At 2.4GHz you can measure the return loss on each pad using a semirigid coax cable having an SMA connector at one end, as the one in the picture below:
https://www.rfmw.com/Images/P1dB Pigtaila.jpeg
You have to do a manual one-port calibration of your Network Analyzer (open, short, load) using this semirigid coax, connecting its SMA to Port 1 of the analyzer.
For OPEN, let the end of the cable in open air, central pin not connected to anything.
For SHORT, solder locally the central pin to the shield of the cable.
For LOAD, solder between the central pin and the shield of the coax three 150 ohms SMD resistors 0402 (place the resistors at 120 degrees one from each other - a bit delicate job). The reason of using 3 resistors in parallel is to minimize their parasitic inductance, and to get a wideband 50 ohms load.
Save the calibration, remove the resistors, solder the cable to the pads on your PCB and you can run your return loss measurements.
Do all the solder work with coax cable DISCONNECTED from the Network Analyzer.