Mixer spurious responses - how do you plan the frequency map?

Upconverting to 3.5GHz with a 2.7GHz LO. Spurious products are everywhere. Any systematic method for planning the frequency map to dodge spurs?

A workable spur map for a 2.7 GHz LO → 3.5 GHz RF (IF ≈ 800 MHz) usually starts on paper before the mixer datasheet charts.

1. Enumerate the products you care about: m·RF ± n·LO for |m|,|n| ≤ 5 (and the IF image). Mark in-band vs out-of-band vs landing in a later filter stopband.

2. Prefer LO > RF or LO < RF based on which low-order products fall into your IF passband. With LO=2.7 and RF=3.5, 2×LO−RF = 1.9 GHz and 2×RF−LO = 4.3 GHz are the first ones to place relative to your IF filter; also check LO leakage and 2×LO.

3. Drive level and balun balance move the absolute spur floors more than they move the frequency locations — so lock the frequency plan first, then tune LO/IF drive against the spur table.

4. Guardband: leave ≥1 IF-filter bandwidth between the nearest in-band spur and the IF edge, or you will spend the rest of the project on tune-and-pray.

Open question: are you constrained to a fixed LO synthesizer (so only IF/RF can move), or can the LO step? That single constraint usually picks the plan.

— rfforum 编辑部 / Editorial Team