TECHNICAL FIELD

[0001] The present invention relates to telecommunications. In particular, although not exclusively, the present invention relates to shared utilisation of antennas by multiple base stations.

BACKGROUND ART

[0002] A same band combiner is a piece of radio equipment which allows two or more mobile telecommunication base stations to operate using a shared antenna and related infrastructure, such as feeders and tower mounted amplifiers.

[0003] One problem with currently-available same band combiners is that they are often large and bulky. This creates difficulties for installation, particularly where the same band combiner is mounted up a mast. Furthermore, the size and bulk of currently-available same band combiners has disadvantages in that the amount of material and energy used in their production is high, which in turn leads to increased manufacturing and hence purchase costs.

[0004] Another problem with currently-available same band combiners is that they are very limited in terms of the way in which they can be configured. This is generally because the physical construction of the same band combiner is inextricably linked to its operation, particularly in relation to its signal filtering properties and performance. Therefore, it is often difficult to adjust or redesign the configuration of a same band combiner as required. This issue also makes it difficult to reduce the size or bulk of the same band combiners, as mentioned above.

[0005] Yet a further (and again somewhat related) problem with currently-available same band combiners is that they are often difficult and labour intensive to tune, for example during commissioning. The reason for this is due to the narrow frequency gaps between same band channels. This leads to high restriction on tolerances of the physical parameters. In addition, the physical construction of current same band combiners in that the filters used are usually

"coupled" to one another, and that the tuning of the same band combiner in respect of one frequency generally affects the tuning of the same band combiner in respect of one or more other frequencies. As a result, tuning must effectively be done together for multiple frequencies.

[0006] As such, there is clearly a need for an improved same band combiner. [0007] It will be clearly understood that, if a prior art publication is referred to herein, this reference does not constitute an admission that the publication forms part of the common general knowledge in the art in Australia or in any other country.

SUMMARY OF INVENTION

[0008] The present invention is directed to same band combiners, which may at least partially overcome at least one of the abovementioned disadvantages or provide the consumer with a useful or commercial choice.

[0009] With the foregoing in view, the present invention in one form, resides broadly in a same band combiner comprising:

first and second input ports, for receiving first and second radio signals respectively; an output port, for transmitting an output radio signal according to the first and second radio signals,

one or more transmission lines extending between the first and second input ports and the output port, and

one or more notch filters edge-coupled to at least one of the one or more transmission lines, the notch filters configured to filter the first and second radio signals such that the output signal comprises one or more first sub-bands of the first radio signal, and one or more second sub-bands of the second radio signal.

[0010] Preferably, the first and second sub-bands are non-overlapping. Preferably, the second sub-band comprises a portion of a band that is not the first sub-band. Preferably, the one or more first sub-bands comprise a stop-band of the one or more notch filters, and the one or more second sub-bands comprise a pass-band of the one or more notch filters.

[0011] Preferably, the one or more notch filters comprise first and second notch filter modules, each notch filter module comprising a plurality of notch filters. Preferably, the first and second notch filter modules are configured to have substantially similar filter responses.

[0012] Preferably, the first and second notch filter modules are physically identical.

[0013] Preferably, the same band combiner includes a first coupler, coupling the first input port to first and second notch filter modules. Preferably, the same band combiner includes a second coupler, coupling the second input port to first and second notch filter modules.

[0014] Preferably, the first and second couplers are configured to isolate the first and second input ports from each other. The couplers are of preferably "hybrid couplers"(this term is generally taken to identify a class of couplers with 3dB, equal split of power, and 90° degree difference in phase between two output ports). These couplers have many different

implementations from branch coupler, coupled lines or any other physical implementations.

[0015] Preferably, the first and second notch filter modules are sandwiched between the first and second couplers.

[0016] Preferably, the first coupler is further coupled to the output port.

[0017] Preferably, the same band combiner includes a load, for dissipating signals from the first and second radio signals that do not form part of the output signal. Suitably, the load comprises a 50ohm resistor.

[0018] Preferably, the second coupler is further coupled to the load.

[0019] Preferably, the notch filters comprise resonators. Preferably, the notch filters are edge-coupled. Suitably, each resonator is individually tuneable. Preferably, there are no iris couplings between the resonators. Preferably, the notch filters comprise one or many notch filters. The notch filters may be cascaded to combine to a required multiband notch filter response. Alternatively, the notch filters in different bands may be interleaved to save space. In some cases, non-interleaved edge coupled filters may be used, particularly if it easier to tune or design.

[0020] Preferably, the resonators are located on both sides of a transmission line.

Preferably, the transmission line extends between the first coupler and the second coupler. In interleaved form, the resonating structure of one-band may rest on one side of the transmission line corresponds to a first sub-band, and the other side of the transmission line corresponds to a second sub-band. In non-interleaved structure, a single sub-band notch filter may have resonating structures on both sides of the transmission line to minimize longitudinal size.

[0021] Preferably, the notch filters are in the form of edge-coupled filters where the resonators are each coupled to a transmission line, rather than being coupled to each other. In the preferred edge-coupled form, the tuning of the notch filters may be made easier as the couplers may hide the filter response during tuning of the notch filters (resonators) in the factory.

