Detailed calculations and measurements on u.h.f. characteristics of amplifying tubes show that the effective input capacitance of a tube increases with the operating frequency when it is approaching the natural resonant frequency of the input circuit of the tube. Due to this effect

the actual cut-off frequency of a wide-band distributed amplifier becomes lower than that originally designed. This effect becomes more serious as the bandwidth of the amplifier increases. In this paper

a new kind of distributed amplifier utilizing mm’-derived low-pass networks as grid and plate lines is described and its characteristics is analyzed. Since the mm’ low pass networks can absorb more parasitic parameters of the tube

the actual and designed cut-off frequencies may agree with each other. Experimental models of amplifier stages with cut-off frequencies of 200 and 300 MHz have been built and results of measurements are given. By using this type of amplifier stage as the element of wide-band distributed amplifiers the design procedure may be considerably simplified.