Integrated Frequency-Reconfigurable Slot Antenna and Connected Slot Antenna Array for 4G and 5G Mobile Handsets

A dual-function slot antenna at microwave and millimeter-wave (mm-wave) band is proposed. The design consists of a slot printed on the edge of the structure ground plane. A short-circuited varactor diode (VAR) is used to achieve the frequency tunability from 2.05 to 2.7 GHz (4G, WLAN) with a maximum realized gain of 4.5 dBi. For mm-waveband, the slot works as a connected slot antenna array (CSAA) by using eight periodic feeders with a wide bandwidth of 23-29 GHz (5G) and a maximum realized gain of 12.5 dBi. To enhance the functionality, two slots are orthogonally arranged for multipleinput multiple-output (MIMO) application. The whole structure is implemented using Rogers 5880 substrate with a board size of 70 × 60 × 0.381 mm 3 . The envelope correlation coefficient (ECC) and isolation are calculated, showing satisfactory MIMO characteristics. The minimum ECC value is 0.01, while the isolation is more than 20 dB among different feeding ports. Due to the integration of 4G and 5G operations into a single narrow slot, the proposed antenna system is compact, simple, and planar in structure and, thus, attractive for future mobile handheld devices.