Which of the following is used to measure SWR?

Standing Wave Ratio (SWR) indicates the impedance match between a transmitter and its antenna system. A directional wattmeter measures forward and reflected power, from which SWR can be easily calculated. Vector network analyzers (VNAs) and modern antenna analyzers measure the complex impedance of the antenna system directly and use this data to instantly compute and display the SWR. Because all three devices provide the necessary information or direct readout to determine SWR, all choices are correct.