Wide band antenna for mobile communications

DETAILED DESCRIPTION It is therefore an object of the present invention to provide a wide band antenna system for mobile communications, in which a dual resonance created by a radiator and a sub-radiator is utilized to provide an increased and stabilized resonant frequency band such that the transmission and reception can be performed more freely and to provide such an antenna system which is reduced in size sufficiently to mount on an automobile and can be manufactured more easily.
To this end, the present invention provides a wide band antenna system for mobile communications, comprising a ground plate having a flat surface, an L-shaped radiator plate having one leg of L arranged parallel to said ground plate with the other leg being positioned perpendicular to said ground plate, said radiator plate being disposed having a gap between the lower end of said vertical leg and the upper surface of said ground plate, a coaxial feed cable for connecting said ground plate with an outer conductor and also for connecting an inner conductor with substantially the center of said vertical leg end of said radiator plate, and an additional conductive no-feed element (sub-radiator) formed by an L-shaped plate rigidly mounted on said ground plate at a position in close proximity to said radiator plate, said sub-radiator having one leg extending parallel to said ground plate with the end thereof being spaced away from the end of the parallel leg of said radiator plate by a given distance, the vertical leg of said L-shaped plate having the end connected with said ground plate to provide an increased band width.
In such an arrangement, the opened end of the radiator plate is located opposite to that of the sub-radiator with a given spacing therebetween.
This is intended to utilize the variations of a feed point impedance due to a current induced in the sub-radiator to provide a very widened frequency band in which the real part of the impedance can be maintained, at the same value as or a value very near to the impedance of the feed line (normally equal to 50 Ohms) under a resonant condition (or when the imaginary part of the impedance is equal to zero)