Mode-Controlled Wideband Slot-Fed Ground Radiation Antenna Utilizing Metal Loads for Mobile Applications

In this communication, we introduce a mode-controlled ground radiation antenna comprised of a resonance-controlled ground plane and a nonradiating feeding slot for wideband applications in mobile devices. A 110 mm \times50 mm ground plane for 850-MHz operation is studied as a test case. The resonant frequency of the ground plane is lowered by adding metal loads at the top and bottom intended for strong coupling with a miniature feeding slot located at one end, so that the ground plane is resonant as a half wavelength dipole-type radiator. The metal loads can be the structures of strips, plates, or wires, and they can take the form of broken metal rims or frames with cuts or gaps in smartphones. In addition, the metal loads are connected to the ends of the ground plane by lumped elements (inductors and/or capacitors) for easy control of the resonance mode and compact design. Equivalent circuit model and corresponding equations are provided for theoretical analysis. The impedance bandwidth based on 3:1 VSWR is 210 MHz (from 760 to 970 MHz), with an average efficiency of 77%. Geometrical characteristics of the metal loads are shown to be important parameters for the antenna performance.