Homepage - RF Cafe
Webmaster: Kirt Blattenberger | KB3UON | Sitemap | ©1996-2014     Visit RF Cafe on
      Menu below is just a small sample of what is here!          Visit RF Cafe on Facebook Visit RF Cafe on Twitter Visit RF Cafe on LinkedIn
Custom Search
More than 10,000 searchable pages indexed.
•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

input impedance of RF trace on PCB - RF Cafe Forums

Because of the high maintenance needed to monitor and filter spammers from the RF Cafe Forums, I decided that it would be best to just archive the pages to make all the good information posted in the past available for review. It is unfortunate that the scumbags of the world ruin an otherwise useful venue for people wanting to exchanged useful ideas and views. It seems that the more formal social media like Facebook pretty much dominate this kind of venue anymore anyway, so if you would like to post something on RF Cafe's Facebook page, please do.

Below are all of the forum threads, including all the responses to the original posts.

Post subject: input impedance of RF trace on PCB Posted: Fri May 11, 2007 3:22 pm


Joined: Tue Apr 24, 2007 1:10 pm
Posts: 2

From PA2460 datasheet, we got

FR4,1.2mm; trace line: MLIN: W=12mil; L=616mil.
What can we expect to know?
what is the input impedance Zin of this line?
thickness between trace and ground?
1.2mm = what? 4-layer board thickness? or ...
dlelectric constant = 4.3?
I mean, we should either know Zin or exactly dimension / dielectric constant to calculate Zin. but we don't know any thing.
May someone help us?
Thank you very much.


Post subject: Posted: Sat May 12, 2007 7:53 am

Site Admin

Joined: Mon Jun 27, 2005 2:02 pm
Posts: 373
Location: Germany

You can get the following from this information:

The data sheet of this PA IC shows that the board is a 2-layers board therefore the 1.2mm is the width of the substrate itself. (From the metal to the GND layer).

The lines that you mention are micrstrip transmission lines. You can easily calculate the impedance of the line under the following link:


At frequency of 500MHz the impedance of this line (With the parameters you provided) is almost 125 ohm.

There is a freeware transmission line calculator available from Microwave Office call TXLine which you can download and use for calculating the impedance of the line based on physical parameters.

Hope this helps.


Post subject: Posted: Wed May 16, 2007 4:36 pm


Joined: Wed May 16, 2007 4:16 pm
Posts: 5
One thing to keep in mind is that the impedence of a microstrip trace is usually not an issue if the length is relative small in terms of wavelengths. I use an emperically derived rule of thumb where I don't really care about the strip impedence until the length is >1/16th wavelength.

What you really want to be careful with when designing source and load traces is to make sure that you are minimizing parasitic capacitance to ground. Having ground plane or grounded vias too close to the trace can cause shorts at RF.

Posted  11/12/2012
A Disruptive Web Presence

Custom Search
Over 10,000 pages indexed! (none duped or pirated)

Read About RF Cafe
Webmaster: Kirt Blattenberger

RF Cafe Software

RF Cascade Workbook
RF Cascade Workbook is a very extensive system cascaded component Excel workbook that includes the standard Gain, NF, IP2, IP3, Psat calculations, input & output VSWR, noise BW, min/max tolerance, DC power cauculations, graphing of all RF parameters, and has a graphical block diagram tool. An extensive User's Guide is also included. - Only $35.
RF system analysis including
frequency conversion & filters

RF & EE Symbols Word
RF Stencils for Visio

Product & Service Directory
Personally Selected Manufacturers
RF Cafe T-Shirts & Mugs

RF Cafe Software

Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel
Your RF Cafe Progenitor & Webmaster
Click here to read about RF CafeKirt Blattenberger... single-handedly redefining what an
                                 engineering website should be.

View the YouTube RF Cafe Intro Video Carpe Diem! (Seize the Day!)

5CCG (5th MOB): My USAF radar shop

Airplanes and Rockets: My personal hobby website

Equine Kingdom: My daughter Sally's horse riding website