GB579778A - Improvements relating to radio antennae - Google Patents

Abstract

579,778. Aerials. STANDARD TELEPHONES & CABLES, Ltd., and WILLOUGHBY, E. O. Nov. 5, 1943, No. 18436. [Class 40 (v)] An aerial system having a substantially flat amplitudefrequency characteristic over a wide frequency band is provided by coupling a tubular radiating element to a transmission line by means of a resonant stub formed inside the tubular radiator. A hollow conducting cylinder 1, Fig. 1, with conical end 3, half-wave resonant at the mean frequency and supported by an insulating bush 6 in an insulating tubular casing 5 above the earth plate 4, forms the radiating element. A central conductor 7 connected to the closed upper end 2 forms with the cylinder 1 a short-circuited stub which is tuned by condenser 11 to be half-wave resonant at the mean operating frequency. The aerial is fed from a transmission line 8 by a quarterwave matching transformer 10, connection being made to the central conductor 7 so that the impedance across the open end of the stub is in series with the aerial, and the variations in impedance of the aerial and stub neutralize one another at frequencies other than the mean value. As a refinement, the reactance introduced by the stub may be made to overcompensate for the aerial reactance in order to take account of the reactance introduced by the transformer 10 at frequencies other than that at which it is correctly one-quarter wavelength long. In a modification, Fig. 2 (not shown), a dipole system comprises two halfwave elements, similar to that shown in Fig. 1, arranged end to end and fed through two coaxial lines or a two-wire screened or unscreened line. Fig. 4 shows a dipole arrangement in which the coaxial line 8 and matching transformer 10 are brought coaxially through the lower cylindrical member 1A, the outer conductor of the line being connected to the member 1A while the inner conductor is connected to the inner conductor 7 of the upper element. With this arrangement the conductor 7 and cylinder 1 form the only stub in series with the aerial system and have to introduce the required reactance to neutralize both members of the dipole. In order to prevent energy being transferred to the outer conductor of the line 8, a short-circuiting disc 15 is provided inside the cylinder 1A a quarter wavelength from the open end. In a modification, Fig. 5 (not shown), a two-wire screened feed is employed, one conductor being connected to the conductor 7 and the other to the cylinder 1A at its upper end. A short-circuiting disc 15 is fitted to make the lower portion of cylinder 1A operate as a quarter wave suppressing stub, the upper portion having additional capacity to cause it to operate in the same manner. Various methods of mounting the dipole aerials on a mast or supported from guys are illustrated in Figs. 3, 6 and 7 (not shown). Specification 541,870 is referred to.