30. Waveguide attenuators.
a. As you recall, an attenuator is a device used to reduce electrical
energy.
The two main types of attenuators used with waveguide are the
shutter and resistive card.
b. Part A of Figure 128 shows a shutter attenuator with its locking
screw. As you lower the shutter into the waveguide, it reflects some of the
energy traveling down the guide. The reflected energy is a loss, and the
power on the other side of the shutter is less than that on the input side.
We can say then, that the shutter attenuates (reduces) the power. The more
you lower the shutter into the waveguide, the more attenuation you get. The
locking screw holds the shutter at the desired position.
Notice that a
shutter attenuator looks like the iris used in waveguide tuning. Actually,
any tuning device results in some loss of power and can be used as an
attenuator. The methods we use specifically for attenuation, however, are
more convenient for this purpose.
Figure 128.
Waveguide Attenuators.
31. Next, dissipative attenuator (resistive card).
a. You use a resistive card such as the one shown in Part B of Figure
128 as a variable attenuator.
The card is inserted into the waveguide
parallel to the electric field and does not introduce reflections. Instead,
the card is coated with a resistive material that absorbs (or dissipates)
energy.
The further you insert the card into the waveguide, the more
attenuation you get.
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