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/* Physical Line Calculators and Designers */
=== Physical Line Calculators and Designers ===
When you place a generic T-line part in your circuit, you have to specify its characteristic impedance (Z0), effective permittivity (eeff) and attenuation constant (alpha). In the case of physical transmission line parts like mircostrip, coaxial line or CPW, you specify the physical [[parameters]] of the line such as various dimensions and material properties. [[RF.Spice A/D]] then automatically calculates the necessary transmission line [[parameters]] at the time of simulation based on your physical data.
For every physical transmission line type listed above, the '''Device Manager''' of [[RF.Spice A/D]] provides a corresponding '''Line Calculator'''. The line calculators are accessible form the '''Tools Menu''' of the Device Manager. The line calculators take the substrate properties and the physical dimensions of a line types and calculate its characteristic impedance (Z0) and effective permittivity (eeff). The Line Calculator dialog also has an "Operational Frequency" input with a default frequency of 1GHz, which is used to calculate the guide wavelength of the transmission line at that frequency. In many practical applications, you need quarter-wavelength line segments. In that case, you must first calculate the guide wavelength of the transmission line as defined by λ<sub>g</sub> = λ<sub>0</sub> / √ε<sub>eff</sub>, where λ<sub>0</sub> = c/f is the free space wavelength at the operational frequency.
Some of physical line types such as microstrip, stripline, coaxial line, twin-lead line and twisted-pair line, have loss [[parameters]]: dielectric loss tangent and metal conductivity. For these lines, the line calculator calculates the conductor attenuation constant (α<sub>c</sub>) and dielectric attenuation constant (α<sub>d</sub>), both in Neper per meter (Np/m). Note that the total attenuation constant is the sum of these two: α = α<sub>c</sub> + α<sub>d</sub>. You can convert the value of attenuation constant from Np/m to dB/m using the relationship 1Np = 8.6859dB.
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