Perhaps you should try some spelling variations:
"medium connectivity" » "media connectivity", "maximum connectivity", "minimum connectivity"
"array directivity" » "array connectivity", "beam directivity"
"array directly" » "arrays directory", "arrays direct", "library directly"

Try widening your search to All Fields.

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: (((("array directivity") OR ("array directly"))) OR ("medium connectivity")).
• The words AND, OR and NOT may confuse the search; try adding quotes: "((((\"array directivity\") OR (\"array directly\"))) or (\"medium connectivity\"))".
• Removing quotes may allow a broader search: (((( array directivity ) OR ( array directly ))) or ( medium connectivity )).
• Adding a wildcard symbol may retrieve word variants: (((("array directivity") OR ("array directly"))) or ("medium connectivity"))*.