A few years ago I built a similar one designed by AA5TB
The thing I liked about his design was that he explains both how and why it works with instructions on how to adapt it for other meters etc. As a result I actually learned a lot while building it.
Hi,
This sort of terminating power meter is easy to build and very useful. I have a collection built over decades for particular needs. Be aware that the diode you use will affect the calibration as will the load resistors. Both behave differently at RF compared to DC.
Power levels below 5 W need to be calibrated against a known reference. A simple circuit like this does have limitations.