
261Microwave Components
If E is the amplitude of the input signal, A is the amplitude of output sig-
nal,
θ
is the angle between end cards and the central card and E is parallel to
the central card then the output can be given by A = E cos
2
θ
. The attenuation
(in dBs) = 20 log
10
{E/(E cos
2
θ
)} = 20 log
10
(s
2
θ
). This attenuation is a function of
frequency.
Another class of attenuator called coaxial cutoff attenuator is shown in
Figure 7.43. It contains two coupling loops separated by a cutoff section.
The variable attenuators present two problems. First, just as xed pads,
they are frequency sensitive; thus, it is necessary to calibrate them at ...