Sub TabFunc()

Const Rbegin = "B4"
Const xBegin = 0, xEnd = 1, xStep = 0.1
Const yBegin = 0, yEnd = 1, yStep = 0.1
Const argMax = 1

Dim Rxy, arg
Dim Nx, Ny, i, j, x
Nx = Round((xEnd - xBegin) / xStep + 1, 0)
Ny = Round((yEnd - yBegin) / yStep + 1, 0)

ReDim MasOut(Nx, Ny)

MasOut(0, 0) = ""
For i = 1 To Nx
    MasOut(i, 0) = xBegin + xStep * (i - 1)
Next

For j = 1 To Ny
    MasOut(0, j) = yBegin + yStep * (j - 1)
Next

For i = 1 To Nx
    x = xBegin + xStep * (i - 1)
    For j = 1 To Ny
        arg = x ^ 2 + (yBegin + yStep * (j - 1)) ^ 2
        If arg <= argMax Then MasOut(i, j) = Atn(arg / (Sqr(1 - arg ^ 2) + 0.000000000000001)) Else MasOut(i, j) = "?? ???."
    Next
Next

Sheets.Add After:=Sheets(Sheets.Count)
Range(Rbegin + ":" + Range(Rbegin).Offset(Nx, Ny).Address) = MasOut

End Sub