what design can be used to get generate EM electromagnetic field with strength about 60-65 V/m, in form of directed beam that cover the area of approx. ≈ 400cm2, within frequency range ≈ 2000-2500 MHz, at a min distance from the emitter? What is suitable for this, only microwave tubes or other approach?

 

It's not my field....I would study wave-guides.

 

how to convert EM field strength from Watts to volts per meter (V/m) units?

 

You can't, without more information. One unit is power and the other field strength. Apples and oranges.

 

For example, what is field strength (V/m) at the output of magnetron tube used in microwave oven? Suppose that power regulator is set to min power 140W.

 

https://www.semtech.com/images/promo/Semtech_ACS_Rad_Pwr_Field_Strength.pdf

Power density and electric field strength are related by impedance.

 

e=IR

Like it or not.

 

tranzz4md has it right. This is explained in a very nice write-up from the FCC in the document at the link below.

http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf

Go to the section titled What is the relationship between "microvolts per meter" and Watts? on page 32 of the pdf file (page 29 of the document).

 

Thank you, that's helpful document.

PG/4πD² = E² /120π
For P=120 Watt, G = 1, D = 0.24 meter,
I got E = 251 V/m

Is my calculation correct?

I used P=120 Watt, its just minimal electrical power that marked on microwave oven power regulator, the actual power on magnetron output can be completely different. I used G=1 just for sample in this calculation.

 

Using your numbers I get essentially the same result: 250 V/m.

 

There's probably mistype in this document:

4BD² is the surface area of the sphere centered at the radiating source whose surface is D meters from the radiating source.
120B is the characteristic impedance of free space in ohms.

I think it shold be 4πD² and 120π ?

 

The 4BD² is clear. What is "B"?

 

I thought "B" printed due to π (pi) symbol conversion issue, possibly π symbol not converted correctly?

 

Thank you for making that clear.

Here is an image from Acrobat Reader on my computer. It shows 4πD² and 120π. So maybe you are seeing a font problem.


But in post #9 you wrote "PG/4πD² = E² /120π"

Does that mean you figured it out back then? If so, good work!

 

This equation in pdf doc is displayed on my computer exactly the same, since it's embedded image. But two sentences below equation (blue text in my post #11) contain these garbled symbols, that display "B" instead of π.

 

That's probably what happened then.

Happens to me when I send manuscripts to magazines. The editors immediately change the fonts the their preferred font, which changes the symbles to text fonts, making a mess of things that can remain undetected for a number of editing iterations.

 

tranzz4md has it right. This is explained in a very nice write-up from the FCC in the document at the link below.

http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf

Go to the section titled What is the relationship between "microvolts per meter" and Watts? on page 32 of the pdf file (page 29 of the document).

 

Thanks Santa perfect gift for the holiday.