So I'm trying to use one of Analog's evaluation board PLL circuits (ADF4350, here). I need to generate frequencies around 1 GHz, ideally in a +/- 250 MHz range, but in steps of < 1 KHz.
Using the ADF4350 evaluation board, I'm able to specify (say) 0.5KHz between channels. But, I notice that (for example) it is able to produce a really nice, clean 1000 MHz signal, but stepping it to (ie) 1000.001 MHz produces symmetric sidebands that are about -30 dBc and spaced about 1 KHz from the center frequency. It doesn't make a difference whether I'm in low noise or low spur mode.
Has anyone experienced a similar problem? I'm wondering if it's worth trying to custom design something with a different loop filter, or if I should start looking around for other options. This is going to be used in locking electronics for a very narrow line-width laser, and sidebands like that will almost certainly broaden the line :/