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**Published on ** January 18, 2013

The terms + definitions commonly used in antenna design and RF design are provided below. Today we will review: Smith Chart, VSWR, Return Loss, and Γ or Reflection coefficient.

A Smith Chart is a graphical aid designed for RF engineers to solve transmission line and matching problems. Impedance values (real and reactive) are plotted on a graph of Reflection Coefficient, Γ, using the following relationship:

*Z* is the input impedance of your system (for example, the impedance of the antenna you are trying to match). The value *Z* usually contains real and reactive components. As an example, the antenna impedance may be 30+j56. *Z _{0}*

*V _{incident}* is the incident voltage,

The amount of reflected power is measured by the quantity |Γ|^{2} (please note that |Γ|is the *magnitude* of Γ). Typically, reflected power is represented in dB by the equation shown below.

For example, if Γ* _{dB}* = -10 dB, then |Γ|

Γ* _{dB}* £ -10 dB

_{Γdb} is the parameter most often measured on a network analyzer. Another commonly used term is Return Loss, which is simply = -Γ* _{dB}*.

Finally, this leads to an explanation of the Voltage Standing Wave Ratio (VSWR). VSWR is determined by the ratio of the peak amplitude of a standing wave to the minimum amplitude of a standing wave along the transmission line. VSWR can be calculated by:

Low values for VSWR indicate a good antenna match. For a description on how standing and traveling waves are formed, please see our blog on 'Antenna Matching Within an Enclosure Part I: Theory and Principle’.