[G0HZU_JMR]

The new kid on the block is of course the little £35 nanovna but if you want to experiment with a sig gen driving a return loss bridge then you could look on ebay.

Lots of people in China are selling the same PCB based 3000MHz return loss bridge for about £7 on ebay. I seriously doubt it will work well to 3000MHz but you could make a copy of their circuit using a similar balun if you want to make it yourself.

You could fit a 50 ohm terminated AD8307 logamp as the detector and this will report the return loss with a scaling of 25mV/dB. However, the AD8307 will only work up to about 500MHz and it will show a reasonably flat response to maybe 100MHz of so. It will work down to RF levels of -70dBm so there would be no problems with sensitivity and it would be easy to calibrate on an analogue meter scale because the response of the logamp is 25mV/dB.
The quick and dirty alternative would be to use a 50 ohm terminated scope as the detector. However, this would soon become tiresome I think.