Patent Application
20240340043
The present invention relates to the field of base station antennas for mobile communication.
Base station antennas for mobile communication normally comprise an antenna feeding network, a backplane and a plurality of radiating elements (for example dipoles) arranged in front of the backplane. The backplane typically comprises an electrically conductive reflector onto which, or in front of which, the radiating elements are arranged.
Radiating elements are commonly placed as an array in front of the backplane, in some cases as a one-dimensional array (a column) extending in the vertical direction, but two-dimensional arrays are also used.
The purpose of the antenna feeding network is to distribute the signals from a common connector to all radiating elements of an array when transmitting and combining the signals from all the radiating elements to the same common connector when receiving. Such an antenna feeding network can be realized using different types of transmission lines. Transmission lines have a forward path and a return path. Typical transmission lines are flexible coaxial cables using e.g. PTFE as dielectric between inner and outer conductor, or air-filled coaxial lines as disclosed in WO2005/101566A1, U.S. Pat. No. 7,619,580 (which is hereby incorporated by reference in its entirety), or stripline technology with a flat conductor being placed between two ground planes, or microstrip technology using a flat conductor placed over a ground plane, or any other transmission line technology or a combination of the technologies cited above. For a coaxial line, the center conductor is the forward path and the outer conductor is the return conductor. For a stripline or microstrip line, the conductive strip is the forward conductor, and the ground plane(s) the return conductor. In all those cases, it is possible to use a dielectric as e.g. PTFE between the forward conductor and the return conductor, or just air, or a combination of those two. Using essentially air results in significantly lower losses.
Such antennas often use means for setting the elevation angle in order to optimize the performance of a cellular network. Those means include mechanically tilting the antenna, or electrically tilting the antenna beam using phase delay arrangements in the antenna feeding network (electrical downtilt). In the latter case, the electrical downtilt can often be controlled remotely.
As the number of frequency bands used for mobile communication, e.g. as defined by 3GPP, has increased over the years, it has become advantageous to use wideband antennas which can be used for several frequency bands.
However, for wideband antennas, the antenna radiation characteristics, such as elevation beamwidth can be significantly different at one end of the frequency range compared to the other end of the frequency range.
With the introduction of multi-band radios (such as dual- or triple-band radios), the number of array antennas can be reduced since each array antenna can serve several bands simultaneously. But if one feeding network is used for all frequency bands, the same tilt must be used for all bands. This complicates the process of setting a suitable electrical downtilt (EDT) since the different frequency bands have different antenna radiation and propagation characteristics. For example, the 1800 MHz band will have the same EDT as the 2600 MHz band, but the elevation beamwidth at 1800 MHz is approximately 50% wider than at 2600 MHZ.
When cell planning, the EDT is normally set to cover a certain geographical area with sufficiently high signal level, but it is also important to ensure that the spillover into the next cell in front is sufficiently low at all frequencies in order not to cause interference. This is not a problem when adjusting the tilt for each frequency band individually, but with a wideband antenna, the vertical beamwidth is significantly larger at a lower frequency, LrF, than at a higher frequency, HrF. For example, if the EDT is set such that the upper 3 dB points at the higher frequency, HrF, and at the lower frequency, LrF, are within the targeted area/cell it will lead to severe degradation in signal level in the area close to the cell border at HrF, as illustrated in
If the EDT on the other hand is set to ensure minimum degradation in the area close to the cell border, for example by setting the EDT such that upper 3 dB point at HrF is at the cell border, the spillover into the next cell will be significant at LrF resulting in interference. This is illustrated in
The frequency-dependency of the beam peak and the upper 3 dB point of a prior art radiation pattern is illustrated in
A solution to this problem is to use two or more separate feeding networks connected to the same array of antenna elements, each feeding network having its own EDT control, the signals of the different feeding networks being combined close to the antenna elements using e.g. filters. The problem with such a solution is that the complexity and cost of the antenna are significantly increased, and it will result in significantly higher losses in the feeding networks and the combining filters, resulting in degraded coverage and data throughput.
