Technique for designing a 3dB RF hybrid

[molloy]

rf hybrid 3db combiner

I should design a 3dB hybrid (splitter or combiner) in frequency approx 50-100MHz. So i cant use microstrip techniques and besides the power in it could be very large (i.e. 300W). Any suggestions about the technique to use?
thanks

 

[AL0117]

rf hybrid

Hi,

You could try a Wilkinson type divider, and use coaxial cable for the 2 transmission lines. This is basically composed by 2 quarter wavelength 70.7 ohm transmission lines, which transform the impedance of 50 ohm at the terminations to 100 ohm.The 100 ohm resistor across improves the isolation and the output match. Your resistor should be choosed carefully, cause in worst case it has to widthstand to the reflected power.

You can use the method described in the Sevick book "TRANSMISSION LINE TRANSFORMERS" chapter 18 to decrease the characteristic impedance of a 75 ohm coaxial cable, and you will get the necessary 70.7 ohm lines.
You can use tXLine to mde the calculations.

Hope this help.

rgds, Al

 

[molloy]

motorola rf hybrid

Unfortunately i cant use a wilkinson i need a 90° coupler to use in a balanced amplifier
thanks

 

[AL0117]

Re: RF hybrid

Hi,

It is similar. You could use a 3 dB branchline coupler, and use coaxial
cable for the transmission lines. However, the Sevick book has some examples for this too. Look also for Motorola appnotes, they have an older appnot : .. transformers for power amplifiers (the title is not exact, I will look in my archive for it)

Regards, Al

oops, I found some links:

hxxp://www.bychoice.com/motorolaApps.htm there is a complete list there

replace xx with tt

 

[molloy]

Re: RF hybrid

I cant find on the net the Motorola AN-749 about broadband transformer for RF. Anyone has it?
thanks

 

[g579]

Re: RF hybrid

Enclosed
g579

 

[tcitak]

Re: RF hybrid

hello