I just solved this same problem.
If you have more than one group of radio buttons, you can still use them in arrays:
<input type="radio" name="radiobutton[0]" value="a"><br>
<input type="radio" name="radiobutton[0]" value="b"><br>
<input type="radio" name="radiobutton[0]" value="c"><br>
<br>
<input type="radio" name="radiobutton[1]" value="x"><br>
<input type="radio" name="radiobutton[1]" value="y"><br>
<input type="radio" name="radiobutton[1]" value="z">
for example.
When you submit that form, and assuming you pick "a" and "x", you will have an array "radiobutton" that looks like
radiobutton[0] = "a";
radiobutton[1] = "x";
It works because each group has a unique name, but still uses the array syntax.
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