大学物理大学-射频电路第13讲射频滤波器(II)

ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology带通滤波器高通滤波器带阻滤波器第13讲内容ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology耦合谐振器带通滤波器的设计过程由滤波器的衰减特性经过频率变换，定出相应的低通原型的衰减特性，选定响应函数，综合各元件的归一化值；根据结构实现的方便性，把低通原型转化为变形低通原型中的一种，并决定其电路参数；把变形低通原型中的电抗元件变换成带通滤波器中的串联谐振电路或并联谐振电路，决定其电抗或电纳斜率参数；用射频结构具体实现上述电路的变换器和支路元件，决定结构的具体形状和尺寸。13.1带通滤波器ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology半波长传输线段可等效为串联谐振电路。半波长传输线段也可等效为并联谐振电路。00(1)ggXZ001220000ggddZddX20002gZ20000220gYddB串/并联谐振器的实现方案0Z/2ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology1/4波长短路线、1/2波长开路线可等效为并联谐振电路。1/4波长开路线、1/2波长短路线可等效为串联谐振电路。0ZlinZResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology13.1.1电容间隙耦合带通滤波器ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnologyResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology从J变换器确定的间隙电容导纳为谐振器的电长度为两电容间隙之间传输线的长度为201,01,01,1YJYJYBkkkkkk1,,11,,100221arctanarctan2kkkkkkkkkBBYY20gkklResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology【例13-1】设计一个切比雪夫电容间隙耦合带状线滤波器，在通带f1=3.0GHz到f2=3.2GHz内有0.5dB的波纹，在带外fs1=2.5GHz和fs2=3.5GHz有30dB以上的衰减。解：1.确定切比雪夫低通原型选用确定n，可得n=3。归一化元件值为GHzfff10.32100645.0012fffW1010116.7sssffWff2020213.7sssffWff2s0967.1,5963.1,0000.123140gggggResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology2．确定J变换器的导纳3．确定间隙容纳及两间隙间带状线长度01340001231200120.25220.07692JJWYYggJJWYYgg269.012001001034001YJYJYBYB077.012012012023012YJYJYBYBResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology0112130022116142arctanarctan.BBYY231220022117122arctanarctan.BBYY0001310229.684.3024.602ccmfllcmlcmResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology4.确定电容间隙如果电容间隙很小，间隙电容C可用平板电容公式来确定，即（微微法）于是，间隙宽度式中，利用了，A为导带截面积。如果电容间隙较大，就不能看成简单串联电容，而是一个型网络，这时，对上述过程需要进行修正。1,225.0kkrAC121,01,10225.0225.0kkrrkkBACACBkk01,ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology【例13-2】设计一3节微带间隙耦合带通滤波器。相对带宽W=0.028，中心频率f0=6GHz，带内纹波为0.1dB。解：设计过程与上题完全一样。选用切比雪夫低通原型，元件值为1474.12,0316.131,0.140ggggg2065.00316.10.1028.0204,3001YJYJ0404.01474.10316.112028.003,202,1YJYJResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology耦合电容电纳半波长谐振器的电长度耦合电容2157.0)2065.0(12065.0204,3001YBYB0405.0)0404.0(10404.0203,202,1YBYB131202157200405289762arctan(.)arctan(.).21200405200405306082arctan(.)arctan(.).pFCCpFCCgggg021483.011443.03,22,14,31,0ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology用介电常数为10.8、厚度为1.27mm的介质基片来实现。半波长谐振器的宽度为W＝1.1mm，特性阻抗50。还要根据耦合电容来决定间隙的宽度，传统的公式误差较大。可采用前面章节介绍的EM仿真方法来求间隙的宽度。ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology微带间隙特性GHzYY6)(2211GHzYY6)(2112)(pFCg)(pFCp8.10rmmh27.1mmW1.1()smm0.05j0.0045977-j0.0044340.117620.004340.1j0.0039240-j0.0036040.095600.008490.2j0.0032933-j0.00269080.071380.015980.5j0.0026847-j0.00142290.037440.033540.8j0.0025310-j0.00081100.021510.045621.0j0.0024953-j0.00055580.014740.051451.5j0.0024808-j0.00018760.004980.06083ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology然后根据上面给出的滤波器对间隙电容值的要求，利用插值来确定间隙宽度sj,j+1也可以利用插值得到与间隙相关的并联电容值在f0=6GHz时微带的波导波长为，因此，并联电容对应的开路线的有效长度为mmss057.04,31,0mmss801.03,22,1pFCCpFCCpppp0457.00049.03,22,14,31,0，mmg27.180mmllee0269.0227.18)501(100049.010621292311mmllee2505.0227.18)501(100457.010621291321212212eeelllResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology最终，谐振器的实际长度为mmll148.85.25.00269.08976.2227.1831mml399.82505.02505.00608.3227.182ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnologyMicrowaveOffice仿真5.566.5Frequency(GHz)Graph1-50-40-30-20-1006GHz-0.9125dB6.084GHz-1.305dB5.916GHz-1.447dBDB(|S(1,1)|)Schematic2DB(|S(2,1)|)Schematic2ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology两端开路的1/4波长平行耦合线可以等效为J变换器。/220000[1()]eZZJZJZ20000[1()]oZZJZJZ等效条件13.1.2平行耦合线谐振器滤波器ResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnologyResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology2,1,10,10002,1,10,10001()11()1jjjjejjjjjjojjJJZYYYJJZYYYResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology【例13-3】设计一个五阶的微带带通滤波器，相对带宽W=0.15，中心频率f0=10GHZ，带内波纹是0.1dB，。解：采用Chebyshev型，滤波器低通原型参数为050Z061524311.14681.37121.9750gggggggResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnology根据奇偶模阻抗得出微带耦合线的实际尺寸。假定微带基片的相对介电常数为10.2，厚度为0.635mm。于是，每节1/4波长耦合线的实际长度为其中是微带开路端的等效长度。jrojrejljl210)()(4jlResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofTechnologyResearchInstituteofAntennasRFTechniquesSouthChinaUniversityofT