滤波器设计向导教学教材.doc

滤波器设计向导

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滤波器设计向导
[注]：滤波器向导能够帮助你设计出初步满足条件的各类滤波器，在此基础上，加上具体设计要求（通带或阻带特性的优化目标），就可以快速完成特定期间的设计。
The Microwave Office Filter Wizard is a filter synthesis plug-in application that accesses the simulation routines of MWO through a standard COM/API interface. Using the Filter Wizard, you can synthesize Bandpass, Bandstop, Highpass and Lowpass filters（带通、带阻、高通和低通） utilizing a variety of transmission response approximations including Butterworth, Chebyshev, and Bessel-Thomson.（响应类型）

进入向导：
在设计界面的左下方“project”按钮的最下方选“Wizards”你可以看到画面：
点击下一步：

上面的图形非常形象的给你提供可选择的各类滤波器。
There are four broad categories that transmission response shape requirements typically fall under:
Lowpass
Highpass
Bandpass
Bandstop (also called Band-reject or Notch).
You select one of these transmission response shapes when you begin the wizard.
选取你所需要设计的类型及可再点击下一步开始向导设计。你可进一步根据需要选择滤波器的类型：

MWO supports the following approximations in this release:
Butterworth (Maximally Flat Magnitude) - represents a compromise between high selectivity and flat group delay.
Chebyshev (Equal Ripple Passband Magnitude) - achieves high selectivity with low passband insertion loss at the expense of group delay flatness.
Bessel-Thomson (Maximally Flat Group Delay) - achieves maximally flat passband group delay, but suffers from poor selectivity.
每种响应的特性如上。确定后继续下一步：
这个画面要求你设定滤波器的级数（根据实际上升沿的陡度定，取大些比较保险）、带内参数（波动幅度）、端口及负载阻抗等。
The Parameter Specifications window controls the attenuation response.
These parameters include:
□ Filter order - the number of reactances in a Lowpass or Highpass filter, and number of resonators in a Bandpass or Bandstop filter.
□ Band Edge(s) - edges of the frequency band to which the Passband Parameter Value applies.
□ Passband Parameter - choice of Return Loss, Ripple, Ripple Factor, VSWR, Reflection Coefficient and Maximum Attenuation.
□ Passband Parameter Value - numerical minimum or maximum of the selected Passband Parameter.
□ Source and Load Impedances - equivalent resistances of the generator (source) and load to which the filter's input and output ports are attached.
Selecting the filter technology
选好后就可以进入下一个设计画面了：
The following figures show the Filter Technology window for the supported filter technologies.
注意并非所有的模型都支持上述响应。比如对于低通滤波器就只能选取第一种，下面的材料选取同样。
Only options for currently available technologies are selectable.
Lowpass Filter Technology
Currently, Lowpass filters can be constructed as either a Lumped Element or Ideal Transmission Line circuit as shown in the following figure.
选择其一，就可进入下一步设计。
只能选分立元件的原因是上面选择“ideal Electric Mode”造成的。如果你设计的是微带线器件，前面就要选其它类型的，比如“Shunt stub Transmission Line”等。
再点击下一步有：
这个选择框问你想使用串行“Series”，还是使用并行“Shunt”元件。所使用的元件是否带有损耗等。
Lumped-Element Lowpass Prototypes
A lossless Lumped-Element Lowpass prototype is a reciprocal two-port network with a lowpass attenuation characteristic designed to operate between a 1 ohm source impedance, RS, and a properly matched load impedance, RL [RL = RS in Butterworth, Bessel, and odd-order Chebychev prototypes, while, for even-order Chebyshev prototypes, RL = RS (1 + 2 e ( e ± (1 + e2)1/2), where e2 = 10(r/10) - 1 and r is the passband ripple in dB]. The prototype band edge frequency is defined as 1 radian/second (or about 0.159 Hz). The prototype can be realized as a ladder network consisting of lossless shunt capacitors and series inductors, as a cascade of impedance inverter coupled series inductors, or as a cascade of admittance inverter coupled shunt capacitors.
设置好后，就可以进入综合输出画面了：
这个画面给出了可以提供的各种输出，你按需求打钩就大功告成了。
这个画面综述了你整个设计过程的基本设置。点击完成就进入了工程画面，
打开电路图窗口，选“Windows Tile Vertical”排好窗口，再点击分析按钮，OK！
这个器件还可以按具体设计要求，加上新的优化目标进一步修正，这些内容上面几节课已经讲过了，请同学们多练习。
其它设计参数：
Hairpin-Line Resonators （半波传输线振荡器）
Hairpin-line resonators are half-wave transmission line resonators folded in the shape of a hairpin. Generally, the spacing between the arms of the hairpin is made relatively small to achieve compactness. Consequently, the coupling between the adjacent arms of the hairpin is too significant to ignore. The two ends of a hairpin resonator are either both open-circuited, or both grounded. Consequently, unlike interdigital and combline resonators, you need not ground hairpin resonators. Adjacent hairpin resonators typically have their ends facing in opposite directions, in an interdigital fashion.
Interdigital Resonators （四分之一波长传输线振荡器）
Interdigital resonators are quarter-wave transmission line resonators arranged parallel to one another, grounded on one end, and open-circuited on the other. Adjacent resonators have opposite ends grounded.
Combline Resonators （短于四分之一波长的传输线振荡器）
Combline resonators are typically less than a quarter wavelength long, are grounded at one end, and are capacitively loaded at the other open-circuited) end. Adjacent resonators are grounded on the same end. Combline filters are typically more compact than interdigital filters, but tend to have a less symmetric transmission characteristic (with more attenuation on the higher frequency side and less attenuation on the lower frequency side).
Shunt Stub Transmission Line Resonators （四分之一波长开路传输线）
Shunt stub transmission line resonators are a quarter wavelength long with one end grounded. Adjacent resonators are attached to each other at their ungrounded ends by quarter wavelength connecting transmission line sections.
Half-Wave Parallel-Coupled-Line Resonators （半波波长耦合微带传输线）
Parallel-coupled-line resonators are a half wavelength long and straight, with quarter wavelength portions coupled to adjacent resonators. The two ends of the resonators are either both open-circuited or both grounded. Consequently, unlike interdigital and combline resonators, you need not ground parallel-coupled-line resonators.
When you choose a transmission line structure, you can specify the substrate parameters for the desired fabrication technology as shown in the following figure.
悬着了微带类型的传输线，你需要进一步定义基板的工艺参数：
省缺是“自定义”，你也可以在下拉菜单选择需要的材料

