DESIGN AND SIMULATION OF TWO, FOUR AND SIX ELEMENT BROADBAND MICROSTRIP BALUN CIRCUITS AT 5 GHZ FOR WIRELESS APPLICATIONS A Project Presented to the faculty of the Department of Electrical and Electronic Engineering California State University, Sacramento Submitted in partial satisfaction of the requirements for the degree of MASTER OF SCIENCE in Electrical and Electronic Engineering by Suvarna Mahale FALL 2015 DESIGN AND SIMULATION OF TWO, FOUR AND SIX ELEMENT BROADBAND MICROSTRIP BALUN CIRCUITS AT 5 GHZ FOR WIRELESS APPLICATIONS A Project by Suvarna Mahale Approved by: ______________________________, Committee Chair Dr. Preetham B. Kumar ______________________________, Second Reader Dr. Fethi Belkhouche ______________________________ Date ii Student: Suvarna Mahale This is to certify that this student has met the requirements for format contained in the University format manual, and that this project is suitable for shelving in the Library and credit is to be awarded for the project. __________________________, Graduate Coordinator ________________, Dr. Preetham B. Kumar, Date Department of Electrical and Electronic Engineering iii Abstract of DESIGN AND SIMULATION OF TWO, FOUR AND SIX ELEMENT BROADBAND MICROSTRIP BALUN CIRCUITS AT 5 GHZ FOR WIRELESS APPLICATIONS by Suvarna Mahale The broad goal of this project is to improve the efficiency of a broadband microstrip balun circuit at a center frequency of 5 GHz, for possible wireless applications. To obtain this result, the design optimization, simulation, fabrication and testing of the balun are done with stricter requirements as compared with traditional coupler design. Starting with a conventional four-port coupler design, key modifications in the design have been implemented to obtain the desired magnitude and phase values at the two output ports. These modifications include center-tapping the output line of an even order multi-stage coupler, and including appropriate termination at the through port. The final outcome of this effort resulted in three designs: 2, 4 and 6 section balun networks, which show good amplitude and phase balance. The fabrication of the balun networks that were evolved in this work will be carried out in the next continuing project of another graduate student. ____________________________, Committee Chair Dr. Preetham B. Kumar ______________________ Date iv ACKNOWLEDGEMENTS I would like to take this opportunity to thank everyone who is responsible for me to complete the project work. My sincere acknowledgements to the Department of Electrical and Electronics engineering for providing the technical resources and permitting me to work on this project. My special thanks to Dr. Preetham Kumar, Graduate Coordinator at Sacramento State University, who has mentored me throughout the length and breadth of this project. Without his support and motivation, I could not have achieved the desired success in this project. I would also like to thank my second reader Dr. Fethi Belkhouche for his time, guidance and patience on reviewing the project report document. I am thankful to my project partner Praveen Kumar Veeranki Krishna who worked with me to complete this project and who is going to continue work forward on the design. Also not to forget the Office of Graduate Studies, its staff has been extremely helpful in coordinating my project plan. Last but not the least; I would like to thank my family and friends for being supportive under all circumstances. v Table of Contents List of Figures .............................................................................................................. vii List of Tables ................................................................................................................ ix 1. INTRODUCTION ................................................................................................... 1 1.1. Principal of Balun Circuit: ............................................................................... 2 1.2 Workflow of Balun design Project: .................................................................. 3 1.3 Organization of the project report .................................................................... 3 2. MICROSTRIP LINES AND BALUNS .................................................................. 5 2.1 Implementation of Microstrip Balun Transformer ........................................... 7 2.2 Fundamental Balun Design .............................................................................. 7 3. DESIGN OF MICROSTRIP BALUN CIRCUIT .................................................. 11 3.1 Design requirements of wideband balun design ............................................ 11 3.2 Design approach to development of broadband microstrip balun.................. 12 3.2.1 Center-tapped transformer principle to obtain phase balance ................. 12 3.2.2 Multi-section Coupled line couplers ....................................................... 13 3.2.3 Calculation of multi-section coupler structure impedances .................... 14 3.3 Schematic of 2-section Balun Design ............................................................ 16 3.3.1 Design of the 2 section balun with short circuit ..................................... 16 3.3.2 Schematic of 2-section Balun Design with open circuit termination ..... 17 3.4 Comparison of the amplitude balance of 2-section balun designs ................. 17 3.4.1 ADS simulation of prototype balun circuit with short circuit termination18 3.4.2 ADS simulation of prototype balun circuit with open circuit termination19 4. DESIGN AND SIMULATION OF INCREASED SECTION BALUNS DERIVED FROM PROTOTYPE STRUCTURE ........................................................................... 22 3.5 Schematic of 4-section Balun Design ............................................................ 22 3.6 Comparison of the amplitude balance of 4-section balun design: ................. 23 3.7 Comparison of phase balance of 4-section Balun design:.............................. 24 v 4.4 Schematic of 6-section Balun Design ............................................................ 25 4.5 Comparison of the amplitude balance of 6-section balun design: ................. 27 4.6 Comparison of phase balance of 6-section Balun design:.............................. 28 5. CONCLUSION AND RECOMMENDATIONS .................................................. 29 References: .................................................................................................................... 30 vi List of Figures Figure 1: Representation of a 2 Port Balun Circuit ........................................................ 2 Figure 2: Microstrip line layout ...................................................................................... 5 Figure 3: Diagram of L-C Lumped Balun ..................................................................... 8 Figure 4: Coaxial Balun ................................................................................................. 8 Figure 5: Simple Coupled Line Balun ........................................................................... 9 Figure 6: Simple Coupled Line Balun, using Broadside Coupler Structure .................. 9 Figure 7: Multi-section binomial transformer design principle .................................... 13 Figure 8: N- Section coupled line coupler ................................................................... 13 Figure 9: Design of 2-section Balun Circuit with short circuit termination ................. 17 Figure 10: Design of 2-section Balun Circuit with open circuit termination ............... 17 Figure 11: S – Parameters magnitude balance comparison (2-section) (Short circuit termination) ................................................................................................................... 18 Figure 12: S-Parameters phase balance comparison (2-section) (Short circuit termination) ....................................................................................................................................... 19 Figure 13: S–Parameters magnitude balance comparison (2-section)(Open circuit termination) .................................................................................................................. 20 Figure 14: S – Parameters phase balance comparison (2-section) (Open circuit termination) ................................................................................................................... 21 Figure 15: Design of 4-section Balun Circuit ............................................................... 23 Figure 16: S – Parameters magnitude balance comparison (4-section) ....................... 24 vii Figure 17: S-Parameters phase balance comparison (4-section) .................................. 25 Figure 18: Design of 6-section Balun Circuit ............................................................... 26 Figure 19: S – Parameters magnitude balance comparison (6-section) ....................... 27 Figure 20: S-Parameters phase balance comparison (6-section) .................................. 28 viii List of Tables Page Table 1: Common Applications of Balun Circuit 2 ix 1 1. INTRODUCTION The origin of the word balun is “balanced to unbalanced” transformer. The function of an electrical balun circuit is to convert signals from a single-ended input to a balanced output mode, having two signals of equal amplitude but 180 degrees out of phase, over the specified frequency range with minimum loss and low voltage standing wave ratio. The circuit has one input port