GB628986A - Improvements in or relating to aerials - Google Patents

Abstract

628,986. Aerials. CORK, E. C. Oct. 1, 1946, No. 29182. [Class 40 (vii)] An aerial coupled to energizing or receiving apparatus capable of operating over a wide frequency band comprises a series capacity loaded conductor, the loading being at intervals of less than a quarter wavelength and causing it to function over the frequency band substantially as a half or quarter-wave resonator with substantially uniform efficiency. A wide frequency band consists of a band of a width 8 per cent or more of its mean frequency and the efficiency should be such that nowhere in the band the reflection co-efficient exceeds 10 per cent. A capacity loaded dipole, Fig. 1, may have the loading elements either equal or unequal in magnitude and distribution. Preferably, the loading is non-uniform to cause more current to flow in the extremities of the aerial whose physical length may be of the order of 4 freespace wavelengths. Because of the more extended current distribution the aerial has a greater directivity than a normal dipole and it is stated that the lobes of the polar diagram may show a tendency to split. By inclining the arms 10 and 11 as shown, this tendency may be overcome although the radiation within the V then exceeds that in the opposite direction. Another embodiment, Fig. 2 (not shown), is formed of a plurality of insulated but overlapping tubular conductive elements which form a capacitively loaded aerial electrically similar to that of Fig. 1. A feeder may be connected either at the adjacent ends 13, 14, or to the extreme ends and the invention is also applicable to unipoles. To provide a D.C. or low-frequency de-icing current path the capacities may be shunted by a high radio frequency impedance line or coil. Specification 586,578 is referred to.