direct analog synthesis?

Anybody know the principles of direct analog synthesis. It is used in the latest Aeroflex frequency synthesizers, the fastest in the world.

Breakthrough new 1960's technology! You get a bank of oscillators, a switch, and switch one of the oscillators into a mixer. The output of that mixer drives another mixer. You divide the bank of oscillators by something like 10, select one of the divided oscillators to feed to the 2nd mixer. Ad nauseum....

Somewhere along the way they probably add a DDS into the mix to get the sub 1 MHz step sizes.

i found the data sheet of the synthesizer. It is capable of switching between two frequencies in (10MHz - 18GHz) range in less than 1 uS. This technique maybe old, but very impressive.

http://www.aeroflex.com/products/sig...ets/FS2000.pdf

The trouble is spurious signals, from all those mixers. If you need low spurious, you need a boatload of very expensive microwave filters, and an emi tight packaging/interconnect nightmare.

But you must use direct sythesizer in fast switching.