微带滤波器设计最常见的问题及处理方法：
***************************************
Err1：如图
W/H不满足条件是微带滤波器设计最常见的错误，应为软件过分强调器件性能而忽视了理论模型（近视场解）的基本条件。最直接的方法是先牺牲部分性能，将不满足条件的变量宽高比强制限定到要求内。
从板材选取处可以看到，高度为0.635mm
那么你应当确保所有W的变量下限:
A）严格大于0.005*0.635=0.03125
B）最好大于0.03125
如果违法规则A，优化中止è应为模型已经不成立了；
如违反规则B，设计出来的器件在实际制作后性能有明显差异。
按A或B改好初值和下限后，就可以在点击“分析”按钮了。

这个图形明显不满足要求！！！
产生这个问题是由于上面强行调节了W4等参数，滤波器的性能变差，需要加上限定条件修正，分别加入阻带优化条件f<4.5GHz, f>6.5GHz S21<-20dB, 两个基本目标，缓慢拉动Turn 观察输出图形变化情况：特别是拉动W2是可以大致达到带通要求：
再进行优化，反复应用不同优化方法（不妨从Pointer Robust Optimization 开始）即可得到理想的滤波器。

第一次优化 cost=0.49 第二次优化cost=0.28

选取不同的优化方法还可使cost更小。
本样例可在教师服务系统相关目录下载得到。

补充课程讲解：
1． 选取不同的优化方法有助于脱离“伪最优”区域；
2． 反复优化可以使得cost达到更优；
3． 当你特别想某个参量得到修正时，可以加大该参量对应的“权函数”，默认为1，到10甚至更大。

Good Luck！

更详细的说明请参见软件的Help Topic。“wizard”

Institute of Optical Wave Technology
Dec 5，2005 
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