What the correct URL for searching on KM Index

I have an application that supposed to mimics a KM search over TREX Index.

When Pressing the button "search" I operate the following url:

<i>"/irj/servlet/prt/portal/prtroot/com.sap.km.cm.basicsearch?layoutSetMode=exclusive&ResourceListType=com.sapportals.wcm.SearchResultList&SearchType=ctrlpers&QueryString="str"&SelectedSearchIndices="+ Index</i>

The var "str" stands for the input field (the search Item)

The var "Index" stands for the Index.

It doesn't work!

What am I doing wrong?

Thanks,

Meytal.