Which specifications describe a mixer?

From RF Design Wiki · By the RF Design Wiki editorial team · Published October 21, 2026 · Last reviewed October 21, 2026 · How we research

Mixer performance is described by conversion gain or loss (IF output relative to RF input), noise figure (SSB or DSB), linearity (IIP3, P1dB), LO drive level, port isolation (LO-RF, LO-IF, RF-IF) and spurious products at m·f_RF ± n·f_LO, usually tabulated as an m×n spur chart.^[1]^[2]

What is the difference between SSB and DSB noise figure?

A mixer down-converts noise from both the RF band and the image band. If the signal occupies only one sideband (heterodyne receiver), the SSB NF is about 3 dB higher than the DSB NF measured with a broadband noise source. Direct-conversion and radiometer applications use DSB NF. For passive mixers, SSB NF ≈ conversion loss.^[3]^[2]

Why does isolation matter?

LO-RF leakage radiates from the antenna and in direct-conversion receivers self-mixes to DC offset; LO-IF leakage can saturate IF amplifiers; RF-IF feedthrough passes signals unconverted. Double-balanced designs improve all three.^[2]

How should spurious products be handled?

Choose the IF and LO plan so that low-order m×n products do not fall in the IF band; spur charts and frequency-planning tools show conflicts. Half-IF spurs (2×2) are a classic superheterodyne problem; filtering before the mixer suppresses them.^[1]

Frequently asked questions

Is conversion loss the same as noise figure?

For a passive mixer they are approximately equal (SSB).

What is LO-RF isolation?

How much LO power appears at the RF port, in dB below the LO input.

What is a spur chart?

A table of relative levels of m×n mixing products for given drive levels.

References

Online sources accessed October 21, 2026; printed works cited by edition. See all sources.

“Mixer and amplifier application notes (e.g., 'Understanding Mixers — Terms Defined, and Measuring Performance')”. Mini-Circuits. application note.
“RF Microelectronics, 2nd ed.”. B. Razavi, Prentice Hall. 2012.
“Fundamentals of RF and Microwave Noise Figure Measurements (Application Note 57-1)”. Keysight Technologies. application note.

Categories: Mixers and frequency generation

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