Network Analyzer and Power Meter

[targal]

Hello Fellas,

I have a question about microwave measurement tools.

I'm working on a project about KU-Band waveguide component design and test.
My problem is, I couldn't get a satisfactory answer about the differences between power meter and VNA. Should I need a Power Meter, if I have a 4 port VNA?

My peak power is approximately 500W.
I need to measure
VSWR, Return Loss, Insertion Loss and the device's power handling capability.

Are there any articles, books that you can suggest? Or what are your opinions?

Thanks.

 

[biff44]

power meters measure power...like watts.

Network analyzers measure reflection or transmission ratios, like in dB.

It is a little like saying: "my car has a speedometer to measure speed, and a gas usage readout to measure miles per gallon...so why do I need both???"


They are two entirely different things. What exactly are you trying to measure? Do realize that 500 watts peak will easily blow either one up, especially a VNA, unless you really know what you are doing.

 

[Azulykit]

There are a number of fundamental differences between the two devices. A VNA (vector network analyzer) is used to measure the first three parameters you mention. It basically has two parts, a generator to inject a signal and a receiver to study how the item you are testing responds. (this is a simplistic description). A power meter simply measures power output from a source. Note that it will not tell you the power capacity of a device, only what it is measuring at the moment you connect.

Typically a VNA can cost $150 K while a power meter might cost $30 K. This gives you a hint about the relative complexity and usefulness of each instrument.

I would start by looking for the manuals on each device. Manuals usually start with a theory of operation and then go into how to manipulate the knobs.

What have you done with the information you have been provided? What are your conclusions? Why?

You might also describe the parameters you are trying to measure. If you do that, you will have a better understanding of what each instrument can do for you.

I would be careful around 500 W of RF. You do not say what duty cycle and you could do yourself harm as well as damaging equipment (as was mentioned above).

 

[tony_lth]

Assume your duty cycle is 1%, so your average power is 5W. Usually the power sensors maximum is +20dBm, so you should at least attenuate the signal 20dB.

And power meter uaually measure all the power over the entire spectrum, the power meter tell you the sum power of your useful signals and spurs and harmonic etc.

 

[noobler]

very expensive instruments so do it right the first time!

 

[Phytech]

Network Analyzer is not supposed to be fed with high powers. When you do the power measurement, you either use a power meter or a spectrum analyzer, with Attenuator (power attenuator off cause) to lower the power level that your equipment can handle.

The connection looks like: Power amplifier+DUT+Attenuator+Spectrum Analyzer (or Power meter).

Good luck with your measurement.

 

[G0HZU]

Hello Fellas,

I have a question about microwave measurement tools.

I'm working on a project about KU-Band waveguide component design and test.
My problem is, I couldn't get a satisfactory answer about the differences between power meter and VNA. Should I need a Power Meter, if I have a 4 port VNA?

My peak power is approximately 500W.
I need to measure
VSWR, Return Loss, Insertion Loss and the device's power handling capability.

Are there any articles, books that you can suggest? Or what are your opinions?

Thanks.

It's a while since I played with waveguide

However, if your final application requires through powers of 500W pk then you will have to be able to measure the insertion loss and VSWR of your waveguide very carefully to avoid introducing tiny measurement errors.

Will you be looking to do the waveguide insertion loss and VSWR tests at low power (milliwatts) ?

The last time I did waveguide measurements at >15GHz I used a dedicated waveguide coupler with very high directivity and precision detectors. Eg I used these with a Marconi 6500 Amplitude analyser. Also you have to make sure all your test equipment is well terminated (ultra low VSWR to avoid measurement errors) this was all done at the milliwatt level.

You don't actually need a VNA to complete your measurements and you may get more accurate results using band specific (waveguide) test equipment (eg high directivity waveguide coupler). This is because you will need to use waveguide transitions to connect up to the VNA and these would need to be very high quality. It depends on what VSWR you are trying to measure. eg I had to measure very low VSWR due to the waveguide having to handle several kW mean power. At the time I was told that the only way to do this reliably was to do it all in waveguide but maybe things are different today. I don't really do anything with waveguide any more so I am a little out of date

I can even remember measuring VSWR of waveguide using a slotted line!

As for power handling we used to test waveguide sections by connecting it up to a high power radar transmitter (several Megawatts peak) and running it for 30 minutes. Then look for signs of arcing inside the waveguide after the test. Some people used to listen to the waveguide while the test was running LOL ! I guess you won't need to do anything this extreme

Basically, you need to post up your spec requirements for insertion loss and return loss (and maybe transmitter duty cycle) before anyone can advise the best way to measure these accurately.

 

[targal]

Thank you all for your precious answers.

The underlying cause of my question is, If you use compatible sensors with your VNA, you can measure power without a power meter. But in data sheets of VNA's, it is mentioned that power meter's would give more accurate results. Ashort note: Power meter and VNA must be used with attenuators of course.

So I have to measure this component's VSWR, insertion loss. Frequency band of this component is 13.5-14.75 GHz, and we hope to have a 1.20:1 VSWR. This component is going to be used in broadcast systems, so depending on the broadcast type, satellite, antenna etc. average power is 250W in most applications.

@ Gohzu: I'm not looking for any extreme tests By the way, my aim is 0.2 dB insertion loss, -20 dB Return loss. Actually I don't know the duty cycle of HPA.

 

[biff44]

If you have a VNA with the capability of measuring absolute power, then yes you do not need a power meter! You would want to limit the power hitting the network analyzer! You would need a combination of directional couplers and attenuator pads (maybe high power ones).

and all that stuff would have to be calibrated to get an accurate reading.

 

[targal]

Thanks Biff44.