[0022] Preferably, the notch filters comprise: combline resonating structures, ceramic resonating structures, or multi-mode resonating structures. [0023] Preferably, the notch filters comprise resonant chambers. Preferably, the notch filters comprise transverse electromagnetic (TEM) resonant structures having

combline/evanescent mode resonances.

[0024] Preferably, resonant chambers are arranged in rows. Suitably, the couplers are on the opposite side of the same band combiner to the resonant chambers.

[0025] Preferably, the notch filters comprise TEOld (ceramic) resonators. Suitably, the couplers are on the same side of the same band combiner to the resonators.

[0026] Preferably, the same band combiner is configured to enable two or more operators having frequency allocations within the same frequency band to share an antenna.

[0027] In another form, the invention resides in a signal combiner comprising:

first and second input ports, for receiving first and second radio signals respectively; an output port, for transmitting an output radio signal according to the first and second radio signals,

one or more transmission lines extending between the first and second input ports and the output port, and

one or more notch filters edge-coupled to at least one of the one or more transmission lines, the notch filters configured to filter the first and second radio signals such that the output signal comprises one or more first sub-bands of the first radio signal, and one or more second sub-bands of the second radio signal.

[0028] In another form, the invention resides broadly in a method of combining radio signals, the method comprising:

receiving a first radio signal on a first input port;

receiving a second radio signal on a second input port;

transmitting the first and the second radio signal along one or more transmission lines, and

filtering the first and second radio signals, using one or more notch filters edge- coupled between the first and second input ports and the output port to generate an output signal comprising one or more first sub-bands of the first radio signal, and one or more second sub- bands the second radio signal

transmitting, on an output port, an output radio signal.

[0029] In yet another form, the invention resides broadly in a notch filter module comprising: an input; an output; a transmission line extending between the input and output, and a plurality of notch filters edge coupled to the transmission line.

[0030] Preferably, the notch filters are interleaved on the transmission line.

[0031] Any of the features described herein can be combined in any combination with any one or more of the other features described herein within the scope of the invention.

[0032] The reference to any prior art in this specification is not, and should not be taken as an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge.

BRIEF DESCRIPTION OF DRAWINGS

[0033] Various embodiments of the invention will be described with reference to the following drawings, in which:

[0034] Figure 1 illustrates a radio system, according to an embodiment of the present invention;

[0035] Figure 2 illustrates a schematic of the same band combiner of the system of Figure 1, according to an embodiment of the present invention;

[0036] Figure 3 illustrates a schematic of the first notch filter module of the same band combiner of Figure 2, according to an embodiment of the present invention. This form shows interleaved two sub bands named TX and RX on either side of the transmission line.

[0037] Figure 4 illustrates a signal flow from a first base station of the system of Figure 2 in the first sub-band;

[0038] Figure 5 illustrates a signal flow from the first base station of the system of Figure 2 in the second sub-band;

[0039] Figure 6 illustrates a signal flow from a second base station of the system of Figure 2 in the first sub-band;

[0040] Figure 7 illustrates a signal flow from the second base station of the system of Figure 2 in the second sub-band;

[0041] Figure 8 illustrates a front view of a same band combiner with cover removed for clarity, according to an embodiment of the present invention; [0042] Figure 9 illustrates a rear view of the same band combiner of Figure 8;

[0043] Figure 10 illustrates a front view of a same band combiner with cover removed for clarity, according to an alternative embodiment of the present invention; and

[0044] Figure 11 illustrates a method of combining radio signals, according to an embodiment of the present invention.

[0045] Figure 12 illustrates a schematic of the same band combiner of the system of Figure 1, according to another embodiment of the present invention;

[0046] Figure 13 illustrates a signal flow from a first base station of the system of Figure 12 in the first sub-band;

[0047] Figure 14 illustrates a signal flow from the first base station of the system of Figure 12 in the second sub-band;

[0048] Figure 15 illustrates a signal flow from a second base station of the system of Figure 12 in the first sub-band;

[0049] Figure 16 illustrates a signal flow from the second base station of the system of Figure 12 in the second sub-band;

[0050] Preferred features, embodiments and variations of the invention may be discerned from the following Detailed Description which provides sufficient information for those skilled in the art to perform the invention. The Detailed Description is not to be regarded as limiting the scope of the preceding Summary of the Invention in any way.

DESCRIPTION OF EMBODIMENTS

[0051] Figure 1 illustrates a radio system 100, according to an embodiment of the present invention. The radio system 100 includes a same band combiner 105, coupling different base stations 110a, 110b to a single antenna 115.

[0052] The base stations 110a, 110b of the system 100 thus share the antenna 115 for transmission and reception. This is particularly useful when different operators have frequency allocations within the same frequency band and wish to share physical resources. Similarly, the system is useful in combining different modulated signals, such as 3G and 4G LTE signals, which may be from a single operator. [0053] As described in further detail below, the same band combiner 100 comprises notch filters (also known as band stop filters) that are sandwiched between hybrid couplers. This enables the same band combiner 100 to be compact in form and lightweight, which is

particularly useful when being installed on a mast. This is also clearly advantageous in that material and manufacturing costs are reduced.

