RF Electronics Chapter 5: Frequency Mixers Page 149
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 5.60. Branchline coupler balanced mixer layout.
Figure 5.61 shows the conversion loss of the microwave mixer of figure 5.59. The
conversion loss is 1.23 dB worse than that of the basic Branchline coupler balanced mixer
shown as the red curve in figure 5.57. The conversion loss includes approximately 0.5 dB
losses in the PCB tracks.
Figure 5.61. Conversion loss of a balanced mixer with a Branchline coupler.
Figure 5.62 shows the simulated IF spectrum of the mixer and it can be seen that the mixer
performs well. The components above 1 GHz can easily be filtered out using a simple
low pass filter at the IF output, as shown in figures 5.56 and 5.58.
Figure 5.63 shows the hardware for the PCB layout of figure 5.60. Notice the many vias
connecting the top ground-plane to the bottom ground-plane, to ensure that a good earth
is obtained at the end of the quarter wavelength long lines TL4 and TL5 in figure 5.59,
which are needed to provide a DC path for the diode currents.
RF Electronics: Design and Simulation
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