U.S. patent application number 13/465800 was filed with the patent office on 2012-08-30 for base station for a cellular communication system.
This patent application is currently assigned to SPX CORPORATION. Invention is credited to Torbjorn Johnson, John Schadler.
Application Number | 20120220339 13/465800 |
Document ID | / |
Family ID | 41255468 |
Filed Date | 2012-08-30 |
United States Patent
Application |
20120220339 |
Kind Code |
A1 |
Johnson; Torbjorn ; et
al. |
August 30, 2012 |
Base Station for a Cellular Communication System
Abstract
A base station for a cellular communication system is provided.
The base station includes a transceiver and a phased-array antenna.
The phased-array antenna includes a plurality of sectors, each of
which includes a plurality of vertically-arranged antenna panels,
each of which includes a plurality of radiators arranged in
columns. The vertical spacing between the radiators in each column
is a predetermined value, and the vertical spacing between the
radiators in adjacent columns is one-half of the predetermined
value.
Inventors: |
Johnson; Torbjorn; (Vaxholm,
SE) ; Schadler; John; (Raymond, ME) |
Assignee: |
SPX CORPORATION
Charlotte
NC
|
Family ID: |
41255468 |
Appl. No.: |
13/465800 |
Filed: |
May 7, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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|
12435036 |
May 4, 2009 |
8175648 |
|
|
13465800 |
|
|
|
|
61049950 |
May 2, 2008 |
|
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Current U.S.
Class: |
455/562.1 |
Current CPC
Class: |
H01Q 1/246 20130101;
H01Q 21/26 20130101; H01Q 15/14 20130101; H01Q 3/26 20130101; H01Q
19/10 20130101 |
Class at
Publication: |
455/562.1 |
International
Class: |
H04W 88/08 20090101
H04W088/08 |
Claims
1. A base station for a cellular communication system, comprising:
a transceiver; and a phased-array antenna, coupled to the
transceiver, having a plurality of sectors, each sector having a
plurality of vertically-arranged antenna panels, each antenna panel
having a plurality of radiators arranged in columns, wherein the
vertical spacing between the radiators in each column is a
predetermined value, and the vertical spacing between the radiators
in adjacent columns is one-half of the predetermined value.
2. The base station of claim 1, wherein the predetermined value is
approximately one wavelength.
3. The base station of claim 2, wherein each column includes at
least eight transverse quadrilateral crossed dipole radiators.
4. The base station of claim 3, wherein a line drawn between the
center of two radiators in adjacent columns forms about a 45 degree
angle with respect to a centerline of the antenna panel.
5. The base station of claim 1, wherein the plurality of sectors
includes at least six sectors.
6. The base station of claim 5, wherein each sector includes at
least eight antenna panels.
7. The base station of claim 6, wherein each sector forms a
directional antenna beam having a horizontal beam width of
approximately 7.degree. to approximately 65.degree., and a vertical
beam width of approximately 0.66.degree. to approximately
2.degree..
8. The base station of claim 7, wherein each sector forms a
directional antenna beam having a horizontal beam width of
approximately 30.degree. to approximately 45.degree..
9. The base station of claim 1, wherein the phased-array antenna
broadcasts a signal that has a near zone field strength, a middle
zone field strength and a far zone field strength, and wherein the
near zone is located approximately 0 km to 1 km, the middle zone is
located approximately 1 km to 5 km, and the far zone is located
approximately 5 km to 30 km.
10. The base station of claim 9, wherein the phased-array antenna
near zone field strength is approximately 10 dB less than a
conventional cellular antenna field strength, and the phased-array
antenna far zone field strength is approximately 17 dB to 27 dB
greater than the conventional cellular antenna field strength.
11. The base station of claim 1, further comprising a passive feed
system that distributes a predetermined signal power and a
predetermined signal phase to and from each antenna panel.
12. The base station of claim 1, wherein each antenna panel
includes a passive feed system that distributes a predetermined
signal power and a predetermined signal phase to and from each
antenna radiator.
13. The base station of claim 12, wherein the passive feed system
is a stripline.
14. A method for broadcasting cellular signals using a base
station, comprising: forming a vertically-shaped beam using a
plurality of vertically-arranged antenna panels, each antenna panel
having a plurality of radiators arranged in columns, the vertical
spacing between the radiators in each column being a predetermined
value and the vertical spacing between the radiators in adjacent
columns being one-half of the predetermined value; and transmitting
a power distribution that has an essentially uniform field strength
over a near zone, a middle zone and at least a portion of a far
zone.
