EXTENDED APERTURE LOG-PERIODIC AND QUASI LOG-PERIODIC ANTENNA

摘要

1299896 Aerials TECHNOLOGY FOR COMMUNICATIONS INTERNATIONAL 2 Dec 1969 [9 Dec 1968] 58862/69 Heading H4A A broadband aerial comprises a feed means extending along an axis and a plurality of different linear radiating elements, one end of each of which is directly coupled to the feed means. The spacings between adjacent elements increase in a preselected manner from one end to the other of the feed means. Capacitive means is associated with at least one element, for capacitively loading said element at at least one location intermediate its two ends. As described, a transposed transmission line 80, Fig. 6, feeds twelve parallel V-shaped dipoles 81 to 92. The lengths of the three lower frequency dipoles 81 to 83 decrease in log-periodic fashion, as indicated by the lines 98 from point 95 on the axis. The lengths of the intermediate frequency dipoles 84 to 89 exceed by progressively increasing amounts the lengths of simple logperiodic dipoles which would occupy their positions, and capacitance loadings are provided along them in compensation. There is a single capacitor in each element of the dipoles 84 to 86, and two, spaced apart in series, in each element of the dipoles 87 to 89. The lengths of the three higher frequency dipoles 90 to 92 again decrease in log-periodic fashion, as is indicated by the lines 99 from the point 95, and there are two capacitors in series along each dipole element. The aerial operates over a wide frequency band with a nearly constant aperture. The capacitors may be constituted as shown in Fig. 2. Here an element 35 comprises an inner portion 36, which is connected to a feeder 12a, an outer portion 38, and a central portion 37, which overlaps the other portions at 41, 42 to provide two capacitors in series. In other embodiments, all elements have lengths in log-periodic relationship, but capacitors are provided intermediate their ends. Dipoles may be used (Figs. 1, 3, not shown) or monopoles with intermediate phasing units along the feeder (Fig. 5, not shown). In an array of four aerials 121 to 124, Fig. 7, the respective feed lines may be spaced apart only about one quarter wavelength at the lowest frequency, so avoiding grating lobe formation when the radiated beam is steered by phasing the respective sources 161 to 164. The lengths of the outwardly extending elements of the end aerials 121, 122 are in log-periodic relationship. The lengths of all other elements are the same, and appropriate capacitive loadings are introduced using either one capacitor or two to four capacitors in series. Such arrays may also be arranged in annular or part-annular fashion (Figs. 9, 10, not shown). In another embodiment, two aerials 173, Fig. 8, are supported by a mast 175 and converge to a common vertex 180, to provide a radiation pattern which in elevation is substantially independent of frequency.