RF Electronics Chapter 5: Frequency Mixers Page 165
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
signal of -27 dBm is required. Figure 5.92 shows the resulting spectrum for the image
reject mixer, when used as an upper sideband up-converter. Comparing this with figure
5.83, the signal at 1550 MHz has increased by 3 dB, due to the signals from both mixers
being added. The 1450 MHz signal is removed due to the signals from both mixers being
subtracted. The signals at 1400 MHz (LO-2*IF) and 1600 MHz (LO+2xIF) are second
harmonics of the IF and thus will have 180 degree phase shift at the output of the IF
Branchline coupler, so that these signals do not have image rejection and should have the
same amplitude. The signal at 1350 MHz (LO-3*IF) due to the third harmonic of the IF
signal and has a 270 degree phase shift at the output of the IF Branchline coupler. That
causes a single sideband signal at 1350 MHz, with no signal at 1650 MHz. These
harmonic relationships can be verified by tuning FIF.
Figure 5.93. Conversion gains of the image reject up-conversion mixer of figure 5.91.
Figure 5.94. RF output current of image reject mixer.
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