GB963185A - Improvements in or relating to distributed high-frequency amplifiers - Google Patents

Abstract

963,185. Distributed amplifiers. TELEFUNKEN PATENTVERWERTUNGS G.m.b.H. April 17, 1963 [April 17, 1962], No. 14987/63. Headings H3T and H3W. In a distributed amplifier of the type in which the anodes of a number of valves I-IV, Fig. 2a, are connected to successive points in a tapered transmission line, the load impedance and gain are increased by using impedance matching transformers between sections of line. The Specification gives a mathematical explanation of the basis for design. It is shown that if Z1 is the characteristic impedance of the first section of line, connected to valve V1, Fig. 3, and m the voltage step-up ratio of the following transformer, then the second valve should, for matching purposes, work into an impedance of Z1m so that the second section of line must have a combined impedance of Z2=m<2>/m+1 Z1. Transformers may be used between successive sections of the anode line; alternatively, the first section of line may be transformer connected to the second which is followed by a number of tapered line sections without transformer connection. When the line impedance has become sufficiently reduced, transformer connection is again used, to be followed by a further tapered line (Fig. 4, not shown) Autotransformers may be used, the leakage inductance being thrown into the impedances of the line, which is of band-pass type. In a further push-pull embodiment, the transformer is of 1: 2 ratio and comprises two equal lengths of concentric transmission line, Fig. 6, with the inners and outers cross-connected at the input end, the output being taken from the two inner conductors: the characteristic impedance of the lines may be increased by the use of helical inner conductors. The arrangement may be neutralized so as to use triode valves or transistors. The capacities shown across the two input sides of the transformer network and which terminate the preceding filter network may comprise the anode to ground capacities of a further pair of valves (Fig. 8, not shown).