GB1265251A - - Google Patents

Abstract

1,265,251. Microwave attenuators. INTERNATIONAL BUSINESS MACHINES CORP. 29 June, 1970 [30 June, 1969], No. 31373/70. Heading H1W. A transmission line attenuator comprises a distributed series resistance extending along a first section of the line and a distributed shunt resistance formed by a lossy dielectric material extending along a second section of the line, the characteristic impedance of the attenuator decreasing in the propagation direction along the first section and the characteristic impedance increasing in the propagation direction along the second section such that reflections due to impedance discontinuities and parasitic reactances associated with lumped resistive elements are avoided. The attenuators shown are T-attenuators in which the transmission line comprises a dielectric strip 54 supporting a conductive strip 52 on one side and a ground plane 50 on the other. The strip 52 is of metal such as copper except in the sections 30A and 30B which are the series resistive sections of the attenuator in which a resistive material is used e.g. a resistive alloy. The characteristic impedance in these sections is reduced in the direction of propagation (left and right in Figs. 6B and 7A) either by reducing the dielectric thickness (Fig. 6B) or increasing the width of strip 52 (Fig. 7A). Between the two series resistive sections there is a shunt resistive section 30C where there is disposed a lossy dielectric material and in this section the characteristic impedance is increased in the direction of propagation. As shown the characteristic impedance decreases approximately linearly in the series resistive sections and increases approximately hyperbolically in the shunt resistive section. The attenuator may alternatively be a #-attenuator.