GB1185494A - Improvements in or relating to Filter Networks - Google Patents

Abstract

1,185,494. Filter networks. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. 27 April, 1967 [27 May, 1966], No. 19485/67. Heading H3U. Four terminal filter networks are provided, analogous to known " zero four terminal networks ", which may be designed to work as band pass, band stop, high pass or low pass filter, as desired. A known " zero four terminal network ", Fig. 1, operating solely as a band stop filter when on no load comprises a resistance-capacity circuit 1 having distributed constants and consisting of a metal surface conductor on which is a layer of a dielectric material over which there is a resistance coating. To provide a zero circuit action a resistancecapacity circuit 2 of predetermined dimensions is positioned in a shunt branch, this shunt branch ensuring that at a certain frequency the amplitude of the voltage transmitted by the four terminal network is zero. In a modification of the known network the circuit 2 forms a bridge connected in shunt with the circuit 1 (Fig. 2, not shown). The present invention uses circuits similar to those of Figs. 1, 2 but in which the circuit components are related by the following equation where Au = voltage transmission factor of the four terminal network. Ra = the selected terminating impedance. RL = resistance of the resistance-capacity circuit 1 with distributed constants, L being proportional to the length of the resistance layer and R = resistance per unit of length. Rn = the selected impedance of the circuit 2. γ = #jCR, i.e. the propagation coefficient in the case of a homogeneous conductor (C = distributed capacitance). The different types of filters are obtained by appropriate selection of the value and nature of the impedances Ra and Rn, these selections being given in the Specification.