Patent GB-875293-A (GB)
Title: Logarithmically periodic antenna
IPC: H01Q11/10
Filed: 1958-11-07
Abstract: 875,293. Aerials. COLLINS RADIO CO. Nov. 7, 1958 [March 14, 1958], No. 35854/58. Class 40(7) A wide-band aerial system comprises two half portions each arranged about a centre line extending from the centre of system. The half-portions have apices adjacent each other and the system centre and comprise a plurality of radial members included within an angle of half the portion apex angle from the portion centre line. Each radial member has a plurality of conductive teeth extending away from the centre line and the teeth of one radial member are staggered with respect to those of another radial member in the same portion. In simpler embodiments of the invention there are two radial members in each half portion and these may extend in the same plane. In an embodiment of the type, Figs. 1 and 2, the apex angle is α and the centre point indicated at 12. The aerial is fed by a co-axial line 29 carried along the centre line of the portion 11 and connected to the apices of the half-portions 10 and 11 across the gap at 12. The outer conductor of the co-axial line in conductively connected to the part 11 along its length to convert the feed to a substantially balanced one. In this embodiment the teeth are cut-in to lines making an angle #/2 with the centre lines 13 or 14 and have their sides at right-angles to the centre lines. The radial distances of the inner sides of adjacent teeth from the apex of half portion have a ratio equal to a constant (#) and the similar distances to the inner and outer sides of a given tooth have a ratio equal to a second constant (o). It is preferred to arrange for o to equal ##. It may be noted from the Figure that the two half portions are not mirror images but that one is reversed with respect to the other, and that the thickness of the radial members increases from the apices outwards. The tooth side ratio is maintained down to a small value and then the members finally terminated in a triangle for practical reasons. The sizes of the smallest and of the largest teeth control the bandwidth which may in theory be made infinite. As shown in Fig. 2, the two half portions may be arranged with an angle #, of less than 180 degrees, between them to give a directive pattern as indicated at 26. They may also have their centre lines continuous, or the members of the half portions may make an angle of other than 180 degrees with each other along the centre lines. Instead of being formed of conductive sheet material the aerial may be formed in skeleton form from rod or wire (Fig. 3, not shown). The skeleton form may be simplified by making #=0 and forming the half portions on single central backbones co-incident with the centre lines (Fig. 4, not shown). A further simplification is shown in Fig. 5 in which the trapezoidal teeth shape is modified into a triangular shape. In the embodiments the constant ratio relationships quoted above still apply and alternate ones of the zig-zag rod elements are parallel. The mounting of an aerial of the type shown in Fig. 5, but formed of wire, on masts carrying suitable guy wires is described with reference to Figs. 6A and 6B (both not shown). There may be more than two radial members in each half portion and where the half portions are aligned the system is omnidirectional or substantially omnidirectional. A system with four radial members per half portion and constructed along the lines described with reference to Fig. 4 (not shown) is illustrated in Fig. 11. In this embodiment, as in similar embodiments using sheet metal radial members and skeleton triangular teeth (Figs. 8 and 12, respectively, both not shown), the teeth are spirally related, that is they form a regular spiral staircase round the half portion. This spiral teeth arrangement is a characteristic however many radial members are used and in the limit when the number of radial members is infinite the half portions become spiral-grooved cones (Fig. 9, not shown). It is stated that omnidirectional systems of the form having more than two radial members may be mounted over a ground plane. Modified tooth forms are illustrated in Figures 13 and 14a. If preferred any of the embodiments may be fed by a balanced feeder led in along the plane mid-way between the two half portions.