first off, i don't think you can include() files via HTTP protocol. You'll want to use a file system style path reference. ideally, it would be a relative path reference like this:
include('project/searchField.php');
secondly, if you want the variable $homepage to be defined when searchField.php gets evaluated, then just assign its value before you do the include like this:
$homepage = "myfile.html";
include('project/searchField.php');
Not sure what your code is doing, but i hope you find this useful.