This increases the apparent directivity of the coupler by twice the value of the input attenuator or the return loss of the input attenuator, whichever is less. When they are comparable the vectorial sum of the signals reflected from attenuator and that reflected by the DUT and attenuated by the input attenuator arriving the coupler have to be considered. Safe Attenuator At Output With high drives, network analyzers are driven into compression which can result in measurement errors. With excessive drives the analyzer can be damaged. This, even though it is a good practice, adds additional measurement steps.
Attenuators have frequency response.
To avoid errors with assumed safe attenuator values it is a good practice to measure the frequency response of safe attenuators and store it in computer. Normally this is done at low powers. Care should be taken to choose an attenuator which does not change attenuation value at high power. Calibration Of Network Analyzer Network analyzers are not basically designed for absolute power measurements. So, they have to be calibrated with power meters.