Hi,
Try my code for your requirement.
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title></title>
<script language ="javascript" >
function f2() {
location.href = "Search.aspx?PropertyType=" + document.getElementById("cmb_type").value;
}
</script>
</head>
<body>
<form id="form1" runat="server">
<div>
<input type="button" id="btn" value="search" onclick="f2()"/>
<select id="cmb_type" style="width:100px;">
<option value="type">type</option>
<option value ="sgh">subtype</option>
</select>
</div>
</form>
</body>
</html>
input type must be button not submit k
the javascript method invoke only for button type only
All the best