June 14, 2009
June 14, 2009
June 17, 2009
14.38.1 - 14.38.10
A Laboratory Experience in Impedance Matching using Transmission Line Stubs
Abstract Impedance matching is a fundamental concept of RF circuit design. The proper application of impedance matching circuits allows for maximum power transfer between devices with minimum reflection of input signals. This concept is traditionally presented in mathematical form in conjunction with a Smith chart presentation. This paper presents a laboratory approach which uses these traditional forms of presentation in conjunction with real-time visualizations and low cost hardware demonstrations to present impedance matching concepts in multiple forms to address a range of student learning styles.
This paper details a successful laboratory experience focused on presenting impedance matching concepts at frequencies near 100 MHz through the design, simulation and measurement of a stub matching network. The procedures include hand and Smith Chart calculations reinforced using Applied Wave Research's Microwave Office to provide interactive simulations of the network. The designs and simulation results are then verified through the construction and measurement of the impedance matching system on a spectrum or network analyzer.
The laboratory exercises are designed to be performed in two hours. The exercises have been completed by 64 undergraduate students working in pairs over a period of two years with a completion rate over 90%. The laboratory presents concepts in multiple presentation forms to accommodate a range of student learning styles. This paper presents procedures, student perspectives and performance results on this laboratory experience.
The concept of impedance matching has historically been poorly understood by students in our program. While students are often able to follow an algorithmic approach which ultimately leads to a numerical solution, in the end they are routinely unaware of the role and contributions of each component in the matching network. This inability to relate mathematical expressions to the physical components in a network propagates through to later topics and courses which explore more advanced RF filter applications which commonly interchange between transmission lines and discrete inductances and capacitances. The purpose of this laboratory experience is to reinforce the relationship between the mathematics used in the design of single stub impedance matching networks and the physical components in the network. This is supported with the addition of interactive simulations using Microwave Office to complement existing mathematical and hardware presentations.
This laboratory is designed to be completed in a two-hour laboratory session for those successfully completing pre-laboratory exercises. While a number of RF simulation packages may be used to perform the listed simulations, the real-time tuning capabilities of Microwave Office provide for a high degree of interactivity which is a primary component of this
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