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could I using three 18 ohm resistors as power divider in PLL at 8GHz?

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fenfei

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I found that ADF4106 evaluation board using three 18 ohm resistors as power divider in pll at 5.6GHz.
Now I want to design a 8GHz synthesizer,could this circuits be used at 8GHz? Or I have to use a microwave power divider in microstrip?
Thanks!
 

It is a trick how to make a homebrew resistive splitter to work at high frequencies.
Place 3 identical 50 ohms SMD resistors in parallel (16.6ohms) on each branch. In this way minimize the parasitic inductance of each resistor, placing them in parallel. Also ideally for minimum coupling should be used a star configuration (120 degrees between them)
 

it's better not use resistor as power divider at 8G. Under 4G, I think it's OK. Because ADF4106 is only 6G, you need use freq divide-by-2, say HMC432. So the H432 input power do not need so high, and you can use microstrip coupler to couple VCO power to HMC432. The insertion loss of coupler is less than 0.5dB.
good luck.
 

I won't say yes or know, it's a matter of acceptable matching error and properties of available resistors (e.g. package size). Connecting three 50 ohm resistors in a delta is equivalent to using 3x3 50 ohm resistors in an Y topology, I think.
 

3 x 50 ohms all in parallel on each branch, and branches in star configuration, to minimize the coupling between branches at high frequencies. In this way using 0201 resistors and proper PCB material and layout can reach flat response up to 10 GHz.
This approach doesn't have anything in common with delta configuration.
 

This approach doesn't have anything in common with delta configuration.
Click to expand...
No, it hasn't. I'm however under the impression, that a delta configuration with 0201 resistors would also perform well. Do you know empirical measurements or simulations, that show the said coupling problem in a delta configuration.
 

Actually, I've found out that the Y does a better job for me than the delta configuration. A simple 6db resistive splitter in Y has about 8dB of loss at 20GHz. See attached photo of the prototype.




PS: @fenfei, use two 33R in parallel for a Y configuration at it should work good at 8GHz.
 

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