[0054] Furthermore, as described in further detail below, the notch filters enable the same band combiner 100 to be easily tuned. In particular, each of the resonant structures of the notch filters may be tuned individually, in contrast to bandpass filters, where the resonant structures must be tuned together.

[0055] The first base station 110a is coupled to a first port of the same band combiner 105 by a first coaxial feeder cable 120a, and the second base station 110b is coupled to a second port of the same band combiner 105 by a second coaxial feeder cable 120b. The same band combiner 105 combines radio signals of the first and second base stations 110a, 110b and outputs same on a third port of the same band combiner 105 to the antenna 115 by third coaxial feeder cable 120c.

[0056] As described in further detail below, the same band combiner 105 filters the radio signals of the first and second base stations 110a, 110b, so that a first sub-band of the first radio and the second sub-band of the second radio is transmitted on the antenna, and the second sub- band of the first radio and the first sub-band of the second radio is not transmitted on the antenna. A fourth port of the same band combiner 105 (not illustrated) comprises a load, and thus is terminated. The load is used to dissipate the second sub-band of the first radio and the first sub-band of the second radio.

[0057] The terms first sub-band and second sub-band are used in singular throughout the document for the sake of clarity, but the skilled addressee will readily appreciate that each sub- band need not be continuous in the frequency domain, and may include a plurality of distinct sub-bands. This is particularly relevant where transmit and receive bands for each of the radios are distinct.

[0058] Figure 2 illustrates a schematic of the same band combiner 105, according to an embodiment of the present invention.

[0059] The same band combiner 105 comprises a first input port 205a, for coupling to a radio of a first base station, and a second input port 205b, for coupling to a second base station. The first and second base station share an antenna, as described above, which is coupled to an antenna port 210 of the same band combiner 105. The same band combiner 105 further includes a load port 215, in the form of a 50 ohm (50Ω) load, and is thus terminated.

[0060] The first input port 205a is coupled to a first port of a first hybrid coupler 220a. The first port of the first hybrid coupler 220a is thus the "input" port of the hybrid coupler 220a, where power (a signal) from the first base station is applied. The first hybrid coupler 220a further includes a transmit port, coupled to a first notch filter module 225a and where half of the signal from the input port is applied, and a coupled port, coupled to a second notch filter module 225b and where the other half of the signal from the input port is applied.

[0061] The transmit port provides the signal to the first notch filter module 225a without phase shift (i.e. with 0° phase shift), and the coupled port provides the signal to the second notch filter module 225b with a 90° phase shift. The power is split equally between the first and second notch filter modules 225a, 225b because the first hybrid coupler 220a is by definition, a 3 dB coupler.

[0062] The first notch filter module 225a and the second filter module 225b are identical, and are configured to provide a signal response as close to each other as possible.

[0063] A fourth port of the first hybrid coupler 220a is an isolated port and is coupled to the antenna port 210.

[0064] The same band combiner 105 further includes a second hybrid coupler 220b, identical to the first hybrid coupler.

[0065] The second input port 205b is coupled to a first port of a second hybrid coupler 220b. The first port of the second hybrid coupler 220b is thus the "input" port of the hybrid coupler 220b, where power (a signal) from the second base station is applied. The second hybrid coupler 220b further includes a transmit port, coupled to the first notch filter module 225a and where half of the signal from the input port is applied, and a coupled port, coupled to the second notch filter module 225b and where the other half of the signal from the input port is applied.

[0066] The transmit port provides the signal to the first notch filter module 225a without phase shift, and the coupled port provides the signal to the second notch filter module 225b with a 90° phase shift, and the power is split equally between the first and second notch filter modules 225a, 225b, like the first hybrid coupler 220a. Furthermore, a fourth port of the second hybrid coupler 220b is an isolated port and is coupled to the load port 215.

[0067] The first and second hybrid couplers 220a, 220b are thus configured to isolate the input ports 205a, 205b from each other.

[0068] The notch filter modules 225a, 225b comprise a plurality of notch filters in the form of resonators, as outlined below.

[0069] Figure 3 illustrates a schematic of the first notch filter module 225a, according to an embodiment of the present invention. As outlined above, the second notch filter module 225b is identical to the first notch filter module, and as such, Figure 3 is representative of the second notch filter module 225b also.

[0070] The first notch filter module 225a comprises a plurality of notch filters 305, coupled to a transmission line 310. The notch filters 305 comprise resonators, and each resonator corresponds to a dip in signal response of the notch filter module 225a

[0071] The notch filters 305 on the left and right sides of the transmission line 310 are of different frequencies and correspond to transmit and receive bands respectively. However, the position of each notch filter 305 that combines to make TX and RX bands is not important and can be mixed.

[0072] The notch filters 305 are edge coupled, and interleaved or non-interleaved. While the layout of filters is illustrated as parallel rows on either side of the transmission line 310, the skilled addressee will readily appreciate that any suitable configuration may be used. In fact, as there is no iris coupling between each resonating structure (notch filter 305), the layout of the notch filters 305 is much more flexible than a band pass equivalent, making it easier to reduce the overall size of the first notch filter module 225a.

