PROGRAM:  GRATING.F 

   Program GRATING computes the exact reflection and transmission
      coefficients for a p.e.c. strip grating. For this exact
      solution, the strip width to cell size ratio is 0.5 and the 
      excitation is normally incident. The solution is due to Weinstein using 
      the factorization method.

   The geometry is
                           |
                           |
                          \ /
                           .

  ...     -----     -----     -----     -----     ... (in/out of screen)
            |<--Ty-->|

      where Ty is measured in wavelengths. THE MAXIMUM CELL SIZE IN
      WAVELENGTHS IS 1.0

   The field reflection and transmission coefficients are computed for the
      polarization with the electric field perpendicular to the grid. 
      For the polarization with the electric field parallel to the grid simply
      interchange R and T. Cell sizes are entered as input.

AUTHOR: Tom Cwik
	Jet Propulsion Laboratory
	MS 238-725
	Pasadena CA  91109

	cwik@yosemite.jpl.nasa.gov
 
LIBRARIES: none 

SAMPLE I/O:
            microwave{cwik}3: grating
            ENTER: BEGIN Ty, END Ty, DELTA Ty
            .1 .9 .1
            microwave{cwik}4: cat grating.dat

     Ty      |R|     <R      |T|     <T      P CHECK  TERMS SUMMED
   0.100   0.068    86.1   0.998    -3.9     1.000       17
   0.200   0.137    82.1   0.991    -7.9     1.000       23
   0.300   0.208    78.0   0.978   -12.0     1.000       28
   0.400   0.281    73.7   0.960   -16.3     1.000       32
   0.500   0.357    69.1   0.934   -20.9     1.000       36
   0.600   0.437    64.1   0.900   -25.9     1.000       39
   0.700   0.523    58.5   0.852   -31.5     1.000       43
   0.800   0.620    51.7   0.785   -38.3     1.000       45
   0.900   0.735    42.7   0.678   -47.3     1.000       48