AWR eBooks

RF Electronics Chapter 2: Computer Simulation Page 24 2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0. Figure 2.26. Frequency response of the amplifier of figure 2.25. The gain measurement in figure 2.26 is made using Linear Gain VGT to provide the voltage gain from port 1 to port 2. To provide a flat frequency response above 1 GHz, a 0.7 pF capacitor is added across the output. Plotting S11 and S22 for the 50 Ω input and output ports in figure 2.25, shows that this does not provide a good input and output return loss. This results in a gain that is 2 dB less than the data sheet specification. The 50 Ω source and load impedance is not optimum for a low noise figure and as a result, the noise figure is 0.6 dB worse than the data sheet specification. Chapter 8 "Amplifiers: Stability, Noise and Gain" shows how good noise figures can be obtained and Chapter 9 "Impedance matching of Power Amplifiers" shows how the input and output impedances can be matched for a good 50 Ω return loss and best amplifier gain. To prevent having to wait for transients to die down, harmonic balance simulation is preferable for the waveform simulations of this amplifier. For most transistors, the effect of supply voltage, temperature, and component variations can be investigated, to ensure that the design works properly for all expected component tolerances. However not all device models include a temperature model. Determination of Transmission Line Parameters In many applications, a printed circuit layout using microwave printed circuit board materials needs to be made. The widths and lengths required can be determined. For earlier versions of AWR, a program TXLine, which can be downloaded from the AWR website had to be used to calculate microstrip line parameters. With the current version of AWR DE, the line parameters can be determined by right clicking on a transmission line and selecting synthesise to open the Transmission Line Calculator. TX line and the Transmission Line Calculator cover most of the different coupled lines or strip lines available. In many cases, it is more convenient to use the schematic circuit realisation of the transmission line models to determine the required line parameters, rather than using the Transmission Line Calculator. Figure 2.27 shows a Microstrip line, which we want to be a quarter wavelength long with a 50 impedance at 1 GHz. Figure 2.27 uses a Rogers RO4003 substrate, with a dielectric constant of 3.38, a loss tangent of 0.0027, a substrate thickness of 0.8128 mm and 35 micron (1 oz.) copper RF Electronics: Design and Simulation 24 www.cadence.com/go/awr

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