| 摘要 |
The invention relates to a directive broad band antenna element of V-shaped dipole type with bent wire- or strip-shaped dipole antenna (A). The dipole antenna is divided into two sections, a first section (S1) where the radiation is minimized (or prevented) by a small distance between the conductors and a reduced phase velocity, and a second section (S2), where the radiation is enhanced by increasing the phase velocity by means of introduced series capacitances (C1, C2, . . . Cn). The series capacitances have respective values which depend on the local angle between the dipole conductors and a radiation axis (x), and are chosen such that the phase velocity is increased to a value which effects radiation contributions from different parts of the conductors to cooperate in the desired radiation direction. Because of the series capacitances, the curvature of the conductors can be made much sharper and the extension of the antenna in the radiation direction will be much smaller for a given frequency band than in the case without series capacitances. This in combination with the reduced (inhibited) radiation from the first section (S1) causes the displacement of the center of radiation (the phase center) with frequency to be limited. Thus the antenna element can operate over a very extended frequency band (on the order of 2 to 3 octaves) and still serve as a primary radiator for illuminating a secondary radiator having a focal point, such as a parabolic reflector or an electromagnetic lens. The reduced phase velocity at the first section (S1) can be achieved by means of a small dielectric disc (D) place between the dipole conductors of the first section and/or zig-zag shaped or inwardly toothed conductors in the first section (S1). |
