GB536950A - Improvements in phase-shifting networks particularly applicable to radio guiding systems - Google Patents

Abstract

536,950. Impedance networks ; directive wireless systems. STANDARD TELEPHONES & CABLES, Ltd., and McPHERSON, W. L. Dec. 1, 1939, No. 31247. [Classes 40 (iii) and 40 (v)] A phase-shifting network, particularly applicable to radio beacon systems, is designed to give alternative phase shift values according as a single connection is made or broken, the impedance being the same in each case. The invention depends on the fact that the T-networks shown in Figs 1a, 1b when connected to a load of impedance Z present the same impedance, which may be made equal to Z if X 1 , X, are suitably related, and produce equal and opposite phase chances. As shown in Fig 2a, the series arms EF, FG constitute circuits which are resonant at the input frequency, and the inductances X4 form an antiresonant circuit with a shunt condenser when the contact S is closed. In the latter condition, therefore, the arms EF, FG are of very high impedance and the network is equivalent to that of Fig. 1a. When the contact S is open, on the other hand, the arms EF, FG are of very low impedance and the network is equivalent to that of Fig. 1b, provided the condenser X 3 = 2X 2 X 1 /(2X 2 -X 1 ). The reactance values X4 are not related to the phase shift nor to the load impedance, and are chosen to give the best impedance values with the switch S open and closed. In a modification, the anti-resonant circuit is inductively coupled to the arms EF, FG. The network may be used as an impedance matching network between two impedances Z 1 , Z, by making X 1 , X, numerically equal to each other and to Z 1 , Z 2 , in which case the opening and closing of the contact S alters the phase shift by 180 degrees. The network may be generalized to give any desired phase shift values, the elements X 1 , 2X 1 , X 2 , X 3 being replaced by reactances dependent on those values. Fig. 5 shows a particular form which gives zero phase shift with the contact S open. The networks described are suitable for use in connection with a radio beacon operating on the " dot-dash principle, in which a part of the aerial system acts alternatively as a reflector or director in accordance with the phase of the energy supplied thereto. The change from one radiating condition to the other is thus effected instantaneously by opening and closing of the contact S, which may be operated as required by a control relay.