You can contact the National Air & Space Museum Archives section where all of the Captured German and Japanese Air Technical Documents are kept. Just submit a request and they will provide you with the titles of the "hohentwiel radar" documents that they have. Then it's up to you to decide on what you want to order.
http://airandspace.si.edu/collections/archival/german-japanese-tech-docs.cfm
They will most likely have what you are looking for, it's just the process that can take a while.