Set more variables to URL

[Earliboy]

Hello,
I'm currently editing a php script. The current URL is /file.php?id=2. I got an form which sets limit_rows so after refresh the url should look like /file.php?id=2&limit_rows=500
May its cause I'm too tired but what i get out of this is /?&limit_rows=500.

May you find whats wrong or what i forgot to add.

?>
	<center>
	<h5>Enter number of lines you want to see.</h5>
	<table>
		<form action="&" method="get">
			<input type="text" name="limit_rows" />
				<br/>
			<input type="submit" value="Refresh" />
		</form>
	</table>
	</center>
	<br>
<?php
	echo isset($_GET['limit_rows']) ? htmlspecialchars($_GET['limit_rows']) : '';

And no, the ?> isnt wrong, i just don't wanna copy&paste a 2k line script ^^.

Thanks for help.
Earli.