Aerial systems

摘要

758,772. Aerials. BELLING & LEE, Ltd. May 20, 1955 [June 16, 1954], No. 17694/54. Class 40 (7). An aerial system intended for operation in resonance on two frequencies comprises two aerials for the higher frequency, consisting of quarter wavelength extensions of the inner conductor of a coaxial line, which are supported collinearly at the extremities of a member or members forming a half-wave aerial element at the lower frequency. As shown, the lower frequency aerial element consists of two members 10 supported centrally in an insulator (not shown) and having their inner end connected to a feeder 11. The higher frequency aerials consist of outwardlyextending quarter-wave elements 13 and quarter-wavelength sleeve portions 12 surrounding the extremities of the members 10 and attached to them at their ends. The elements 13 are connected together by a conductor 14 coaxial with the members 10 and forming with them a matching transmission line. It is stated that the higher frequency aerials are effectively coupled to the transmission line 11 in the construction shown. If desired, however, separate feeder arrangements can be provided for the signals of the two frequencies; or a common transmission line may be coupled to symmetrically spaced points on conductor 14 by a delta matching section, the lower frequency element in this case being continuous (Fig. 2, not shown). Instead of sleeves 12, ground plane systems for the elements 13, consisting of radially extending groups of rods, discs, or the like may be provided. In reckoning the length of the lower frequency aerial element the effect of the sleeves or ground plane members must be allowed for. The two frequencies to be handled should differ by a ratio of more than 2: 1.