced.A transmission zero point with a rejection of over 20 dB was generated at 4.4 GHz in the passband,and the notch characteristic was obtained.With this structure,the frequency component of the in-band interference signal can be suppressed.Based on the analysis of the transmission characteristics of the zero-feed structure and its zero generation mechanism,this paper presents a T-type dual-mode filter.After adopting the zero-degree feed structure,the filter additionally generated three transmission zero points at the 1.5 GHz,2.5 GHz,and3.2 GHz with the rejection levels exceeding 50 dB,40 dB,and 40 dB,respectively.4.In order to increase the rectangular coefficient of the filter,the characteristics of the CQ coupling structure are analyzed.Based on this,a filter based on a rectangular composite left-handed resonator is proposed.With the CQ structure,two additional transmission zeros are added on both sides of the passband.The left zero has a frequency of 1.5 GHz and a degree of rejection of 40 dB.The right zero frequency is 4.3GHz and the rejection is 24 dB.Then based on the CQ structure,the characteristics of the TCQ structure are analyzed,and a TCQ structure filter based on a split resonant ring is developed.The filter uses the TCQ structure,and the transmission bands at the 0.80GHz,0.82 GHz,0.88 GHz,and 0.90 GHz transition bands exceed 70 dB,35 dB,50 dB,and 70 dB,respectively.Source and load couplings are applied to the input and output of the quarter-wave filter,and the out-of-band suppression of the four transmission zeros on both sides of the passband is higher than 40 dB,thereby increasing the slope of the transition band.