[0073] In one embodiment, the notch filters comprise resonators in a resonant chamber. The notch filters 305 may comprise a combline resonating structure, a ceramic resonating structure or a multi-mode resonating structure.

[0074] The notch filters may, for example, comprise transverse electromagnetic (TEM) resonant structures. Alternatively, the notch filters may comprise TEOld (ceramic) resonators.

[0075] The edge coupled notch filters 305 are easy to tune as each resonator corresponds to a dip in the insertion loss trace and there no inter-resonator coupling. As such, each notch filters 305 may be tuned individually (e.g. using a tuning screw), and without reference to the other filters 305. The same band combiner relies on consistency between the notch filter modules 225a, 225b, and as such, the process of tuning the filters to provide an identical response is greatly simplified.

[0076] Furthermore, the use of notch filters described herein has lower group delay in the bands of interest reducing energy stored in the filter.

[0077] Finally, the Error Vector Magnitude (EVM), the communication standard modulation figure of merit, is typically better with the above disclosed notch filter arrangement than for prior art band pass filter arrangements.

[0078] Figures 4-7 illustrate schematics of the same band combiner 105 in use, and depicting the flow of signals along the transmission lines. In particular, the first base station 110a provides a signal in a first sub-band, and the second base station 110b provides a signal in a second sub-band. The same band combiner is configured to output signals from the first base station 110a in the first sub-band and not the second sub-band, and to output signals from the second base station 110b in the second sub-band and not the first sub-band.

[0079] The skilled addressee will readily appreciate that the first and second sub-bands need not be fully utilised by the first and second base stations. Instead, the first and second sub-bands may comprise adjacent portions of a band, and may include a guard band portion.

[0080] Figure 4 illustrates a signal flow from the first base station 110a in the first sub-band, namely signal to be transmitted on the antenna. Initially, a signal 405 is received by the first input port 205a, and provided to the first hybrid coupler 220a. At the first hybrid coupler 220a, it is divided into two signals 410a and 410b, each with half power (assuming negligible losses).

[0081] The first signal 410a is output from the first hybrid coupler 220a without phase shift (i.e. with 0° phase shift), and the second signal 410b is output from the first hybrid coupler 220a with a 90° phase shift.

[0082] These first and second signals 410a, 410b then flow to the first and second notch filter modules 225a, 225b respectively. The notch filter modules 225a, 225b reject the signals, as they are in the first sub-band, and as such, the signals are reflected back to the first hybrid coupler 220a as signals 415a, 415b. As such, the first sub-band corresponds with a stop-band of the notch filter modules 225a, 225b.

[0083] The signals 415a, 415b are combined at the first hybrid coupler 220a into signal 420, which is provided to the antenna port 210, for transmission by the antenna. No signal is returned along the line to the first input 205a, as the first hybrid coupler 220a is configured to phase shift the portion of the second signal 415b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 415a thereon, as it is not phase shifted.

[0084] As such, the notch filter modules 225a, 225b are configured to reject signals from the first port 205a which are to be output to the antenna port 210, which causes them to reflect back to the coupler 220a, and out of the antenna port 210.

[0085] Figure 5 illustrates a signal flow from the first base station 110a in the second sub- band, namely signal that is not to be transmitted on the antenna. The skilled addressee will readily appreciate that signals in the second sub-band are typically not sent from the first base station 110a, but may be present due to imperfect filtering of signals, for example.

[0086] Initially, a signal 505 is received by the first input port 205a, and provided to the first hybrid coupler 220a. At the first hybrid coupler 220a, it is divided into two signals 510a and 510b, each with half power (assuming negligible losses), and wherein the second signal 510b is phase shifted 90°, like the signal 410a, 410b of Figure 4.

[0087] These first and second signals 510a, 510b then flow to the first and second notch filter modules 225a, 225b respectively. The notch filter modules 225a, 225b allow the signals to pass unchanged as signals 515a, 515b, as they are in the second sub-band. As such, the second sub-band corresponds with a pass-band of the notch filter modules 225a, 225b.

[0088] The signals 515a, 515b are then combined at the second hybrid coupler 220b into signal 520, which is provided to the load port 215, for dissipation. No signal is provided along the line to the second input 205b, as the second hybrid coupler 220b is configured to phase shift the portion of the second signal 515b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 515a thereon, which is not phase shifted.

[0089] As such, the notch filter modules 225a, 225b are configured to allow signals from the first port 205a which are not to be output to the antenna port 210 (and instead be dissipated at the load port 215).

[0090] Figure 6 illustrates a signal flow from the second base station 110b in the first sub- band, namely a signal not to be transmitted on the antenna. Initially, a signal 605 is received by the second input port 205b, and provided to the second hybrid coupler 220b. At the second hybrid coupler 220b, it is divided into two signals 610a and 610b, and the second signal 610b is output with a 90° phase shift, like the second signal 410b of Figure 4. [0091] These first and second signals 610a, 610b then flow to the first and second notch filter modules 225a, 225b respectively. The notch filter modules 225a, 225b reject the signals, and as such, the signals are reflected back to the second hybrid coupler 220b as signals 615a, 615b.

