what is the best substrate for a microstrip power divider ?

hello!

i made a braodband ( 1-3 Ghz) wilkinson power divider with FRF4 substrate and it works very well.
but when i try to make another one (2Ghz - 18Ghz) with FRF4 Er = 4.5 or Duroid Er= 2.57 i've got problem with S21 parameters .
between 6Ghz and 18Ghz i've got a S21 who decrease between -8dB an -30 dB?

can somebody tell me why? it's the substrate is the cause of my problem
which topology is the best ? straight lines or curves?

thanks a lot

PS: don't care of my english i'm a beginner

Definitely the reason of poor S21 at those frequencies is the FR4 material.
For higher frequencies you can use one of these materials from Rogers:
http://www.rogerscorporation.com/mwu/pdf/prodselect.pdf
Curves lines usually are used in broadband splitters to minimize the total physical length.

thanks vfone for your explanation.

i use curves lines but it's difficult to join them together and respect the λ/4

another question more.

can you have explanation about the relation between frequecies and substrate?
for example which substrate you'll use for a divider at f0= 5Ghz?

The loss tangent of the material is frequency dependant
Here you can find formulas for Er and Dielectric Losses:
http://qucs.sourceforge.net/tech/node31.html

a good material at high freq is RT 5880 or materials from Taconic like RF-35. RT 5880 has low tand=0.00019 n is very stable at high freq works very well in Ku band.

it is not only the loss tangent. there are more effects associated to the substrate material which are important at high frequencies: surface waves, which are generated by leakage and are linked to the substrate thickness and epsilon.

I suppose you use SMA connectors soldered to the MIC traces. These connections are also important.

You also mention that it is a wilkinson splitter: do you know the parasitics of the resistor?

regards

hello!




to answer to dowjones: i use cms resitors but i don't know their parasitics .

i use SMA connector soldered to the μstrip.

thanks