Patent GB-1001240-A (GB)
Title: Improvements in or relating to beam aerials
IPC: H01Q11/08
Filed: 1962-06-06
Abstract: 1,001,240. Aerials. H. EHRENSPECK. June 6, 1962 [June 13, 1961], No. 21841/62. Heading H4A. Relates to an end fire aerial comprising one or two helices adapted to produce linear or plane polarization, the crosssection of the helices being circular, square or triangular Such an aerial may comprise (1) a single helix having a mean turn circumference of one wavelength (#) at the intended frequency of use, (2) two helices arranged side by side in close proximity to one another each having a mean turn circumference of half a wavelength (#/ 2 ) or (3) a single helix having a mean turn circumference of #/2 and located adjacent a ground plane. When the aerial comprises one helix it may be fed at one end at two points S 1 , S 2 , Fig. 5, diametrically opposite on the end turn. A discussion with reference to Figs. 6 and 7 (not shown) of the voltage and current distributions on such a turn indicates that if its circumference is one wavelength each half behaves as a centre-fed halfwave dipole to produce linear polarization. An embodiment in accordance with this aspect of the invention comprises a single turn helix of the dimensions indicated above, fed at S 1 , S 2 , Fig. 8, supported at points A 1 , A 2 , A 3  &c. and B 1 , B 2 , B 3  &c. (A and B being diametrically opposite) by metallic or plastic rods. For an aerial comprising two helices in contact or close proximity along a common tangent and fed at points S 1 , S 2 , Fig. 13, on the end turns at opposite ends of diameters meeting at the common tangent, a discussion with reference to Figs. 10 and 11 (not shown) indicates that if the circumference of each is #/2, the aerial produces linear polarization. The two helices may be wound in the same or opposite directions. One embodiment according to this aspect of the invention is shown in Fig. 13 in which 3 and 4 represent supporting rods. Such an arrangement may also be produced from a single helix by compressing the turns of the helix with metal or insulating support rods 1 and 2, Fig. 12, or the double helix may be formed from a single wire wound with figure - eight turns. In another embodiment the fed end turn of each helix is formed in to a folded dipole 7, 8, Fig. 14, the dipole being connected to a feeder and a reflector 9 being disposed behind the dipole. In a further embodiment the helices W 1 , W 2 , Fig. 15, diverge from each other by a small angle and are excited by a dipole F and reflector R. The angle of divergence is made adjustable to vary the tuning of the aerial and a resistor 12 may be provided to improve matching. In the case of a single helix adjacent a ground plane, tuning may be effected by varying the displacement of the helix from, or its inclination to, the ground plane. To increase the frequency range of the aerial a variation of diameter and/or pitch of the turns with length may be employed. The aerial may be made from a collapsible spring or may be formed of metallized plastic tube cut into a helix. The Specification also refers to known linearly polarized helical aerial systems comprising two parallel spaced contrawound helices. Fig. 2 (not shown), or two collinear contrawound helices, Fig. 3 (not shown).