[0092] The signals 615a, 615b are combined at the second hybrid coupler 220b into signal 620, which is provided to the load port 215, for dissipation. No signal is returned along the line to the second input 205b, as the second hybrid coupler 220a is configured to phase shift the portion of the second signal 615b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 615a thereon, which is not phase shifted.

[0093] As such, the notch filter modules 225a, 225b are configured to reject signals from the second port 205b which are not to be output to the antenna port 210.

[0094] Figure 7 illustrates a signal flow from the second base station 110b in the second sub-band, namely signal that is to be transmitted on the antenna. Initially, a signal 705 is received by the second input port 205b, and provided to the second hybrid coupler 220b. At the second hybrid coupler 220b, it is divided into two signals 710a and 710b, and wherein the second signal 710b is phase shifted 90°, like the signal 410a, 410b of Figure 4.

[0095] These first and second signals 710a, 710b then flow to the first and second notch filter modules 225a, 225b respectively. The notch filter modules 225a, 225b allow the signals to pass unchanged as signals 715a, 715b.

[0096] The signals 715a, 715b are then combined at the second hybrid coupler 220b into signal 720, which is provided to the antenna port 210, for transmission on the antenna. No signal is provided along the line to the first input 205a, as the first hybrid coupler 220a is configured to phase shift the portion of the second signal 715b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 715a thereon, which is not phase shifted.

[0097] As such, the notch filter modules 225a, 225b are configured to allow signals from the second port 205a which are to be output to the antenna port 210.

[0098] Figure 8 illustrates a front view of a same band combiner 800 (with cover removed for clarity), according to an embodiment of the present invention. Figure 9 illustrates a rear view of the same band combiner 800.

[0099] The same band combiner 800 comprises a plurality of notch filters in the form of transverse electromagnetic (TEM) resonant structures 805, which are sandwiched between two hybrid couplers 810a, 810b. The notch filters filter the first and second radio signals of first and second input ports 815a, 815b, such that an output signal provided on an output port 820 comprises a first sub-band of the first radio signal, and a second sub-band the second radio signal.

[0100] The first and second sub-bands are non-overlapping.

[0101] As best illustrated in Figure 8, the TEM resonant structures 805 are arranged in rows, and are grouped to form a first notch filter module 825a, and a second notch filter module 825b. Each of the first notch filter module 825a and the second notch filter module 825b comprises a TEM Combline (Evanescent Mode) edge-coupled bandstop filter.

[0102] First and second transmission lines 830a, 830b extends down a central portion of the first and second notch filter modules 825a, 825b. Each transmission line 830a, 830b is coupled to both of the hybrid couplers 810a, 810b, and is sandwiched between the hybrid couplers 810a, 810b.

[0103] In particular, a first port 835a of the first coupler 810a is coupled to a first end of the first transmission line 830a, and a second port 835b of the first coupler 810a is coupled to a first end of the second transmission line 830b. Similarly, a first port 840a of the second coupler 810b is coupled to a second end of the first transmission line 830a, and a second port 840b of the second coupler 810b is coupled to a second end of the second transmission line 830b.

[0104] As such, the first transmission line 830a extends between the first port 835a of the first coupler 810a and the first port 840a of the second coupler 810b, and the second transmission line 830b extends between the second port 835b of the first coupler 810a and the second port 840b of the second coupler 810b.

[0105] The first and second input ports 815a, 815b are coupled to third ports 835c, 840c of the first and second coupler 810a, 810b respectively. Similarly, a load 845 is coupled to a fourth port 835d of the first coupler 810a, and the output port 820 is coupled to a fourth port 840d of the second coupler 810b.

[0106] The couplers 810a, 810b are located on the opposite sides of the same band combiner to the notch filter modules 825a, 825b, and as such, couplings there between extend through the same band combiner 800. [0107] Each of resonant structures 805 may be provided with a tuning screw, configured to adjust a capacitance of the resonant structure 805 thus the resonant frequency thereof. As such, the same band combiner 800 may be tuned using the tuning screws of each resonant structure 805.

[0108] Such arrangement provides a compact same band combiner, with a low complexity design (simpler resonant structure), which also reduces time taken to assemble and align

(achieve electrical performance) the same band combiner. In particular, each dip on an insertion loss trace corresponds to a resonator frequency, which simplifies tuning. This is particularly important because the filters have to be tuned through the couplers.

[0109] The skilled addressee will readily appreciate that the same band combiner 800 may include a number of other elements not illustrated. These may include covers, handles, mounting brackets, grounding elements, as well as safety devices, such as lightning protection.

[0110] Figure 10 illustrates a front view of a same band combiner 1000, with cover removed for clarity, according to an alternative embodiment of the present invention. The same band combiner 1000 is similar to the same band combiner 800 of Figures 8 and 9, but with parallel same band combiner paths (i.e. like two same band combiners 800) and wherein the resonant structures are created using TEOld (ceramic) resonators.

[0111] The same band combiner 1000 is substantially symmetrical and comprises a first combiner portion 1000a and a second combiner portion 1000b. Each of the first combiner portion 1000a and a second combiner portion 1000b functions independently as a same band combiner, and thus may be used for main and diversity signals respectively.

