GB592942A - Antenna construction - Google Patents

Abstract

592,942. Aerials. STANDARD TELEPHONES & CABLES, Ltd. Aug. 4, 1944, No. 14972. Convention date, Sept. 30, 1942. [Class 40 (v)] A vertical antenna structure consists of a conductive mast surrounded by two radiating elements, one disposed a short distance above the other, with the mast extending above the upper end of the upper element to ensure that the effects of the mast on the impedance of each radiating element are similar. As shown in Fig. 1, a hollow conductive mast 14 supports two cylindrical radiators 10 and 12, the top of the mast 14 extending a few inches above the top of the upper radiator 10. The radiators 10 and 12 are fed by a transmission line 18 extending through the mast and through an opening 22 between the said radiators. The transmission line 18 may comprise a series of tapering sections 26 forming an aperiodic impedance transformer, or it may be an ordinary line, suitable impedance matching precautions being taken. Fig. 2 shows a modification in which the radiators 41, 42 each comprise telescoping sections 43 and 44. The inner sections 43 each comprise a twelve-sided tubular member composed of three pieces of stamped sheet metal secured together at the flanged edges 46 by soldering, brazing, welding, &c. The upper end of the telescoping section 43 is secured to the mast 40 by means of an annular insulator 54 bolted to a supporting ring 55 fixed to the mast and having a peripheral ring 56 to which the upper edge of the section 43 may be welded. The lower end of the said section 43 is secured to the mast by means of an annular insulator 50.. The connections between the radiators 41, 42 and the transmission line 70 are made through sealed openings in the mast comprising short ducts closed by an insulating cover, Fig. 4 (not shown). The radiating elements are preferably so proportioned as to present a low impedance, e.g. 400 ohms or less as viewed from the transmission line end and preferably each of the said elements is one half of a wavelength long although they may be much shorter, e.g. one tenth of a wavelength.