Basic experiment of microwave technology - Filter Design

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One 、 New filter engineering and design schematic
Create a new one workspace, And create schematic . Place capacitors in the figure 、 Inductors are connected by wires . Double click capacitance and inductance , Set the capacitance to 2pF, Inductance is 1.5nH, That is to complete the schematic design of the filter circuit .

Two 、 Set simulation parameters and execute simulation
1. Set simulation parameters
Place... In the schematic S Parameter controller , And the specific parameter settings are shown in the figure below . And insert two ports Term With the earth , Connect... With wires .

2. Simulation results
The amplitude response curve of low-pass filter is shown in the figure below .

3. Filter circuit tuning
Because the actual circuit has parameter requirements , Filter design cannot be achieved in one step , To achieve the design goal , Adjust the filter parameters . Click the corresponding icon , eject “Tune Parameters” After the dialog box, select in the schematic L1、C1、C2.

Click... In the dialog box “Enable/Disable” after , modify Tune Parameters .

Parameters can be adjusted after setting the tuning range , Observe S21 Parameter changes . The following figure shows the tuning process and the results .

3、 ... and 、ads Filter Design Wizard tool in
1. Filter design index
（1） With the flattest response , Ripple coefficient in passband is less than 2
（2） The cut-off frequency is 4GHz
（3） stay w=8GHz The insertion loss of must be greater than 15dB
（4） The input and output impedance is 50Ω
2. Generation of filter circuit
Create a new schematic and add a dual port low-pass filter . In the filter design guide, set the filter design parameters and the parameters of the amplitude frequency curve according to the following figure . After setting the parameters , Click on “Design” Button , The system will automatically set a lumped parameter filter .

Set all parameters of the filter to display in the schematic window . The following figure on the left shows the setting process , The lower right figure shows the results .

The specific circuit in the model can be viewed as shown below .

Modify the filter simulation settings as shown in the following figure .

The simulation results are as follows .

Four 、 Lumped parameter filter is converted to microstrip filter
Richards Transformation is the theory that a section of open or short-circuit transmission line is equivalent to distributed inductive components , The series inductance is equivalent to a short-circuit stub . But in the actual microstrip circuit design, the series circuit stub cannot be realized .Kuroda Equivalent gives a conversion method between parallel stub and a transmission line and between series stub and a transmission line .
1.LC Filter to microstrip filter conversion
Convert the inductance into a series short-circuit stub , The capacitance is converted into a parallel open transmission line . Conduct Kuroda A unit device is added at the input and output of the transformation . Select two groups of types to convert according to requirements , The schematic diagram after conversion is shown in the figure .

Add all stub to microstrip line conversions , Set the substrate thickness to 30mil, The dielectric constant is 4.4 Convert after .

You can check the sub circuit diagram of filter components in the schematic diagram, as shown in the following figure .

2.kuroda Post equivalent simulation
Place the terminal load and ground in the schematic , Connect... With wires . place S Parameter simulation controller , The parameter setting is shown in the figure .

The simulation results are as follows , It can be found that the filter is 4GHz The insertion loss at is 1.369dB, Basically meet the design requirements .

5、 ... and ． Step low impedance filter ads Simulation
1. Filter schematic design and parameter setting
add to 8 Connect microstrip lines , As shown in the figure below .

Add microstrip line parameter setting control , And set the corresponding parameters as shown in the figure below .

open “LineCalc” window , Enter the corresponding parameters as shown in the figure below , Transmission lines are available “W” and “L” Corresponding value .

The length and width of microstrip line are the main parameters of filter design and optimization , So instead of , It can be easily modified and optimized later . Therefore, the parameter settings of eight microstrip lines are modified as shown in the figure below .

because MLIN The length and width of are changed to variables , So add variable control VAR, Set the corresponding value as shown in the figure below .

2. Simulation parameter setting and schematic simulation
Place two “Term” Element and ground , Corresponding connection . place S Parameter scan control , And set the corresponding frequency range and step size as shown in the figure below .

The simulation results are shown in the figure below .

3. Filter parameter optimization （ See report for details ）

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