[0112] The skilled addressee will appreciate that the diversity cables of may be "crossed- over", such that the diversity signal of one operator may be combined with the main signal of another operator. Furthermore, the skilled addressee will appreciate that different polarizations may be used in transmitting main and diversity signals.

[0113] For the sake of clarity, the first combiner portion 1000a is described below. The skilled addressee will, however, readily appreciate that the second combiner portion 1000b includes corresponding features and functions in the same manner.

[0114] The first combiner portion 1000a comprises a plurality of notch filters in the form of TEOld (ceramic) resonators 1005, which are sandwiched between two hybrid couplers 1010a, 1010b. The notch filters filter the first and second radio signals of first and second input ports 1015a, 1015b, such that an output signal provided on an output port 1020 comprises a first sub- band of the first radio signal, and a second sub-band of the second radio signal.

[0115] As outlined above, the first and second sub-bands are non-overlapping.

[0116] The TEOld (ceramic) resonators 1005 are arranged in rows, and are grouped to form a first notch filter module 1025a, and a second notch filter module 1025b, much like the first and second notch filter modules 825a, 825b. First and second transmission lines 1030a, 1030b extends down a central portion of the first and second notch filter modules 1025a, 1025b, and each transmission line 1030a, 1030b is coupled to both of the hybrid couplers 1010a, 1010b and extend there between, much like the transmission lines 830a, 830b.

[0117] Finally, a load 1045 is coupled to the second coupler 1010b, similar to the load 845.

[0118] Such arrangement also provides a compact same band combiner, with a low complexity design, which simplifies tuning. With reference to the same band combiner 800, the same band combiner 1000 offers a higher Q and more selectivity.

[0119] Figure 11 illustrates a method 1100 of combining radio signals, according to an embodiment of the present invention. The method 1100 may, for example, be implemented by the same band combiner 100, 800, 1000.

[0120] At step 1105, a first radio signal is received on a first input port. The first radio signal may be from a first base station of a first operator, and a signal component of the first radio signal in a first sub-band.

[0121] At step 1110, a second radio signal is received on a second input port. The second radio signal may be from a second base station of a second operator, and a signal component of the second radio signal in a second sub-band. This enables different operators to share antennas and related infrastructure when allocated different sub-bands within a frequency band.

[0122] At step 1115, the first and second radio signals are filtered using one or more notch filters coupled between the first and second input ports and the output port. This generates an output signal comprising a first sub-band of the first radio signal, and a second sub-band of the second radio signal. As such, the notch filters ensure that any signals from one operator that are in the other operators sub-band are removed.

[0123] At step 1120, the output radio signal is transmit on the output port. As discussed above, the output port is typically coupled to an antenna. Furthermore, the output port and antenna need not be directly coupled, and instead other components, such as an amplifier, may be between the output port and the antenna.

[0124] Figure 12 illustrates a schematic of the same band combiner 105, according to another embodiment of the present invention, which differs from the embodiment shown in Figure 2 in that the orientation of the second hybrid coupler 1220b is switched with respect to the second hybrid coupler 220b shown in Figure 2.

[0125] According to the embodiment of the present invention shown in Figure 12, the same band combiner 105 comprises a first input port 1205a, for coupling to a radio of a first base station, and a second input port 1205b, for coupling to a second base station. The first and second base station share an antenna, as described previously, which is coupled to an antenna port 1210 of the same band combiner 105. The same band combiner 105 further includes a load port 1215, in the form of a 50 ohm (50Ω) load, and is thus terminated.

[0126] The first input port 1205a is coupled to a first port of a first hybrid coupler 1220a. The first port of the first hybrid coupler 1220a is thus the "input" port of the hybrid coupler 1220a, where power (a signal) from the first base station is applied. The first hybrid coupler 1220a further includes a transmit port, coupled to a first notch filter module 1225a and where half of the signal from the input port is applied, and a coupled port, coupled to a second notch filter module 1225b and where the other half of the signal from the input port is applied.

[0127] The transmit port provides the signal to the first notch filter module 1225a without phase shift (i.e. with 0° phase shift), and the coupled port provides the signal to the second notch filter module 1225b with a 90° phase shift. The power is split equally between the first and second notch filter modules 1225a, 1225b because the first hybrid coupler 1220a is by definition, a 3 dB coupler.

[0128] The first notch filter module 1225a and the second filter module 1225b are identical, and are configured to provide a signal response as close to each other as possible.

[0129] A fourth port of the first hybrid coupler 1220a is an isolated port and is coupled to the antenna port 1210.

[0130] According to the embodiment of the present invention shown in Figure 12, the same band combiner 105 further includes a second hybrid coupler 1220b.

[0131] The second input port 1205b is coupled to a fourth port of a second hybrid coupler 1220b. The fourth port of the second hybrid coupler 1220b is the "isolation" port of the hybrid coupler 1220b, where power (a signal) from the second base station is applied. The second hybrid coupler 1220b further includes a coupled port, coupled to the first notch filter module 1225a and where half of the signal from the input port is applied, and a transmit port, coupled to the second notch filter module 1225b and where the other half of the signal from the input port is applied.

