.cut File Format

Introduction

The .cut file format is used for storing field data generated by objects of the Grasp classes Spherical Cut, Planar Cut, Surface Cut, and Cylindrical Cut.

Currently supported formats

The following table shows the formats that grasp2alm can read.

ICOMP	ICUT	NCOMP	Description
3	1	2	Spherical cut far field, linear \(E_{co}\) and \(E_{cx}\)

File Structure

A .cut file consists of a series of records that describe the characteristics and data of field cuts. Each file may contain multiple cuts, and for each cut, all records must be repeated. There are three primary types of records:

1. Record Type 1: TEXT

   This record contains identification text to label and describe the cut. It is represented by a string of characters.

2. Record Type 2: Parameters

   This record defines the parameters for the cut:

   • V_INI: Initial value (real number)

   • V_INC: Increment value (real number)

   • V_NUM: Number of values in the cut (integer)

   • C: Constant value (real number)

   • ICOMP: Polarization control parameter (integer)

   • ICUT: Control parameter of the cut (integer)

   • NCOMP: Number of field components (integer)

   See Parameter Definitions for Spherical Cuts for more information about Sperical Cuts.

3. Record Type 3: Field Values

   These records contain the actual field values for each point in the cut. The number of components stored depends on the value of NCOMP:

   • If NCOMP = 2: the record contains two components of the field, F1 and F2.

   • If NCOMP = 3: the record includes an additional third field component, F3.

   For each data point I (single row):

   • the parameter V is \(\mathrm{V\_INI}+\mathrm{V\_INC} \cdot (\mathrm{I}-1)\)

   • F1, F2 (and F3 if applicable) store the real and imaginary parts of the field components in the direction associated to V and C.

   See Field Component Details Based on ICOMP for more information

Example of a typical .cut file:

identification text
V_INI V_INC V_NUM C ICOMP ICUT NCOMP
F1.real F1.img F2.real F2.img F3.real F3.img
...

Parameter Definitions for Spherical Cuts

The V and C values are angles in degrees whose definition is controlled by the parameter ICUT:

• ICUT = 1: A standard polar cut where \(\phi\) is fixed (C) and \(\theta\) varies (V)

• ICUT = 2: A conical cut where \(\theta\) is fixed (C) and \(\phi\) varies (V)

Regarding ICOMP, it could be one of the following values:

• 1: Linear \(E_\theta\) and \(E_\phi\)

• 2: Right hand and left hand circular (\(E_{rhc}\) and \(E_{lhc}\))

• 3: Linear \(E_{co}\) and \(E_{cx}\) (Ludwig’s third definition)

• 4: Linear along major and minor axes of the polarization ellipse, \(E_{maj}\) and \(E_{min}\)

• 5-8: Various XPD (Cross-Polar Discrimination) fields

• 9: Total power \(|\vec{E}|\) and \(\sqrt{E_{rhc}/E_{lhc}}\)

Finally, when the field is a near field, NCOMP is equal to 3 and the file contains also a third radial component \(E_{r}\).

Field Component Details Based on ICOMP

• ICOMP = 1, 2, 3, 5, 6, or 7:

  • F1, F2 (and optionally F3) contain the real and imaginary parts of the field in a linear scale.

• ICOMP = 4:

  • Real part of F1: Major axis of the polarization ellipse (linear scale)

  • Real part of F2: Minor axis of the polarization ellipse (linear scale)

  • Imaginary parts of F1 and F2 are zero.

• ICOMP = 8:

  • Real part of F1: Major axis divided by the minor axis of the polarization ellipse (linear scale)

  • Real part of F2: Minor axis divided by the major axis of the polarization ellipse (linear scale)

  • Imaginary parts of F1 and F2 are zero.

• ICOMP = 9:

  • Real part of F1: Total power \(|\vec{E}|\) of the field (linear scale)

  • The imaginary part of F1 is zero.

  • F2: Complex square root of the ratio rhc/lhc. The phase indicates the rotation angle of the polarization ellipse.