I. Introduction
Millimeter-wave communication, as one of the key technologies for the fifth-generation (5G) wireless communications, has attracted drastically increasing attention worldwide [1]. Among the potential millimeter-wave bands, Q-band communication has attracted much attention in recent years [1]–[3]. In particular, a new millimeter-wave wireless communication standard Task Group, known as the IEEE 802.11aj Task Group, was founded in September 2012 for promoting Q-band millimeter-wave communication standard [2], [3]. In the World Radiocommunication Conference 2015, 40 GHz band or Q-band was selected as one of the study bands to develop 5G mobile communications [4]. Several research have been carried out in this area, especially for the design of antennas for Q-band communications [5]–[11].