Hi,
One possibility is to use Analog Devices's Trupwr detector family (AD8361-2) see h**p://products.analog.com/products/info.asp?product=AD8361 and h**p://products.analog.com/products/info.asp?product=AD8362
and for RF/IF gain&phase detector see h**p://products.analog.com/products/info.asp?product=AD8302 or h**p://products.analog.com/products/info.asp?product=AD8313
Of course there are other dedicated ICs from different manufacturers, see Maxim etc.
They also have application notes on some of the above ICs.
For other ideas, see a useful page at h**p://www.qsl.net/n9zia/wireless/appendixF.html
rgds, unkarc