AD8302 front-end

[ealex]

hello

i'm planning to make a simple / low quality VNA based on the AD8302 chip from analog:
http://www.analog.com/media/en/technical-documentation/data-sheets/AD8302.pdf

the entire thing will run up to 50MHz, that's the limit of the DDS i've already built.
reading the documentation i understand that, for the best range, both inputs should be at -30dBm if both signals are equal, as the allowed input range is [0 .. -60dBm]
that will allow measuring 30dBm gain or 30dBm loss in one go.

i'm thinking of making the input stage like this:


the idea is to extend the range of measurement via SW1 and SW2:
- SW1 and SW2 opened -> 60dBm of attenuation, it can measure gains of mostly 60dBm
- SW1 and SW2 closed -> 0 dBm attenuation, it can measure DUT attenuation down to 60dBm
- SW1 closed and SW2 opened -> 30dBm attenuation, it follows the datasheet recommendation

the main problem is that i don't know how to choose the relays for SW1 and SW2 - grab the cheapest RF / small signal relay ? or look after some specific parameters ?

also, is the entire thing work trying to do ? or i should just use coaxial attenuators inserted in front of the entire thing ?