Understanding Mixer Isolation: LO, RF, and IF Ports

This page explains mixer isolation between ports, specifically covering LO to RF isolation, LO to IF isolation, and RF to IF isolation.

Isolation: This refers to the ratio of applied power at one port of the mixer to the power output derived from another port. Both the input and output power will have the same frequency. Since isolation is a ratio of two powers, it’s measured in dB (decibels).

Mixers typically have three ports:

• LO (Local Oscillator)
• RF (Radio Frequency)
• IF (Intermediate Frequency)

As we know, a mixer combines two input frequencies and produces the sum and difference of those frequencies. Depending on the application, either the sum or difference is extracted using an appropriate filter. For more information, refer to an RF Mixer tutorial.

LO to RF Isolation

LO to RF isolation is the degree of attenuation experienced by the LO signal as it travels from the LO port to the RF port. It’s measured at the RF port while the IF port is terminated with the required impedance.

LO to IF Isolation

LO to IF isolation is the degree of attenuation experienced by the LO signal as it travels from the LO port to the IF port. It’s measured at the IF port while the RF port is terminated with the required impedance.

RF to IF Isolation

RF to IF isolation is the degree of attenuation experienced by the RF signal as it travels from the RF port to the IF port. It’s measured at the IF port while the LO port is terminated with the required impedance.

It’s worth noting that the following terms are equivalent:

• RF to LO isolation is equivalent to LO to RF isolation.
• IF to LO isolation is equivalent to LO to IF isolation.
• IF to RF isolation is equivalent to RF to IF isolation.

These alternative terms are often used with double-balanced mixer types.