RF to DC generator

I am wondering if there is any efficent way to generate DC voltage from the received RF signal. Thanks.

I think select the strongest station, rectify it and filter the DC component. Maybe try something like a charge pump with parallel such circuits to get more power.

but you need the DC to make what ?
to power something or to mesure de power in RF ?

http://www.home.agilent.com/cgi-bin/...rea=-536884607

I know this circuit. It works. But the efficiecy is very low, around 10-15%, it depends on the received RF frequency ( the higher the worse).