how to design a two-way power divider with a high isolation

hi
any suggestion to design a two_way power divider with coaxial method?
I've designed one ,but the isolation is very poor
how to improve the isolation?
thanks

Hi

I think you must upload your design schematic or layout for adviser.

Best regards

HOHOH

Sometimes putting a capacitor in parallel with the resistor greatly improves isolation.

Try using a 120ohm resistor so that the parallel cap brings it down closer to 100ohms.

The cap basically reduces the inductance of the resistor and reduces the phase delay through the resistor.

This may not work well for broadband applicatons.

Rod

Hi,

resistors must be small compared to quarter wavelength sections, the phase shift trough the resistor will affect isolation severly!

flyhigh

hmm, seems different methodes to matching not so perfect components or source impedance on common port.


Remeber isolation cannot be 6 dB better than common ports source/loads return loss.

ie. open, not connected common port give 6 dB isolation, common port with 14 dB return loss from source/load give 20 dB isolation etc.

It is a catch 22 though, The input return loss is only as good the output terminations which can degrade due to inductance of the isolation resistor.

dear friends
I am designing a power divider with coaxial line,not on the PCB
because the coaxial line can stand higher power >100w
for this reason , I don't know how to design the isolation resistor.
and the isolation is <6db

thanks

Oh nowww you tell us.

I suppose your bandwidth isn't very broad.

You should use 75ohm coax cable. quarterwave length.

Put a 100ohm resistor between the output center conductors.

I know this is very simplified. But I don't know your frequency or bandwidth
or what is restricting you from using an isolation resistor.

Rod

oh,thanks for your suggestion
but what you mean the isolation resister?
you mean adding a coxial line between the two port which is 100ohm or other?

Rolaki talk of Wilkinson-divider, not at powersplitter as yanghui3j example.

yanghui3j:s power splitter is impossible to make isolation above 6 dB between ports.

Powersplitter has bad impedance on outports port. correctly terminate power splitter and feed power to one of outport give 1/2 of power going to common (-3 dBm), 1/4 going to second outport (-6dB (isolation...)) and 1/4 power reflected back to source again depend of bad impedance (25 Ohm) in outport (6 dB return loss)


Wilkinson is a bridge - near wheatstone-bridge with two of resistors converted to quarter wave transformer and two 50 Ohm resistor (often combined to one 100 Ohm) to make balance for canceling power going from port 2 to port 3 (1 is common port) and make isolation. Connected impedance to outport has very little infuence of isolation between port 2 and 3 and unbalanced power burns away in 2x50 or 100 Ohm resistor, yes this resistors need possibly to handle all power you sending if splitter is not termiated or connected to badly load. Wilkinson can have 25 resp 75 Ohm on outport and isolation still least same as 50,50 Ohm termination, but source impedance on common port is very sensitive to how much isolation you can make, ie. 6 dB + return loss of source port.

if you want more bandwidth, you can using multisection or tapered quarter wave transformer, but in most case cost of deep of isolation... (see pozar's book 'microwave engineering' to calculate it)

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you can also use quadrature 90 degree hybrid, coupled line, rat-race and lange couplers -see pozars book for design, but every splitters/combiners needs good control of impedance in least one (source...) port or more ports if you want high isolations between ports. Outside impedances is part of 'bridge' and how well bridge can cancel unbalanced loads between ports and make isolations.