Measurement instrument, measurement system, and testing method of testing a device under test

A measurement instrument for testing a device under test, the measurement instrument comprising:

• a common port configured to be connectable to a signal output of the device under test, wherein the common port is configured to receive a forward-travelling signal from the device under test;
• a signal line connected to the common port;
• and
• a signal processing circuit, wherein the signal processing circuit comprises a signal analysis circuit and a signal generator circuit,
• wherein the signal analysis circuit is connected with the common port so as to receive the forward-travelling signal from the common port,
• wherein the signal analysis circuit is configured to analyze the forward-travelling signal in order to assess a performance of the device under test,
• wherein the signal generator circuit is connected to the signal line, wherein the signal generator circuit is configured to generate a backward-travelling signal that is forwarded to the common port,
• wherein the signal generator circuit comprises a reference signal input, the reference signal input being configured to receive a reference signal from a reference signal generator, and
• wherein the signal generator circuit is configured to generate the backward-travelling signal based on the reference signal.