GB664330A - Improvements in antenna systems - Google Patents

Abstract

664,330. Aerials. RADIO CORPORATION OF AMERICA. Oct. 13, 1949 [Oct. 14, 1948], No. 26319/49. Class 40 (vii). An antenna comprises a tubular conductor having longitudinal slots, such as 31-34, Fig. 2, disposed about its periphery, a pair of diametrically opposite slots being so energized as to cause the radio frequency currents from each slot to flow in opposite directions around the periphery. If an east-west pair of slots is energized from a first source no potentials are set up across the slots of the north-south pair and these may then be energized from a second source. The horizontal pattern due to one pair of diametrically opposite slots above is given accurately by cos # when the diameter of the tube lies between <SP>1</SP>/ 10 and <SP>1</SP>/ 4 of the wavelength. If the east-west pair of slots are energized from the same source in phase quadrature with the north-south pair a rotating field is established providing the equivalent omnidirectional radiation of that produced by a turnstile antenna. An embodiment, Figs. 2 and 8, suitable for the transmission of television signals comprises a vertical stack of four elements 21-24, the slots being 0.85# in length and spaced apart # from centre to centre. Fig. 8 illustrates the arrangement of feeders in which the north-south pair of one element 24, are shown energized by branched lines 57 and the east-west pair by branched line 37. An additional quarter wavelength section 51 is included in feeder 37 to produce the phase quadrature energization. Feeders 53, 54 connect respectively with the aural and visual transmitters and supply signals through a diplexer 52 such as that disclosed in Specification 636,081. The remaining elements in the stack 21, 22, 23 are connected by a network lines, Figs. 5 and 6 (not shown), so that corresponding slots in each element are energized in the same phase. The antenna is also shown connected to radiate simultaneously a F.M. signal applied in the same phase to all the slots by line network 80-86. The slots are excited as full-wave elements for the television signal and as one and one-half wave elements for the F.M. signal. Lines 38, 39, 58, 59 conveying the television signals connect with the centre of the slots, and lines 83-86 conveying the F.M. signal are connected one-half the distance between the centres and ends of the slots. Interaction is prevented by making the feeder assembly for one signal a quarter wavelength for the other signal and vice versa. In a second similar embodiment, Fig. 7 (not shown), for use as an. omni-directional range beacon, producing a rotating field and a stationary reference field, the suppressed-carrier sideband signals are applied through feeders. 37 and 57, and the carrier signal is applied through feeder 80. In this case both sets of feeders connect with centre of the slots and the length of each final branch line is made an odd multiple of #/4 to obtain desirable impedance matching. For this embodiment a single element may be employed with a diameter of 0.3# and slot length between 0.5 and 1#.