Improvements in and relating to aerial systems for radio navigational aids

摘要

636,126. Aerials. CULLEN, A. L. Feb. 21, 1947, No. 5201. [Class 40 (vii)] An aerial system comprises an energized primary loop P producing a uniform radiation field and two parasitic secondary loops S1 and S2 disposed in an adjacent parallel plane and arranged to overlap the primary loop so that by inductive coupling the induced currents in the two secondary loops are in antiphase and in quadrature with that in the primary. The resultant combined radiation pattern varies as 1+m sin #, where m may be given any value by choice of the offsets d1 and d2. The loops S1 and S2 which are connected in parallel and tuned to resonance by condenser C are centred at the ends of a diameter of the primary loop and embrace points of current maxima. One loop is offset inwards and the other outwards, whereby their. mutual couplings are of opposite sign and result in induced currents in antiphase. A practical embodiment of the system for use as an omnidirectional beacon is disclosed in Figs. 6, 7 and 8 (not shown) and comprises a horizontal array mounted on a vertical shaft for rotation in azimuth. Energy is fed to the primary loop by a transmission line extending through the shaft to a matching stub connected across the parallel conductors of the loop adjacent the cross-over. Adjustable matching condensers also bridge the parallel conductors. A uniform current distribution is necessary and to achieve this the primary loop diameter should not be greater than one-eighth of a wavelength and the secondary loop diameters not less than one-half of this. An alternative embodiment of the invention, Fig. 1 (not shown), employs a conventional circular loop with a condenser in series at the mid-point.