3.5 to 30 MHz Automatic Antenna Impedance Matching System By William Blodgett Senior Project ELECTRICAL ENGINEERING DEPARTMENT California Polytechnic State University San Luis Obispo August 2012 © 2012 William Blodgett TABLE OF CONTENTS Acknowledgements ...................................................................................................................................... iv Abstract ......................................................................................................................................................... v Chapter 1. Introduction ................................................................................................................................. 1 Chapter 2. Background ................................................................................................................................. 3 Chapter 3. Requirements ............................................................................................................................... 7 Chapter 4. Design.......................................................................................................................................... 9 Chapter 5. Test Plans .................................................................................................................................. 18 Chapter 6. Development and Construction ................................................................................................. 20 Chapter 7. Integration and Test Results ...................................................................................................... 36 1. Directional Coupler ............................................................................................................................ 36 2. RF Power Sensor ................................................................................................................................ 42 3. Power Supply ...................................................................................................................................... 45 4. Stepper Motors ................................................................................................................................... 45 5. IMS Power Meter ............................................................................................................................... 50 6. Matching Network .............................................................................................................................. 53 Chapter 8. Conclusion ................................................................................................................................. 61 Chapter 9. Bibliography .............................................................................................................................. 62 Chapter 10. Appendices .............................................................................................................................. 65 Appendix A: Senior Project Analysis .................................................................................................... 65 Appendix B: Time Schedule Allocation ................................................................................................ 71 Appendix C: Parts List and Costs ........................................................................................................... 72 Appendix D: Schematics ........................................................................................................................ 74 1. DC Power Supply ........................................................................................................................... 74 2. Matching Network.......................................................................................................................... 75 3. Stepper Motors ............................................................................................................................... 76 4. Control Unit ................................................................................................................................... 77 5. Directional Coupler ........................................................................................................................ 78 6. RF Power Sensors .......................................................................................................................... 79 7. Front Panel ..................................................................................................................................... 80 Appendix E: Software ............................................................................................................................ 81 i LIST OF TABLES AND FIGURES Table 1 - Loss Comparison of 450 Ω Balanced Line versus 50 Ω Coaxial Cable. ........................ 3 Table 2 - IMS Requirements and Specifications Table .................................................................. 8 Table 3 – IMS System Level Functionality Table ........................................................................ 10 Table 4 – IMS Subcomponent Level Functionality Table ............................................................ 11 Table 5 - 5 V DC Power Supply Requirements ............................................................................ 14 Table 6 – Amateur Radio HF Bands ............................................................................................. 19 Table 7 - ATmega32 Microcontroller Pin Connections ............................................................... 26 Table 8 - IMS Power Look Up Table Calculation ........................................................................ 31 Table 9 - DC Power Supply Test Data.......................................................................................... 45 Table 10 - Power Meter Comparison ............................................................................................ 50 Table 11 - IMS Forward Power Calibration ................................................................................. 52 Table 12 - IMS Reflected Power Calibration ............................................................................... 52 Table 13 - IMS SWR Meter Comparison to VNA ....................................................................... 53 Table 14 - Results of IMS match testing into dummy load .......................................................... 54 Table 15 - IMS vs. Commercial Antenna Tuner Specifications ................................................... 61 Table 16 - Antenna Impedance Matching System Bill of Materials (Page 1 of 2) ....................... 72 Table 17 - Antenna Impedance Matching System Bill of Materials (Page 2 of 2) ....................... 73 Figure 1 - Typical Impedance Matching System (IMS) Setup ...................................................... 1 Figure 2 - Feedpoint impedance of a 100 ft long dipole antenna in free space .............................. 5 Figure 3 - Smith Chart operation and schematic for the two L network configurations. ............... 6 Figure 4 – Transmission Line Loss Comparison. ........................................................................... 6 Figure 5 – System Level Block Diagram, Impedance Matching System ....................................... 9 Figure 6 – IMS Subcomponent Block Diagram ........................................................................... 10 Figure 7 - Directional Coupler Circuit Diagram .......................................................................... 13 Figure 8 - Power Supply Block Diagram ...................................................................................... 14 Figure 9 - 1:1 Balun Design ......................................................................................................... 15 Figure 10 - RF Power Sensor Design ........................................................................................... 16 Figure 11 – Directional Coupler ................................................................................................... 20 Figure 12 - Power Supply Circuit Board ...................................................................................... 21 Figure 13 - IMS Power Supply as built ........................................................................................ 21 Figure 14 - IMS Matching Network ............................................................................................. 22 Figure 15 - Matching Network RF Switch ................................................................................... 23 Figure 16 - IMS Balun .................................................................................................................. 23 Figure 17 - RF Power Sensors ...................................................................................................... 24 Figure 18 - Bottom of Microcontroller Board .............................................................................. 25 Figure 19 - Microcontroller Module ............................................................................................. 25 Figure 20 - IMS Front Panel ......................................................................................................... 27 ii Figure 21 - IMS Rear Panel .......................................................................................................... 27 Figure 22 - IMS Interior ................................................................................................................ 28