It is understood that the “upper 3 dB point” referred to above is the point at an upper portion of the main beam where the amplitude is reduced with −3 dB compared to the peak of the main beam.
An object of the invention is to provide a base station antenna arrangement which overcomes or at least improves on the problems mentioned in the background section.
These and other objects are achieved by the present invention by means of an antenna arrangement and a radio communication antenna according to the independent claims.
According to the invention, an antenna arrangement is provided, which antenna arrangement comprises an antenna element array comprising at least two antenna elements spaced apart in a vertical direction of the antenna arrangement, and an antenna feeding network configured to provide signals to said antenna element array to produce a beam. The antenna feeding network comprises:
In other words, the antenna arrangement comprises an antenna element array having a vertical extension. The antenna element array may also be described as comprising at least a first and a second antenna element, where the first antenna element is positioned above the second antenna element as seen in a height direction of the antenna or reflector or antenna array. The height direction may also be referred to as a vertical direction. The antenna feeding network is configured to provide signals to the antenna element array to produce a beam in the sense that it is configured to distribute signals from the input to the outputs/antenna elements, for example by comprising transmission lines interconnected by splitters. The phase delaying arrangement is arranged to delay the signals to one or more of the outputs to tilt the beam, i.e. to provide an electrical tilt. The phase delaying arrangement is configured to delay the signals as a function of the frequency, i.e. to provide an electrical tilt which varies with frequency.
The invention is based on the insight that by introducing a phase delaying arrangement with a frequency-dependent phase delay in the antenna feeding network and adapting this frequency-dependent phase delay to the desired frequency range of the antenna array, an electrical tilt which is suitable for all frequencies within said frequency range can be achieved. For example, by configuring the phase delay such that lower frequencies are downtilted more than higher frequencies, it is ensured that the signal is focused within the cell and that the spillover to the neighboring cells is sufficiently low. Furthermore, less downtilt at higher frequencies ensures that the signal level is sufficient on the cell borders and in the rest of the cell. The invention should not be confused with conventional phase shifters for adjusting electrical tilt where the goal is usually the opposite-providing an electrical downtilt which is as constant over frequency as possible.
The invention may also be described as antenna arrangement comprising an antenna element array with at least two antenna elements spaced apart in a vertical direction of the antenna arrangement, and an antenna feeding network configured to provide signals to said antenna element array to produce the beam. The antenna feeding network comprises:
Further according to the invention, an antenna feeding network for a radio base station antenna comprising an antenna element array comprising at least two antenna elements spaced apart in a vertical direction is provided. The antenna feeding network is configured to provide signals to the antenna element array to produce a beam, and comprises:
In embodiments, the antenna element array is configured to transmit and receive signals to and from a cell within a frequency range ranging from a lower frequency, LrF, to a higher frequency, HrF. The phase delaying arrangement is configured to provide said delay as a function of frequency such that an elevation angle associated with a first upper point of reduced amplitude of a main beam radiated from said array at the lower frequency, LrF, is within a predetermined interval from an elevation angle associated with a second upper point of reduced amplitude of a main beam radiated from said array at said higher frequency, HrF, the first and second upper points of reduced amplitude being of equally reduced amplitude relative a beam peak of the respective main beam. The predetermined interval may be ±2 degrees, or ±1 degree, or ±0.5 degrees. The equally reduced amplitude may be within an interval from −10 dB to −1 dB, or within an interval from −6 dB to −2 dB, or within an interval from −3.5 dB to −2.5 dB relative a beam peak of the respective main beam. In a preferred embodiment, the equally reduced amplitude is −3 dB relative the beam peak of the respective main beam (the “upper 3 dB points”), i.e. the first and second upper points of reduced amplitude are the “upper 3 dB points”, and the predetermined interval is +1 degree.