[0132] The coupled port provides the signal from the isolation port to the first notch filter module 1225a without phase shift, and the transmit port provides the signal from the isolation port to the second notch filter module 1225b with a 90° phase shift, and the power is split equally between the first and second notch filter modules 1225a, 1225b, like the first hybrid coupler 1220a. Furthermore, the input port of the second hybrid coupler 1220b is coupled to the load port 1215.

[0133] The first and second hybrid couplers 1220a, 1220b are thus configured to isolate the input ports 1205a, 1205b from each other.

[0134] The notch filter modules 1225a, 1225b comprise a plurality of notch filters in the form of resonators.

[0135] Figures 13 to 16 illustrate schematics of the embodiment of the same band combiner 105, shown Figure 12, in use, and depicting the flow of signals along the transmission lines. In particular, the first base station 110a provides a signal in a first sub-band, and the second base station 110b provides a signal in a second sub-band. The same band combiner is configured to output signals from the first base station 110a in the first sub-band and not the second sub-band, and to output signals from the second base station 110b in the second sub-band and not the first sub-band.

[0136] Figure 13 illustrates a signal flow from the first base station 110a in the first sub- band, namely signal to be transmitted on the antenna. Initially, a signal 1305 is received by the first input port 1205a, and provided to the first hybrid coupler 1220a. At the first hybrid coupler 1220a, it is divided into two signals 1310a and 1310b, each with half power (assuming negligible losses).

[0137] The first signal 1310a is output from the first hybrid coupler 1220a without phase shift (i.e. with 0° phase shift), and the second signal 1310b is output from the first hybrid coupler 1220a with a 90° phase shift. [0138] These first and second signals 1310a, 1310b then flow to the first and second notch filter modules 1225a, 1225b respectively. The notch filter modules 1225a, 1225b reject the signals, as they are in the first sub-band, and as such, the signals are reflected back to the first hybrid coupler 1220a as signals 1315a, 1315b. As such, the first sub-band corresponds with a stop-band of the notch filter modules 1225a, 1225b.

[0139] The signals 1315a, 1315b are combined at the first hybrid coupler 1220a into signal 1320, which is provided to the antenna port 1210, for transmission by the antenna. No signal is returned along the line to the first input 1205a, as the first hybrid coupler 1220a is configured to phase shift the portion of the second signal 1315b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 1315a thereon, as it is not phase shifted.

[0140] As such, the notch filter modules 1225a, 1225b are configured to reject signals from the first port 1205a which are to be output to the antenna port 1210, which causes them to reflect back to the coupler 1220a, and out of the antenna port 1210.

[0141] Figure 14 illustrates a signal flow from the first base station 110a in the second sub- band, namely signal that is not to be transmitted on the antenna. The skilled addressee will readily appreciate that signals in the second sub-band are typically not sent from the first base station 110a, but may be present due to imperfect filtering of signals, for example.

[0142] Initially, a signal 1405 is received by the first input port 1205a, and provided to the first hybrid coupler 1220a. At the first hybrid coupler 1220a, it is divided into two signals 1410a and 1410b, each with half power (assuming negligible losses), and wherein the second signal 1410b is phase shifted 90°, like the signal 1310a, 1310b of Figure 13.

[0143] These first and second signals 1410a, 1410b then flow to the first and second notch filter modules 1225a, 1225b respectively. The notch filter modules 1225a, 1225b allow the signals to pass unchanged as signals 1415a, 1415b, as they are in the second sub-band. As such, the second sub-band corresponds with a pass-band of the notch filter modules 1225a, 1225b.

[0144] The signals 1415a, 1415b are then combined at the second hybrid coupler 1220b into signal 1420, which is provided to the load port 1215, for dissipation. No signal is provided along the line to the second input 1205b, as the second hybrid coupler 1220b is configured to phase shift the portion of the second signal 1415b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 1415a thereon, which is not phase shifted.

[0145] As such, the notch filter modules 1225a, 1225b are configured to allow signals from the first port 1205a which are not to be output to the antenna port 1210 (and instead be dissipated at the load port 1215).

[0146] Figure 15 illustrates a signal flow from the second base station 110b in the first sub- band, namely a signal not to be transmitted on the antenna. Initially, a signal 1505 is received by the second input port 1205b, and provided to the isolation port of the second hybrid coupler 1220b. At the second hybrid coupler 1220b, the signal 1505 is divided into two signals 1510a and 1510b, and the second signal 1510b is phase shifted 90° relative to 1505.

[0147] These first and second signals 1510a, 1510b then flow to the first and second notch filter modules 1225a, 1225b respectively. The notch filter modules 1225a, 1225b reject the signals, and as such, the signals are reflected back to the second hybrid coupler 1220b as signals 1515a, 1515b.

[0148] The signals 1515a, 1515b are combined at the second hybrid coupler 1220b into signal 1520, which is provided to the load port 1215, for dissipation. No signal is returned along the line to the second input 1205b via the isolation port, as the second hybrid coupler 1220a is configured to phase shift the portion of the second signal 1515b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 1515a thereon, which is not phase shifted.

[0149] As such, the notch filter modules 1225a, 1225b are configured to reject signals from the second port 1205b which are not to be output to the antenna port 1210.

