Title of Invention

A TILT-DEPENDENT BEAM-SHAPE SYSTEM

Abstract The present invention relates to a system for changing the radiation pattern shape of an antenna array 83; 88 during electrical tilting. The antenna array 83; 88 has multiple antenna elements 84, and the system comprises a phase- shifting device 10; 20; 40; 85 provided with a primary port 11 configured to receive a transmit signal, and multiple secondary ports 121-124; 12 configured to provide phase shifted output signals to each antenna element 84. The system further comprises a phase-taper device 20; 40; 85; 87 that changes phase taper over the antenna elements, and thus the beam shape, with tilt angle ϑ. The invention is adapted for use in down-link as well as up-link within a wireless communication system.
Full Text Technical Held
The present invention relates to a system for adapting the beam-shape of an
antenna in a wireless communication network.
Background
Variable beam tilt is an important tool for optimizing radio access networks
for cellular telephony and data communications. By varying the main beam
pointing direction of the base station antenna, both interference environment
and cell coverage area can be controlled.
Variable electrical beam tilt is conventionally performed by adding a variable
linear phase shift to the excitation of the antenna elements, or groups of
elements, by means of some phase-shifting device. For cost reasons, this
phase-shifting device should be as simple and contain as few components as
possible. It is therefore often realized using some kinds of variable delay
lines. In the description, the terms "linear" and "non-linear" should be
understood to refer to relative phase over multiple secondary ports of a
multiport phase shifting network, and not the time or phase behaviour of a
port in itself.
Conventional multi-port phase shifters, with one primary port and a number
N (N>1) secondary ports, are implemented with linear progressive variable
phase taper over the secondary ports. In addition to the linear progressive
phase taper, fixed amplitude and phase tapers are often used as a means for
generating a tapered nominal secondary port distribution.
Figures la and 1b illustrate a conventional phase shifter 10, with one
primary port 11, and the phase shifter generates in down-link linear
progressive phase shifts over four secondary ports 121 -124. A variable-angle
"delay board" 13 has multiple trombone lines 14, one for each secondary
port 121-124. The trombones lines 14 are arranged at linearly progressive

radii. By a proper choice of junction configurations, line lengths, and line
impedance values, the nominal phase and amplitude taper of the phase
shifter can be controlled, for example to achieve uniform phase over the
secondary ports as indicated by "0" in Figure la. By changing the delay line
lengths (i.e. the length of the trombone lines 14), in this case by rotation of
the delay board 13 relative to a fixed board 15, the secondary ports 121-124
experience linear progressive phase shifts as indicated in Figure lb. In up-
link, the secondary ports 121-124 receive signals from an antenna (not
shown) which are combined within the phase shifter to a common receive
signal at the primary port 11.
The use of non-linear phase-shifting devices for controlling electrical down
tilt has been contemplated, such as mentioned in US 5,798,675, by Drach,
US 5,801,600, by Butland et al.
A system for tilt-dependent beam shaping using conventional linear phase
shifters is disclosed in JP 2004 229220. The system has different beam
width depending on the tilt angle, but this is achieved by a tilt angle control
section (41) in combination with a vertical beam width control section (42) in
the base station controller (4), see figure 6 in JP 2004 229220.
Traditionally, base station antennas have had a variable beam tilt range of
approximately one beamwidth. This together with the fact that most mobile
connections today are circuit switched voice with a fixed requirement on bit-
rates, has not triggered any interest in improving the Signal-to-interference +
noise ratio (SINR) close to the antenna. Normally it is good enough.
For particular cell configurations, e.g. highly placed antennas in combination
with small cells, the need for using antennas with large beam tilt is greater.
For antennas with conventional narrow elevation beam radiation patterns,
the large beam tilt causes users close to the base station to experience a
lower path gain than users close to the cell border, since the difference in
path loss for the near and far users is smaller than the difference in directive
antenna gain. For packet-based data communication this is not optimal

