RF Electronics Chapter 5: Frequency Mixers Page 147
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
possible, while impeding the higher frequency signals. To make the removal of the LO
and RF signals at the IF port as effective as possible, the size of capacitor C1 is chosen
to act as a short circuit to the RF and LO signals but have little effect at the IF frequency.
If needed, a low pass LC filter can be used at the IF port. A filter with a 480 MHz cut off
frequency will reduce the RF/LO signals significantly and also reduce the conversion
loss. The low pass filter is disabled (greyed out) in figure 5.56. That results in the
Branchline BM plots shown in figure 5.57 and 5.58. Enabling that filter and removing the
bypass wire, results in the Branchline BM + IF Filter plots shown in figure 5.57 and 5.58.
Figure 5.57. Conversion loss of a Branchline coupler balanced mixer.
Figure 5.58 IF spectrum of the Branchline coupler balanced mixer.
A balanced mixer should not produce a DC component, since the signals across the diodes
are balanced. The RF frequency is 1700 MHz and the LO frequency is 1565 MHz. Tuning
RF Electronics: Design and Simulation
147 www.cadence.com/go/awr
