IN-LINE FOLDED MICROWAVE FILTER

FILTRE HYPERFREQUENCE REPLIE A CAVITES EN SERIE

English Abstract

Abstract
An in-line folded microwave filter comprises a plurality of
resonant cavities connected in a series between an input and
an output at opposite ends of the filter. The resonant
cavities are arranged in two parallel sub-series with the
signal path proceeding from the input to a first cavity in one
sub-series, then to a first cavity in the second sub-series,
then to a second cavity in the second sub-series, then to a
second cavity in the first sub-series, and so on through the
cavities up to the output.

Claims

Claims
1) A microwave filter comprising a plurality of resonant
cavities coupled together in a series between an input and an
output at opposite ends of the filter, the cavities being
arranged in two parallel sub-series with the signal path
proceeding from the input to a first cavity in one sub-series,
then to a first cavity in the second sub-series, then to a
second cavity in the second sub-series, then to a second cavity
in the first sub-series, and so on up to the output.
2) A filter as claimed in claim 1 in which the input and
output of the filter face in opposite directions.
3) A filter as claimed in claims 1 in which the two sub-
series of resonant cavities are separated by a common partition
wall.
4) A filter as claimed in claim 1 in which adjacent
cavities in each sub-series are separated by partition walls.
5) A filter as claimed in claim 4 in which the adjacent
cavities in the same sub-series are coupled by means of an iris
in the respective partition wall.
6) A filter as claimed in claim 5 in which the iris is
offset towards a first side of the filter.
7) A filter as claimed in claim 3 in which a cavity of one
sub-series and a cavity of the other sub-series are coupled by
means of an iris in the common partition wall between these
cavities.
8) A filter as claimed in claim 7 in which the iris is
offset towards a second side of the filter.
9) A filter as claimed in claim 7 in which the iris is
adjacent one of the sub-series partition walls.

Description

2054996
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IN-LINE FOLDED MICROWAVE FILq!ER
This invention relates to a microwave filter for
filtering input signals to within a predetermined frequency
band.
One type of microwave filter comprises a plurality of
5 resonant cavities coupled together in a series. Typically the
series of resonant cavities are arranged in a straight line
between an input and an output of the filter.
In some circumstances there is a limited space in which
to install a microwave filter, in particular only a short space
10 may be available between the end of an input waveguide and the
end of an output waveguide, between which the filter is to be
fitted.
In accordance with this invention, there is provided a
filter comprising a plurality of resonant cavities coupled
15 together in a series between an input and an output at opposite
ends of the filter, the cavities being arranged in two parallel
sub-series with the signal path proceeding from the input to
a first cavity in one sub-series, then to a first cavity in the
second sub-series, then to a second cavity in the second sub-
20 series, then to a second cavity in the first sub-series, and
so on up to the output.
Typically therefore, the filter may comprise 2n
resonant cavities coupled in a series but have half the length
of a normal filter of the same number of cavities.
Preferably the input and output of the filter face in
opposite directions, so that the filter receives the input
signal in one direction and the output signal continues
travelling in the same direction.
Preferably the two sub-series of resonant cavities are
separated by a common partition wall. Adjacent cavities in
each sub-series are also separated by partition walls.
Coupling between adjacent cavities in the same sub-series is
effected by means of an aperture or iris in the respective
partition wall: preferably this iris is offset towards one
35 side of the filter. Coupling between a cavity of one sub-
series and a cavity of the other sub-series is effected by
means of an aperture or iris in the common partition wall
between these cavities: this iris is offset towards the
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20~996
opposite side of the filter; further this iris is adjacent one
of the sub-series partition walls. These arrangements avoid
or minimise coupling between non-consecutive cavities of the
overall series.
An embodiment of the invention will now be described by
way of example only and with reference to the accompanying
drawings in which:
FIGURE 1 is a plan view of a microwave filter in
accordance with the invention, shown with its top closure plate
10 or lid removed;
FIGURE 2 is a side view of the filter;
FIGURE 3 is a view of one end of the filter; and
FIGURE 4 is a view of the opposite end of the filter.
Referring to the drawings, there is shown a microwave
filter body 10 formed in one-piece and comprising two parallel
side walls 11, 12 connected along their centre lines by a
partition wall 13. on one side of the partition wall 13 there
are three rectangular resonant cavities 23, 24, 25 and on the
other side of the partition wall 13 there are three rectangular
20 resonant cavities 26, 27, 28. The six cavities 23 to 28 are
coupled in a series between rectangular input and output
apertures 14, 15 in end walls 16, 17 of the filter, as will be
described below, with cavities 23 to 25 forming one sub-series
and cavities 26 to 28 forming a second sub-series. Adjacent
25 cavities in each sub-series are separated by partition walls
41 to 43. The sub-series of cavities 26 to 28 are open to the
top of the body 10 but are closed by a top closure plate or lid
50 fitted to the body 10: similarly the second sub-series of
cavities are closed by a bottom plate 52 fitted to the body 10.
Cavity 23 is coupled to cavity 26 by an elongate slot
or iris 30 in the common partition wall 13 adjacent the end
wall 16. Cavity 26 is coupled to cavity 27 by a rectangular
aperture or iris 31 in the wall 42 between these cavities.
Cavity 27 is coupled to cavity 24 by a slot 32 in common
35 partition wall 13, adjacent partition wall 42. Cavity 24 is
coupled to cavity 25 by a rectangular aperture, similar to
aperture 31, in the partition wall 41 between those cavities.
Cavity 25 is coupled to cavity 2~ by a slot 33 in common
partition wall 13, adjacent partition wall 43. Cavity 28 is
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20~4996
coupled to the output through aperture 15 in the end wall 17.
It will be noted that the slots 30, 32, 33 are offset
towards side wall 11 of the filter, whilst the apertures e.g.
31 in the partition walls 42, 41 are offset towards the
5 opposite side wall 12. These arrangements, together with the
positioning of the slots 30, 32, 33 adjacent the partition
walls 16, 42, 43, avoid direct coupling between non-consecutive
cavities in the series 23, 26, 24, 27, 25, 28.
In use, the opposite ends of the filter are coupled to
input and output lengths of rectangular-section waveguide. The
resonant cavities support TEol mode wave patterns.
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Representative Drawing