Mixer Port Isolation
Understanding Mixer Isolation
Mixer port isolation is often the specification that drives mixer topology selection. Inadequate LO-to-RF isolation causes the LO to leak to the antenna, potentially radiating interference or triggering emissions violations.
Isolation by Mixer Type
| Mixer Type | LO-RF | LO-IF | RF-IF |
|---|---|---|---|
| Single-ended | 0 dB | 0 dB | 0 dB |
| Single-balanced | 20-30 dB | 0-20 dB | 0-20 dB |
| Double-balanced | 30-40 dB | 30-40 dB | 25-35 dB |
| Triple-balanced | 40-50 dB | 40-50 dB | 35-45 dB |
Frequently Asked Questions
What is mixer port isolation?
Port isolation measures leakage between LO, RF, and IF ports. LO-RF isolation prevents LO radiation from the antenna. Double-balanced: 30-40 dB. Triple-balanced: 40-50 dB. Critical for emissions compliance and receiver performance.
Why does LO-to-RF isolation matter?
The LO signal leaking to the antenna radiates interference. If the LO is +17 dBm and isolation is 30 dB, -13 dBm leaks to the antenna. This may violate emission regulations, especially if the LO falls in a protected band.
How can I improve isolation beyond the mixer?
Add a filter between the mixer RF port and the antenna to reject the LO frequency. Use an isolator to prevent backward signal flow. Additional isolation beyond the mixer's inherent specification can be obtained with external filtering.