radio button arrays and php3

hi there i dont know if this happens in php4 but say i have a list of radio buttons in an array like <input type="radio" name="secondary_banner[]"> <input type="radio" name="secondary_banner[]"> it only returns the one selected into the array, so instead of having 2 keys i only get the one , the empty one doesnt seem to get submitted , how can i make both turn up in the array ?