usage of the available power. Therefore, for antennas with large beam tilt,
some degree of radiation pattern null-fill below the main beam, or even some
cosec-like beam-shaping is desirable.
In large cells, on the other hand, when no or small beam tilt is employed, the
antenna pattern should be optimized for maximum peak gain. The path gain
for the users at the cell border will anyway be smaller than for users closer
to the base station because the path loss varies rapidly with vertical
observation angle in the case of large cells and observation angles close to
the horizon.
Summary
An object with the present invention is to provide a system that allows a
radiation pattern of an antenna to be optimized both for high maximum gain
at small tilt angles, and high degree of null filling below the main beam at
large tilt angles.
A solution to the object is achieved by providing a system for changing the
beam shape of an antenna, preferably having multiple antenna elements
arranged in an array, in dependency of a tilt angle. Electric tilting is achieved
by including a phase-shifting device that will provide phase shifts over
secondary ports from the phase-shifting device. A phase-taper device
provides changed phase taper over the antenna elements with tilt angle.
An advantage with the present invention is that a single antenna may be
used in an adaptive system, to fulfil the need for increasing the quality of a
communication link and thus increase the bit rate associated with one or
more simultaneous users, by maintaining an optimal antenna pattern,
which depends on the distance to the base station.
Further objects and advantages will become apparent for a skilled person
from the detailed description.

Brief description of the drawings
Figs, la and 1b show a linear phase shifter.
Figs. 2a and 2b show a first embodiment of a non-linear phase shifter.
Figs. 3a and 3b show diagrams illustrating phase shifts from the linear and
non-linear phase shifters.
Fig. 4 shows a second embodiment of a non-linear phase shifter.
Fig. 5 shows antenna element excitation at 0° beam tilt.
Fig. 6 shows antenna element excitation at 9° beam tilt.
Figs. 7a-7d show elevation radiation patterns utilizing the present invention.
Fig. 8 shows a wireless telecommunication network having base stations
including the present invention.
Fig. 9 schematically illustrates the tilt dependent beam shape according to
the present invention.
Detailed description
A base station, including an antenna with multiple antenna elements, is
arranged within a cell, where the characteristics of the antenna determine
the size of the cell and the cell coverage area all else being equal. To
accomplish the same signal strength in the entire cell, independent of the
distance to the base station, the antenna gain G(O) divided by the path loss
L{&) should be constant in the cell, as a function of observation angle 9:

However, the constant C changes with cell configuration, i.e. antenna
installation height and cell size, which in turn means that the optimal

antenna radiation pattern changes with beam tilt angle, as illustrated in
figures 7b-7d, lines 71. The tilt dependent radiation pattern can be
accomplished by changing the phase taper over the antenna with tilt-angle,
e.g. by providing a non-linear phase shifter as described in connection with
Figures 2a, 2b, 3b and 4. The non-linear phase shifter facilitates different
phase tapers for different beam tilt angles, and thus will provide tilt-
dependent beam shape of the antenna.
The terms "phase shift" and "time delay" are used interchangeably in the
following description and it should be understood that these terms refer to
equivalent properties in the present context, except if otherwise noted.
An essential part of the invention is to provide non-linear phase taper over
the secondary ports of a phase shifter network. A method for achieving this
is to use a multi-secondary port true time delay network in which the
relative delay line lengths are, in general, non-linearly progressive. A true
time delay network generates frequency-dependent phase shifts, a property
which makes it particularly suitable for antenna applications, such as beam-
steering.
The principle idea of a first embodiment of a non-linear phase shifter 20, in
down-link, is illustrated in Figures 2a and 2b using a true time delay
network, similar to the one illustrated in Figures la and 1b. The key
property of the delay network (and the method as such) is to provide non-
linear relative time delays over the secondary ports, by arranging trombone
lines 24 (in this particular embodiment) in a non-periodic fashion on a delay
board 23. By a proper choice of junction configurations, line lengths, and
line impedance values, the nominal phase and amplitude taper of the true
time delay network with non-linear delay dependence can be controlled, for
example to achieve uniform phase over the secondary ports as indicated by
"0" at the secondary ports 121-124 in Figure 2a. In contrast with the true
time delay network in Figure 1, changes in the delay line lengths by rotation
of the delay board relative to a fixed board 25 produces non-linear

