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Smith Chart™ Resources - Forbidden Regions

Smith Chart "Forbidden Regions" - RF Cafe

Smith Chart "Forbidden Regions Infographic

This is the basis for my very popular "We Are the World's Matchmakers" design, available on the Cafe Press website.

This list of Smith Chart software is a mixture of professional packages for purchase, shareware, and freeware, plus links to websites featuring Smith Chart topics.

Forbidden Regions of Impedance Matching

Smith Chart coasterBecause of the way in which the addition of series and parallel capacitances and inductances move along lines of admittance and reactance, there are certain areas on the Smith Chart, known as forbidden regions, within which the combinations of inductance and capacitance cannot be used to translate the impedance to the center of the chart (perform an impedance match). The reason can be made clear by an example.

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Smith Chart forbidden region upper left - RF Cafe               Smith Chart forbidden region upper right - RF Cafe
Series-added reactive components (inductors and capacitors) move the impedance point along constant resistance lines as shown in red and purple to the right. Shunt-added reactive components move the impedance point along the constant conductance lines as shown in blue and green to the right. Recall that adding a shunt capacitor increases overall capacitance, and adding a series capacitor decreases the overall capacitance. The opposite is true for inductance. Smith Chart tuning paths for series and shunt inductors and capacitors - RF Cafe Suppose the impedance of a source lies in the Forbidden Region in the Smith Chart in the upper right (above). Adding series inductor increases the overall inductance and therefore moves the point along the red line (constant resistance), which keeps the impedance within the Forbidden Region. The addition of a shunt capacitor increases the overall capacitance and moves the point along the green line (constant conductance), but can never move the point to the center where 50 Ω lies.
Smith Chart forbidden region lower left - RF Cafe               Smith Chart forbidden region lower right - RF Cafe
Exodus Advanced Communications Best in Class RF Amplifier SSPAs

About RF Cafe

Kirt Blattenberger - RF Cafe Webmaster

Copyright: 1996 - 2024

Webmaster:

    Kirt Blattenberger,

    BSEE - KB3UON

RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling 2 MB. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer. The World Wide Web (Internet) was largely an unknown entity at the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps while tying up your telephone line, and a nice lady's voice announced "You've Got Mail" when a new message arrived...

Copyright  1996 - 2026

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged.

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