Patent ID: 7872612

Claim:
An antenna apparatus which is connected to a first transmission line having a predetermined characteristic impedance, the first transmission line including a pair of first planar line conductors electrically separated from each other such that magnetic lines of force are generated surrounding the first planar line conductors and perpendicularly intersect electric lines of force when electromagnetic waves travel on the first transmission line, the antenna apparatus comprising: a tapered line portion connected to one end of the first transmission line, the tapered line portion including a second transmission line including a pair of second planar line conductors electrically separated from each other such that magnetic lines of force are generated surrounding the second planar line conductors and perpendicularly intersect electric lines of force when electromagnetic waves travel on the second transmission line, the tapered line portion keeping a predetermined characteristic impedance constant and expanding at least one of a width of the second transmission line and an interval in a tapered shape at a predetermined taper angle; and an aperture portion having a radiation aperture connected to one end of the tapered line portion, the aperture portion including a pair of parallel planar line conductors separated from each other, wherein a size of one side of the aperture end plane of the aperture portion is set to be equal to or higher than a quarter wavelength of the minimum operating frequency of the antenna apparatus.