15. The method of claim 14, wherein each column includes at least
eight transverse quadrilateral crossed dipole radiators and the
predetermined value is approximately one wavelength.
16. The method of claim 14, wherein the near zone is located
approximately 0 km to 1 km, the middle zone is located
approximately 1 km to 5 km, and the far zone is located
approximately 5 km to 30 km.
17. The method of claim 16, wherein the near zone field strength is
approximately 10 dB less than a conventional cellular antenna field
strength, and the far zone field strength is approximately 17 dB to
27 dB greater than the conventional cellular antenna field
strength.
18. The method of claim 16, wherein the horizontal beam width is
approximately 7.degree. to approximately 65.degree., and the
vertical beam width is approximately 0.66.degree. to approximately
2.degree..
19. A cellular base station, comprising: a transceiver; and a
phased-array antenna, coupled to the transceiver, having a
plurality of sectors, each sector having a plurality of radiators
arranged in columns, wherein the vertical spacing between the
radiators in each column is about one wavelength, and the vertical
spacing between the radiators in adjacent columns is about one-half
wavelength.
20. The cellular base station of claim 19, wherein the phased-array
antenna broadcasts a signal that has a near zone field strength, a
middle zone field strength and a far zone field strength, and
wherein the near zone is located approximately 0 km to 1 km, the
middle zone is located approximately 1 km to 5 km, and the far zone
is located approximately 5 km to 30 km.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. patent
application Ser. No. 12/435,036, filed on May 4, 2009, which claims
priority to U.S. Patent Application Ser. No. 61/049,950, filed on
May 2, 2008, the contents of which are incorporated herein by
reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates, generally, to cellular
communication systems. More particularly, the present invention
relates to base stations for cellular communication systems and
methods for broadcasting cellular signals using base stations.
BACKGROUND OF THE INVENTION
[0003] Cellular radiotelephone system base transceiver stations
(BTSs), at least for some United States (U.S.) and European Union
(EU) applications, may be constrained to a maximum allowable
effective isotropically radiated power (EIRP) of 1640 watts. EIRP,
as a measure of system performance, is a function at least of
transmitter power and antenna gain. As a consequence of
restrictions on cellular BTS EIRP, U.S., EU, and other cellular
system designers employ large numbers of BTSs in order to provide
adequate quality of service to their customers. Further limitations
on cells include the number of customers to be served within a
cell, which can make cell size a function of population
density.
[0004] One known antenna installation has an antenna gain of 17.5
dBi, a feeder line loss of 3 dB (1.25'' line, 200 ft mast) and a
BTS noise factor of 3.5 dB, such that the Ga-NFsys=17.5-3.5-3.0=11
dBi (in uplink). Downlink transmitter power is typically 50 W. With
feeder lines, duplex filter and jumper cables totaling -3.5 dB, the
Pa input power to antenna is typically 16 W, such that the EIRP is
16 W+17.5 dB=1,000 W.
[0005] In many implementations, each BTS is disposed near the
center of a cell, variously referred to in the art by terms such as
macrocell, in view of the use of still smaller cells (microcells,
nanocells, picocells, etc.) for specialized purposes such as
in-building or in-aircraft services. Typical cells, such as those
for city population density, have radii of less than 3 miles (5
kilometers). In addition to EIRP constraints, BTS antenna tower
height is typically governed by various local or regional zoning
restrictions. Consequently, cellular communication providers in
many parts of the world implement very similar systems.
[0006] Restrictions on cellular BTS EIRP and antenna tower height
vary within each countries. Not only is the global demand for
mobile cellular communications growing at a fast pace, but there
are literally billions of people, in technologically-developing
countries such as India, China, etc., that currently do not have
access to cellular services despite their willingness and ability
to pay for good and inexpensive service. In some countries,
government subsidies are currently facilitating buildout, but
minimization of the cost and time for such subsidized buildout is
nonetheless desirable. In these situations, the problem that has
yet to be solved by conventional cellular network operators is how
to decrease capital costs associated with cellular infrastructure
deployment, while at the same time lowering operational expenses,
particularly for regions with low income levels and/or low
population densities. An innovative solution which significantly
reduces the number of conventional BTS site-equivalents, while
reducing operating expenses, is needed.
