ifr2d -- a Method of Moments code to compute broadside scattering and IFR
off of cylindrical struts.

Walter Brisken (wbrisken@nrao.edu) 2003/11/24

to use: 
	ifr2d <input file> [options]

Run with no arguments to get help.

Currents, scattered field, and IFR are calculated for a strut with cross
section described by the polygon(s) in <input file> for each value of <r>.
By default, a range of <r> between <r1>=0.05 and <r2> = 2.0 with <dr> = 0.05
is used to drive computation.  <r1>, <r2> and <dr> can be overridden at the
command line.  Alternatively, <r> can be set on the command line if only
a single <r> is desired.  This is useful when currents or fields are 
being studied.  The structure being studyied is assumed to be of infinite
extent in the z axis.  An incoming plane wave from the -x axis is the source
of excitation.

INPUT FILE
~~~~~~~~~~
<input file> is an ascii text file containing vertices of the polygonal
structure to be computed.  Each row must be of one of the three supported
types:

COMMENT a line beginning with # -- all input is ignored

DATA a line containing two floating point numbers designating the X and Y
coordinates of a vertex.  Consecutive DATA lines will cause a line segment
to join the two vertices.

SPACER a non-COMMENT, non-DATA line, ususally just a blank line.  The end 
of the file is equivalent to a SPACER line.  When a SPACER line is
encountered, the polygon is closed -- ie a line segment is drawn between
the most recent vertex and the first vertex of the polygon.

A disconnected strut can be made by separating two polygons by a SPACER
line.

It is important that each polygon is simply connected, does not cross itself,
and is defined in a clockwise manner.  Also, two polygons that cross
each other will likely produce non-sensical results.
The polygon(s) are gridded with current elements with a minimum spacing of
<dx>.  <dx> defaults to 0.1 but can be set on the command line as well.  

OUTPUT FILES
~~~~~~~~~~~~
Six files are created as output.  The filenames are made by appending 
different suffixes to the input filename.

<input file>.polygon  

A two column text file showing the gridding of the polygon.

<input file>.ifr  

A seven column text file containing:

	r		The ratio of strut width to wavelength
	|IFR_E|		The magnitude of the induced field ratio for E 
			orthogonal to the z axis.
	|IFR_H| 	The magnitude of the induced field ratio for E 
			parallel to the z axis.
	Re{IFR_E},
	Im{IFR_E} 	The real and imaginary parts of IFR_H
	Re{IFR_H},
	Im{IFR_H} 	The real and imaginary parts of IFR_H

<input file>.TE.currents,
<input file>.TM.currents  

Two column files containing tabulated currents on the structure.  A given 
line corresponds to the same line in the <input file>.polygon file.  The 
two columns are the two complex parts of the current.  Note that if 
multiple values of <r> are executed, the results will be appended.  Before 
each output set will be a comment line containing the value of r for the 
following set.

<input file>.TE.field,
<input file>.TM.field

Two column file conaining tabulated far field patterns in the Transverse 
Electric and Transverse Magnetic cases.  They are tabulated every degree 
and contain the real and imaginary parts of the field. Note that if 
multiple values of <r> are executed, the results will be appended.  Before 
each output set will be a comment line containing the value of r for the 
following set.