




Technical Notes 




Characteristic Impedance

The Characteristic Impedance of a coaxial transmission line is a function of the ratio of the inner and outer conductor diameters and the dielectric constant of the insulating medium.






Where:


 Characteristic Impedance


D

 Inside diameter of the outer conductor (inches)


O

 Diameter of the inner conductor (inches)



 Dielectric constant






Voltage Standing Wave Ratio (VSWR)

VSWR is the ratio of the maximum and adjacent minimum wave, expressed in terms of reflection coefficient.






VSWR is a real number; a value 1.0 implies a perfectly matched load.





Insertion Loss

The composite Insertion Loss of a transmission line is determined by the loss associated with the inner and outer conductor, the dielectric medium and characteristic impedance mismatches.
1. Conductor Loss is a function of transmission line dimensions and materials.


Where:

CL

 Conductor Loss (dB)

L

 Conductor length (inches)



 Characteristic Impedance (Ohms)


 Dielectric constant


D

 Inside diameter of the outer conductor (inches)


 Dielectric constant


O

 Diameter of the inner conductor (inches)

f

 Frequency (Hz)


2. Dielectric Losses.


Where:

DL

 Dielectric Loss (dB)



 Loss tangent


C

 Velocity of propagation


L

 Conductor length (inches)


f

 Frequency (Hz)


3. Mismatch Loss is a function of reflected energy due to deviations from the characteristic impedance of the transmission line system.





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