Design of the current driver for inducing radiating ground edge current in a printed circuit board

Abstract

A new current driver is proposed to effectively excite ground edge current for radiation without additional space reserved for antenna design. Since the current driver functions as a feeding structure as opposed to a radiator, it can be designed as small as possible without deteriorating the antenna radiation properties. A circuit model of the miniaturised balun (balanced to unbalanced transformer) is introduced to explain the current-inducing mechanism and to provide some valuable physical insights into the characteristics of the current driver. The effect of a shielding metal box for the proximity circuitry near the current driver is also investigated. And it is shown that the nearby shielding box has minor effect on the performance of the driver, which demonstrates the feasibility of the current driver as an effective antenna structure in a compact wireless terminal. The current driver operating at 2.45 GHz is printed on an FR4 substrate of 0.4 mm and occupies only a small area of about 4 mm by 4 mm. The simulated and measured results come to a great agreement. Nearly omni-directional radiation patterns with a peak gain of about 1 dBi are obtained. Owing to the design flexibilities and the compactness, the current driver is feasible for wireless applications.