1 of 15

Manfred Wendt – CERN

​

U.S. Particle Accelerator School USPAS 2024�Design and Engineering�of Modern Beam Instrumentation

Hampton (VA), January 29 – February 2, 2024

​

Qucs Exercises�– Filter Network Analysis –�

Page 1

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

2 of 15

Learning Objectives

  • Introduction to basic circuit analysis and simulations
    • Based on the “Qucs” software
  • Fundamental concepts of lossless ladder filter networks
    • Low-pass maximally-flat (Butterworth) filter
      • S-parameter analysis
      • Impulse response using the transient simulator
    • Learning about other filter configurations
      • Chebychev, Gaussian, etc.
      • High-pass filter networks
      • Diplexer
      • Band-pass filters
  • Stripline equivalent circuit

Page 2

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

3 of 15

Getting familiar with Qucs

  • Start QucsStudio
    • Read about the basics in the getting started tutorial (which is based on the original Qucs)
    • More info at: https://qucsstudio.de/Docs/
    • Start a Project
      • Name it, e.g. “uspas_prj”, which will be located in the “.qucs” subfolder under “username”
  • Build a simple, lossless low-pass filter subnetwork
    • Arrange the schematics as shown:

​

​

​

​

​

​

​

​

    • Modify the circuit symbol:

​

    • Give your low-pass filer a name
      • E.g. “LP_cap_dual”

IMPORTANT:

The Qucs graphics shown in ths document

were generated with an older version of Qucs!

Some details may show slightly different in�the actual QucsStudio version!

Page 3

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

4 of 15

A S-Parameter Simulation

  • Arrange a 2-port S-Parameter simulation schematics

​

​

​

​

​

​

​

​

​

​

    • Load your low-pass filter subnetwork by dragging it between the two power sources.
    • Give your simulation schematics a name
      • E.g. “S_2port”

Page 4

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

5 of 15

Simulation Result

  • Perform a simulation
  • Display the results
    • Drag a “Cartesian” display �on the work area
      • Select the “S21magn_dB” �for the display
    • Add a Smith-Chart display
      • Select “S[1,1]” for display

The actual QucsStudio version may generate

some of the simulation results automatically

Page 5

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

6 of 15

Transient Simulation (1)

  • Build up a transient simulation for the dame low-pass filter

​

​

​

​

​

​

​

​

​

​

    • Locate a “Name” label on the output signal
      • Give it a useful name, e.g. “vout”
    • Don’t forget to name the network!

Page 6

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

7 of 15

Transient Simulation (2)

  • Perform a simulation
  • Display the result of “vout” in a “Cartesian” display

​

​

​

​

​

​

​

​

​

    • This is the impulse response of �a maximally-flat (Butterworth) type low-pass filter of 3rd order

Page 7

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

8 of 15

Fun with Filter Networks

  • Arrange a dual low-pass network configuration
    • Verify the same behavior

Page 8

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

9 of 15

More on Low-pass Filters

  • Experiment with other low-pass configurations
    • Setup different LP filter configuration �and make use of the Deactivate/Activate function to select a particular style:

​

Page 9

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

10 of 15

Diplexer (1)

  • Arrange a high-pass filter network
    • Name it “HP_cap_dual”

​

​

​

​

​

  • Build a 3-port S-parameter�analysis for a diplexer
    • Include low- and high-pass�filters and simulate
    • Display the magnitude in dB�of S21 and S31, and the�input impedance in the�Smith-chart

1

Page 10

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

11 of 15

Diplexer (2)

  • Improve the diplexer by using single terminated low- and high-pass filter networks:
    • Notice the different, asymmetric component values
    • What is the improvement?

Page 11

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

12 of 15

Ideal Stripline Electrode (1)

  • Simulate the time domain response of an ideal stripline electrode to a Gaussian bunch signal
    • Equivalent stripline schematic, and Gaussian bunch current file

External file:

“gauss.csv”

​

Left column: �time [s]

​

Right column:

bunch current [A]

Page 12

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

13 of 15

Ideal Stripline Electrode (2)

  •  

Page 13

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

14 of 15

Home Exercise (1)

  • Analysis / simulation of a Gaussian band-pass filter
    • Apply the LP-to-BP network transformation rules

LP

BP

BP values

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

center frequency:

Page 14

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt

15 of 15

Home Exercise (2)

  •  

Page 15

January 29th – February 2nd , 2024, USPAS Hampton (VA), U.S.A. – Filter analysis with Qucs – M. Wendt