RF Electronics Chapter 2: Computer Simulation Page 25
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
cladding, as specified in MSUB. To calculate the line width required for a 50
impedance and a quarter wavelength line length at 1 GHz, right-click on the MLIN
element in the project of figure 2.27 and select Synthesize. That then opens the
Transmission Line Calculator window shown in figure 2.28.
Figure 2.27. Basic Microstrip line circuit.
Figure 2.28. Transmission Line Calculator Window.
In the Transmission Line Calculator on the Electrical side, change the Z0 re value to 50
Ohms and the EL value to 90 degrees and select those as targets. In the left hand Physical
side, select W and L in Synthesize. Then click to perform the calculation. The width is
calculated as 1.84309 mm and the length as 45.975mm. Selecting OK puts those values
in the schematic for W and L. If needed we can copy those values to variables W50 and
L90 to use in other schematics.
The same line width determination can be done by making some very simple test circuits
and optimising the relevant parameters. For figure 2.27, when the line is exactly 50 ,
then the return loss (S
11
) is very small regardless of frequency, as described in Chapter 4
"Transmission Line Transformers and Hybrids" of this book. Optimising the line width
to give the lowest return loss S
11
at 1GHz, results in a 1.84314193242188 mm line width
and a return loss of 69.34 dB. That width is close to the result from the Transmission Line
Calculator.
When the length of a quarter wavelength long line needs to be determined, then the circuit
of figure 2.29 can be used. The open circuited stub will reflect as a short-circuit, when
RF Electronics: Design and Simulation
25 www.cadence.com/go/awr
