GB592760A - Improvements in dipole antenna systems - Google Patents

Abstract

592,760. Aerials. STANDARD TELEPHONES & CABLES, Ltd., and WILLOUGHBY, E. O. Feb. 6, 1945, No. 3047. [Class 40 (v)] A broadband dipole antenna system, especially for use on aircraft, comprises two conducting elements to each of which one conductor of a feeder is connected, each element being electrically unbalanced with respect to earth about its feed point, the elements overlapping along the whole of their lengths so that the system is electrically balanced with respect to earth about a point intermediate of its ends. The ends of the overlapping elements are joined so that their oppositely disposed edges constitute short-circuited transmission lines, the design being such that the reactance changes at frequencies differing from the resonance frequency are substantially equal and opposite to the changes of the series resonant circuit formed by the equivalent overall dipole across the feeder. The antenna, Figs. la, 1b and 1c, comprises a conducting member 1 of streamlined cross-section with a Z-shaped slot 2 extending longitudinally as shown on both sides. The member 1 thus slotted comprises two overlapping elements consisting of the portions 4 5 and 6, 7 respectively, joined by end portions 8 and 9 respectively. The element 4, 5 is connected to the outer conductor 10 and the element 6, 7 to the inner conductor 11 of a coaxial feeder, the outer conductor 10 forming a support. By this arrangement the portion 4, 8 of the element 4, 5 has a greater capacity to earth than the portion 5 on the opposite side of the feed point and similarly the portion 6, 9 of the element 6, 7 has a greater capacity to earth than the portion 7, the effective dipole being formed by the difference of the capacities to earth of the elements on each side of the antenna. In the arrangements of Figs. 2a, 2b, 2c (not shown), the antenna is formed of a tubular member of streamlined cross-section closed at its ends and divided by central transverse slots into two portions. One portion is divided along its upper surface by two longitudinal slots leaving a central tongue and the other portion is similarly divided along its under-surface by .slots leaving a tongue. In a further arrangement, Figs. 3a, 3b, 3c (not shown), the antenna is in the form of a cylindrical member closed at its ends by conducting discs, the member being slotted in the same way as in Figs. 2a, 2b, 2c. The lengths of the shortcircuited transmission lines constituted by the longitudinal slots in the various embodiments may be designed of such length as to be antiresonant at the mid-band operating frequencies If the transmission lines are less than #/4 at the mid-band frequencies, a condenser may be provided as illustrated in Fig. 4 (not shown). The capacity of this condenser may be varied by a control extending outside the antenna. Alternatively, these slot transmission lines may be shortened electrically by filling the tubular members and slots with suitable dielectric material.