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These can have lowpass or bandstop characteristics. Lowpass filters are formed by
means of a corrugated wavelength structure with adjacent high and low impedance
sections.
The normal construction for bandpass filters is to place inductive obstacles, typically
an array of posts, along a waveguide at spacings close to a half wavelength apart.
The size, number and transverse spacings for the posts are the parameters that vary
the filter bandwidth while the longitudinal spacing determines the center frequency
of the filter.
Bandstop filters can be made by placing short-circuited cavities approximately a
quarter wavelength apart along the filter body.
The major advantages of waveguide filters are high power handling and low-loss performance.
Waveguide filters are fabricated in aluminum, brass, copper and Invar. Materials
are selected to ensure that the lowest possible passband insertion losses are achieved.
The advantage of Invar construction is its low thermal expansion, which provides
optimum temperature stability. Aluminum construction is best suited where weight
is of major importance. All filters have tuning screws that are locked and sealed
with epoxy.
The interface is normally in the appropriate waveguide size. However, for most types,
integral coaxial transitions on one or both ports are available as options.
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