AWR eBooks

RF Electronics Chapter 7: RF Filters Page 220 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 7.16. Replacement of inductors using Microstrip transmission lines For Rogers RO4003 substrate with H = 0.83 mm and T = 35 µm, the width for a 50 transmission line is 1.843 mm. the thinnest line that is desirable is 0.5 mm and the thickest is 10 mm. That corresponds to impedances of 96.5 and 14.3 respectively. One needs to find out what length of transmission lines corresponds to the inductance required for the filter. In Cadence AWR DE it is easy to compare the impedance of an inductor with one of a transmission line, as shown in figure 7.16. The circuit of figure 7.16, together with the line width restrictions results in the line widths and line lengths shown in table 7.2. The length of the transmission line is tuned to ensure that at low frequency both have the same impedance. It can be seen that the short section of transmission line accurately represents the inductor for frequencies up to 10 GHz. This process is repeated for all the inductances. Note for larger inductances, at higher frequencies the transmission line will be a quarter wavelength resulting in an infinite impedance or half a wavelength, resulting in a very small impedance. For lowpass filters, the length of the transmission line should be less than one-quarter wavelength for all frequencies or interest. Figure 7.17. Replacement of capacitors using series Microstrip transmission lines. The Capacitors can be replaced with open circuited transmission lines as shown in figure 7.17. The resulting line sections have been placed in table 7.2 and it can be seen that some line sections are wider than they are long, which will cause some errors in the simulation as the actual fields will be different from what is assumed in the simulation of the transmission lines. Figure 7.18. PCB Layout of the 2 GHz Lowpass filter. RF Electronics: Design and Simulation 220 www.cadence.com/go/awr

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