Please help me wilkinson power splitter/combiner questions - RF Cafe Forums
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Post subject: Please help me wilkinson power splitter/combiner questions.
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
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 resistor?
If possible, Please give me
detail information. These questions puzzeled me many days. Many thanks!!!
My email is: firstname.lastname@example.org
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'
gives you plenty of
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
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_transposed_conjugated * S = E (unity matrix) (4)
|S21|² + |S31|² = 1 (5)
|S32|² = 1 (6)
|S13|² + |S23|² = 1 (7)
S32* S31 = 0 (8)
Sik = Ski (9)
Let's 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.
dividider is matched, but not lossless, because his scattering matrix breaks formula (4)
Unread postPosted: Fri May 27, 2005 11:42 pm
As a power splitter, there is no
power dissipated in resistor .
As a combiner, half the power is dissipated in the resistor.
combiner 2 signals in phase and amplitude, no power is dissipated in the resistor.