html in php (double quotes)

how do i echo out this html?

<a href="#login" onclick="popup('popUpDiv')">Login</a>

in php i tried:

echo '<a href="#login" onclick="popup('popUpDiv')">Login</a>';

but that doesnt work because of 'popUpDiv',
i tried arrays, it still doesnt seem to work

echo "<a href='#login' onclick='popup("."'popUpDiv')'>Login</a>"

i must be doing something wrong