LO To RF Isolations: Why A 10dB Buffer Is Best

The LO to RF isolation of a mixer is a critical performance specification in most broadband applications. LO feedthrough can not only contaminate a system, but the noise fed from the LO path can degrade a system’s noise figure. The datasheet of a mixer is an important, authoritative source for understanding it’s performance. As broadband industry leaders we at Marki Microwave put immense effort into producing comprehensive, repeatable datasheets. However, the isolations experienced in a real system can vary from the datasheet for several reasons. In this note we will look at the most common reasons: varying LO power, variation over temperature, and unit to unit variation. After reviewing common reasons that LO-RF isolation can vary, we’ll look at an LO-RF isolation in an uncommon way based on a recent customer inquiry we received.