In embodiments, the phase delaying arrangement is configured to provide the delay as a function of frequency such that in normalized radiation patterns from said array radiated at LrF and HrF, respectively, a main beam associated with LrF crosses a main beam associated with HrF at respective upper points of reduced amplitude which are within an interval from −10 dB to −1 dB, or within an interval from −6 dB to −2 dB, or within an interval from −3.5 dB to −2.5 dB relative a beam peak of the respective main beam. For example, the main beam associated with LrF may cross/coincide with the main beam associated with HrF at upper points of reduced amplitude of −2 dB or −3 dB (the “upper 3 dB points”).
In embodiments, the phase delay decreases with increased frequency such as to provide less electrical downtilt with increased frequency (at least within the frequency range of the antenna array). The phase delay may be described as a progressive phase delay between respective antenna elements in the array, starting from the topmost element. The progressive phase delay may decrease approximately linearly with increased frequency.
In embodiments, the phase delaying arrangement, or more specifically, the at least one phase delaying component having a frequency-dependent phase delay, comprises one or more components selected from the following list:
The one or more components is/are configured to act on the phase of signals being transmitted through said phase delaying arrangements.
In embodiments, the phase delaying arrangement, or more specifically, the at least one phase delaying component having a frequency-dependent phase delay, comprises a filter configured to provide said phase delay as a function of frequency. The filter may have an all-pass, a low-pass, high-pass, band-stop, or band-pass characteristic. The non-linear phase response in a filter can be tailored to get the desired phase delay. Filters can be realized in an antenna feeding network by means of overlapping regions (of inner conductors of a coaxial line or stripline for example) which behave as a series capacitance on the inner conductor, which alters the phase delay differently at lower frequencies compared to higher frequencies. By varying the length of the overlapping region, the difference in phase delay between lower and higher frequencies can be optimized.
In embodiments, the phase delaying arrangement comprises signal splitters configured to split one incoming signal to a least a first output and a second output, wherein the signal splitters are configured to provide a difference in phase delay at said first output and said second output which varies with frequency. The signal splitters may be part of the antenna feeding network for splitting signals from an input transmission line to two output transmission lines. The two output transmission lines can have different impedances and thus form two phase delaying components with different phase delay. As a person skilled in the art would know, such splitters split power unequally between the two outputs and are often used in phased array antennas to taper the antenna lobe to break the symmetrical pattern of the antenna pattern with significant sidelobes and deep nulls in the antenna diagram.
In embodiments, the antenna feeding network comprises transmission lines comprising at least one of a coaxial line, a stripline, a microstrip line or a combination thereof, the phase delaying arrangement being formed at least partly by at least one of said transmission lines or being arranged to co-act with at least one of said transmission lines. The at least one of the transmission lines may comprise at least one pair of conductors separated by air, or a dielectric material such as PTFE, or a combination thereof, acting as dielectric.
In embodiments, the phase delaying arrangement is configured to vary the phase delay of the signals such as to control the (electrical) tilt of the beam. The frequency dependency of the phase delay may be variable, i.e. the phase delay may be varied differently for different frequencies. The phase delaying arrangement may comprise means for varying the phase delay manually. Alternatively, the phase delaying arrangement may comprise means for varying said phase delay remotely, i.e. in a corresponding manner as a RET.
In embodiments, the antenna arrangement/antenna feeding network further comprises an electrical tilt adjustment arrangement configured to provide variable phase adjustment such as to adjust an overall electrical tilt of the beam. The electrical tilt adjustment arrangement may be configured to adjust said overall electrical tilt in a substantially non-frequency dependent manner. This allows the overall electrical tilt of the antenna to be adjusted. Such embodiments comprising an electrical tilt adjustment arrangement with a phase delay substantially non-dependent on frequency may be combined with a frequency dependent phase delaying arrangement. In embodiments, the frequency dependent tilt of the phase delaying arrangement is constant/non-adjustable, whereas the non-frequency dependent tilt of the electrical tilt adjustment arrangement can be used to adjust the overall tilt (for all frequencies) of the antenna. Electrical tilt adjustment is described in detail in applicant's previous application WO2009041896, U.S. Pat. No. 8,576,137 (which is hereby incorporated by reference in its entirety).