BRIEF SUMMARY OF THE INVENTION
[0007] Embodiments of the present invention provide a base station
for a cellular communications system and a method for broadcasting
cellular signals using a base station.
[0008] In one embodiment, a base station for a cellular
communication system includes a transceiver and a phased-array
antenna coupled to the transceiver. The phased-array antenna
includes a plurality of sectors, each sector includes a plurality
of vertically-arranged antenna panels, and each antenna panel
includes a plurality of radiators arranged in columns. The vertical
spacing between the radiators in each column is a predetermined
value, and the vertical spacing between the radiators in adjacent
columns is one-half of the predetermined value.
[0009] In another embodiment, a method for broadcasting cellular
signals using a base station includes forming a vertically-shaped
beam using a plurality of vertically-arranged antenna panels, and
transmitting a power distribution that has an essentially uniform
field strength over a near zone, a middle zone and at least a
portion of a far zone. Each antenna panel includes a plurality of
radiators arranged in columns, the vertical spacing between the
radiators in each column being a predetermined value and the
vertical spacing between the radiators in adjacent columns being
one-half of the predetermined value.
[0010] In a further embodiment, a cellular base station includes a
transceiver and a phased-array antenna coupled to the transceiver.
The phased-array antenna includes a plurality of sectors, and each
sector includes a plurality of radiators arranged in columns. The
vertical spacing between the radiators in each column is about one
wavelength, and the vertical spacing between the radiators in
adjacent columns is about one-half wavelength.
[0011] There have thus been outlined, rather broadly, certain
embodiments of the invention, in order that the detailed
description thereof herein may be better understood, and in order
that the present contribution to the art may be better appreciated.
There are, of course, additional embodiments of the invention that
will be described below, and which will form the subject matter of
the claims appended hereto.
[0012] In this respect, before explaining at least one embodiment
of the invention in detail, it is to be understood that the
invention is not limited in its application to the details of
construction and to the arrangements of the components set forth in
the following description or illustrated in the drawings. The
invention is capable of embodiments in addition to those described
and of being practiced and carried out in various ways. Also, it is
to be understood that the phraseology and terminology employed
herein, as well as the abstract, are for the purpose of description
and should not be regarded as limiting.
[0013] As such, those skilled in the art will appreciate that the
conception upon which this disclosure is based may readily be
utilized as a basis for the designing of other structures, methods
and systems for carrying out the several purposes of the present
invention. It is important, therefore, that the claims be regarded
as including such equivalent constructions insofar as they do not
depart from the spirit and scope of the present invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 depicts a perspective view of a base transceiver
station antenna, in accordance with an embodiment of the present
invention.
[0015] FIG. 2 compares standard cell coverage with coverage
provided by a base transceiver station antenna in accordance with
an embodiment of the present invention.
[0016] FIGS. 3A and 3B depict horizontal and vertical radiation
patterns for a phased-array antenna, in accordance with embodiments
of the present invention.
[0017] FIGS. 4A and 4B illustrate various aspects of the "Robin
Hood" principle, in accordance with embodiments of the present
invention.
[0018] FIG. 5 illustrates antenna panel power and phase for
phased-array antennas, in accordance with embodiments of the
present invention.
[0019] FIG. 6 presents phased-array antenna signal strength as a
function of distance, in accordance with embodiments of the present
invention.
[0020] FIG. 7A depicts a perspective, semi-transparent view of a
phased-array antenna panel, according to an embodiment of the
present invention.
[0021] FIGS. 7B and 7C each depict a perspective view of a
phased-array antenna panel, according to respective embodiments of
the present invention.
[0022] FIGS. 8A, 8B, and 8C each depict a perspective view of an
end portion of a phased-array antenna panel, according to
respective embodiments of the present invention.
[0023] FIG. 9 depicts a perspective front view of a phased-array
antenna panel, in accordance with an embodiment of the present
invention.
[0024] FIG. 10 depicts a perspective rear view of a phased-array
antenna panel, in accordance with an embodiment of the present
invention.
[0025] FIGS. 11A to 11D depict perspective views of an antenna
panel stack, in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] Embodiments of the present invention provide a super
economical broadcast system and method.
I. Overview of the Invention
[0027] The inventive super economical broadcast system encompasses
various antenna design and radio network planning concepts that
solve the needs of cellular operators in GSM-960/1800/1900,
CDMA-450/850 and UMTS-2170 standards with full support for all
sub-standards and modulations in the 380 to 3,800 MHz frequency
range. Advantageously, the inventive super economical broadcast
system reduces specific capital expenditures and operational
expenses, i.e., e.g., due to 10-30 times increase of a site's
coverage area and application of optimized radio coverage planning
methods, while exceeding standard technologies in terms of
technical efficiency, applicability and profitability levels.
[0028] In accordance with various embodiments of the present
invention, the number of required BTSs is decreased 10-20 times,
maintaining or increasing quality of service, and allowing removing
all redundant BTSs for use in new network construction or expansion
of existing networks. This improved efficiency of resource
management allows an operator to delay or even stop purchases of
new equipment (BTS, transceivers), leading to economy of financial
resources, higher profitability and increased business
capitalization. Modernization of cells, in accordance with the
teachings of the present invention, leads to better fault-tolerance
of radio access networks due to implementation of modem and more
reliable equipment. Maintenance expenses are also reduced, mean
time between failures (MTBF) is significantly increased and total
cost of ownership (TCO) of a cellular network is greatly reduced,
keeping or even increasing profitability levels.
[0029] A preferred embodiment of the inventive super economical
broadcast system includes, inter alia, installation of optimized
sites with a maximal possible site capacity of 432 Erlang and a
super long range, i.e., e.g., up to 40 km for indoor coverage.
Anticipated costs per 1 km.sup.2 of network are more than ten times
lower than costs of coverage created with cheaper and less
qualitative BTSs and standard antennas. These optimized sites
amplify signals both in their uplink and downlink channels,
improving link budgets by 18-30 dB in comparison with standard
antennas and masts, even for 10-20 times larger coverage areas.
Amplification in downlink can reach as much as 80 W per carrier,
allowing mobile terminals to reduce energy consumption and minimize
RF interference.
[0030] These optimized sites are also characterized by maximal
flexibility of capacity expansion, i.e., e.g., from an initial
configuration of 7.5-15 Erlang to 432 Erlang (+2,880%) in mature
networks. This ensures maximal adaptive capabilities for the
network in contrasting demographic, economic and strategic
conditions of modern telecommunication markets.
[0031] The inventive super economical broadcast system is similarly
applicable to broadcasting networks, where powerful amplifiers and
high-mounted antennas provide line-of-sight radio coverage on a
territory within a radius of 40-50 km (5,000 to 8,000
km.sup.2).
[0032] The inventive super economical broadcast system
advantageously allows an operator to quickly launch voice services
with minimal capital expenditures on vast geographical areas,
giving millions of people an opportunity to improve quality of
their lives. This way, an operator receives economical and
profitable technologies that may become key elements of business
development strategies for many years to come. By adapting the
teachings of the present invention, operators can tap into
self-financing opportunities that may be supported by high,
internal rates-of-return. An operator may well need only 15-25% of
the total amount of capital expenditures to start a project
self-financing process--the rest may be financed by large,
generated gross profits.
[0033] The inventive super economical broadcast system may be most
profitable in regions with relatively low spending levels on
telecommunication services (ARPU US$1-4), with absent or old
analogue telecommunication infrastructures. In such regions, a
mobile cellular infrastructure with the lowest CAPEX levels (50-150
US$/km.sup.2) may provide the best economic and technical benefits.
Flexibility in increasing a cell's capacity, operating expenses
reduced by 50-95%, compatibility with all new standards (GPRS,
EVDO, HSDPA, WiMAX, UMB, OFDM/MIMO) may jointly ensure that the
lowest total cost of ownership and enable expansion into markets
with low income and/or low population densities.
II. Detailed Description of Several Embodiments of the
Invention
[0034] According to one aspect of the present invention, cell
spacing, i.e., the distance between adjacent BTSs, is
advantageously increased relative to conventional cellular systems
while providing a consistent quality of service (QoS) within each
cell. Preferred embodiments of the present invention increase the
range of each BTS. Conventional macrocells typically range from
about 1/4 mile (400 meters) to a theoretical maximum of 22 miles
(35 kilometers) in radius (the limit under the GSM standard); in
practice, radii on the order of 3 to 6 mi (5-10 km) are employed
except in high-density urban areas and very open rural areas. The
present invention provides full functionality at the GSM limit of
22 mi, for typical embodiments of the invention, and extends well
beyond this in some embodiments. Cell size remains limited by user
capacity, which can itself be significantly increased over that of
conventional macrocells in some embodiments of the present
invention.