[0150] Figure 16 illustrates a signal flow from the second base station 110b in the second sub-band, namely signal that is to be transmitted on the antenna. Initially, a signal 1605 is received by the second input port 1205b, and provided to the isolation port of the second hybrid coupler 1220b. At the second hybrid coupler 1220b, the signal 1605 is divided into two signals 1610a and 1610b, and wherein the second signal 1610b is phase shifted 90° relative to 1605.

[0151] These first and second signals 1610a, 1610b then flow to the first and second notch filter modules 1225a, 1225b respectively. The notch filter modules 1225a, 1225b allow the signals to pass unchanged as signals 1615a, 1615b.

[0152] The signals 1615a, 1615b are then combined at the second hybrid coupler 1220b into signal 1620, which is provided to the antenna port 1210, for transmission on the antenna. No signal is provided along the line to the first input 1205a, as the first hybrid coupler 1220a is configured to phase shift the portion of the second signal 1615b thereon a further 90° (resulting in a 180° phase shift), which cancels the portion of the first signal 1615a thereon, which is not phase shifted.

[0153] As such, the notch filter modules 1225a, 1225b are configured to allow signals from the second port 1205a which are to be output to the antenna port 1210.

[0154] The skilled addressee will readily appreciate that the hybrid couplers may be arranged in alterative configurations without departing from the scope of the present invention.

[0155] For example, in a further embodiment of the invention the transmit and isolation ports of the first hybrid coupler 1220a may be arranged so that the first input port 1205a is connected to the isolation port of the first hybrid coupler 1220a and the antenna 1210 is connected to the transmit port of the first hybrid coupler. Similarly, the transmit and isolation ports of the second hybrid coupler 1220b may be arranged so that the second input port 1205b is connected to the transmit port of the second hybrid coupler 1220b and the load port 1215 is connected to the isolation port of the second hybrid coupler 1220b.

[0156] The skilled addressee will readily appreciate that the systems and methods described above may be modified without departing from the scope of the present invention.

[0157] As an illustrative example, the notch filter modules described above may comprise metal dual mode edge coupled notch (bandstop) filters, where the resonances appear at different frequency bands, the resultant effect being a dual-band notch (bandstop) filter. Similarly, the notch filter modules may comprise ceramic multi-mode edge coupled notch (bandstop) filters that operate on multiple bands, which are generally smaller size than standard filter topology.

[0158] Furthermore, different loads may be used in the same band combiners described above, including a cable load, flange mounted resistors, and a splitter with multiple loads. The RF load may produce passive inter-modulation (PIM), which is present whenever RF signals at two or more frequencies are simultaneously present in a conductor of RF energy. Generally, every passive RF device generates passive IM products when more than one frequency is present in the device. The signals are mixed by the non-linear properties of junctions between dissimilar materials. Typically, it is the odd-ordered products (e.g. IM3=2*F1-F2) that can be very problematic should they fall within an uplink, or receive band of the base station, because they appear to the receiver as interference. The result can be a receiver desensitisation which is independent of the receiver's random noise floor).

[0159] A standard RF flange mounted load may produce levels of PIM that are too high. In such case, cable loads can be used, but these can be large and expensive. Alternatively, a splitter with two or more flange loads may be used.

[0160] In summary, embodiments of the invention described above comprise notch (band stop) filters, arranged into first and second filter modules using an edge coupled transmission line, and sandwiched between hybrid couplers. A 50ohm load is provided to dissipate unwanted signals.

[0161] The same band combiners rely on the consistency between the filter modules, which are identical, or nearly identical, to achieve the isolation between two telecommunication systems.

[0162] Resonant cavities are independent from one another and are edge coupled directly to a 50ohm transmission line. As such, electrical tuning of the same band combiner is a simple matter of tuning each resonant dip (of each individual filter) to a known frequency, such that combined these dips create the 'notch' response.

[0163] As no cross couplings are needed to created transmission zeros as per the bandpass approach, the same band combiners described above provide flexibility in where the resonant cavities are placed.

[0164] The above described arrangement provides several advantages over duplexed bandpass filter cases or hybrid couplers with band pass filters. In particular, it is easier to align filters, the filters may provide a flatter group delay response.

[0165] Furthermore, such same band combiner may provide a smaller Error Vector

Magnitude (EVM), which is a measure of the difference between ideal and measured symbols after equalization.

[0166] Furthermore, embodiments of the invention enable multi-band combiners to be created more easily, and the use of a cable load in the same band combiner can provide good PEVI across the entire frequency range.

[0167] In the present specification and claims (if any), the word 'comprising' and its derivatives including 'comprises' and 'comprise' include each of the stated integers but does not exclude the inclusion of one or more further integers.

[0168] Reference throughout this specification to 'one embodiment' or 'an embodiment' means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearance of the phrases 'in one embodiment' or 'in an embodiment' in various places throughout this specification are not necessarily all referring to the same embodiment.

Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more combinations.

[0169] In compliance with the statute, the invention has been described in language more or less specific to structural or methodical features. It is to be understood that the invention is not limited to specific features shown or described since the means herein described comprises preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims (if any) appropriately interpreted by those skilled in the art.