In embodiments, both frequency independent and frequency dependent phase delays can be set remotely. This allows the tilt to be set individually at both LrF and HrF,
Further according to the invention, a radio communication antenna is provided. The radio communication antenna comprises an input for connection to a transmit-receiver unit, and a reflector or backplane which may be described as having a lower end and an upper end defining a height direction therebetween. An antenna element array is positioned on or in front of said reflector, the array comprising at least first and second antenna elements. The first antenna element is positioned above the second antenna element as seen in the height direction, i.e. the antenna element array comprises at least two antenna elements spaced apart in the height/vertical direction. The antenna elements are configured to transmit and receive signals within a frequency range comprising at least two frequency bands. A first of said at least two frequency bands is located in a lower part of the frequency range, and a second of said at least two frequency bands is located in a higher part of the frequency range, i.e. the first frequency band is at a lower frequency range than the second frequency band. A feeding network is configured to distribute a signal from the input to the antenna elements to produce a beam, the feeding network comprising at least one phase delayer. The phase delayer(s) is/are configured to electrically tilt the antenna beam in said first frequency band with a first tilt angle, and to tilt the antenna beam in said second frequency band with a second tilt angle, the first tilt angle being different from the second tilt angle.
It is understood that the first tilt angle and the second tilt angle are representative tilt angles (such as mean tilt angles) for the respective frequency band and are not necessarily constant within the respective frequency band. The phase delayer(s) may alternatively be described as being configured to electrically tilt the antenna beam in said first frequency band with tilt angles within a first interval, and to tilt the antenna beam in said second frequency band with tilt angles within a second interval, the first and second interval being different such as non-overlapping.
In embodiments, the first tilt may be more downwardly directed than the second tilt.
In embodiments, at least one of said first or second tilt is a downtilt. In embodiments where the first and second tilts are downtilts, the first tilt angle is larger than said second tilt angle.
In embodiments, the phase delayers are configured to delay signals from the input to the antenna elements, wherein signals to the first antenna element are delayed with a first phase delay, and signals to the second antenna element are delayed with a second phase delay, the second phase delay being larger than the first phase delay. A difference between the first phase delay and said second phase delay may be a function of the frequency. The difference between the first phase delay and the second phase delay may be larger in the first frequency band than in said second frequency band. Put differently, the signals to the first antenna element are delayed with a first phase delay, and the next-coming antenna elements are delayed progressively, i.e., a second phase delay being larger than the first phase delay, a third phase delay being larger than the second phase delay, and so forth.
In embodiments, the antenna may be configured to cover a certain geographical area, where said geographical area is essentially the same for said first frequency band and at least the second frequency band. In other words, the coverage at the first frequency band may correspond to the coverage at the second frequency band. The geographical area may be a cell in a cellular network. To achieve essentially the same coverage, the phase delayers may be configured to provide the delay as a function of frequency such that an elevation angle associated with a first upper point of reduced amplitude of a main beam radiated from said array at a first frequency within said first frequency band is within a predetermined interval from an elevation angle associated with a second upper point of reduced amplitude of a main beam radiated from said array at a second frequency within said second frequency band, the first and second upper points of reduced amplitude being of equally reduced amplitude relative a beam peak of the respective main beam. The predetermined interval may be ±2 degrees, or ±1 degree, or ±0.5 degrees (i.e. the predetermined interval is between 2 degrees below the elevation angle to 2 degrees above the elevation angle, or 1 degree below the elevation angle to 1 degree above the elevation angle, or 0.5 degree below the elevation angle to 0.5 degree above the elevation angle). The equally reduced amplitude may be within an interval from −10 dB to −1 dB, or within an interval from −6 dB to −2 dB, or within an interval from −3.5 dB to −2.5 dB relative a beam peak of the respective main beam. The first and second upper points of reduced amplitude may be −3 dB relative the beam peak of the respective main beam (the “upper 3 dB points”, i.e. the equally reduced amplitude is −3 dB), and the predetermined interval may be ±1 degree. Hereinbelow, the notation ±x is used to indicate an interval from v−x to v+x where v is a reference value, e.g., elevation angle associated with an upper point of reduced amplitude of main beam or a particular frequency, and +x is a deviation above or below v.
