Multi-band Filter
Description
The present invention relates to a multi-band filter, in particular to a multi-band
5 filter for space-based applications. More particularly, the present invention relates
to a multi-band filter including a plurality of bandpass filters connected in parallel
between an input manifold and an output manifold.
Communications satellites are commonly required to receive, process, and transmit
lo signals across multiple communications channels. For this purpose, such satellites
are typically provided with an output multiplexer (OMUX), an example of which
will be briefly described with reference to Fig. 1.
The output multiplexer 100 is of a type commonly referred to as a manifold
I5 multiplexer, comprising a plurality of bandpass filters 101, 102, 103, 104 disposed at
varying lengths along a manifold 105. Each filter 101, 102, 103, 104 attenuates any
frequencies within an input signal a, b, c, d which fall outside of the filter's
passband, a centre frequency of which can be tuned by manually adjusting a tuning
screw 106. The filtered signals a', b', c', d' are combined within the manifold into a
20 frequency-multiplexed output signal a'+b'+c'+d'. However, each filter has a
separate input. The output multiplexer does not function as a multi-band filter.
The present invention provides, in a first aspect, a multi-band filter comprising: at
least one input manifold; at least one output manifold; and a plurality of filters
25 connected in parallel between said input manifold(s) and said output manifold(s),
wherein each filter is directly coupled between a said input manifold and a said
output manifold; wherein the filters have a first section proximal to the input
manifold which is coupled to the input manifold and a second section proximal to
the output manifold which is coupled to the output manifold.
30
Thus, the multi-band filter can effectively filter a signal through a plurality of passbands.
Preferably, the first and second sections of a said filter are symmetrical between the
input manifold and output manifold.
The present invention provides, in a second aspect, a system comprising: at least
5 one amplifier; and at least one multi-band filter as described, wherein said output
manifold of the multi-band filter is coupled to a said amplifier, or, a said input
manifold of a multi-band filter is configured to receive a signal from a said
amplifier.
lo The present invention provides, in a third aspect, a method of forming a multi-band
filter comprising: forming at least one input manifold; forming at least one output
manifold; and forming a plurality of filters, connecting the filters in parallel between
said input manifold(s) and said output manifold(s), wherein each filter is directly
coupled between a said input manifold and a said output manifold; wherein the
I5 filters have a first section proximal to the input manifold which is coupled to the
input manifold and a second section proximal to the output manifold which is
coupled to the output manifold.
20 Embodiments of the present invention will now be described, by way of example
only, with respect to the following drawings, in which:
Figure 1 is a plan view of a manifold multiplexer as known in the art;
Figure 2 is a schematic view of a first embodiment of a multi-band filter according
to the present invention;
25 Figure 3 is a perspective view of a filter forming part of the present invention;
Figure 4 is a graph showing an output from a multi-band filter according to the
present invention;
Figure 5 is a second embodiment of a system including a second embodiment of a
multi-band filter according to the present invention;
30 Figure 6 is a third embodiment of a system including a third embodiment of a multiband
filter according to the present invention;
Figure 7 is a fourth embodiment of a system including a fourth embodiment of a
multi-band filter according to the present invention;
Figure 8 is an enlarged plan view of a part of the multi-band filter according to the
present invention.
The present invention is a multi-band filter, having a plurality of pass-bands. The
5 multi-band filter is configured for use in a satellite system, preferably using cavity
waveguide filters and waveguide manifolds to achieve a high Q factor.
Figure 2 shows a multi-band filter 10 according to the present invention. The multiband
filter 10 comprises an input manifold 12 and an output manifold 18. A
lo plurality of bandpass filters 13,14,15,16 are connected in parallel between the input
manifold 12 and the output manifold 18.
The input manifold 12 is a linear waveguide, having a single input 12a. The
manifold 12 has an end cap 12b terminating the waveguide. The waveguide input
I5 manifold 12 is dimensioned to guide microwave frequency (1 to 40 GHz) input
signals. The input manifold 12 has a plurality of output ports allowing an input
signal to pass into the bandpass filters 13,14,15,16. The output ports are at a
specific distance from the end cap 12b, according to the frequency to which that
filter 13,14,15,16 is tuned.
20
The output manifold 18 is a substantially linear waveguide, having a single output
port 18a. The output manifold 18 has an end cap 18b terminating the waveguide.