[0035] Commensurate with the increase in cell size, the BTS antenna
tower height is increased, retaining required line-of-sight (for
the customary 4/3 diameter earth model) propagation paths for the
enlarged cell. Preferred embodiments of the present invention
increase the height of the BTS antenna tower from about 200 feet
(60 meters) anywhere up to about 1,500 ft (about 500 m). In order
for the transmit power and receive sensitivity of a conventional
cellular transceiver (user's hand-held mobile phone, data terminal,
computer adapter, etc.) to remain largely unchanged, both the EIRP
and receive sensitivity of the tower-top apparatus for the SEC
system are increased at long distances relative to conventional
cellular systems and reduced near the mast. These effects are
achieved by the phased-array antenna and associated passive
components, as well as active electronics included in the present
invention.
[0036] Standard BTS equipment, such as transceivers, electric power
supplies, data transmission systems, temperature control and
monitoring systems, etc., may be advantageously used within the SEC
system. Generally, from one to three or more cellular operators
(service providers) may be supported simultaneously at each BTS,
featuring, for example, 36 to 96 transceivers and 216 to 576 Erlang
of capacity. Alternatively, more economical BTS transmitters (e.g.,
0.1 W transmitter power) may be used by the cellular operators,
further reducing cost and energy consumption. These economical BTSs
have a smaller footprint and lower energy consumption than previous
designs, due in part to performance of transmitted signal
amplification and received signal processing at the top of the
phased-array antenna tower rather than on the ground.
[0037] FIG. 1 presents a perspective view of a BTS antenna, in
accordance with an embodiment of the present invention.
[0038] The base transceiver station 10 includes an antenna tower 12
and a phased-array antenna 14, with the latter disposed on an upper
portion of the tower 12, shown here as the tower top. The antenna
14 in the embodiment shown is generally cylindrical in shape, which
serves to reduce windload, and has a number of sectors 16, such as,
for example, 6 sectors, 8 sectors, 12 sectors, 18 sectors, 24
sectors, 30 sectors, 36 sectors, etc., that collectively provide
omnidirectional coverage for a cell associated with the BTS. Each
sector 16 includes a number of antenna panels 18 in a vertical
stack. Each elevation 20 includes a number of antenna panels 18
that can surround a support system to provide 360.degree. coverage
at a particular height, with each panel 18 potentially belonging to
a different sector 16. Each antenna panel 18 includes a plurality
of vertically-arrayed radiators, which are enclosed within radomes
that coincide in extent with the panels 18 in the embodiment
shown.
[0039] Feed lines, such as coaxial cable, fiber optic cable, etc.,
connect cellular operator equipment to the antenna feed system
located behind the respective sectors 16. At the input to the feed
system for each sector 16 are diplexers, power transmission
amplifiers, low-noise receive amplifiers, etc., to amplify and
shape the signals transmitted from, and received by, the
phased-array antenna 14. In one embodiment, the feed system
includes rigid power dividers to interconnect the antenna panels 18
within each sector 16, and to provide vertical lobe shaping and
beam tilt to the panels 18 in that sector. In another embodiment,
flexible coaxial cables may be used within the feed system.
[0040] FIG. 2 compares standard cell coverage with coverage
provided by a BTS antenna according to an embodiment of the present
invention. Table 1 compares antenna parameters and coverage for a
conventional cellular site to two different embodiments of the
present invention. The GSM 870-960 MHz band is used for this
comparison.
TABLE-US-00001 TABLE 1 Standard Site 1.sup.st Embodiment 2.sup.nd
Embodiment Antenna Parameters Sectors @ Beam 3 @ 65.degree. 6 @
45.degree. 9 @ 30.degree. Width Elevations 1 8 12 Panels 3 48 108
Antenna Aperture 2.5 m 20 m 30 m Installation Height 48 m 126 m 247
m Antenna Gain 17.5 dBi 28.0 dBi 31.0 dBi Uplink PL Efficiency +0.0
dB +26.6 dB +36.4 dB Signal Gain Factor 1 457 4365 Coverage Cell
Radius 5 km 23 km 41 km Indoor Coverage Area 80 km.sup.2 1710
km.sup.2 5280 km.sup.2 Coverage Area Factor .sup. 1.0 21.4 66.1
Okumura-Hata exp. .sup. 4.0 4.0 4.0
[0041] Generally, antenna tower 12 is a guyed or self supporting
antenna mast that supports approximately 3,000 to 20,000 lbs of
payload, has a total mast height from about 200 feet to about 1,500
feet, and is capable of supporting the SEC antenna with high wind
load resistance. Alternatively, standard antenna masts, chimneys,
towers or other constructions may be used, provided the desired
structural rigidity and payload ratings are satisfied. A solar
power collector, microwave link, wind generator, etc. may be
provided to reduce power and landline communication infrastructure
burdens for the BTS.
