.grd File Format

Introduction

This format is used for storing field values in a rectangular grid. Files of this type are generated by objects of the classes Spherical Grid, Planar Grid, Surface Grid, and Cylindrical Grid. The file extension is .grd.

The field points are in all cases parameterized by two variables which are generally denoted X and Y and which run from XMIN to XMAX and from YMIN to YMAX, respectively. The file is organized so that X varies faster than Y.

The variables X and Y should be considered as general names for the actual variables which may e.g. be \(\phi\) and \(\theta\) for points on a sphere or any of the other options as specified by IGRID below.

All angles are in degrees.

Currently supported formats

The following table shows the formats that grasp2alm can read.

KTYPE

ICOMP

NCOMP

IGRID

Description

1

3

2

7

\(\theta\phi\mathrm{-grid}\) far field beam, linear \(E_{co}\) and \(E_{cx}\)

File Structure

A .grd file consists of four primary types of records:

  1. Record Type 1: TEXT

    Record with identification text. This record is repeated until a record containing ++++ as the first 4 characters is reached.

  2. Record Type 2: File format

    An integer that specifies the file format:

    • KTYPE = 1: standard format for 2D grid. For files used in TICRA Tools, this variable is always 1.

  3. Record Type 3: Parameters

    This record defines the parameters for the grid (they are all integers):

    • NSET: Number of field sets or beams.

    • ICOMP: Control parameter of field components.

    • NCOMP: Number of components.

    • IGRID: Control parameter of field grid type.

  4. Record Type 4: Center definition

    This record contains a list of two coordinates. The number of entries (rows) is equal to NSET.

    • IX, IY: two integers representing the center of each set or beam

All the following records are repeated NSET times.

  1. Record Type 5: Grid limits

    Four parameters represent the limits of the 2D grid.

    • XS, YS, XE, YE: four real numbers, the unit of X and Y follows the settings in the generating project, angles are in degrees.

    The grid points (X,Y) run through the values:

    \[ \begin{align}\begin{aligned}\mathrm{X} = \mathrm{XCEN} + \mathrm{XS} + \mathrm{DX}*(\mathrm{I}-1)\\\mathrm{Y} = \mathrm{YCEN} + \mathrm{YS} + \mathrm{DY}*(\mathrm{J}-1)\end{aligned}\end{align} \]

    where

    \[ \begin{align}\begin{aligned}\mathrm{DX} = (\mathrm{XE}-\mathrm{XS})/(\mathrm{NX}-1)\\\mathrm{DY} = (\mathrm{YE}-\mathrm{YS})/(\mathrm{NY}-1)\end{aligned}\end{align} \]

    with

    \[ \begin{align}\begin{aligned}\mathrm{XCEN} = \mathrm{DX}*\mathrm{IX}\\\mathrm{YCEN} = \mathrm{DY}*\mathrm{IY}\end{aligned}\end{align} \]

  2. Record Type 6: Number of columns and rows

    This record specifies the number of columns and rows for the current beam:

    • NX: number of columns (integer)

    • NY: number of rows (integer)

    • KLIMIT: specification of limits in 2D grid (integer)

      =0 Each row contains data for all NX columns

      =1 The number of data points for each row is defined in the record n°7

The following records 7 and 8 are repeated NY times for each beam

  1. Record Type 7: Number of columns and rows

    This record is read if and only if KLIMIT = 1. It specifies how a single row J is structured.

    • IS: Column number of first data point in row J

    • IN: Number of data points in row J

    If IN is 0 (there are no values in the row) skip record n°8, otherwise continue to the next record reading the field components.

  2. Record Type 8: Field components

    If KLIMIT is 0 then IS and IN are always assumed to be 1 and NX, respectively. With \(\mathrm{IE}=\mathrm{IS}+\mathrm{IN}-1\).

    The record contains a list of \((\mathrm{IE}-\mathrm{IS})\) entries representing the complex field components.

    • F1, F2, F3: Complex field with two or three components depending on NCOMP.

Example of a typical .grd file:

VERSION: TICRA-EM-FIELD-V0.1
Field data in grid
SOURCE_FIELD_NAME: field_name.po
FREQUENCY_NAME: freq
FREQUENCIES [GHz]:
    0.1190000000E+03
++++
KTYPE
NSET    ICOMP   NCOMP   IGRID
IX  IY
XS  YS  XE  YE
NX NY KLIMIT
F1.real F1.img F2.real F2.img F3.real F3.img
...

Parameter Definitions for Spherical Cuts

The field components F1, F2 are controlled by the parameter ICOMP. For near fields, the third component F3 always contains the radial \(E_r\) component.

  • ICOMP:

    • 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 \(\sqrt{E_{rhc}/E_{lhc}}\)

  • NCOMP, number of field components:

    • 2: the file contains twinner producto field components for each point as specified above.

    • 3: if the field is a near field the file also contains the third radial component.

  • IGRID, type of field grid:

    • 1: uv-grid, where u and v are the two first coordinates of the unit vector to the field point

    • 4: elevation over azimuth

    • 5: elevation and azimuth

    • 6: azimuth over elevation

    • 7: \(\theta\phi\mathrm{-grid}\)

    • 9: azimuth over elevation, EDX definition

    • 10: elevation over azimuth, EDX definition