# Question about impedance - RF Cafe Forums

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Antenna_ant
 Post subject: Question about impedance Posted: Fri Jun 10, 2005 8:52 pm
what is impedance ?
why does it matter so much in RF?
What is impedance matching?

Kirt Blattenberger
 Post subject: Posted: Tue Jun 14, 2005 7:55 am

Joined: Sun Aug 03, 2003 2:02 pm
Posts: 308
Location: Erie, PA
Greetings Antenna_ant:

What is impedance?
Impedance is the opposition to current flow and contains both a real and an imaginary component, in the form of (Real +/- j*Imaginary). In the case of a pure resistance, the imaginary component is 0, and in the case of a pure reactance, the real component is 0.

Why does it matter so much in RF?
Impedance is important because mismatch between connected components causes poor efficiency (DC to RF conversion) and causes a perfectly level input to exhibit rippling and/or slope at the output.

What is impedance matching?
Impedance mismatch is when the output impedance of one component does not exactly equal the input impedance of the next component in line. Theoretically, maximum power transfer between two components is achieved when the load impedance is the complex conjugate of the source impedance. For instance, if the source impedance is 25+j10 ohms, then the load impedance must be 25-j10 ohms.

You can poke around on the RF Cafe website and other websites for more detail.

- Kirt Blattenberger

Guest
 Post subject: Posted: Wed Jun 22, 2005 1:51 pm
 Thanks kurt. That was comprehensive.

Posted  11/12/2012