Please Help Me Wilkinson Power Splitter/Combiner Questions -
RF Cafe Forums
Post subject: Please help me wilkinson power splitter/combiner
Unread postPosted: Wed May 25, 2005 5:29 am
Thingking of 2-way equal wilkinson power splitter/combiner and
setting port 1 input(output),port 2 output(input), port 3 output(input)
1. I just know the banlance resistor is 100ohm, but how to get
this value by mathematic formula?
2. All these three ports are
matched. Looking into port 1, I can understand why it is matched
( port 2 resistor and port 3 resistor at joint are the same 2Z0,
and 2Z0//2Z0=Z0). But I can't understand why it is matched looking
into port 2 or port 3?
3. Why say the balance resistor provide
good isolation? How to compute?
4. If power P enters into port
1, I know the power of port 2 and port 3 are the same, P/2. But
if power P enters into port 2, how to compute the power of port
1, port 3, and balance resistor?
5. If port 1 mismatch, how to
compute the power consumed by the balance resistor? If port 2 or
port 3 mismatch,how to compute the power consumed by the balance
If possible, Please give me detail information.
These questions puzzeled me many days. Many thanks!!!
Unread postPosted: Wed May 25, 2005 9:44 am
You need to look for EVEN-ODD mode analysis.
You will find
this analysis in "Microwave Engineering" from POZAR
Unread postPosted: Fri
May 27, 2005 4:09 am
Or just 'google' around:
gives you plenty of useful links.
BTW: There'll be always
power consumed by the resistor, without the resistor the divider
wouldn't be matched at all ports. You've to read something about
"S-Parameter" (scatter parameter).
Unread postPosted: Fri May 27, 2005 9:30 am
I do not understant why you say there is
alway power dissipated in the resistor.
If the system is
perfecly balance, I mean same amplitude, same phase at both outputs(inputs),
same impedance, then there is no dissipation in the resistor, since
both of it's terminals are at the same potential
Unread postPosted: Fri
May 27, 2005 10:27 am
All three ports matched means: Sii=S11
= S22 = S33 = 0
/ 0 S12 S13 \
S =| S21 0 S23 | (3)
\ S31 S32 0 /
no dissipation is expressed by
* S = E (unity matrix) (4)
|S21|² + |S31|² =
|S12|² + |S32|² = 1 (6)
|S13|² + |S23|² = 1 (7)
S31 = 0 (8)
Sik = Ski (9)
say S23 = S32 /= 0. according to (8) and (9) S31 = S13 = 0, what
can't be because of (5), (6), and (9)
A three-port device
can't be matched at all ports and lossless at the same time.
the wilkinson dividider is matched, but not lossless, because
his scattering matrix breaks formula (4)
Unread postPosted: Fri May 27, 2005
As a power splitter, there is no power dissipated
in resistor .
As a combiner, half the power is dissipated
in the resistor.
If you combiner 2 signals in phase and amplitude,
no power is dissipated in the resistor.