GB606424A - Improvements in or relating to sensing antenna couplings for radio direction finders - Google Patents

Abstract

606,424. Aerials; radio direction-finding. STANDARD TELEPHONES & CABLES, Ltd. Feb. 6, 1945, No. 3048. Convention date, Nov. 27, 1943..[Class 40 (vii)] In a direction-finding aerial system cbmprising a single-turn untuned loop aerial and an associated sensing aerial arrangement comprising a sensing aerial and a counterpoise, the sensing aerial arrangement is coupled to its transmission feed line through a dummy loop directly connected to the conductors of the line and having an impedance substantially equal to the terminal impedance of the loop aerial. The invention is described with reference to an aerial structure similar to that described in Specification 592,350 comprising a pair of perpendicular loop aerials 10, 11, Fig. 1, with a sensing aerial 15 and counterpoise elements 16 mounted above them. The dummy loop as shown in Fig. 1 comprises two shielded conductor lines 29, 30 connected at their lower ends to the conductors 25, 26 of the transmission feed line 24, and at their other ends to a coil 31 loosely coupled to a coil 21 connected over leads 17, 18 to the sensing aerial and counterpoise. The conductors 29, 30 preferably have the same characteristic impedance as the conductors forming the loop aerials and are of length equal to half the perimeter of each loop. Balancing condensers 22, 23 and decoupling impedances 19, 20 (resistances or inductances) may be converted as shown. If the loop aerials have series resistances to give wide-band frequency characteristics as described in Specification 592,350, the dummy loop has similar resistances 32, 33. In a modified arrangement, Fig. 2, the dummy loop comprises hollow tubular members 45, 46 coupled to the sensing aerial arrangement by an elongated coil 41. The members 45, 46 may be replaced by a simple shielded loop, Fig. 3 (not shown). In other arrangements, Figs. 4, 5 (not shown), a resistance coupling is provided between the dummy loop and the sensing antenna arrangement, and series resistances such as 19, 20, Fig. 1, are shunted by tuning condensers.