GB635343A - Improvements in radio antennas - Google Patents

Abstract

635,343. Aerials. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 11. 1946, No. 14267. Convention date, May 11, 1945. [Class 40 (vii)] A broad-band aerial for radiating a substantially omnidirectional horizontally - polarized field comprises a hollow vertical conductive cylinder 10, Fig. 1, having a circumference of the order of #/2, with a narrow longitudinal slot 12 of length A conductively closed at each end by members 16, a transmission line TL being coupled across the centre of the slot. As shown, a co-axial line is employed and the inner conductor 20 is connected to one edge of the slot at P1 and the outer conductor 18 is connected to the other edge at P2. The impedance of the aerial may be adjusted by varying the width of the slot. The slot may be formed with inwardly or outwardly extending flanges, Fig. 2 (not shown), the transmission line being bonded to one of the flanges. Suitable dimensions are given for operation in the 80-90 and 90-104 mc/s. frequency bands. In order to reduce high-angle radiation, two or three slots may be disposed collinearly along the cylinder, the array of slots being energized co-phasally by a branched transmission line, Figs. 3 and 4 (not shown) ; in such arrays the band-width may be increased by decreasing the length of each slot to 6/8#. In Fig. 5 two branch lines TL1 and TL2 are energized in phase opposition from the main feeder TL by means of the line balance converter 70 and the two branch lines are connected to the two slots 22 and 32 in opposition, i.e. the centre conductor 50 of line TL1 is connected to the left-hand edge of slot 22 and the inner conductor 60 of line TL2 to the right-hand edge of slot 32, so that the slots are energized. in phase. The impedance of the main line TL must now be twice that of the branch lines TL1 and TL2 to effect an impedance match.