What is absolute output power? Why measure it?

What is absolute output power?

The network analyzer absolute output power measurement displays the power at the analyzer input port. This power is absolute: not referenced to incident or source power (which is ratiometric). When using the logarithmic magnitude format, the values ​​associated with the vertical axis of the grid are in dBm (referenced to 1 mW of measured power).

• 0 dBm = 1 mW

• -10 dBm = 100 mW

• +10 dBm = 10 mW

When using the linear magnitude format, the values ​​associated with the vertical axis of the grid are in Watts (W).

Why measure network analyzer absolute output power?

If the output of an amplifier must be quantified as absolute power, you should measure the absolute output power rather than performing a ratiometric relative power measurement. For example, during a gain compression measurement, you would typically also measure the absolute output power. This measurement shows the absolute power at the amplifier output where 1-dB compression has occurred.

Precision Considerations

The output power of the amplifier should be attenuated sufficiently as required. Too high an output power can lead to the following consequences:

• Damage Analyzer Receiver

• Exceeding the analyzer receiver input compression level, resulting in inaccurate measurements.

The attenuation of the amplifier output power can be achieved using an attenuator or a coupler.

Amplifiers can respond very differently at various temperatures. Testing should be performed with the amplifier at the desired operating temperature.

How to measure absolute power

To measure the network analyzer absolute output power:

1. Preset Analyzer.

2. Select unratioed power measurement (Receiver B).

3. Set the analyzer's source power to 0 dBm.

4. Select the external attenuator (if necessary) so that the amplifier output power is attenuated sufficiently to avoid causing receiver compression or analyzer port-2 damage.

5. Connect the amplifier as shown in the figure below and provide DC bias.

6. Select the analyzer settings appropriate for the amplifier under test.

7. Remove the amplifier and connect the measurement ports together. Store the data to the memory. When measuring the amplifier, if you are using attenuators and cables, be sure to add them to the test setup.

8. Save the instrument state to memory.

9. Reconnect the amplifier.

10. Select Data Math Function Data/Memory.

11. Zoom the displayed measurement results for best viewing and use the cursors to measure the absolute output power at the desired frequency.

12. Print the data or save it to disk.

Principles of how network analyzers measure high frequency electrical networks. You will learn what types of measurements you can make with a network analyzer and how it characterizes the linear and nonlinear behavior of a device. This section starts with RF basics such as transmission lines and Smith charts, and moves on to the concepts of reflection, transmission, and S-parameters. The next section includes all the main elements of a network analyzer, as well as the pros and cons of different hardware approaches. Error models, measures to improve accuracy, and various calibration techniques are then explained. Finally, some typical frequency swept and power swept measurements commonly performed on filters and amplifiers are also included. The Advanced Topics section contains more information.