Improvements in radio antennas


614,419. Aerials. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Jan. 16, 1946, No. 1458. Convention date, Aug. 31, 1944. [Class 40 (vii)] A short-wave broad-band dipole aerial comprises two cylindrical conductors 1 and 3, each of length #/6 and diameter #/16, to which are attached coaxial circular fins of conductive material 15, 17, 19 and 15<1>, 17<1>, 19<1> normal to the axis of the conductors and spaced at intervals of #/32, the central fins 17 and 17<1> having a diameter of #/5 and the other fins having a diameter of #/7, whereby the impedance is maintained relatively high so that the aerial may be matched directly to available transmission lines having characteristic impedances of the order of 50-70# without the use of special impedance transformers. The fins may be regarded as providing a distributed inductance which resonates with the capacitative reactance of the cylindrical conductors over a broad band. Suitable dimensions are given for a dipole operating over a frequency band centred at 600 Mc/s. The two conductors are supported in colinear relationship upon an insulating member 5 which is secured by means of a clamp 7 to a tubular support 9 and a pair of coaxial transmission lines 11 and 13 extend through the support with their outer conductors connected to the support and their inner conductors connected to the adjacent ends of the cylindrical conductors, Figs. 2 and 3 (not shown). In Fig. 4 (not shown), the dipole is mounted coaxially with the focal line of a cylindrical parabolic reflector of focal length .3# and aperture 4.5#.




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