Unambiguous CFG for $a^ib^j$ where $i \le j \le 2i$

Question

could you please help me for finding an unambiguous CFG for the following expression: $a^ib^j$ where $i \le j \le 2i$

Answer 1

$S \rightarrow$ $aSb$ | $J$

$J \rightarrow aJbb$ | $ε$

This has only one derivation tree for a word in that language.