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/* Physical Transmission Lines */
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[[File:tline4.png|thumb|left|480px720px| The schematic symbols of the Generic T-Line Discontinuity devices: (a) Open End, (b) Bend, (c) Step Junction, (d) Tee Junction and (e) Cross Junction.]]
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The physical transmission line types are characterized by their physical dimensions and material properties.
=== 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.
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[[File:tline6.png|thumb|left|480px| Microstrip Line Calculator.]]
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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.
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[[File:tline10.png|thumb|350pxleft|480px| CPW Line Calculator.]]
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[[File:tline12.png|thumb|350pxlrft|480px| Coaxial Line Calculator.]]
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You often need to design a 50Ω transmission line of a certain type. [[RF.Spice A/D]] provides ten physical transmission line design tools for:
* Twin-Lead Line
* Twisted-Pair Line
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[[File:tline7.png|thumb|left|480px| Microstrip Line Designer.]]
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The above line designers ignore the conductor and dielectric losses and calculate the physical dimensions of the line for a given value of the characteristic impedance Z0. For example, given a substrate with thickness h and relative permittivity ε<sub>r</sub>, the "Microstrip Designer" calculates the microstrip width in mm for a given value of Z0 (50 Ohms by default). Some line type like CPW and coaxial line have more than one dimensional parameter that can be varied. For example, CPW has slot width (w) and center strip width (s), while coaxial line has inner and outer conductor radii. In such cases, the line designer dialog provides radio button options to fix one parameter and vary the other.
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[[File:tline11.png|thumb|350pxleft|480px| CPW Line Designer.]]
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[[File:tline13.png|thumb|350pxleft|480px| Coaxial Line Designer.]]
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[[File:tline5.png|thumb|480pxleft|720px| The schematic symbols of the some Physical Transmission Line Discontinuity devices. (Top Row) microstrip components: right-angled bend, mitered bend, tee and cross junctions, (Bottom Row) CPW components: open end, short end, gap and step junction.]]
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