GB654935A - Improvements in and relating to high frequency antennae - Google Patents

Abstract

654,935. Aerials. BRITISH THOMSONHOUSTON CO., Ltd. Nov. 19, 1946, No. 34270. Convention date, Nov. 19, 1945. [Class 40 (vii)] An antenna including a half-wave folded dipole element curved in an arc and having means coupled to the elementfor supplying high-frequency energy thereto, is characterized by one or more conductors two ends of which are in spaced relation, one to each of the folded ends of the element to form a substantially closed loop, the effective length of the element and conductor(s) jointly being an integral, number of wavelengths of the carrier frequency used. The antenna is a development of that described in Specification 561,251, and is of particular value for vertically stacked arrays operating at high frequencies. In such arrays where the antennµ are arranged round a central supporting mast at one wavelength intervals the individual antenna of the prior Specification may not be of sufficient circumference to contain an adequately strong mast. A radiator according to the present invention may, for example, have an electrical length of a full wavelength. Such an antenna (Fig. 2) comprises a pair of closely spaced semi-circular conductors 19, 20, conductively connected at their ends by blocks 21 and 22 which are capacitively coupled respectively with blocks 23 and 24 joined by a further semicircular radiating member 25. Capacity variations between the pairs of blocks made by adjustment of screw mounted discs 27 and 28 enable the total electrical length of the aerial to be adjusted to a full wavelength at the operating frequency. The elements of the antenna may be supported at null points by metallic members 26 attached to the central mast 1 which may also be metallic. The antenna may be fed at 33 and 34 and where a number are fed in parallel as in a vertical stack quarter wave matching sections may be included between each antenna andthe common feeder. In a further embodiment, Fig. 3 (not shown), the circumference of the radiator is equivalent electrically to two wavelengths and is in four sections. Two energized oppositely disposed sections are similar to the sections 19, 20, 21, 22, of the previous embodiment but only occupy a quarter of the total circumference each. They are energized in parallel. The intervening sections are single segments (similar to 25) capacitively coupled to the energized portions at their ends. Mechanical support may be at the mid-point of each section as in the previous case. If a stacked array is arranged round a tapering supporting mast individual antennµ may vary between those of Specification 561,251, at the top to those of the present invention as the mast thickens lower down.