progressive time delays (and, hence, phase shifts) over the secondary ports
121-124, as indicated by "cpi", "cp2w, "q>3*, and "q>4* in Figure 2b. In up-link, the
secondary ports 121-124 of the phase shifter 20 receive signals from an
antenna (not shown) which are non-linearly time-delayed and combined
within the phase shifter to a common receive signal at the primary port 11.
As a non-limiting example, the phase-shifts from a linear and a non-linear
true time delay network in down-link are compared in Figures 3a and 3b for
different rotations (see legend) of the delay board 13 and 23, respectively. In
Figure 3a, the phase advance (relative phase) over the secondary ports 12i-
124 is linear with delay board 13 rotation, which manifests itself as straight
lines 30, 31, 32 and 33 for a given board rotation. This means that for any
given delay board rotation, the relative phase values (between secondary port
n and port 1) are
Acpn = (n-1) Aq> = (n-l)ka,
where n is the secondary port number, a is the board rotation angle, and k
is a constant that depends on implementation aspects, for example wave
number of transmission lines and radial separation of the trombones 14.
The non-linear phase advance (relative phase) over the secondary ports 12i-
124 of a non-linear true time delay network is illustrated in Figure 3b. In
Figure 3b, the phase advance (relative phase) over the secondary ports 121-
124 is non-linear when rotating the delay board 23, which manifests itself as
one straight line 35 for 0° rotation and three non-straight lines 36, 37 and
38 for a given board rotation / 0°. Thus, the relative phase values are not
identical, i.e.,
q>n- wherein N is the number of delay branches. In figure 3b, the phase of delay
branch 3 varies faster than twice that of branch 2 when the board angle
changes.

Figure 4 shows a second embodiment of a non-linear phase shifter 40. This
delay line network is based on translation {rather than rotation) of the delay-
board 43 relative a fixed board 45.. The delay network trombone lines 44 are
shown with equal lengths, but they could also have different lengths (both
the lines on the delay board 43 and the lines on the fixed board 45).
Figure 5 shows an element excitation of a 15 element linear antenna array,
optimized for maximum gain and a suppression of the upper sidelobes to
-20dB. This element excitation produces the radiation pattern in Figure 7a,
i.e. 0° beam tilt. In prior art techniques, linearly progressive phase is added
to the phase taper shown in figure 5 to achieve different tilt angles, 8lltt.
Figure 6 shows the element excitation for 9° beam tilt, where the amplitude
taper is the same as for 0° beam tilt, but the phase taper has been optimized
for null-filling, in accordance with the present invention. This excitation
produces the radiation pattern with 9° beam tilt in Figure 7d.
For beam tilt angles between 0° and 9°, the phase excitation is found by a
linear interpolation of the phase excitations at 0° and 9°. Some of these
radiation patterns 70 are shown in Figures 7b and 7c, with the beam tilt
changing 3° for each subplot. For comparison, the relative path loss 71,
normalized at beam peak, is shown in the same plots. The relative path loss
changes with beam tilt angle 9slj,.
The invention is not limited to the example with constant cell illumination
described above, but is applicable in all cases where it is desirable, for one
reason or another, to have a radiation pattern that changes with beam tilt
angle. Furthermore, the invention is not limited to linear antenna arrays, but
may also be implemented in a base station having a non-linear antenna
array.
The present invention allows the antenna pattern to be optimized both for
high maximum gain at small tilt angles, and for good coverage (high degree
of null filling) close to the antenna at large tilt angles 9llh.

