《现代微波电路和器件设计》课件16、交叉耦合滤波器设计

1、苏 涛西安电子科技大学，电子工程学院2008年春现代微波电路和器件设计16、交叉耦合滤波器设计Rapid Elliptic-Filter Design, 2002 Empowering Profitability, Ansoft Corp.补充部分内容和讨论。关注设计策略的过程、特点和问题。Specifications to be metfo = 400MHzBW* = 15MHzRipple = 0.08dBOut of band rejection 20dB* denotes ripple bandwidthDesign a 3D RF elliptic band-pass filter

2、completely in softwareObtain circuit representation using known filter theory.Link design parameters of 3D prototype filter to circuit parametersusing calibration projects representing only parts of 3D filter.Simulate complete 3D filter in HFSSuntil specs are met.Perform curve fitting in Ansoft Desi

3、gner to obtaincorrections needed.Prototype Low-Pass Elliptic Filter ResponseFilter theory from low pass to bandpassLow-pass to bandpassFo scaled to 400MHzBW adjusted to 15MHzBandpass filter responseEnhanced Circuit Model Linear frequency dependence introduced in impedance inverters.New term small co

4、mpared to constant term, but necessary for design in software.What filter theory gives usf1 = 400 MHzresonant freq. resonators 1&4f2 = 400 MHzresonant freq. resonators 2&3K12= 0.02894coupling constant 1-2 and 3-4K23= 0.02863coupling constant 2-3K14=-0.00942coupling constant 1-4QL= 29.69loaded Q, cou

5、pling to source & loadd12= 0d23= 0 frequency-INdependent couplingd14= 0 (for now) 准椭圆函数和General Chebyshev函数综合 椭圆函数同样可以得到具有带外有限传输零点的响应，而且带内和带外都具有等波纹性质，但是左右对称。对于耦合谐振腔滤波器形式，可否采用椭圆函数综合？与General Chebyshev函数综合有何异同点？ Ansoft例子中直流响应非零的响应能够实现吗？合理吗？如何得到的耦合系数值？3阶椭圆函数综合，经过带通变换后的形式为4腔多耦合带通滤波器的增益函数为 逼近函数，3阶椭圆函数的增益

6、函数分子和分母相差2阶 实现结构，4腔交叉耦合带通滤波器增益函数分子分母相差4阶，做修正 其中， 是3阶准椭圆函数准椭圆函数的构造 显然的，修正后的准椭圆函数带内没有等波纹特性，需要做出等波纹修正，此处我们采用数值修正的方法。 取 导数为零的点，得到（1，1）内各点的最大 ，有注：此处得到的是近似的等波纹特性。aee=a3阶椭圆函数（虚线）与准椭圆函数（实线）带内曲线 3阶椭圆函数与准椭圆函数增益曲线 4阶椭圆函数修正得到准椭圆函数 4阶椭圆函数通过舍去带外零点修正得到准椭圆函数。此时带内最大值和最小值仍然为1和1，无需修正（但是，并不是每次波动都达到最大或最小值）。 4阶椭圆函数与准椭圆函数

7、增益曲线 4阶椭圆函数（虚线）与准椭圆函数（实线）带内曲线 此时，低通原型直流增益非零，与Ansoft例子雷同。CAD原理电路设计Basic resonatorCavity 2020200 mmMetal walls, air insideMetal cylinder R=5 mmCylinder stands on cavity floor, does not touch ceiling.Cylinder length is varied to tune the resonance.Irises in walls, not shown here, will provide coupling

8、to other resonators.Elliptic Filter, basic design L1L2D1423170-175mm170-175mmDisk distance0.6-0.7mmElliptic filter, basic design IIAll iris heights 100mmW12 = W34W14W12W231423Calibration Projects6 variables in 3D design.3 calibration projects used to relate geometry to circuit parameters.确定2腔和3腔之间的耦

