RF Electronics Chapter 5: Frequency Mixers Page 150
2022, C. J. Kikkert, James Cook University, ISBN 978-0-6486803-9-0.
Figure 5.62. IF spectrum of a Branchline coupler balanced mixer.
Figure 5.63. Hardware realisation of the balanced mixer using a Branchline coupler.
Figure 5.64 shows the measured performance of the hardware of figures 5.59, 5.60 and
5.63. This IF spectrum closely resembles the simulation results shown in figure 5.62. For
an LO level of 7 dBm at 1.565 GHz and an RF signal of –5 dBm at 1.7 GHz, the IF signal
was 12.25 dBm, being within 0.6 dB of the performance shown in figure 5.62, and
corresponding to a conversion loss of 7.25 dB. The second harmonic distortion at 270
MHz, at -55 dBm, is nearly the same as the computer simulation. The LO feed-through
is 10 dB larger, but two microwave diodes were selected for the mixer, without being
matched. Third harmonic distortion is 10 dB larger in figure 5.62, than it is in figure 5.64.
In figure 5.64, the signal components in the region 88 to 108 MHz at -80 dBm are the
local 100 kW EIRP FM transmitters, located Mt. Stewart, 2.7 km from James Cook
University. The 170 MHz TV transmitter and a block of five 200 kW DVB-T transmitters
covering the spectrum from 545 to 625 MHz all located at Mt Stewart (Townsville Qld,
Australia) can also be seen on the spectrum.
RF Electronics: Design and Simulation
150 www.cadence.com/go/awr
