[SOLVED] Maximum Power Transfer, Conjugate Matching

Hi guys,

I know conjugate matching provides maximum power transfer. I tried deriving it but am only able to get it for real values.


If Ri = Zi and Rl = Zl where Zi and Zl are complex, I don't see how I would get Zi = Zl*.
I know I am overlooking some simple complex number rule.

SeriousTyro,

Only when the output load is a conjugate of the input source are the reactances completely cancelled out. If the reactances are not completely cancelled, the voltage and current will not be completely in phase, so the power transferred will be less.

Ratch

Ratch said:

SeriousTyro,

Only when the output load is a conjugate of the input source are the reactances completely cancelled out. If the reactances are not completely cancelled, the voltage and current will not be completely in phase, so the power transferred will be less.

Ratch

Click to expand...

as he mentioned there are two approaches in handling complex impedances
1- Absorption: done actually by absorb any stray reactance into the impedance-matching network itself so you can decrease the value of the component, element capacitors are placed in parallel with stray capacitances, and element inductors are placed in series with any stray inductances. The stray component values are then subtracted from the calculated element values, leaving new element values (C┐, L┐), which are smaller than the calculated element values.

2-Resonance: To resonate any stray reactance with an equal and opposite reactance at the frequency of interest.
you can check example in RF Circuit Design, Second Edition Chapter five Impedance Matchin,,, It's very simple

mkhogely,

as he mentioned there are two approaches in handling complex impedances

Click to expand...

Who is "he"?

1- Absorption: done actually by absorb any stray reactance into the impedance-matching network itself so you can decrease the value of the component, element capacitors are placed in parallel with stray capacitances, and element inductors are placed in series with any stray inductances. The stray component values are then subtracted from the calculated element values, leaving new element values (C┐, L┐), which are smaller than the calculated element values.

Click to expand...

I have never come across that method. When you put a capacitance in parallel with another capacitance or an inductance in series with another inductance, the total values of each immitance increases.

2-Resonance: To resonate any stray reactance with an equal and opposite reactance at the frequency of interest.

Click to expand...

You have got to do more than just resonate the circuit. The resistances have to be matched also. I can make any source/load circuit resonate at a particular frequency, but if the resistances are not matched, I won't get maximum power transfer. As I said before, you want a conjugate match.

you can check example in RF Circuit Design, Second Edition Chapter five Impedance Matchin,,, It's very simple

Click to expand...

Perhaps it is, if I know to what book you are referring.

By the way, English begins each sentence with a capital letter. It makes it easier to read.

Ratch