9、合孔宽度和腔内导体棒高度确定1腔和4腔之间的耦合窗口宽度W14，耦合圆盘的直径D和腔内导体的高度L1修正腔1和腔2之间耦合窗口的大小 123Ansoft 滤波器设计实例模型参数化输出变量的设定参数扫描和优化11、建立 41*41*200mm 的滤波器腔体；2、中间十字型隔板，厚度1mm；3、耦合窗口大小立方体，高100mm，宽W23，厚度穿过隔板；4、隔板减去耦合窗口大小立方体；5、腔体减去隔板。 建立一个滤波器腔体的“内胆”（Ansoft默认外界面为PEC） 建立长度为L2的金属棒在2腔和3腔的中心建立长度为L2的金属棒 设定工程类型、解和输出变量1、设定工程类型为Eigen Mode；2、

10、设定解3、设定输出变量f01和f02；4、设定输出变量f0和K23。 参数扫描1、设定参数 W23 扫描，8mm2mm14mm；2、设定参数 L2 扫描，170mm5mm190mm。 参数优化1、设定优化代价函数cost；2、设定优化。PML的设定有载Q值的计算2 PML的设置 有载 Q 值计算3 严格意义上讲，这两腔结构不同，不能应用对称结构的公式；但是，用该公式修正，比原有尺寸要好；AllFirst filter eigen frequenciesResults from calibration projects used to model complete filter.First it

11、eration not centered at 400MHz. Needs to be shiftedCorrected first filterL12 and L23 adjusted to center response on 400MHz.Asymmetry in shoulder height due to frequency dependent coupling factorsCorrected first filterF0 and BW very closeDo NOT see 3 equal ripples of 0.08dB!Curve fittingCurve fitting

12、 resultsOriginal targetsf1 = 399.93 MHz400 MHzf2 = 400.10 MHz400 MHzK12= 0.031220.02894K23= 0.02819 0.02863K14= -0.00930-0.00942QL= 28.4329.69d12= -0.0082d23=-0.0410 were zero in circuit d14= 0.0363Ansoft Designer used to curve fit ideal prototype circuit to HFSS results.K12 too large W12 adjusted (

13、causes F0 shift) L1, L2 adjustedSecond filterChange the goals!Curve fitting shows that we have d12=-0.0004d23=-0.0405d14= 0.0405Further improvement not possible with d12=d14=d23=0.New circuit parameters based on nonzero d-factors are needed.Desired points in theoretical filter characteristics and d-

14、factors are known. Curve-fit used to find new goals for f1, f2, K12, K23, K14, and Q_L.New TargetsOriginal targetsHFSS 2nd filterf1 = 399.85 MHz400 MHz400.11f2 = 400.14 MHz400 MHz400.16K12= 0.029810.028940.02924K23= 0.02876 0.028630.02837K14=-0.00864-0.00942-0.00942QL= 28.9729.6929.84based on d12=-0

15、.0004, d23=-0.0405, d14=0.0405.Filter response with d0Circuit simulation results meet spec on F0, BW, ripple, and stop band.Asymmetry in stop band due to frequency dependent K-factors.Ripple is exactly 0.08dB and symmetric15 MHz0.08 dBThird filterHFSS model adjusted to meet new goals.Ripple is off 0

16、.01dB.BW is correct.Fourth filterLength of resonator changed slightly to make ripple symmetric.First design saves time Rule of thumb first design& manufacturing: 2 weeksmeasurement & tuning: 1 weekAdaption of geometry and / or new design: 2 weeksmeasurement & tuning: 1 weektolerance determination, h

17、igh power tests, etc. : 2 weeksRun calibration projects: 2 daysInitial design: 1 dayCorrected design: 1 dayFinal design: 1 daypower & sensitivity analysis: 2 daysANSOFTTRADITIONALTOTAL: 7 daysTOTAL: 9 weeksTIMEFurther designs save time AND money ANSOFTTRADITIONALMONEY SAVEDTIME SAVED9.Design 342 days8.D