                         LINE-Z.EXE
                              
October 23, 2001
John MacConnell
john.macconnell@ieee.org

LINE-Z.EXE is a MS DOS program that calculates the impedance
of a transmission line (a board trace) given the board
parameters and the trace width for either microstrip or
symmetric stripline.

It also calculates the line width necessary to yield a
desired impedance given the board parameters for either
microstrip or symmetric stripline.

Definitions:

Microstrip is typically a board with traces on the top of
     the board and a ground plane on the bottom of the
     board.  The program assumes no traces run on inner
     layers between the ground plane and the trace on the
     top of the board.

     The ground plane can be on an inner layer with the
     board trace on the top of the board.

     The dielectric thickness is the distance between the
     ground plane and the trace on the top of the board.
     LINE-Z assumes that microstrip lines have an air
     dielectric on one surface.  Microstrip calculations
     will NOT yield correct results for buried traces.

     Example:  A 0.062 board has a ground plane on the
     bottom of the board and a trace on the top of the
     board.  The dielectric thickness is 0.062.

     Example:  A 0.062 board has a ground plane 0.025 below
     the top layer.  The microstrip traces are on the top
     layer.  The dielectric thickness is 0.025.

     Effective dielectric constant:  because microstrip has
     an air dielectric on one side and the board dielectric
     on the other, the apparent dielectric constant is
     different from either the dielectric constant of air or
     the dielectric constant of the board material.  This is
     the "effective dielectric constant".  Use this value
     when designing transmission lines to be a given number
     of wavelengths in length at a specified frequency.
     With stripline, the effective dielectric constant and
     board dielectric constant are the same because the
     trace is completely enclosed by the board material.

Stripline has two ground planes, one on each side of the
     trace.  LINE-Z assumes symmetric stripline, which means
     that the two ground planes are equally spaced from the
     circuit trace.

     The dielectric thickness is the distance between each
     ground plane and the circuit trace.

     Example:  A 0.062 board has ground planes on the top
     and bottom.  A circuit trace is run in the center
     midway between the two ground planes.  The dielectric
     thickness that should be entered into the program is
     0.031.

     Example:  A 0.062 board has a ground plane on the top
     surface and a second ground plane 0.030 below the top
     ground plane.  Traces are run midway between the two
     ground planes.  The dielectric thickness that should be
     entered into the program is 0.015.

The program calculates the following:

For Microstrip:
     The line width and effective dielectric constant given:
          the desired line impedance

          board dielectric constant (approximately 4.8 for
          FR-4)

          thickness of the dielectric

          thickness of the conductor metal

     The line impedance and effective dielectric constant given:
          the width of the conductor

          board dielectric constant

          thickness of the dielectric

          thickness of the conductor metal

For Stripline:
     The line width given:
          the desired line impedance

          board dielectric constant (approximately 4.8 for FR-4)

          thickness of the dielectric between EACH ground
          plane and the trace.

          thickness of the conductor metal

     The line impedance given:
          the width of the conductor

          board dielectric constant

          thickness of the dielectric between EACH ground
          plane and the trace.

          thickness of the conductor metal

REMEMBER:   With stripline, the dielectric thickness is the
            distance from each of the two ground planes to
            the trace in question.