Figure 8 shows a wireless telecommunication system 80, exemplified using
GSM standard, including a first base station BSi. The first base station BSi
is connected via a first base station controller BSCi to a core network 81 of
the telecommunication system 80. A uniform linear antenna array 83
comprises in this embodiment six antenna elements 84. Secondary ports 12
of a non-linear phase shifter 85 is connected to each antenna element 84 of
the uniform linear antenna array 83, and a primary port 11 of the phase
shifter 85 is connected to the first base station BSi. The first base station
controller BSCi controls the variable beam tilt by changing the position of a
non-linear delay board, as previously described in connection with figures
2a, 2b and 4, and thereby altering the beam shape of a beam from the
uniform linear antenna array 83.
The telecommunication system 80 also includes a second base station BSa-
The second base station BS2 is connected via a second base station
controller BSC2 to the core network 81. A non-uniform linear antenna array
88 comprises in this embodiment four antenna elements 84, not necessarily
cross polarized as illustrated. Secondary ports 12 of a linear phase shifter 10
{prior art) are connected, via a phase-taper device 87 that changes the phase
taper over the antenna elements with tilt angle 0liU, to each antenna
elements 84 of the non-linear antenna array 88. A primary port 11 of the
phase shifter 10 is connected to the second base station BS2. The second
base station controller BSC2 controls the variable beam tilt by changing the
position of a linear delay board, as previously described in connection with
figures la and lb, and thereby altering the beam shape of a beam from the
non-uniform linear antenna array 88.
It should be noted that the antenna array may have uniformly, or non-
uniformly, arranged antenna elements 84, and cross polarized antenna
elements are only shown as a non-limiting example and other types of
antenna elements may naturally be used without deviating from the scope of
the invention. Furthermore, antenna elements operating in different

frequency bands may be interleaved without departing from the scope of the
claims.
The illustrated telecommunication system (GSM) should be considered as a
non-limiting example, and other wireless telecommunication standards,
such as WCDMA, WiMAX, WiBro, CDMA2000, etc. may implement the
described invention without deviating from the scope of the invention. Some
of the described parts of the GSM system, e.g. base station controller BSC1
and BSC2 may be omitted in certain telecommunication standards, which is
obvious for a skilled person in the art.
Figure 9 illustrates an antenna array 83 arranged in an elevated position,
such as in a mast 90. A non-linear phase shifter 85 is connected to the
antenna array 83 (as described in connection with figure 8) and is controlled
by a base station controller BSC1. A non-tilted beam 91 (corresponding to
the 0° plot in figure 7a) is illustrated in figure 9 together with a tilted beam
92 (corresponding to the 9° plot in figure 7d).
Although the invention has been described in detail using down-link, the
skilled person in the art may readily adapt the teachings for up-link, as is
mentioned above.

WE CLAIM :
1. A system for changing the radiation pattern shape of an antenna
array (83; 88) in down-link during electrical tilting, said antenna array (83;
88) having multiple antenna elements (84), said system comprises a phase-
shifting device (10; 20; 40; 85) provided with a primary port (11) configured
to receive a transmit signal, and multiple secondary ports (121-124; 12)
configured to provide phase shifted output signals to each antenna element
(84), characterized in that said system further comprises a phase-
taper device (20; 40; 85; 87) that changes phase taper over the antenna
elements, and thus the beam shape, with tilt angle idult}.
2. A system for changing the radiation pattern shape of an antenna
array (83; 88)in up-link during electrical tilting, said antenna array (83; 88)
having multiple antenna elements (84), said system comprises a phase-
shifting device (10; 20; 40; 85) provided with multiple of secondary ports
(121-124; 12) configured to receive phase shifted input signals from each
antenna element (84), and a primary port (11) configured to combine the
input signals to a receive signal, characterized in that said system
further comprises a phase-taper device (20; 40; 85; 87) that changes phase
taper over the secondary ports, and thus the beam shape, with tilt angle
' 3. The system according to claim 1 and 2, wherein the same phase-
shifting device (10; 20; 40; 85) is used for down-link and up-link.
4. The system according to any of claims 1-3, wherein said phase-taper
device (87) is arranged between said phase-shifting device (10) and said
antenna elements (84).
5. The system according to any of claims 1-3, wherein said phase-taper
device is integrated with said phase-shifting device, to form a non-linear
phase-shifting device (20; 40; 85).

