1. Xi'an Jiaotong University; Electronic Materials Research Laboratory, Key Laboratory of the Ministry of Education and International Center for Dielectric Research; Xi'an 710049 China
2. Wright-Patterson Air Force Base; Materials and Manufacturing Directorate, Air Force Research Laboratory; OH 45433 USA
3. Center of Microwave and Millimeter Wave Technology, Beijing Institute of Technology; School of Information and Electronics; Beijing 100081 China