Digital attenuators are chained attenuators (could be switched by PIN diodes for example, but also they are made as MMIC's). The attenuation control is done by a binary word. You can check the TOAT-R512 from minicircuits or AT-220 from MACOM, for example.
recent issues on digital attenuators: the old dig att need a -Vee polarisation and this is not useful in RF PCB, where an inverter can generate spourios. Recently (and they will be produced soon) single voltage dig att are developped...try to look at them for your RF design.
bye
If you design an IC, check RF2410 (or substitute) on RF Micro Devices site (www.rfmd.com). In the datasheet, they usualy provide description of internal architecture of the IC. This one is done by FET switching of attenuator networks (P or T, you have basics at Odiseus web page, if you need)