The waveguide input manifold 12 is dimensioned to guide microwave frequency (1
to 40 GHz) input signals. The output manifold 18 has a plurality input ports for
25 receiving signals from the bandpass filters 13,14,15,16. The input ports are at a
specific distance from the end cap 18b, according to the frequency to which that
filter 13,14,15,16 is tuned.
The input manifold 12 and output manifold 18 preferably extend parallel to each
30 other in the same plane, and are substantially identical with similar configurations
and geometries. The configuration of the input manifold 12 and output manifold 18
may be approximately symmetrical, about a centreline extending mid-way between
the input manifold 12 and output manifold 18. Preferably, there is a minor
difference in arrangement between the input manifold 12 and output manifold 18
which will be detailed below.
The multi-band filter 10 may comprise two, three, four or more bandpass filters
5 13,14,15,16 in order to provide two, three, four or more passbands respectively.
The bandpass filters 13,14,15,16 are preferably cylindrical cavity waveguide filters.
The bandpass filters 13,14,15,16 preferably pass a pre-determined range of
frequencies in a symmetrical pass band. The pass bands of the bandpass filters
13,14,15,16 are preferably distinct from each other.
10
Figure 3 shows an example of a cavity waveguide filter forming the bandpass filter
14. The filter 14 is provided with an input 21 connected directly to the input
manifold 12 and an output 28 connected directly to the output manifold 18. The
filters 13,14,15,16 are therefore directly coupled between the input manifold 12 and
I5 output manifold 18, such that a signal is passed from the input manifold 12 to the
output manifold 18 through the filters 13,14,15,16 only, without passing through
any further components. The filter 14 is preferably comprises four resonant cavities
24,25,26,27. The filters 13,14,15,16 are preferably all filters of the same order, for
example, second order filters. The cylindrical cavities 24,25,26,27 within the filter 14
20 are connected by irises, such that a signal received via the input 21 passes from one
cavity to the next towards the output 28. In the present example, a symmetric
transfer function is achieved by cascading the four cavities 24,25,26,27 linearly, the
signal passing through each in turn.
25 In Figure 3, the cavities 24,25,26,27 are connected end-to-end in a straight line. The
present invention is not restricted to filters of this design. Alternatively, the cavities
may be connected by irises at 90' angles.
Figure 4 shows an example of an output from a multi-band filter according to the
30 present invention, having two bandpass filters operating in the range shown. The
output comprises two distinct passbands 82,84. The filters have a high Q-factor,
indicated by the sharp roll-off, which allows channels to be packed closely together
and maintain good in-band performance to avoid distortion of the signal.
The bandpass filters must be matched to the input manifold 12 and output manifold
18. If the band-pass filters are not matched, losses due to reflections and
interferences will arise. The filters are designed to be matched (or tuned) by having
5 one or more cavities configured to compensate for the manifold, and provide the
intended filter characteristics. The matching may relate to matching one or more of
a filter characteristic, Q-factor, frequency band, impedance or phase. A filter in
isolation needs to be adjusted to maintain the original filter characteristics when
coupled to a manifold. The adjustment of the filter characteristics is to the
10 element(s) of the filter proximal to the manifold, for example, by machining of the
dimensions of a cavity and/or adjustment of a first iris and proximal two tuning
screws. This adjustment may be done on the theoretical model - a connection of
theoretical circuit elements such as inverters, lengths of transmission line and
susceptances all analysed in a nodal analysis program with an optimiser attached.
15
The adjustment made or designed to match the filter to the output manifold is also
made or designed to match the filter to the input manifold. The design and/or
adjustments to the filter ends are identical. The present invention allows use of
existing multiplexer design programs to produce an asymmetrical set of filters, in
20 which the filters are matched to an output manifold. The filters are made
symmetrical again by mirroring the proximal cavities only, and introducing the input
manifold. When a filter is tuned in isolation it is matched into a simple load but the
impedance on the manifold is much more complex. The impedance on the manifold
is affected by the manifold itself, the position of the short circuit, the distance and
25 impedance of the other filters on the manifold.
The first filter section is preferably impedance matched to the input manifold 12
and the second filter section is preferably impedance matched to the output
manifold 18. In particular, one or more of the cavities are matched to take account
30 of the impedance presented to them by a port on the manifold to which they are
connected.
In addition, interactions occur between the filters, which must be accommodated. A
final matching and tuning of the cavities to a waveguide manifold is a complex
process, involving fine adjustment of the resonant cavities to obtain the correct
tuning. The filters 13,14,15,16 of the present invention may be provided with tuning
5 means, for example tuning screws, to allow optimisation.
The term 'tuning' generally refers to obtaining the intended frequency of operation,
and 'matching' generally refers to obtaining the intended input and output
impedances. However, these terms may be interchangeable to some extent and these
10 two adjustments are not independent.
Preferably, the filters have a first section proximal to the input manifold which is
matched to the input manifold and a second section proximal to the output
manifold which is matched to the output manifold. The first and second sections
I5 are adjusted substantially identically to maintain the original or required filter
characteristics, and/or match an impedance, when the filters are connected to the
manifold. The calculation of the adjustment and/or design of the filters only needs
to be carried out once (e.g. for the output side), and so does not need to be
repeated (e.g. for the input side).
20
It is known provide an output multiplexer (OMUX) having a plurality of filters and
a single manifold, as shown in Figure 1. The present invention takes advantage of
the matching already achieved in the output multiplexer. The multi-band filter 10
uses a similar manifold as the input manifold 12. However, merely attaching a
25 waveguide manifold to the inputs of the filters 13,14,15,16 will not provide a useful
multi-band filter. The present invention recognises that it is also important to match
the filters 13,14,15,16 to the input manifold 12, as well as to the output manifold
18. The filters are then well coupled to the input and output manifolds.
30 A possible solution to match the filters 13,14,15,16 is by joining together two
identical known filters in series to create a single filter. Each of the two identical
filters is known to be matched to the output manifold, and so will also be matched
to the identical input manifold. However, it is well known that the connection of
two filters in tandem is inefficient. The performance of a filter is not based only on
the number of cavities. For example, two fourth order filters have a poorer
performance than a single eighth order filter. This solution will therefore function,
and may form part of the present invention.
5
Referring to Figure 3, a bandpass filter forming part of the present invention can be
considered as comprising two sections. A first section comprises one or more
cavities 25,26. The one or more cavities 25,26 are proximal to the input manifold
12, i.e. one or more of the cavities are directly connected to the input manifold 12.
10 One or more further cavities of the first section are connected to the cavity or
cavities connected to the input manifold 12. The term "proximal" should be
interpreted as referring to the section which is connected to the manifold, and may
or may not be physically located closest to the manifold.
I5 A second section comprises one or more cavities 24,27. The one or more cavities
24,27 are proximal to the output manifold 18, i.e. one or more of the cavities are
directly connected to the output manifold 18. One or more further cavities of the
second section are connected to the cavity or cavities connected to the output
manifold 18.
20
The filters are preferably single, integrated, filters, directly connected between the
input manifold 12 and output manifold 18. The first and second sections are
preferably integrally formed as a single filter. The single filter is considered a single
filter unit, which is able to independently filter a signal. The single filter unit is not
25 distributed in separate parts around a different component. The single filter
comprises a plurality of cavities which have properties, determined in part by the
dimensions of the cavities and/or adjustment of tuning means (e.g. tuning screws),
configured to form a band-pass filter.
30 The first and second sections preferably have the same configuration. The second
section preferably has the same number of cavities as the first section, which are
dimensioned and connected identically. The input manifold 12 and output manifold
18 also have substantially the same configuration.
The filters are symmetrical between the input and output manifolds 12,18. In
particular, the filter characteristics of the filters are symmetrical between the input
and output manifolds 12,18. Preferably, the dimensions and/or arrangement of
5 cavities 24,25,26,27 are symmetrical between the input and output manifolds 12,18.
Preferably, cavities 24,25,26,27 are symmetrical about a centreline between the input
and output manifolds 12,18. The cavities 24,25 directly connected to the manifolds
12,18 have the same dimensions and configuration as each other. Irises between the
cavities and connecting the cavities to the manifolds are considered as part of the
10 cavities, and preferably also have a symmetrical configuration between the input and
output manifolds. The first and second filter sections have substantially the same
filter characteristics and/or dimensions, arranged in opposite orientations.
Cavities 26,27, which are connected to the cavities 24,25, have the same dimensions
I5 and configuration as each other. The dimensions and configuration of the cavities
of the first section cavities may be different or the same as each other, and similarly,
the dimensions and configuration of the cavities of the second section may be
different or the same as each other. The symmetry of the filters means that the
cavities proximal to the output manifold can be designed to match the output
20 manifold. The cavities proximal to the input manifold can use the same, inverted,
design as the cavities proximal to the output manifold.
The configuration of the at least one cavity 25,26 of the first section is identical to a
part only of the cavities of a filter known to be matched to a known output
25 manifold in an output multiplexer. Preferably, the input manifold 12 is substantially
configured as the output manifold of the same known output multiplexer. In
particular, the first section cavities 25,26 have the same configuration as one or
more of the cavities proximal to the manifold of the output multiplexer. A further
part of the known filter, comprising one or more cavities distal from the output
30 manifold, is not included in a filter according to the present invention. The design
of the input manifold and/or one or more proximal filter cavities are based on the
output manifold and proximal filter cavities of the known output multiplexer, which
is only a part of an output multiplexer.
Similarly, the configuration of the at least one cavity 24,27 of the second section is
identical to a part only of the cavities of a filter known to be matched to an output
manifold in an output multiplexer. Preferably, the output manifold 18 is
5 substantially configured as the output manifold of the same known output
multiplexer. In particular, the second section cavities 24,27 have the same
configuration as one or more of the cavities proximal to the manifold of the known
output multiplexer. A further part of the known filter, comprising one or more
cavities distal from the output manifold, is not included in a filter according to the
lo present invention. The design and/or adjustment of the output manifold and/or
one or more proximal filter cavities are based on the output manifold and proximal
filter cavities of the known output multiplexer, which is only a part of an output
multiplexer.
I5 The present invention provides a method of forming and/or designing a multi-band
filter as described, using a part of a known output multiplexer. The filters of the
multi-band filter are based on only the part of the known filter which is proximal to
the output manifold, such that the filters of the present invention are symmetrical
and do not require substantial further adjustment to match the manifolds and have
20 the intended filter characteristics. The forming may include adjustment of tuning
screws to a required setting.
The method of forming and/or designing a multi-band filter may comprise
designing a theoretical (base) filter having an n number of cavities, wherein one or
25 more cavities of the n cavities (e.g. four cavities) are designed to be configured to
couple to one only of an input or output manifold, preferably an output manifold.
A said filter of the multi-band filter is designed having a number n cavities (e.g. four
cavities), of which the first section has a number n/2 cavities (e.g. two cavities) and
configured as the n/2 cavities of the base filter, and the second section has a
30 number n/2 cavities (e.g. two cavities) and configured as the n/2 cavities of the
base filter proximal the manifold. The configuration of the cavities is substantially
symmetrical, with the cavities connecting to the input and output manifolds
adjusted (formed) in the same manner to match the input and output manifolds.
Referring to Figure 3, the two cavities 25,26 are configured as a part only of a filter
comprising four cavities, which is matched to a manifold of the output multiplexer.
The cavities 25,26 are configured as the two cavities proximal to the manifold of the
5 output multiplexer, in the same positions as known to a person skilled in the art.
The cavities 24,27 are also configured as the two cavities proximal to the manifold
of the output multiplexer, in the same positions (i.e. adjacent to the manifold and
separated from the manifold) as known to a person skilled in the art.
lo The cavities of the known output multiplexer proximal to the manifold provide
matching of the filter to manifold, and so the filter of the present invention will be
matched to both the input manifold 12 and output manifold 18. The filters are
therefore symmetrical between an input end and an output end.
I5 The multi-band filter according to the present invention may form part of a satellite
system, and in particular, part of a telecommunications satellite system.
In a first embodiment of a satellite system, the multi-band filter is located on an
input side of the system. The multi-band filter is located before a low noise
20 amplifier (LNA), such that the output port 18a of the output manifold 18 is
connected to an input of the LNA. An LNA may be required to handle both a BSS
signal and a FSS signal which may be separated by a considerable frequency gap.
The use of a single wide-band filter to cover the whole band may be inefficient. The
multi-band filter of the present invention may be configured to pass both signal
25 frequencies, and filter out an intermediate frequency range.
In a second to seventh embodiment of a satellite system, the multi-band filter is
located on an output side of the system. Figures 5 to 7 show various arrangements,
which are examples only. The multi-band filter is located after an amplifier and
30 prior to a feed.
Figure 5 shows a second embodiment of satellite system 30 including a multi-band
filter having two pass bands. The multi-band filter comprises an input manifold 32,
first bandpass filter 33, second bandpass filter 34, and an output manifold 38. The
filters 33,34 are configured as described above, i.e. having cavities which are
symmetrical between the input and output manifold to which they are connected.
The filters 33,34 are directly coupled between the input manifold 32 and output
5 manifold 38, such that a signal is passed from the input manifold to the output
manifold through the filters only, without passing through any further components.
The input manifold 32 receives an input signal from an amplifier 31. The amplifier
31 is preferably a high power amplifier, and in particular, a travelling wave tube
amplifier (TWTA). The output manifold 38 outputs the filtered signal to a feed 39
10 for transmission.
Figure 6 shows a third embodiment of a satellite system 40 including a plurality of
multi-band filters. The multi-band filters comprise a total of six filters. The multiband
filters comprise three input manifolds 42a,42b,42c. The input manifolds
I5 42a,42b,42c each receives an input signal from one amplifier 41a,41b,41c. The
amplifiers 41a,41b,41c are preferably travelling wave tube amplifiers (TWTA).
A plurality of filters are connected to each input manifold 42a,42b,42c. In
particular, two band-pass filters are connected to each input manifold 42a,42b,42c.
20 Filters 44a,44b are connected directly to input manifold 42a, filters 45a,45b are
connected directly to input manifold 42b, and filters 46a,46b are connected directly
to input manifold 42c. The filters are directly coupled between a said input manifold
and a said output manifold, such that a signal is passed from the respective input
manifold to the respective output manifold through the filters only, without passing
25 through any further components.
A plurality of output manifolds 48a,48b output the filtered signals to a plurality of
feeds 49a,49b for transmission. The number of output manifolds 48a,48b may be
the same, more or less than the number of input manifolds 42a,42b,42c. In Figure 6,
30 there are two output manifolds 48a,48b, each directly connected to three filters.
Output manifold 48a is connected to filters 44a,44b,45a, and output manifold 48b is
connected to filters 45b,46a,46b.
The filters 44a,44b,45a, 45b,46a,46b are configured as described above, i.e. having
cavities which are symmetrical between the input and output manifold to which they
are connected.
5 The arrangement shown in Figure 6 allows a single amplifier to carry two or more
channels, with the channels routed to different downlink beams. This type of
satellite system provides for flexibility in configuring which feed transmits each
channel. A further satellite system may comprise a different configuration and
number of filters, input and output manifolds. The system may comprise a plurality
10 of input manifolds and/or a plurality of output manifolds, wherein a set of filters
connected to at least one of said input manifolds is partially different to a set of
filters connected to at least one of said output manifolds. Thus, one input manifold
is connected via filters to a plurality of output manifolds, or, one output manifold is
connected via filters to a plurality of input manifolds.
15
Figure 7 shows a fourth embodiment of a satellite system 50 including a plurality of
multi-band filters. The multi-band filters comprise a total of four filters. The multiband
filters comprise two input manifolds 52a,52b. The input manifolds 52a,52b
each receive an input signal from one amplifier 51 a,51 b. The amplifiers 51 a,51 b are
20 preferably travelling wave tube amplifiers (TWTA).
A plurality of filters are connected to each input manifold 51a,51b. In particular,
two band-pass filters are connected to each input manifold 51a,51b. Filters 53a,53b
are connected directly to input manifold 52a and filters 54a,54b are connected
25 directly to input manifold 52b. The filters are directly coupled between a said input
manifold and a said output manifold, such that a signal is passed from the
respective input manifold to the respective output manifold through the filters only,
without passing through any further components. The filters 53a,53b, 54a,54b are
configured as described above, i.e. having cavities which are symmetrical between
30 the input and output manifold to which they are connected.
A single output manifold 58 outputs the filtered signals to a single feed 59 for
transmission. The number of output manifolds 58 is therefore less than the number
of input manifolds 52a,52b.
5 Figure 8 shows an enlarged view of part of the output manifold 18 of any
embodiment. The filters require a particular effective path length between the input
manifold 12 and output manifold 18 in order to function. The effective path length
is dependent on the operating frequency of the filter, and so an effective path
length between the input manifold and output manifold is unique for each filter.
10
Preferably, the input manifold and output manifold extend substantially parallel to
each other. The effective path length for each filter is selected by providing at least
one of the input manifold and output manifold with one or more stepped sections.
I5 Figure 8 shows the output manifold 18 having stepped sections 120,121. The output
manifold 18 is linear in sections 11 1,112,113 beyond the stepped sections 120,121.
A signal 115 from a first filter enters the output manifold 18 at stepped section 120,
and a signal 117 from a second filter enters the output manifold 18 at stepped
section 121. The input manifold and output manifold extend parallel to each other
20 beyond the step(s). Preferably, only the output manifold is stepped. Alternatively,
only the input manifold is stepped, or both the input and output manifolds are
stepped. The adjustment of the filters to maintain the original filter characteristics
has been described as substantially identical for the two ends of the filter. Any
further adjustment of the end of the filter in view of the connected stepped
25 manifold is considered to remain within a substantially identical adjustment.
Alternatively, the effective path length may be determined without having a stepped
input manifold or output manifold. The input and output manifolds may be straight
waveguides. The effective path length may be varied using one or more screws
30 located in the output manifold and/or input manifold adjacent a said filter, or in the
iris of a filter adjacent the output manifold and/or input manifold.
The filters of the multi-band filter have been described as band-pass filters, and
preferably, none of the pass-bands of the filters overlap. Alternatively, one of the
filters may be a high-pass filter and one of the filters may be a low-pass filter, and
preferably, none of the pass-bands of the filters overlap. The bandpass filters of the
5 multi-band filter preferably have a fixed, predetermined, pass-band.
One or more of the filters may comprise a third section comprising one or more
cavities located between the first and second sections. Cavities of the third section
may not be symmetrical between the input and output manifolds. The cavities of the
10 first, second and third sections may be integrally formed, or may be formed in
separate filter units.
The input and output manifolds have been described as waveguide manifolds. The
input and/or output manifold may be a rectangular cross-section waveguide or a
I5 ridge-guide waveguide. Alternatively, the input and output manifolds may be any
type of transmission line. For example, the input and/or output manifold may be
formed from co-axial cable or fibre-optic cable. The selection of the appropriate
type of transmission line may depend on the frequency of the signals being carried,
and the power of the signals.
20
The bandpass filters of the present invention have been described as having four
cavities. Alternatively, the bandpass filters may have fewer or more cavities. In
particular, the filters may each comprise, 2, 6 or 8 cavities. Analogously to the filters
described above, the cavities proximal to the input manifold are configured as the
25 equivalent cavities proximal to the manifold in an output multiplexer. In addition,
the cavities proximal to the input manifold are symmetrical with the cavities
proximal to the output manifold.
The first and second sections proximal to the input and output manifolds have been
30 described as each comprising two cavities. Alternatively, the first and second
sections may each comprise one or more cavities, for example, one or three cavities.
Preferably, the first and second sections have the same number of cavities, which
are arranged symmetrically.

Claims
1. A multi-band filter comprising:
at least one input manifold;
at least one output manifold; and
a plurality of filters connected in parallel between said input manifold(s) and
said output manifold(s), wherein each filter is directly coupled between a said input
manifold and a said output manifold;
wherein the filters have a first section proximal to the input manifold which
10 is coupled to the input manifold and a second section proximal to the output
manifold which is coupled to the output manifold.
2. The multi-band filter as claimed in claim 1 wherein the first and second
sections of a said filter have filter characteristics which are substantially symmetrical
I5 between the input manifold and output manifold.
3. The multi-band filter as claimed in claim 1 or 2 wherein the first section is
configured to have a filter characteristic and/or impedance for coupling to the input
manifold, and the second section is configured to have a filter characteristic and/or
20 impedance for coupling to the output manifold, wherein the first and second filter
sections are configured substantially identically.
4. The multi-band filter as claimed in any one of the preceding claims wherein a
said filter comprises a plurality of cavities configured to filter an input signal;
wherein the first section comprises one or more cavities proximal to a said
input manifold and configured for the input manifold, and the second section
comprises one or more cavities proximal to the output manifold and configured for
the output manifold.
30 5. The multi-band filter as claimed in claim 4 wherein the one or more cavities
of the first section have a position and configuration which have a symmetry with
the one or more cavities of the second section about a centerline between a said
input manifold and a said output manifold.
6. The multi-band filter as claimed in any one of the preceding claims wherein
one or more cavities of the first section are configured as one or more cavities
proximal to a manifold of an output multiplexer, and one or more cavities of the
5 second section are also configured as one or more cavities proximal to a manifold
of an output multiplexer, and preferably,
the input and output manifolds are substantially configured as the manifold of the
output multiplexer.
lo 7. The multi-band filter as claimed in any one of the preceding claims wherein
each filter comprises four cavities, such that the first section comprises two cavities
and the second section comprises two cavities.
8. The multi-band filter as claimed in claim 6 and 7 wherein the first section
15 and second section comprises two cavities out of four cavities forming part of an
output multiplexer, the two cavities being the two cavities of the output multiplexer
proximal to a manifold of the output multiplexer.
9. The multi-band filter as claimed in any one of the preceding claims wherein
20 the at least one input manifold and at least one output manifold are waveguides.
10. The multi-band filter as claimed in any one of the preceding claims wherein
each filter is formed as a single filter unit.
25 11. The multi-band filter as claimed in any one of the preceding claims wherein
an effective path length between a said input manifold and a said output manifold is
unique for each band-pass filter, and preferably, at least one of the input manifold
and output manifold is stepped.
30 12. The multi-band filter as claim any one of the preceding claims wherein the
filters are bandpass filters.
13. The multi-band filter as claim any one of the preceding claims comprising a
plurality of input manifolds and/or a plurality of output manifolds, wherein a set of
filters connected to at least one of said input manifolds is partially different to a set
of filters connected to at least one of said output manifolds.
5
14. A system comprising:
at least one amplifier; and
at least one multi-band filter as claimed in any one of the preceding claims,
wherein said output manifold of the multi-band filter is coupled to a said amplifier,
10 or, a said input manifold of a multi-band filter is configured to receive a signal from
a said amplifier.
15. The system as claimed in claim 14 wherein the output manifold is coupled to
a low noise amplifier (LNA) on an input side of a satellite system.
15
16. The system as claimed in claim 14 further comprising a feed configured to
receive an output from a said output manifold of a said multi-band filter.
17. The system as claimed in claim 14, 15 or 16 further comprising a plurality of
20 input manifolds and/or a plurality of output manifolds, wherein a set of filters
connected to at least one of said input manifolds is partially different to a set of
filters connected to at least one of said output manifolds.
18. A method of forming a multi-band filter comprising:
forming at least one input manifold;
forming at least one output manifold; and
forming a plurality of filters,
connecting the filters in parallel between said input manifold(s) and said
output manifold(s), wherein each filter is directly coupled between a said input
30 manifold and a said output manifold;
wherein the filters have a first section proximal to the input manifold which
is coupled to the input manifold and a second section proximal to the output
manifold which is coupled to the output manifold.
19. The method as claimed in claim 18 comprising configuring the first section
to have the required filter characteristics and/or impedance when coupled to the
input manifold, and the second section is configured to have the required filter
5 characteristics and/or impedance when coupled to the output manifold, wherein the
first and second filter sections are configured substantially identically.
20. The method as claimed in claim 18 or 19 wherein a said filter comprises a
plurality of cavities configured to filter an input signal;
10 wherein the first section comprises one or more cavities proximal to a said
input manifold and configured for the input manifold, and the second section
comprises one or more cavities proximal to the output manifold and configured for
the output manifold.
I5 21. The method as claimed in claim 20 wherein a base filter is designed having
an n number of cavities, wherein one or more cavities of the n cavities are designed
to be configured to couple to one only of an input or output manifold, wherein a
said filter of the multi-band filter is designed having a number n cavities, of which
the first section has a number n/2 cavities and configured as the n/2 cavities of the
20 base filter proximal the manifold, and the second section has a number n/2 cavities
and configured as the n/2 cavities of the base filter proximal the manifold, such
that the configuration of the cavities is substantially symmetrical to couple to the
input and output manifolds.