Patent ID: 8378894

Claim:
A planar antenna device, comprising: a dielectric layer; and an upper and a lower conductor layer that vertically sandwich the dielectric layer, wherein the lower conductor layer is used as a ground, wherein the upper conductor layer forms a single radiating element having a structure in which five or more radiating element pieces are connected to a feeder line, a beginning portion of each of the radiating element pieces being aligned, and the lengths of each of the radiating element pieces defining a terminating portion for the upper conductor and exposing the dielectric layer beyond the terminating portion, and wherein the lengths and widths of the five or more radiating element pieces are selected such that the planar antenna device transmits electric power in at least a 1.5 GHz band in a range of operating frequencies between 4 GHz and 6 GHz for near field communication in which a communication distance is less than or equal to a wavelength corresponding to an operating frequency in the range, wherein the five or more radiating element pieces are each formed into rectangular strips on one side of the feeder line, and are connected in a width direction of the single radiating element to form the single radiating element, wherein, when the single radiating element includes N number of the radiating element pieces having the widths represented as W 0 , W 1 , . . . , and W N-1 and the lengths represented as L 0 , L 1 , . . . , and L N-1 , respectively, and connected in the width direction to the feeder line, the feeder line having a width W N , the widths and the lengths of the radiating element pieces are selected, for an effective wavelength λ g determined by the operating frequency, in order to satisfy each of formula (1) through formula (6): L 0 [[≈]]=λ g /2 (1) ∑ i = 0 N - 1 ⁢ W i + W N / 2 ≈ λ g / 2 ( 2 ) W 0 >W 1 > . . . W N-2 (3) L 0 >L 1 > . . . >L N-2 (4) W 0 [[≈]]=W N-1 (5) L 0 [[≈]]=L N-1 (6) wherein N represents an integer equal to or greater than five, and a subscript of W i and a subscript of L i represents an integer ranging from zero to N−1 assigned to each of the radiating element pieces as a serial number in order of decreasing distance from the feeder line, and wherein the width W N of the feeder line is selected based on an impedance of a transmission line.