Lab 6 Design and Test of Microstrip Circuits

Objective:

The objective of this lab is to become familiar with microstrip design and testing concepts. You will use what you have learned about the design of transmission line and microstrip circuits to design a small printed circuit board with 50 ohm traces and matching networks.

Equipment: Smith Chart Software Orcad PSpice Express PCB Software Soldering Iron Network Analyzer Background Material: In addition to the lecture material, there are many other references that you can use to gain a better understanding of the concepts presented in this lab. Please review the following references before writing up your final lab report. Also, the material in these references is testable.

• Lines and Fields in Electronic Technology, W. Stanley, Chapter 5 and Chapter 7. • Java applet to calculate lumped element matching networks

http://www.ee.oulu.fi/~timor/javaa/matcher2.html • Link to Smith Chart software for the PC. This is a self-extracting archive.

http://etidweb.tamu.edu/porter/entc355/smith_v191.exe • Tutorial on stub impedance matching

http://www.odyseus.nildram.co.uk/RFMicrowave_Theory_Files/SmithChartPart2.pdf

• Tutorial on lumped element matching networks http://www.odyseus.nildram.co.uk/RFMicrowave_Theory_Files/SmithChartPart3.pdf

• Link to Express PCB website and software http://www.expresspcb.com • Link to microstrip design software

http://etidweb.tamu.edu/porter/entc355/setup302.exe

Pre-Laboratory Exercise (due at the beginning of class): Design a 1 GHz quarter-wave transformer to match a 50Ω microstrip line to a 200Ω load. Start by doing hand-calculations and then simulate your circuits in APPCAD. Vary the width in the simulator until Ro is as close as possible to the desired value. Create one table for the 50Ω microstrip line and one for the quarter-wave transformer, where hand-calculated values can be compared with values obtained from the simulator for the following parameters: λeff ,εeff , width and Ro. Use electrical data for the ExpressPCB miniboard (remember to use integers for widths and lengths in mils). Attach a separate sheet of paper with your hand-calculations.

Procedure: This is a two week lab. Your goal is design a small printed circuit board with microstrip circuits, fabricate and populate the board, and then test it using a network analyzer. To get started you need to read and understand the following design statement: For this project, you will build a printed circuit board with four separate circuits on it (remember that the bottom of the board should remain all copper):

1. A single 50 ohm microstrip trace terminated in a 50 ohm surface mount resistor. The other end of the line should go to the edge of the board.

2. A short 50 ohm microstrip line connected through a quarter wave matching network to a 150 ohm load.

3. An amplifier with RF Choke, bias resistor and LC output filter connected with 50 ohm microstrip traces.

4. A 150 ohm load matched to a 50 ohm microstrip line using a single stub tuning network.

Assume that all of your circuits will be operating at 1 GHz.

Part 1 Each lab team should partner with the team that sits directly across from them (other side of the bench) to form groups of four. Your first step is to design the networks necessary to build the circuits discussed above. All calculations should be done by hand. Keep in mind as you do your design that you will be using ExpressPCB to fabricate your circuits. Any technical information you need about their printed circuit boards is available on their website. You should then use the tools provided in the links at the beginning of this document to verify your design. Please provide evidence of the hand calculation and the verification in your final report. Part 2 You will then layout your circuits using the software provided by Express PCB. The link to this software is provided above. Once your layout is finished, you will submit your design to ExpressPCB and have your circuits fabricated. If you use the MiniBoard service, you will receive three copies of your board and it will cost approximately $60.00. Part 3 Once you receive your printed circuit boards, you will use the soldering stations in 009 to populate your boards. You will be provided 50 ohm (actually 51) and 150 ohm resistors. You will place everything on the boards with the exception of the connectors. These will be added later. Part 4 During the second week of lab, you will test your microstrip circuits. To do this, you will work with Dr. Porter to schedule a time to add connectors to your board and use the network analyzer to make measurements of your circuits. These measurements should include: • Reflection measurements for circuits 1,2 and 4 from above. • Frequency and amplitude characterization for circuit 3 from above.

Post-lab Questions:

1. Each team will turn in a final report with the following sections: a. Summary of Project b. Theory (Discussion of Microstrip, matching networks, transmission

lines,…) c. Design and Calculations (show the PCB layout, all calculations, all Smith

Charts, all verifications…) d. Testing – This is a discussion of your testing methods and a presentation

of your results. e. Explanation of Results and Errors – This is a detailed discussion of your

results and explanations as to whether the circuits you designed worked as expected. If they did not, explain why. Quantify and explain your errors.

2. Design a lumped element matching network to match a 120 ohm load to a 50 ohm

transmission line. While you are not going to fabricate this, you need to present your design in the report discussed above and show verification that it will work.