To achieve essentially the same coverage, it is also foreseeable that the phase delayers are configured to provide a delay as a function of frequency such that in normalized radiation patterns from said array radiated at first and second frequencies within said first and said second frequency band, respectively, a main beam associated with the first frequency crosses a main beam associated with the second frequency at respective upper points of reduced amplitude which are within an interval from −10 dB to −1 dB, or within an interval from −6 dB to −2 dB, or within an interval from −3.5 dB to −2.5 dB relative a beam peak of the respective main beam. For example, the main beam associated with the first frequency may cross/coincide with the main beam associated with the second frequency at upper points of reduced amplitude of −2 dB or −3 dB (the “upper 3 dB points”)
Further according to the invention, a method for optimizing a cellular mobile network is provided. The cellular mobile network is configured to transmit and receive in at least two frequency bands using an antenna configured to operate over a frequency range comprising the at least two frequency bands, wherein a first of said at least two frequency bands is located in a lower frequency range of said antenna, and where a second of said at least two frequency bands is located in a higher frequency range of said antenna, the antenna providing an antenna lobe. The method comprises configuring an electrical downtilt of the antenna such that the downtilt at said first frequency band is larger than the downtilt at said second frequency band. The method may further comprise configuring the electrical downtilt such that a coverage at said first frequency band corresponds to a coverage at said second frequency band. The configuring may comprise configuring a frequency dependent delay characteristic of the electrical downtilt such that an elevation angle associated with a first upper point of reduced amplitude of a main beam radiated from said array at a first frequency within said first frequency band is within a predetermined interval from an elevation angle associated with a second upper point of reduced amplitude of a main beam radiated from said array at a second frequency within said second frequency band, the first and second upper points of reduced amplitude being of equally reduced amplitude relative a beam peak of the respective main beam. The predetermined interval may be ±2 degrees, or ±1 degree, or ±0.5 degrees. The upper points of reduced amplitude may be within an interval from −10 dB to −1 dB, or within an interval from −6 dB to −2 dB, or within an interval from −3.5 dB to −2.5 dB relative a beam peak of the respective main beam. The upper points of reduced amplitude may both be −3 dB relative the beam peak of the respective main beam (the “upper 3 dB points”), and the predetermined interval may be ±1 degree.
Alternatively, the configuring may comprise configuring a frequency dependent delay characteristic of the electrical downtilt such that in normalized radiation patterns from said array radiated at first and second frequencies within said first and said second frequency band, respectively, a main beam associated with the first frequency crosses a main beam associated with the second frequency at respective upper points of reduced amplitude which are within an interval from −10 dB to −1 dB, or within an interval from −6 dB to −2 dB, or within an interval from −3.5 dB to −2.5 dB relative a beam peak of the respective main beam. For example, the main beam associated with the first frequency may cross/coincide with the main beam associated with the second frequency at upper points of reduced amplitude of −2 dB or −3 dB (the “upper 3 dB points”).
The features of the embodiments described above are combinable in any practically realizable way to form embodiments having combinations of these features. In particular, features and advantages of embodiments of the antenna arrangement may form corresponding embodiments with corresponding advantages of the radio communication antenna or method according to the invention and vice versa. Further, features and advantages of embodiments of the radio communication antenna may form corresponding embodiments with corresponding advantages of the method according to the invention.
Above discussed and other aspects of the present invention will now be described in more detail using the appended drawings, wherein:
The progressive phase delay is given by:
where Δϕ(f)=kd sin θ0(f),
and k is the wavenumber in free space, and d is the antenna element spacing, and θ0(f) is the beam peak direction at frequency f. The wavenumber in free space would be recognized by a person skilled in the art as k=ω/c, where ω=2πf, and c=speed of light.
