GB611052A - Improvements in or relating to coupling arrangements between aerials and transmission lines - Google Patents

Abstract

611,052. Electric resonators; aerials. STANDARD TELEPHONES & CABLES, Ltd., and WILLOUGHBY, E. O. Aug. 24, 1945, No. 21804. [Class 40 (viii)] [Also in Groups XL (a) and XL (c)] For matching two circuits having unequal impedances, such as two transmission lines or a transmission line and a valve or aerial, the inner conductor of a coaxial resonator is split longitudinally into two unequal parts which screen one another from the outer conductor, or an analogous arrangement of parallel wires may be adopted. The resonator may embody an aerial or a valve circuit. Impedance-transformation ; aerials. A transmission line 6, Fig. 14, is connected to a coaxial quarter-wave section 1, which is short-circuited at 2; and the solid or hollow inner conductor is formed with a tongue 5 so that the parts 3, 5 constitute a second quarter-wave resonator short-circuited at the end 6, but connected at the other end to a circuit which may comprise an aerial 14 and ground 15, or a second transmission line, Figs. 1, 2, 3 (not shown). The impedance ratio depends on the relative sizes of the surfaces of the large part 3 and small part 5, which electrostatically screen one another with respect to the outer conductor 1, so that the impedance between the ends of the parts 1, 5 is high. The parts 3, 5 may be replaced by wires, Figs. 6, 7 (not shown), and Fig. 31, one or more wires which correspond to the tongue 5 being screened by the remainder which correspond to the part 3, or for very high impedance a wire or rod may be enclosed in a tube having a longitudinal slot. Alternatively, Figs. 8, 9 (not shown), the short-circuit at 2 may be removed and a second transmission line corresponding to the load 14, 15 may be connected between the casing 1 and the part 3, or a balanced line may be connected to the upper ends of the parts 3, 5. Two resonators of the kind described may be joined together for connecting two balanced circuits, Figs. 12,. 13 (not shown), and the two-cleft inner conductors, being eccentric with respect to the common outer conductor, may be rotatable for varying the impedance. In modifications, the outer conductor 1 may be abolished, its function being then performed by the ground. In a further modification, an antenna of the kind described in Specification 580,569 comprises an upper plate 9, Fig. 15, a ground plate 15, a set of wires 3 connecting the two plates, and a wire 5 serving for an external connection, the wires being embedded in a hemisphere 17 of dielectric material. A folded antenna for aircraft, Fig. 16, may comprise quarter-wave parts 3, 5, separated by a slot 4, and have an earth plane 15 and a section of the form shown in Fig. 18, or in Fig. 19 where the dielectric is very thin, or the antenna may be tapered, Fig. 20 (not shown). The conductor 16 of the feeder may be connected to the free end of the part 5 as shown, or may pass through a channel in the part 3 up to a higher point on the part 5, Fig. 17 (not shown). Such an antenna may be balanced by supplying a plain counterpoise to form a dipole, Fig. 21 (not shown), which may have zero reactance at the midband and two other frequencies. In these arrangements, the antenna serves to match its low radiation resistance to the higher impedance of the feeder. In a tunable transformer giving a high impedance ratio, Fig. 29 (not shown) and Fig. 26, the tongue 5 may be replaced by an inner conductor 47 which is screened from the outermost conductor 1 except for a slot 46 in the intermediate conductor 3. The transformer is tuned by means of a piston 49, Fig. 27 (not shown) and Fig. 26, and two opposite slots 46 may be employed, Fig. 28 (not shown), to facilitate tuning. To make the impedance ratio adjustable, Figs. 29, 30 (not shown), the conductor 3 may be mounted eccentrically within the conductor 1, and the capacity between the innermost conductor 47 and outermost conductor 1 can then be varied by rotating the intermediate conductor 3 with its slot 46. As a limiting case, the parts 3, 47 may be replaced by an eccentrically located pair of strips or rods, which can be rotated within the casing 1. A hollow half-wave dipole, Fig. 39, may be slotted to form tongues 114, 115, and contain a valve oscillator, Fig. 40 (not shown), or one tongue may be in each half of the dipole, Figs. 41, 42 (not shown).