[0042] In some embodiments, phased-array antennas 14 use between 24
and 288 antenna panels 18, arranged into three to thirty-six
sectors 16, each of which includes two to sixteen, preferably eight
to twelve, elevations 20 of antenna panels 18. Generally, each
sector 16 forms a directional antenna beam that has a bandwidth on
the order of 10%, a horizontal beam width of 7.degree. to
65.degree. (preferably 30.degree. or 45.degree. in twelve-sector or
eight-sector embodiments), and a vertical beam width of
0.66.degree. to 2.degree.. For preferred embodiments, vertical
arrangement of eight elevations 20 of antenna panels 18 improves
antenna aperture efficiency for both signal transmission and
reception. Compact circumferential arrangement of sectors 16
establishes a cylindrical shape. Some antenna 14 embodiments may be
adaptable to support capacity increases to meet traffic and growth
demands.
[0043] Frequency assignments other than 870-960 MHz are equally
feasible, specifically to include at least previously-allocated
bands in the vicinity of 460 MHz, 750 MHz, 900 MHz, 2 GHz, 2.8 GHz,
and 3.5 GHz. Such bands, as well as others that may be assigned or
acquired subsequently, may each require apparatus differing
appreciably in size and somewhat in configuration in order to
provide the service described herein. For example, since radiative
devices are often effective over about a 10% range (i.e., +/-5% of
a center frequency), and may be defined in terms of dimensions, it
may be necessary to roughly double the physical size of individual
radiators and the spacing therebetween to service the 460 MHz band,
and to halve these dimensions for the 2 GHz band, compared to the
900 MHz band described above.
[0044] In other embodiments contemplated for the invention, wider
bandwidth radiators may support at least all of the U.S. and EU GSM
and/or CDMA band, for example, and the associated filters may be
capable of accommodating multiple such bands through retuning
rather than manufacturing alternate devices that differ in physical
dimensions. Because the relevant U.S. and EU bands do not overlap,
the transmit and receive frequencies for the respective bands are
closer to each other than are the respective transmit and receive
frequencies of the bands, so that filters for the bands preferably
operate in discrete ranges. This may be of consideration should
multiple, closely-spaced bands be licensed, for example, in which
case multiple filters may support fewer arrays of radiators.
[0045] In one embodiment, each antenna panel 18 is made using, as a
frame and reflector, a single aluminum extrusion that measures
about 8 feet.times.12 inches.times.8 inches (2.5 m.times.5
cm.times.20 cm) and weighs roughly 30 pounds (15 kg). To this
extrusion are attached radiators, signal distribution fittings, a
radome, mounting hardware, etc. The antenna panels 18 are installed
within each sector 16 of the phased-array antenna 14 with very high
coplanarity (e.g., +/-0.25.degree.), provided in part by structural
optimization of all antenna and mast elements. Additionally, these
antenna panels reduce effective wind load areas. Advantageously,
these features combine to increase uplink channel sensitivity
(antenna gain) while improving downlink channel throughput. Other
sector 16 configurations and antenna panel 18 dimensions are also
contemplated by the present invention.
[0046] FIG. 3A depicts a horizontal radiation pattern for a single
sector 16 using radiators configured to realize a 32 degree beam
width, in accordance with an embodiment of the present invention.
The phased-array antenna 14 has a fixed radiation pattern with
asymmetric coefficients for null filling and efficient upper lobe
suppression, created by a number of dipole radiators located in
arrays within the respective sectors 16. In one embodiment, each
antenna panel 18 includes two adjacent, vertically-oriented,
staggered columns of eight dipole radiators. For a sector 16 that
includes eight of these antenna panels 18, two vertical arrays of
64 dipole radiators each are thus provided. In this embodiment, the
dipole radiators in each column are constantly-spaced at
approximately one-wavelength intervals, while the columns are
offset with respect to one another by approximately one-half
wavelength. In other words, adjacent, staggered dipole radiators
are constantly-spaced at one-half wavelength intervals.
