Characteristic Impedance of Transmission Lines

Characteristic Impedance

Consider an ideal, infinitely long transmission line. Exciting the input of this transmission line with the alternating voltage V_in(t) results in the current I_in(t). The characteristic impedance of this transmission line is given by the equation:

$$Z_0=\frac{V_{in}(t)}{I_{in}(t)}$$

Consider a transmission line of length L terminated by load impedance of ZL.

The complex propagation constant for this line is given by the equation:

$$\gamma =(\alpha +j\beta )$$

where ɑ and β are the attenuation and phase constants. The complex characteristic impedance is given by the equation:

$$Z_0=R_0+j{X}_0$$

where R0 and X0 are the real and imaginary parts, respectively.

The input impedance of the line is given by the equation in:

Characteristic Impedances of Microstrip and Coplanar Waveguide Transmission Lines

Create microstrip and coplanar waveguide transmission lines with default properties. Use the getZ0 from RF PCB Toolbox™ to calculate the characteristic impedance of following transmission lines:

• microstripLine

  mline = microstripLine;
  Z0 = getZ0(mline)

  Z0 =
  
    47.6145 - 0.0004i

• coplanarWaveguide

  waveguide = coplanarWaveguide;
  Z0 = getZ0(waveguide)

  Z0 =
  
    47.8622 + 0.0041i