6. The system according to claim 5, wherein said non-linear phase-
shifting device (20; 40; 85} generates non-linear progressive phase shifts over
the secondary ports (121-124) when changing tilt angle ( 7. The system according to any of claims 5 or 6, wherein the phase-
shifting device comprises a delay line network with trombone lines (24; 44).
8. The system according to claim 7, wherein said phase-shifting device
comprises a movable member (23; 43) which provides said non-linear
progressive phase shifts,
9. The system according to claim 8, wherein said movable member (23)
has a rotational movement.
10. The system according to claim 8, wherein said movable member (43)
has a translational movement.
11. The system according to any of claims 1-10, wherein the system is
configured to communicate phase shifted signals to/from antenna elemerus
arranged in a uniform antenna array (83).
12. The system according to any of claims 1-10, wherein the system is
configured to communicate phase shifted signals to/from antenna elements
arranged in a non-uniform antenna array (88).
13. A method for changing the radiation pattern shape of an antenna
array (83; 88) in down-link during electrical tilting, said antenna array (83;
88) having multiple antenna elements (84), said method comprises the steps
of:
• providing phase shifted output signals to each antenna element (84)
from multiple secondary ports (121-124; 12) of a phase shifting device (10;
20; 40; 85), said phase-shifting device is provided with a primary port (11)
configured to receive a transmit signal,
characterized by

• providing changed phase taper over the antenna elements with tilt
angle (#„„) using a phase-taper device (20; 40; 85; 87).
14. A method for changing the radiation pattern shape of an antenna
array (83; 88) in up-link during electrical tilting, said antenna array (83; 88)
having multiple antenna elements (84), said method comprises the steps of:
• providing phase shifted input signals from each antenna element (84)
to multiple secondary ports (121-124; 12) of a phase shifting device (10; 20;
40; 85), said phase-shifting device is provided with a primary port (11)
configured to combine the input signals to a receive signal,
characterized by
• providing changed phase taper over the secondary ports with tilt
angle [&m) using a phase-taper device (20; 40; 85; 87).

15. The method according to claim 13 and 14, comprising the step of
using the same phase-shifting device (10; 20; 40; 85) for down-link and up-
link.
16. The method according to any of claims 13-15, wherein said method
further comprises the step of arranging said phase-taper device (87) between
said phase shifting device (10) and said antenna elements (84).
17. The method according to claim 16, wherein said method further
comprises the step of integrating said phase-taper device with said phase-
shifting device, to form a non-linear phase-shifting device (20; 40; 85).
18. The method according to claim 17, wherein said method further
comprises the step of generating non-linear progressive phase shifts over the
secondary ports (121-124 of the non-linear phase-shifting device (20; 40; 85)
with tilt angle (#„,,).
19. The method according to any of claims 17 or 18, wherein the step of
generating non-linear progressive phase shift is implemented as a delay line
network with trombone lines (24; 44).

