GB844072A - Improvements in and relating to electrical networks - Google Patents

Abstract

844,072. High-frequency bridge networks. BRITISH BROADCASTING CORPORATION. Jan. 27, 1958 [Jan. 22, 1957], No. 2344/57. Class 40(8). The bridge circuit of Fig. 1 comprising impedances A, B, C, D, X, Y is realized by connecting together seven quarter-wavelength sections of transmission line in the configuration shown in Fig. 2, the six junctions being loaded by impedances A, B<SP>1</SP> = Z<SP>2</SP> 0 /B, C, D, X<SP>1</SP> = Z<SP>2</SP> 0 /X, Y<SP>1</SP> = Z<SP>2</SP> 0 /Y where Z 0 is the characteristic impedance of the transmission lines. The impedances B<SP>1</SP>, X<SP>1</SP>, Y<SP>1</SP> may be replaced by quarterwavelength sections of line terminated respectively in impedances B, X, Y. The circuit may be realized using coaxial lines, balanced twin lines or rectangular waveguides having series or parallel junctions. Where series junctions are used, inverse impedances (i.e. A<SP>1</SP> = Z<SP>2</SP> 0 /A &c.) are required at the junctions. In one form of the circuit (Fig. 6, not shown) the impedances X<SP>1</SP>, Y<SP>1</SP> may be provided by two transmitters using frequencies which differ only by a few per cent. The impedance A is that of a common aerial matched as closely as possible to the transmission lines. The impedance C is made equal to A. To obtain good power transfer between the transmitters and the aerial, B<SP>1</SP> and D are replaced by equal impedance elements which are large compared with A at all frequencies required to be transferred from the source X<SP>1</SP> to the aerial and small compared with A at all frequencies required to be transmitted from Y<SP>1</SP> to the aerial. These impedances may be of the form described in Specification 710,345. The bridge may also be balanced by making AC = B<SP>1</SP>D = Z<SP>2</SP> 0 .