A tapered strip transmission line for pulse transformer service

THE need for wide-band impedance-transforming devices has long been recognized. The increasing interest in the use of very short pulses of millimicro-second duration in radar, communication, and other systems accentuates the demand for a device which is capable of faithfully transforming such pulses. As the bandwidth and upper cutoff frequency increase, it becomes more and more difficult to construct suitable lumped-parameter or iron-core transformers of conventional design. Thus, the trend in recent years has been toward distributed systems, particularly of the tapered transmission line variety. Various tapers such as the linear,1 Bessel,2,3 exponential,4¿8 and hyperbolic9 have been proposed and analyzed by several investigators. In addition, many different physical structures employing these tapers have been constructed and tested experimentally. These were the 2-wire open line,4,5 the concentric circular cylinders,7¿9 and the shielded wire and tape helices.10,11 By and large, each experimental model has been physically bulky and difficult to construct. It is the purpose of this paper to investigate a tapered transmission line design which is reduced in physical bulk and which can be fabricated more economically.