consider
	awk '/'^(a b)^'/' /dev/null

	awk: can't open file /b/
	 source line 1

your case is similar:

	T=(a b)
	awk '/'^$T^'/' /dev/null

	awk: can't open file /b/
	 source line 1

and finally

	awk '/'^$"T^'/' /dev/null

success?  note the " before the T in the last one.