The antenna arrangement comprises eight antenna elements 1a-h spaced apart in a vertical direction of the antenna arrangement, and an antenna feeding network configured to provide signals to said antenna element array to produce a beam. The antenna feeding network comprises an input 2 for connection to a radio base station unit, a plurality of outputs connected to a respective antenna element 1a-h of the array of antenna elements. A phase delaying arrangement comprising phase delaying components 3a-h is arranged to phase delay the signals to the outputs of antenna elements 1b-h to tilt the beam. The phase delaying components are connected between the input 2 and a respective antenna element. The phase delaying property of the phase delaying components differ in the sense that they provide a different amount of phase delay. For example, 3c provides twice the phase delay compared to 3b. The phase delaying arrangement is configured to delay said signals as a function of the frequency. The phase delay decreases approximately linearly with increased frequency such as to provide less electrical downtilt with increased frequency. The beam peak direction in
It should also be understood that connections between the input 2 and the phase delaying components 3a-3h may also provide phase delay, but this phase delay may be the same between the input 2 and each phase delaying components 3a-3h, and hence not influence the beam peak direction. Such phase delay can be caused by transmission lines of equal length and equal impedance.
All phase delaying components may provide a combination of a constant phase delay and a progressive phase delay, such that for example the total phase delay provided by phase delaying component 3b would be:
where τ0 is the constant phase delay.
The signal at antenna element 1a is used as a reference, and hence phase delaying component 3a will only provide the constant phase delay τ0. For simplicity, only Δτ(f) is used in the figures.
A person skilled in the art recognizes that the above-described frequency dependent phase delay stands in sharp contrast with prior art antennas with the same beam peak direction for all frequencies, where Δτ should not vary with frequency.
According to the invention, an elevation diagram with frequency-dependent beam peak is proposed, as shown in
Having a perfect alignment of upper 3 dB points of all frequencies, e.g., LrF and HrF, as illustrated in
Similarly, while aligning the 3 dB points at different frequency band can be optimal in a certain geographical environment, in a different environment it might be advantageous to align other points of reduced amplitude. These reduced amplitude lines may, for example, be selected from within the range −10 dB to −1 dB relative to the beam peak.
To realize the proposed radiation pattern in
As known by a person skilled in the art, the phase delay Δτ(f) between the antenna elements can be achieved with different configurations. Two different configurations are shown in
The antenna arrangement embodiment in
The antenna arrangement embodiment in
As known by a person skilled in the art, what matters in a phased array antenna is the difference in phase delay between the different radiators. And it can be seen that for the three configurations in 4, 7a and 7b, the phase of the signals arriving to the radiators will have the same delay, that is there is a progressive increase of phase delay Δτ(f) between two neighbour radiators from the upper radiator to the lower radiator.
The electrical tilt phase shifting components 35a-g can be adjusted remotely (RET) by using rail elements carrying the dielectric elements of 35a-g, which rails are displaceable using electric motor(s), as described for example in applicant's previous application WO2017048184, US Pat. Publ. U.S. Pat. No. 20190044226A1 (which is hereby incorporated by reference in its entirety).
The phase delaying components 23a-g in
Varying the length and the separation distance of the overlapping region, and thereby altering the phase delay at lower frequencies compared to higher frequencies is used in one embodiment to control the tilt of the beam. The adjustment may be performed manually or using electro-mechanical components, the adjustment can be performed remotely.
Herein, implementations using air coaxial lines have been described, but phase delays can also be created using other types of transmission lines such as partially open coaxial lines, stripline, microstrip lines or any other type of transmission lines.
The description above and the appended drawings are to be considered as non-limiting examples of the invention. The person skilled in the art realizes that several changes and modifications may be made within the scope of the invention. For example, the frequency dependent downtilt illustrated in
