This is a follow-up to a previous post on CW (continuous power) Gain compression measurements. Please see that post for a more complete overview of power measurements.
Why Pulsed? A pulsed power measurement may be required if your DUT is intended to function in pulsed mode, such as radar applications. It may also be conducted to reduce heating on components within your test setup and/or the device under test (DUT). This will prolong the lifespan of your DUT.
Ideally, this is what we want to send into our DUT.
We do this by sending an RF signal at our frequency of interest (FOI) from a signal generator and modulate it (turn it ON and OFF) with an RF switch. This particular pulse has a duty cycle of 30% and a pulse width of 0.3 ms. We can change the amplitude of this pulse by simply adjusting our signal generator.
What should my pulse width be? It depends. Your DUT has a rise time - how long it takes to to reach a steady-state condition. Your pulse should be on long enough such that your DUT has had a chance to stabilize AND your test equipment has enough time to make a measurement. Your RF switch should have a rise time << then the rise time of your DUT so that your input pulse isn't distorted... yielding false measurements: AARGH!
Block Diagram: Our block diagram will be as before, except now we have added an RF switch to rapidly turn the RF on and off. A pulse generator modulates the switch and TRIGGERS your test equipment. (see note on triggering below) We have also coupled the output of the device so we can observe the output pulse on an Oscilloscope.
Note that this diagram does not include filters. These may have to be added after your amplifier (and your DUT) if it produces a lot of harmonics. A narrow-band isolator will work well for this too. Just be sure to account for the loss during the calibration.
Aside from the additional equipment listed above, your power meters should be configured for a "peak mode". This is usually buried in a sub-menu somewhere but is important to reading accurate pulsed-power. And now that they are in this mode, you need to tell the meters when to make a measurement i.e. triggering.
Important note on triggering: Use your pulse generator to trigger your power meters; now they will take a measurement at the same time that the RF pulse is sent through the DUT. If your DUT has a long delay, you may need to go into the "delay" menu to tell the power meters to wait X ns before starting the measurement. These work pretty well.
What value should my attenuators be?: You want enough attenuation to protect your expensive test equipment. Make a good estimate of the most power that could possible reach your sensors and add attenuation accordingly- But not so much that you lose dynamic range.
Additional Info:
Why Pulsed? A pulsed power measurement may be required if your DUT is intended to function in pulsed mode, such as radar applications. It may also be conducted to reduce heating on components within your test setup and/or the device under test (DUT). This will prolong the lifespan of your DUT.
Ideally, this is what we want to send into our DUT.
We do this by sending an RF signal at our frequency of interest (FOI) from a signal generator and modulate it (turn it ON and OFF) with an RF switch. This particular pulse has a duty cycle of 30% and a pulse width of 0.3 ms. We can change the amplitude of this pulse by simply adjusting our signal generator.
What should my pulse width be? It depends. Your DUT has a rise time - how long it takes to to reach a steady-state condition. Your pulse should be on long enough such that your DUT has had a chance to stabilize AND your test equipment has enough time to make a measurement. Your RF switch should have a rise time << then the rise time of your DUT so that your input pulse isn't distorted... yielding false measurements: AARGH!
Block Diagram: Our block diagram will be as before, except now we have added an RF switch to rapidly turn the RF on and off. A pulse generator modulates the switch and TRIGGERS your test equipment. (see note on triggering below) We have also coupled the output of the device so we can observe the output pulse on an Oscilloscope.
Note that this diagram does not include filters. These may have to be added after your amplifier (and your DUT) if it produces a lot of harmonics. A narrow-band isolator will work well for this too. Just be sure to account for the loss during the calibration.
Aside from the additional equipment listed above, your power meters should be configured for a "peak mode". This is usually buried in a sub-menu somewhere but is important to reading accurate pulsed-power. And now that they are in this mode, you need to tell the meters when to make a measurement i.e. triggering.
Important note on triggering: Use your pulse generator to trigger your power meters; now they will take a measurement at the same time that the RF pulse is sent through the DUT. If your DUT has a long delay, you may need to go into the "delay" menu to tell the power meters to wait X ns before starting the measurement. These work pretty well.
What value should my attenuators be?: You want enough attenuation to protect your expensive test equipment. Make a good estimate of the most power that could possible reach your sensors and add attenuation accordingly- But not so much that you lose dynamic range.
Additional Info:
- Calibration is similar to the CW calibration.
- The oscilloscope will allow you to read the rise and fall time of you DUT.
- As always, ensure that your test equipment can handle the power required for this test before you turn the RF on.
- Note that some newer Signal Generators contain an internal switch- reducing the amount of required test equipment. However, make sure that its rise time is << your DUT rise time.
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