20. The method according to claim 19, wherein the step of generating
non-linear progressive phase shift is performed by moving a movable
member (23; 43).
21. The method according to claim 20, wherein moving said movable
member (23) includes a rotational movement.
22. The method according to claim 20, wherein moving said movable
member (43) includes a translational movement.
23. The method according to any of claims 13-22, wherein the method
comprises the additional step of configuring the system to communicate
phase shifted signals to/from antenna elements arranged in a uniform
antenna array (83).
24. The method according to any of claims 13-22, wherein the method
comprises the additional step of configuring the system to communicate
phase shifted signals to/from antenna elements arranged in a non-uniform
antenna array (88).
25. A base station adapted to be used in a communication network in
down-link, said base station comprising an antenna array (83; 88) having
multiple antenna elements (84), a phase shifting device (10; 20; 40; 85)
provided with a primary port (11) configured to receive a transmit signal, and
multiple secondary ports (121-124 12) configured to provide phase shifted
output signals to each antenna element (84), said phase shifting device being
configured to be controlled by a controller to perform electrical tilt of a beam
(91; 92),characterized in that said base station further comprises a
phase-taper device (20; 40; 85; 87) that changes phase taper over the
antenna elements, and thus the beam shape, with tilt angle (0im).
26. A base station adapted to be used in a communication network in up-
link, said base station comprising an antenna array (83; 88) having multiple
antenna elements (84), a phase shifting device (10; 20; 40; 85) provided with

multiple secondary ports (121-124; 12) configured to receive phase shifted
input signals from each antenna element (84), and a primary port (11)
configured to combine the received input signals to a receive signal, said
phase shifting device being configured to be controlled by a controller to
perform electrical tilt of a beam (91; 92), c h a r a c t e r i z e d in that said
base station further comprises a phase-taper device (20; 40; 85; 87) that
changes phase taper over the secondary ports (121-124; 12), and thus the
beam shape, with tilt angle (#,,„).
27. The base station according to claim 25 and 26, wherein the same
phase-shifting device (10; 20; 40; 85) is used for down-link and up-link.
28. The base station according to any of claims 25-27, wherein said
phase-taper device (87) is arranged between said phase-shifting device (10)
and said antenna elements (84).
29. The base station according to any of claims 25-27, wherein said
phase-taper device is integrated with said phase-shifting device, to form a
non-linear phase-shifting device (20; 40; 85).
30. The base station according to claim 28, comprising a non-linear
shifting device according to any of claims 4-18.
31. The base station according to any of claims 25-30, wherein the base
station comprises a uniform antenna array (83).
32. The base station according to any of claims 25-30, wherein said base
station comprises a non-uniform antenna array (88).
33. A communication network (80) comprising at least one base station
according to any of claims 25-32.

The present invention relates to a system for changing the radiation pattern shape of an
antenna array 83; 88 during electrical tilting. The antenna array 83; 88 has multiple antenna
elements 84, and the system comprises a phase- shifting device 10; 20; 40; 85 provided with a
primary port 11 configured to receive a transmit signal, and multiple secondary ports 121-124;
12 configured to provide phase shifted output signals to each antenna element 84. The system
further comprises a phase-taper device 20; 40; 85; 87 that changes phase taper over the
antenna elements, and thus the beam shape, with tilt angle ϑ. The invention is adapted
for use in down-link as well as up-link within a wireless communication system.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=tGLJYJtatXoSZ+iUpJEwEA==&loc=wDBSZCsAt7zoiVrqcFJsRw==


Patent Number 279982
Indian Patent Application Number 1764/KOLNP/2009
PG Journal Number 06/2017
Publication Date 10-Feb-2017
Grant Date 06-Feb-2017
Date of Filing 11-May-2009
Name of Patentee TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)
Applicant Address S-164 83 STOCKHOLM
Inventors:
# Inventor's Name Inventor's Address
1 MANHOLM, LARS EKLANDAGATAN 8, SE-412 55 GÖTEBORG
2 JOHANSSON, MARTIN KROKSLÄTTS PARKGATA 69C, SE-431 68 MÖLNDAL
3 PETERSSON, SVEN OSCAR ROTEVÄGEN 1, SE-433 69 SÄVEDALEN
4 ANDERSSON, MATS H IBSENGATAN 16, SE-417 19 GÖTEBORG
PCT International Classification Number H01Q 3/30,H04B 1/18
PCT International Application Number PCT/SE2006/001170
PCT International Filing date 2006-10-16
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA