AddCPWPort
==========
```{function}  AddCPWPort( CSX, prio, portnr, materialname, start, stop, gap_width, dir, evec, varargin )
```
Full definition:
```{code-block} matlab
[CSX,port] = AddCPWPort( CSX, prio, portnr, materialname, start, stop, gap_width, dir, evec, varargin )
```

- CSX:          CSX-object created by InitCSX()
- prio:         priority for excitation and probe boxes
- portnr:       (integer) number of the port
- materialname: property for the CPW (created by AddMetal())
- start:        3D start rowvector for port definition
- stop:         3D end rowvector for port definition
- gap_width:    width of the CPW gap (left and right)
- dir:          direction of wave propagation (choices: 0, 1, 2 or 'x','y','z')
- evec:         excitation vector, which defines the direction of the e-field (must be the same as used in AddExcitation())

variable input:

-  varargin:    optional additional excitations options, see also AddExcitation
- 'ExcitePort'  true/false to make the port an active feeding port (default
                is false)
- 'FeedShift'   shift to port from start by a given distance in drawing
                units. Default is 0. Only active if 'ExcitePort' is set!
- 'Feed_R'      Specify a lumped port resistance. Default is no lumped
                port resistance --> port has to end in an ABC.
- 'MeasPlaneShift'  Shift the measurement plane from start t a given distance
                in drawing units. Default is the middle of start/stop.
- 'PortNamePrefix' a prefix to the port name

Important: The mesh has to be already set and defined by DefineRectGrid!

example:

    CSX = AddMetal( CSX, 'metal' ); %create a PEC called 'metal'
    start = [0       -width/2  0];
    stop  = [length  +width/2  0];
    [CSX,port] = AddCPWPort( CSX, 0, 1, 'metal', start, stop, gap_width, 'x', ...
                                  [0 0 -1], 'ExcitePort', true, 'Feed_R', 50 )
Explanation:
  - this defines a stripline in x-direction (dir='x')
    --> the wave travels along the x-direction
  - with an e-field excitation in -z-direction (evec=[0 0 -1])
  - the excitation is active and placed at x=start(1) ('ExcitePort', true)
  - a 50 Ohm lumped port resistance is placed at x=start(1) ('Feed_R', 50)
  - the width-direction is determined by the cross product of the
      direction of propagtion (dir='x') and the excitation vector
      (evec=[0 0 -1]), in this case it is the y-direction
  - the stripline-metal is created in a xy-plane at a height at z=start(3)
    --> The upper and lower reference plane (ground) must be defined by
    the user

Thorsten Liebig <thorsten.liebig@gmx.de> (c) 2014

See also InitCSX DefineRectGrid AddMetal AddMaterial AddExcitation calcPort