By virtue of how they present information, SDR receivers can also function as spectrum analyzers. Receivers from SDRplay and Airspy blur the line between receiver and test equipment in a way that is beneficial to hams who don't have thousands of $$$ to spend on dedicated equipment.
SDRplay will soon be releasing a dedicated spectrum analysis program for use with their receivers.
But no need to wait - certain measurements can be taken now using the same software (SDPuno) used to run their receivers.
Antenna return loss is indirectly proportional to SWR and is the method used to determine SWR of higher frequencies that make "antenna analyzers" and SWR meters impractical. If you've ever priced an analyzer, and have a need for one, that makes measurements above 450 MHz, you may be pleased to learn of this method.
At my work QTH we periodically need to measure the SWR of antennas and feedlines (waveguides) that operate at 1, 5, 8 and 14 GHz. Although the equipment used is different, this is one method of how it's done: