Apparatus for Allowing Radio Frequency Selectivity and Method of
Use Thereof
This invention relates to apparatus for allowing radio frequency selectivity
and a method of use thereof, and particularly, although not necessarily
exclusively, to filter, multiplexer or combiner apparatus for use in a wireless
communication network.
A wireless communication network typically includes a plurality of cell sites
which allow radio frequency (RF) signals to be transmitted to and received
from mobile phone units. Each cell site typically includes a mast, at the top
of which is typically mounted an antenna for transmitting and/or receiving
one or more radio frequency signals, and optionally a tower mounted
amplifier (TMA) for amplifying the radio frequency signals from the antenna
to a base transceiver station (BTS). The BTS is typically located at the base
of the mast and is connected to the TMA, if provided, and antenna via two
feeder cables. The BTS typically includes a transceiver that generates one or
more radio frequency signals for transmission to a mobile phone unit, as
well as receiving one or more radio frequency signals from the mobile
phone unit.
Conventionally the wireless connections between a cell site and a mobile
phone unit have been made using a number of different frequency bands
per region. For example, in the UK these frequency bands are at 900MHz,
1800MHz and 2100MHz. Each frequency band has also conventionally
been assigned to a particular technology; the 900MHz and 1800MHz bands
have historically been licensed for second generation (2G) system use only,
and the 2100MHz band has been licensed for third generation (3G) system
use. As 3G systems support higher data rates than 2G systems, the licenses
for frequency bands previously restricted to 2G systems only have now been
amended to allow 3G systems and potentially fourth generation (4G)
systems to be deployed within them. In addition, further bandwidth is being
made available via freeing up additional frequency bands. Mobile
communication operators therefore need to invest significant amounts of
money in their networks to provide the latest technologies in multiple bands
whilst continuing to support legacy technology/band combinations.
Consequently, mobile communication operators are under pressure to
reduce capital expenditure (CAPEX) and operating expenditure (OPEX)
wherever possible in their wireless communication networks.
A significant opportunity for cost saving for a mobile communication
operator is sharing of network infrastructure in that a single operator can
share infrastructure between equipment operating in different bands or
operating in the same band and utilising different technologies (e.g. 2G and
3G) and/or the infrastructure can be shared between two different
operators.
Conventionally, a BTS at a cell site has been required for each frequency
band, each operator and each technology. A common cell site configuration
would therefore comprise splitting the area to be covered by the wireless
communications network into three 120 degree sectors, with each sector
serviced by an antenna configuration that provides a pair of statistically
independent reception and/ or transmission paths to the mobile phone units.
There are several methods for producing such an antenna configuration
including spatial diversity and X-polarised antennas. The feeder cables,
TMAs and antennae are often referred to as an antenna system. In all cases
the antenna systems will have a pair of ports, each port associated with one
of the statistically independent paths. Within each sector the cell site may
transmit on one or both antenna ports but it will receive on both. The use
of two statistically independent paths for receiving a signal is referred to as
receive diversity and improves the sensitivity of the BTS receiver. Receiver
sensitivity directly impacts the cell site coverage and capacity.
It is known to be able to provide combiner apparatus that facilitates sharing
of apparatus at a cell site for two different operators using different radio
frequency bands, or a single operator using different radio frequency bands,
as shown in figure 1. The combiner apparatus 19 uses any or any
combination of one or more band pass and/ or bandstop filters tuned to the
different radio frequency bands (i.e. 1800MHz and 2100MHz) to provide
isolation of the transmission and receiving signals of the different frequency
bands. A separate BTS 13, 15 will typically be provided for each different
operator or for the different radio frequency bands and the combiner
apparatus 19 combines the transmission signals from the respective BTS's
13, 15 onto the common antenna system and, in turn, splits combined
received signals from the common antenna system to the respective BTS's.
In Figure 1, the antenna is shown as reference numeral 1, the TMA is shown
as reference numeral 9, the cable joining the antenna 1 to the TMA is shown
as reference numeral 11, the mast is shown as reference numeral 5, the
cables joining the BTSs 13, 15 to the combiner apparatus 19 are shown as
reference numeral 17, and the cable joining the combiner apparatus 19 to
the TMA is shown as reference numeral 3.
The provision of combiner apparatus at a cell site that allows two BTS's that
operate in a single frequency band (i.e. two different operators using the
same frequency band or a single operator using the same frequency band for
different technologies) to share an antenna system is generally more
challenging. This is because the guard band between the respective
operating radio frequency sub bands of the BTS's can be small. This in turn
reduces the isolation between input ports of the combiner apparatus which,
in some cases, can lead to transmission signal noise generated by one BTS,
falling within the receive band of the other BTS, leaking through the
combiner apparatus into the other BTS, thereby desensitising its receiver
and reducing its coverage and uplink capacity. A further problem is that
even if the combiner apparatus operates successfully, the need for a high
degree of isolation between the respective radio frequency sub bands of the
single frequency band results in relatively high performance filters being
required within the combiners to be provided as part of the system. Such
high performance filters are relatively large and are therefore either difficult
to physically fit in the available space of the combiner apparatus or require
the size of the combiner to be relatively large. High performance filters are
also expensive pieces of equipment which can reduce the cost advantage to
be gained by sharing infrastructure.
In an attempt to overcome the abovementioned problem it is known to use
combiner apparatus, often referred to as a directional filter, that uses two
3dB hybrid couplers 102, 104 with a pair of identical pass band filters 106,
108 arranged in parallel between the couplers, an example of which is shown
in figure 2. In this arrangement the hybrid couplers 102, 104 provide the
directivity which isolates the sub-bands within the single frequency band of
BTS1 and BTS2, thereby allowing filters to be used in the apparatus that are
smaller in size and have lower performance characteristics than conventional
apparatus. A feature of the filters 106, 108 used in the arrangement shown in
figure 2 is that each filter includes a plurality of cascading resonators 110
coupled together, as shown in figure 3, with each radio frequency signal
passing through a particular filter passing through each of the coupled
resonators 110 in turn. As such, the resonators 110 of each filter are coupled
together and typically this requires them to be made from the same
resonator technology with substantially the same Q (Quality Factor), and
typically a high Q, to provide high resonator performance characteristics.
This leads to large and expensive filters within the apparatus.
Cross coupling 112 between the filter resonators and/or the filter input
and/or output, as shown in figure 4, could be used to provide transmission
zeros in the response improving the frequency selectivity of the combiner
and reducing the size of the guard band between the two radio frequency
sub-bands. However, as the guard band is decreased the resonator's Q has
to increase to maintain the band edge insertion loss performance and this
leads to large expensive resonators and hence large expensive combiners. In
addition, the couplings that are required to produce cross couplings can be
extremely difficult to physically realise as the resonators that need to be
coupled together are physically remote from one another and therefore it
may not be possible to generate all the transmission zeros required for the
optimum response
It is therefore an aim of the present invention to provide alternative
apparatus for allowing radio frequency selectivity that has improved
performance with reduced costs and size associated with the same.
It is a further aim of the present invention to provide a method of using
apparatus for allowing radio frequency selectivity that has improved
performance with reduced costs and size associated with the same.
It is a yet further aim of the present invention to provide combiner
apparatus.
It is a yet further aim of the present invention to provide a method of using
combiner apparatus.
According to a first aspect of the present invention there is provided
apparatus for allowing radio frequency selectivity for use in a wireless
communication system for the passage of one or more receiving and/or
transmission frequency signals therethrough, said apparatus including at
least a first set of first and second 90 degree phase shift coupling means, and
at least one pair of resonating means coupled between the at least first and
second 90 degree phase shift coupling means, wherein at least one further
set of first and second 90 degree phase shift coupling means are cascaded,
either directly or indirectly, with said at least first set of first and second 90
degree phase shift coupling means, with or without at least one pair of
resonating means located between the first and second 90 degree phase shift
coupling means of the at least one further set.
The arrangement of the present invention allow transmission zeros to be
created in the transfer function of the apparatus without the requirement for
cross coupling between the resonating means or resonators as there is in the
prior art. In addition, it allows resonating means or resonators made from
different technologies, having a different Q and/ or the like to be used in the
same apparatus without the problems associated with the prior art.
In one embodiment the apparatus is in the form of combiner apparatus.
In an alternative embodiment the apparatus is in the form of multiplexer
apparatus.
In a further alternative embodiment the apparatus is in the form of filter
apparatus. The filter apparatus could be any or any combination of a
bandpass, bandstop, lowpass, highpass filter apparatus and/or the like.
The cascading between the different sets of first and second 90 degree phase
shift coupling means is arranged such that one or more radio frequency
signals can pass between the different sets of first and second 90 degree
phase shift coupling means. For example, in one embodiment the cascading
is undertaken using one or more transmission lines.
The at least one pair of resonating means could include a single resonator
with at least two resonator modes or sections provided in or associated with
the same coupled together. Alternatively, or in addition, the at least one pair
of resonating means could include at least two separate (i.e. physically
independent and distinct) resonators coupled together.
Preferably the resonating means include any or any combination of one or
more ceramic rods, combline resonators, ceramic pucks and/ or the like.
In one embodiment the resonating means used in the apparatus are
substantially the same (i.e. provided with substantially the same or similar Q
value, formed from the same material and/ or the like).
In one embodiment two or more of the resonating means used in the
apparatus are different (i.e. provided with different Q values, formed from
different materials and/ or the like). Thus, in one embodiment the resonating
means can be arranged such that narrow band resonating means or
resonators are provided which contribute most to the band edge insertion
loss and are typically made from high Q technologies, whilst wider band
resonating means or resonators are also provided which are typically made
from low Q technologies. This in turn reduces the cost of the apparatus. In
this embodiment there is no necessity for interaction between the different
resonator technologies.
In one embodiment the first and second 90 degree phase shift coupling
means each typically form part of a four port network coupling device with
two input ports and two output ports. Each input port is coupled to both
output ports but each input port is substantially isolated from the other
input port. The signals coupled to the two output ports have a 90 degree
phase difference.
Preferably in the above embodiment the coupling between the at least one
pair of resonating means is electromagnetic coupling.
Preferably in the above embodiment each of the output ports of the first of
the 90 degree phase shift coupling means is coupled to a different resonating
means of the pair of resonating means. Each of the output ports of the
second of the 90 degree phase shift coupling means is coupled to a different
resonating means of the pair of resonating means. The cascade of sets of 90
degree phase shift coupling means, with or without a pair of resonating
means located between the 90 degree phase shift coupling means, is
achieved by connecting and or coupling, either directly or indirectly, the
second input port of the first 90 degree phase shift coupling means of the
first set to first input port of the first 90 degree phase shift coupling means
of the second set and the second input port of the second 90 degree phase
shift coupling means of the first set to the first input port of the second 90
degree phase shift coupling means of the second set. Typically, subsequent
sets are cascaded in a similar manner.
In one embodiment the first and/ or second 90 degree phase shift coupling
means is or includes a 3dB hybrid coupling device.
In one embodiment the apparatus includes at least a first set of first and
second 90 degree phase shift coupling means with at least one pair of
resonating means provided between the same, and at least one further set of
first and second degree phase shift coupling means with no resonating
means provided therebetween.
For example, in the embodiment where there are n sets of first and second
90 degree phase shift coupling means with one pair of resonating means
provided between the 90 degree phase shift coupling means of each set, a
response with n-1 transmission zeros can be obtained. In the embodiment
where there are n sets of first and second 90 degree phase shift coupling
means with one pair of resonating means provided between the 90 degree
phase shift coupling means of each set, and one set of first and second 90
degree phase shift coupling means with no resonating means provided
between them, a response of n transmission zeros can be obtained. These
embodiments allow a greater number of transmission zeros of the apparatus
response to be realised with a practical design compared to the prior art.
In one embodiment the apparatus includes the first set of first and second
90 degree phase shift coupling means with at least one pair of resonating
means provided between the same, and at least one further set of first and
second 90 degree phase shift coupling means with at least one pair of
resonating means therebetween.
In one embodiment each of the paths separating two or more sets of 90
degree phase shift coupling means in the apparatus will have a phase shift
and the difference between the shifts will be substantially 180 degrees.
However, the phase difference could be any required value or could be zero.
Thus, in this embodiment a plurality of sets of 90 degree phase shift
coupling means with associated resonating means can be provided that are
cascaded together to provide a desired transfer function. Any number of
phase shifts can be provided as required. The phase shifts can be provided
in any of the paths between the 90 degree phase shift coupling means,
providing they result in the required phase difference in the paths.
Preferably the phase difference is created using one or more transmission
lines with electrical lengths that produce the required phase difference.
In one embodiment the 90 degree phase shift coupling means is in the form
of a transmission line with an electrical length of substantially 90 degrees
(also referred to as a quarter wavelength transmission line). The transmission
line is coupled to the at least one pair of resonating means with one end of
the transmission line coupled to one of the resonating means and the other
end of the transmission line coupled to the resonating means and a coupling
is provided between the at least one pair of resonating means. Thus, in one
example, a transmission line is provided either side of at least one pair of
resonating means and the 90 degree phase shift coupling means can be
considered to be integrated with the resonating means.
In the above embodiment preferably the coupling is electromagnetic
coupling.
In the above embodiment preferably the first and at least second set of 90
degree phase shift coupling means are cascaded by connecting or coupling,
either directly or indirectly, the end of the transmission line within the first
90 degree phase shift coupling means of the first set of 90 degree phase shift
coupling means with the start of the transmission line of the first 90 degree
phase shift coupling means of the second set and the end of the
transmission line within the second 90 degree phase shift coupling means of
the first set of 90 degree phase shift coupling means with the start of the
transmission line of the second 90 degree phase shift coupling means of the
second set. Subsequent sets are cascaded in a similar manner.
In the abovementioned embodiment, the physical couplings between the
transmission lines and the resonator means of a set or between sets can be
of the same coupling type (i.e. all magnetic (+ve) couplings or all electrical (-
ve) couplings). Alternatively, the physical couplings between the
transmission lines and resonator means of one or more sets or between one
or more sets can be of a different coupling type (i.e. some magnetic (+ve)
couplings and some electrical (-ve) couplings), such that it may not be
necessary to have a phase difference of 180 or degrees between two sets
of 90 degree phase shift coupling means and/ or resonators (wherein V = a
required phase shift value).
In one embodiment the physical couplings between the transmission lines
and the resonator means and/ or between the 90 degree phase shift coupling
means and the resonator means can be symmetrical in that they have the
same coupling value.
In one embodiment the physical couplings between the transmission lines
and the resonator means and/ or between the 90 degree phase shift coupling
means and the resonator means can be non-symmetrical or different. This
allows the poles and zeros of the transfer function of apparatus with finite
Q resonators to be recovered.
In one embodiment the apparatus is combiner apparatus and the combiner
apparatus communicates with at least first and second base transceiver
stations (BTSs). Preferably the receiving means of the first base transceiver
station is arranged to receive one or more receiving signals of a first radio
frequency sub-band within a known frequency band and the second base
transceiver station is arranged to receive one or more receiving signals of a
second radio frequency sub-band within said known frequency band. The
first radio frequency receive sub-band is typically different to or distinct
from the second radio frequency receive sub-band.
Preferably the transmission means of the first base transceiver station is
arranged to transmit one or more transmission signals to an antenna of a
first radio frequency sub-band within a known frequency band and the
second base transceiver station is arranged to transmit one or more
transmission signals to an antenna of a second radio frequency sub-band
within said known frequency band. The first radio frequency transmit subband
is typically different to or distinct from the second radio frequency
transmit sub-band.
Preferably, the transfer function of the apparatus will define one or more
passbands and signals whose frequency falls within one of the passbands
will be attenuated by a relatively small amount compared to signals whose
frequencies lie outside the one or more passbands.
Preferably the resonator means of different sets of 90 degree phase shift
coupling means are tuned to different F frequencies.
In one embodiment the resonator means include one or more bandpass
resonators.
In one embodiment the resonator means include one or more bandstop
resonators.
In one embodiment the combiner apparatus is a dual combiner apparatus
including two electronic circuits provided therein. Preferably the two
electronic circuits are mirror images of each other.
In one embodiment the coupling means includes a capacitive coupling, a
transformer, a direct coupling, a pin, one or more screws, solder and/or the
like.
According to a second aspect of the present invention there is provided a
wireless communication system including apparatus for allowing radio
frequency selectivity. The system preferably includes an antenna for
receiving and/or transmitting one or more receive and/or transmit radio
frequency signals, at least first BTS including at least first transmitter and at
least first receiver. The antenna is in communication with the at least first
transmitter and at least first receiver and the one or more receive and/or
transmit signals pass through the apparatus between the antenna and the at
least first transmitter and at least first receiver.
In one embodiment the transfer function of the combiner apparatus is
arranged to provide multiple passband functions (i.e. one passband falls
within the receive band of the first BTS and one passband falls within the
transmit band of the first BTS).
In one embodiment the apparatus is multiplexer or diplexer apparatus, such
as for example a transmit/ receive diplexer within a base station, BTS, Node
B, eNode, Remote Radio Head and/or the like. In this embodiment the
transmit and receive chains of the base station typically connect to the ports
equivalent to the first and second BTSs previously described or vice versa.
For example, the common port could form the antenna port of the base
station. Using such a device could reduce the size and cost of base station
filters which represent a significant proportion of the size, weight and/ or
cost of the base station.
According to a further aspect of the present invention there is provided a
method of using apparatus for allowing radio frequency selectivity.
Embodiments of the present invention will now be described with reference
to the accompanying figures, wherein:
Figure 1 is a simplified view of PRIOR ART combiner apparatus that can be
used on a cell site for allowing two different operators using different radio
frequency bands or a single operator using different radio frequency bands
to use a common antenna and mast;
Figure 2 is a simplified view of PRIOR ART combiner apparatus using two
3dB hybrid couplers with a pair of identical bandpass filters arranged in
parallel therebetween;
Figure 3 is a simplified view of the PRIOR ART combiner apparatus in
figure 2 showing that each filter includes a plurality of resonators coupled
together;
Figure 4 is a simplified view of PRIOR ART combiner apparatus using two
3dB hybrid couplers with a pair of filters arranged in parallel therebetween
with cross couplings provided between the resonators of each filter;
Figure 5 is a simplified view of a cell site of a type to which the combiner
apparatus of the present invention relates;
Figure 6a is a simplified view o f combiner apparatus according
to one embodiment o f the present invention with a 180 degree
phase shift in one o f the paths between two sets o f 90 degree
phase shift coupling means and resonator means;
Figure 6b is a simplified view o f combiner apparatus according
to a further embodiment o f the present invention where at least
one o f the sets o f 90 degree phase shift coupling means has n o
resonator means provided between the same;
Figure 7a illustrates an arrangement o f a set o f 90 degree phase
shift coupling means and resonator means according to one
embodiment o f the present invention;
Figure 7b illustrates an arrangement of a set of 90 degree phase
shift coupling means and resonator means according to a further
embodiment of the present invention;
Figure 8a illustrates an example of sets of 90 degree phase shift
coupling means wherein the coupling means are integrated into
the resonator structure according to one embodiment of the
present invention in which the physical couplings are all of the
same type; and
Figure 8b illustrates an example of sets of 90 degree phase shift
coupling means wherein the coupling means are integrated into
the resonator structure according to one embodiment of the
present invention and the physical couplings are of different
types.
Referring firstly to Figure 5, there is illustrated an example of a
cell site forming part of a wireless communication system for
transmitting and/or receiving radio frequency signals. The cell
site includes antenna 401 , and it should be noted that this
antenna can be formed from several antennas each of which
covers a particular sector from the antenna mast, such as for
example, three antennas spaced around the central longitudinal
axis and each covering 120 degrees. For the purpose of the
description, only one antenna "sector" is described and the
invention herein described can, if required, be used for each of
the antenna sectors. The antenna 401 in this embodiment is
located at the top of a mast 402 and is connected to a tower
mounted amplifier 409 via cables 403, which allows one or more
radio frequency received signals to be amplified before passing
via cables 403 to dual combiner apparatus 405. The dual
combiner apparatus 405 is in turn connected to first and second
base transceiver stations (BTSs) 407, 407'.
In the illustrated example, the BTSs 407, 407' belong to
different operators who transmit and receive radio frequency
signals in the same radio frequency band, such as for example
2 100MHz. Thus, the first BTS 407 is operated by a first service
provider or operator who transmits and receives signals at a first
frequency band having two sub bands; a first sub band within a
known radio frequency band for transmission and a second sub
band within a known radio frequency band for receiving signals.
The second base transceiver station 407' is operated by a second
service provider or operator who transmits and receives signals
at the same first frequency band having two frequency sub
bands; a first sub band within a known radio frequency band for
transmission and a second sub band within a known radio
frequency band for receiving signals. It is to be noted that the
first and second sub-bands of the first operator are different to
the first and second sub-bands of the second operator.
The first and second BTSs 407, 407' are each provided with
transmitting and receiving means 4 11, 4 11' , 4 13, 4 13' for
receiving and/or transmitting one or more signals from the dual
combiner apparatus 405. In operation there is a need for the
combining apparatus 405 to ensure that the appropriate signals
are received at each of the base transceiver stations in order to
allow each of the service providers to maintain their service to
their customers via the common antenna. The dual combiner
apparatus 405 in this embodiment includes a pair of
input/output ports 427, 427' associated with the receiver and
transmitter means of BTS1 , and a pair of input/output ports
429, 429' associated with the receiver and transmitter means of
BTS 2 . In addition, dual combiner apparatus 405 has input port
425 and 425' associated with the combined signals from BTS1
and BTS2. Input/output ports 425, 425' are connected to TMA
409 via the cables 403.
The dual combiner apparatus 405 typically has two copies of an
electronic circuit associated with BTS1 and BTS2. An example
of one of the electronic circuits 202 of the combiner apparatus
405 according to an embodiment of the present invention is
shown in figure 6a.
The circuit 202 includes a first set 204 of first and second 90
degree phase shift coupling means in the form of 3dB hybrid
couplers 206, 208. Each coupler 206, 208 is connected to a pair
of resonating means in the form of a first resonator 2 10 and a
second resonator 2 12 .
The circuit 202 also includes at least a second set 2 14 of first
and second 90 degree phase shift coupling means in the form of
3dB hybrid couplers 2 16, 2 18 . Each coupler 2 16, 2 18 is
connected to a pair of resonating means in the form of a first
resonator 220 and a second resonator 222. This arrangement
allows transmission zeros to be created in the filter transfer
function of the combiner apparatus without a requirement of
cross coupling to be provided between resonators. As such,
smaller sized combiner apparatus can be provided of reduced
cost compared to prior art arrangements. In addition, as there is
no direct coupling between pairs of resonators, different types
or different Q technology resonators can be used within the
same combiner apparatus which is not easily possible with prior
art combiner apparatus arrangements.
It will be appreciated that any further number of sets of first
and second 90 degree phase shift coupling means and resonators
can be provided in circuit 202, as represented by dotted lines
224 and further set example 226.
Although only a single pair of resonators is shown in sets 204,
2 14, 226 for clarity purposes, it will be appreciated that any
number of resonator pairs can be provided in each set between
the 3dB hybrid couplers as required.
It is to be noted that in one embodiment you could have
multiple pairs of resonators within a set of 90 degree phase shift
coupling means of the apparatus. This would means that cross
coupling would need to be included between the resonators to
create some of the transmission zeros and it also means that the
same resonator technology would need to be used within the set.
However, it would allow apparatus to be produced that included
two different types of resonator technologies (i.e. having high
and low Q values) in different sets of 90 degree phase shift
coupling means of the apparatus. All the resonators of a
particular type would need to be grouped together within the
same set.
The transmission path 228 provided between one side of first
set 204 and second set 2 14 has a 180 degree phase shift 230 that
means there is a 180 degree phase difference between path 230
and path 229. This allows the two or more sets of resonators
2 10, 2 12, 220, 222 to be cascaded together to produce a desired
transfer function. 180 degree phase differences will typically
need to be provided between the paths that connect adjacent
sets in the circuit as required.
In use for example, if it is assumed that the resonators of set
204 of circuit 202 are tuned to a first sub band frequency of the
transmission band of BTS 1 and the resonators of set 2 14 are
tuned to a second sub band frequency of the transmission band
of BTS 1, a radio frequency transmission signal travelling from
BTS 1 that is within the first sub-band, through electronic
circuit 202 of the combiner 405 to antenna 401 , will reach 3dB
hybrid coupler 208 of first set 204 and be split in half, with half
of the signal passing through resonator 2 10 and half of the
signal passing through resonator 2 12 . The signal halves pass
through 3 dB hybrid coupler 206 and are recombined in
transmission path 228. This signal undergoes a 180 phase shift
as it travels through path 230. When the signal reaches the 3dB
hybrid coupler 2 16 of the second set of 90 degree phase shift
means 2 14 it is then split in half, with half the signal being
reflected from resonator 220 and half the signal being reflected
from resonator 222. Resonators 220, 222 reflect the signal as
they are resonant in the second sub band rather than the first
sub band. Due to the phase characteristics of the 3dB hybrid
coupler 2 16, the signal halves recombine at point 2 17 .
Subsequent sets, including set 226, are also not resonant in the
first sub band and therefore the signals split, reflect and
recombine in a similar manner and the signal arrives at port 425.
A radio frequency signal that is transmitted from BTSl and falls
within the second sub-band is reflected by set 204 and passes
along path 229 to set 2 14 that passes through to point 2 17 . All
other sets reflect the signal as it passes to port 425.
The resonator sets are tuned such that the sub bands associated
with them add up to the transmission band of the BTSl . None
of the sets resonate within the transmission band of BTS2 and
therefore a signal transmitted from BTS2 will be reflected by all
sets and pass to port 425. Therefore, port 425 will pass
transmission signals from both BTSl and BTS2. The combiner
apparatus can operate in both the transmission and receive
bands if the sum of the sub-bands of the sets cover both the
receive and transmit bands of BTSl .
The recombined transmission signals of BTSl and BTS2 are
combined together and leave the combiner apparatus at port
425.
It is to be noted that port 427 is isolated in the illustrated
example. Preferably, the port could be internally terminated,
such as for example using a 50ohm load.
A further example of an electronic circuit for use in a combiner
apparatus according to the present invention is shown in figure
6b. In this example, set 204 is as previously described but set
2 14 does not have any resonator pairs and so 3dB hybrid
coupler 2 16 is coupled directly to 3dB hybrid coupler 2 18 . This
arrangement allows an additional transmission zero to be formed
in the combiners response. It is possible to replace hybrid
couplers 2 16 and 2 18 with a directional coupler whose coupling
value can be varied to product a transmission zero at a desired
frequency.
Referring to figures 7a and 7b, there is illustrated two different
examples of 90 degree phase shift coupling arrangements that
could be used in each set of the electronic circuit according to
the present invention. The 90 degree phase shift coupling
arrangement in figure 7a is of a type shown in figure 6a, wherein
two distinct 3dB hybrid couplers are provided with at least one
pair of resonators 2 10, 2 12 arranged therebetween.
The 90 degree phase shift coupling arrangement in figure 7b is
integrated into the resonator structure itself using physical
couplings and quarter wavelength transmission lines (i.e.
transmission lines which have an electrical length of 90 degrees).
More particularly, the two ends of two quarter wavelength
transmission lines 232, 234 are each coupled to resonators 236,
238 as shown by arrows 240, 242, 244, 246 respectively.
Resonators 236, 238 are also coupled to each other, as shown by
arrow 248. This coupling arrangement has the advantage of
being more compact than the arrangement using 3dB hybrid
couplers. In addition, this coupling arrangement typically
removes the requirement for a 180 phase shift to be provided
between two or more adjacent sets of coupling arrangements in
the circuit if the physical couplings are of the appropriate type.
It is to be noted that an embodiment of the apparatus can be
provided wherein you can have a combination of the couplers
shown in figure 7a and 7b within one electronic circuit of
combiner apparatus.
Figure 8a illustrates how two or more sets 302, 304 of 90 degree
phase shift coupling arrangements of the type shown in figure
7b can be cascaded together. If the physical couplings provided
between the quarter wavelength transmission lines 232, 234 and
the resonators 236, 238 are all of the same type (i.e. all magnetic
couplings (+ve)), a 180 degree phase shift 230 is still typically
required in one of the paths 306 relative to the other path 307,
between sets 302, 304 to allow cascading of the resonator pairs
together. However, if some of the physical couplings provided
between the quarter wavelength transmission lines 232, 234 and
the resonators 236, 238 are of different types; some are
magnetic (+ve) 308 and some are electrical (-ve) 3 10, the 180
degree relative phase shift 230 can be removed as shown in
Figure 8b.
Claims
1. Apparatus for allowing radio frequency selectivity for use in a wireless
communication system for the passage of one or more receiving
and/or transmission frequency signals therethrough, said apparatus
including at least a first set of first and second 90 degree phase shift
coupling means, and at least one pair of resonating means coupled
between the at least first and second 90 degree phase shift coupling
means, wherein at least one further set of first and second 90 degree
phase shift coupling means are cascaded, either directly or indirectly,
with said at least first set of first and second 90 degree phase shift
coupling means, with or without at least one pair of resonating means
located between the first and second 90 degree phase shift coupling
means of the at least one further set.
2. Apparatus according to claim 1 wherein the apparatus is in the form
of a combiner, a multiplexer or a filter.
3. Apparatus according to claim 1 wherein the cascading between the
different sets of first and second 90 degree phase shift coupling
means is arranged such that one or more radio frequency signals can
pass between the different sets of first and second 90 degree phase
shift coupling means.
4. Apparatus according to claim 3 wherein the cascading is undertaken
using one or more transmission lines.
5. Apparatus according to claim 1 wherein the at least one pair of
resonating means includes a single resonator with at least two
resonator modes or sections provided in or associated with the same
coupled together, and/or the at least one pair of resonating means
includes at least two separate resonators coupled together.
6. Apparatus according to claim 1 wherein the resonating means include
any or any combination of one or more ceramic rods, combline
resonators or ceramic pucks.
7. Apparatus according to claim 1 wherein the resonating means used in
the apparatus are of substantially the same form, are provided with
substantially the same or similar Q value and/ or are formed from the
same material.
8. Apparatus according to claim 1 wherein two or more of the
resonating means used in the apparatus are different in form, are
provided with different Q values and/ or are formed from different
materials.
9. Apparatus according to claim 1 wherein the first and second 90
degree phase shift coupling means each form part of a four port
network coupling device with two input ports and two output ports,
each input port being coupled to both output ports but each input
port being substantially isolated from the other input port, the signals
coupled to the two output ports having a substantially 90 degree
phase difference.
10. Apparatus according to claim 9 wherein the signals coupled to the
two output ports have substantially equal magnitude.
11. Apparatus according to claim 9 wherein each of the output ports of
the first of the 90 degree phase shift coupling means is coupled to a
different resonating means of the pair of resonating means, and each
of the output ports of the second of the 90 degree phase shift
coupling means is coupled to a different resonating means of the pair
of resonating means.
12. Apparatus according to claim 9 wherein the cascade of sets of 90
degree phase shift coupling means, with or without a pair of
resonating means located between the 90 degree phase shift coupling
means, is achieved by connecting and or coupling, either directly or
indirectly, the second input port of the first 90 degree phase shift
coupling means of the first set to first input port of the first 90 degree
phase shift coupling means of the second set, and the second input
port of the second 90 degree phase shift coupling means of the first
set to the first input port of the second 90 degree phase shift coupling
means of the second set.
13. Apparatus according to claim 1 wherein the first and/or second 90
degree phase shift coupling means is or includes a 3dB hybrid
coupling device.
14. Apparatus according to claim 1 wherein the apparatus includes at
least a first set of first and second 90 degree phase shift coupling
means with at least one pair of resonating means provided between
the same, and at least one further set of first and second degree phase
shift coupling means with no resonating means provided
therebetween.
15. Apparatus according to claim 1 wherein where there are n sets of first
and second 90 degree phase shift coupling means with one pair of
resonating means provided between the 90 degree phase shift
coupling means of each set, a response with n-1 transmission zeros is
obtained.
16. Apparatus according to claim 1 wherein where there are n sets of first
and second 90 degree phase shift coupling means with one pair of
resonating means provided between the 90 degree phase shift
coupling means of each set, and one set of first and second 90 degree
phase shift coupling means with no resonating means provided
between them, a response of n transmission zeros is obtained.
17. Apparatus according to claim 1 wherein the apparatus includes the
first set of first and second 90 degree phase shift coupling means with
at least one pair of resonating means provided between the same, and
at least one further set of first and second 90 degree phase shift
coupling means with at least one pair of resonating means
therebetween.
18. Apparatus according to claim 1 wherein each of the paths separating
two or more sets of 90 degree phase shift coupling means in the
apparatus has a phase shift and the difference between the shifts is
substantially 180 degrees.
19. Apparatus according to claim 1 wherein each of the paths separating
two or more sets of 90 degree phase shift coupling means in the
apparatus has a phase shift, the difference between the shifts being
any required value, and the difference between the shifts is created
using one or more transmission lines with electrical lengths that
produce the required phase difference.
20. Apparatus according to claim 19 wherein the 90 degree phase shift
coupling means is in the form of a transmission line with an electrical
length of substantially 90 degrees, or a quarter wavelength
transmission line.
21. Apparatus according to claim 20 wherein the first and at least second
set of 90 degree phase shift coupling means are cascaded by
connecting or coupling, either directly or indirectly, the end of the
transmission line within the first 90 degree phase shift coupling
means of the first set of 90 degree phase shift coupling means with
the start of the transmission line of the first 90 degree phase shift
coupling means of the second set, and the end of the transmission
line within the second 90 degree phase shift coupling means of the
first set of 90 degree phase shift coupling means with the start of the
transmission line of the second 90 degree phase shift coupling means
of the second set.
22. Apparatus according to claim 20 wherein the physical couplings
between the transmission lines and the resonator means of a set or
between sets can be of the same coupling type, or the physical
couplings between the transmission lines and resonator means of one
or more sets or between one or more sets can be of a different
coupling type.
23. Apparatus according to claim 19 wherein the physical couplings
between the transmission lines and the resonator means and/or
between the 90 degree phase shift coupling means and the resonator
means is symmetrical in that they have the same coupling value.
24. Apparatus according to claim 19 wherein the physical couplings
between the transmission lines and the resonator means and/or
between the 90 degree phase shift coupling means and the resonator
means is non-symmetrical or different.
25. Apparatus according to claim 1 wherein the apparatus is combiner
apparatus and the combiner apparatus communicates with at least
first and second base transceiver stations (BTSs).
26. Apparatus according to claim 25 wherein the receiving means of the
first base transceiver station is arranged to receive one or more
receiving signals of a first radio frequency sub-band within a known
frequency band, and the second base transceiver station is arranged to
receive one or more receiving signals of a second radio frequency
sub-band within said known frequency band, the first radio frequency
receive sub-band being different to or distinct from the second radio
frequency receive sub-band.
27. Apparatus according to claim 25 wherein the transmission means of
the first base transceiver station is arranged to transmit one or more
transmission signals to an antenna of a first radio frequency sub-band
within a known frequency band and the second base transceiver
station is arranged to transmit one or more transmission signals to an
antenna of a second radio frequency sub-band within said known
frequency band, the first radio frequency transmit sub-band being
different to or distinct from the second radio frequency transmit subband.
28. Apparatus according to claim 1 wherein a transfer function of the
apparatus will define one or more passbands, and signals whose
frequency falls within one of the passbands will be attenuated by a
relatively small amount compared to signals whose frequencies lie
outside the one or more passbands.
29. Apparatus according to claim 1 wherein the resonator means of
different sets of 90 degree phase shift coupling means are tuned to
different frequencies.
30. Apparatus according to claim 1 wherein the resonator means include
one or more bandpass resonators and/or one or more bandstop
resonators.
31. Apparatus according to claim 1 wherein the apparatus is a dual
combiner apparatus including two electronic circuits provided
therein, the two electronic circuits being mirror images of each other.
32. A method of using apparatus for allowing radio frequency selectivity
for use in a wireless communication system for the passage of one or
more receiving and/or transmission frequency signals therethrough,
said apparatus including at least a first set of first and second 90
degree phase shift coupling means, and at least one pair of resonating
means coupled between the at least first and second 90 degree phase
shift coupling means, wherein said method includes the step of
cascading at least one further set of first and second 90 degree phase
shift coupling means, either directly or indirectly, with said at least
first set of first and second 90 degree phase shift coupling means,
with or without at least one pair of resonating means located between
the first and second 90 degree phase shift coupling means of the at
least one further set.
33. A wireless communication system including apparatus for allowing
radio frequency selectivity according to claim 1.