[0047] A phased-array antenna 14 according to such an embodiment
can realize a signal gain factor of about 29 dBi to 32 dBi, and can
accept antenna input power up to 80 W per carrier. FIG. 3B depicts
the total vertical radiation pattern for a single sector, in
accordance with an embodiment of the present invention.
[0048] When compared to conventional cellular antennas, the
phased-array antenna 14 field strength is increased by 17 dB to 27
dB in the far zone (i.e., 5 km to 30 km), decreased by about 10 dB
in the near zone (i.e., 0 km to 1 km), and left unchanged in the
middle zone (i.e., 1 km to 5 km). These effects produce more
uniform field strength distribution patterns in the near and far
zones of the phased-array antenna 14, which produces, for example,
a tenfold to forty-fold increase of a cell's coverage area when
compared to a conventional cellular antenna. This is an example of
the "Robin Hood" principle, in which power/gain is redirected from
vertical areas of surplus to vertical areas of deficiency to keep
nearby power levels, and EIRP, lower while extending range, as
illustrated in FIGS. 4A and 4B.
[0049] In one embodiment, every +1 dB in path loss gives 25% more
signal.
[0050] The phased-array antenna 14 also supports multiple signal
input and multiple signal output (MIMO) technologies, and
advantageously increases the carrier/interference ratio and
improves throughput due to reduced multi-path direction of arrival
(DOA) speeds, optimum down tilt, and rapid cutoff of over-range
radio frequency interference. Suppression of side and back lobes,
which is further enhanced through abutting of panel 16
frame/reflector components and improving radiator designs,
additionally increases signal reception reliability and helps to
reduce the number of dropped calls in a cell.
[0051] As noted above, feed lines, such as thin, flexible coaxial
cables, connect the BTS cellular operator equipment to the lower
portion of the phased-array antenna 14. In one embodiment, an
active low-loss device for shaping a vertical lobe's radiation
pattern (e.g., LLVLSU--Low Loss Vertical Lobe Shaping Unit), an 80
W single-carrier power amplifier with a low energy density design
for easy maintenance and reliability (e.g., LPDPA--Low Power
Density Power Amplifier), a diplexer/filter, a combiner, a
multicoupler, a low-noise amplifier (LNA), a very low noise
amplifier (VLNA) and cable jumpers are included. The LLVLSU is
responsible for making a cell with a phased-array antenna 14, and
realizes amplitude balancing for null filling in middle and far
zones, implementing the "Robin Hood" principle.
[0052] A thin, flexible coaxial cable decreases a feed line's
weight, purchase cost, and wind load, eases installation, etc.
Additional signal attenuation in thin, flexible coaxial cables is
fully compensated by a single-carrier 80 W power amplifier in a
downlink channel, installed in the lower portion of the
phased-array antenna 14 directly behind the antenna panels 18.
Further signal amplification is done in an uplink channel by a very
low noise amplifier--one with a noise figure less than 1
dB--located likewise behind the antenna panels 16 and
weather-shielded.
[0053] Diplexer/filters, combiners, and multicouplers can have
respective noise figures kept to low levels in part through
component quality control and in part through particular attention
to matching of devices in the course of signal cascading, such as,
for example, the use of the Friis cascading rule. Properly chosen
and configured antenna elements can feature high electrical
efficiency--that is, a voltage standing wave ratio (VSWR) that does
not exceed 1.15 over a 10% passband, for example. Such a low level
of VSWR can be achieved through matching of impedance of all system
components, and can reduce energy losses and failure risks for
high-frequency equipment of a radio BTS. Low VSWR gives numerous
possibilities to fully utilize capacities of a power amplifier and
a phased-array antenna 14. All active RF components are preferably
designed with very low energy densities, utilizing convection
air-cooling methods for additional energy efficiency and featuring
system-level fault tolerance and soft-fail behavior.
[0054] In some embodiments, through use of a passive, low loss
precision vertical lobe shaper (or LLVLSU), a site can redistribute
its radiated power in accordance with the "Robin Hood" principle,
and can ensure significant uniformity of electromagnetic field
strength in near, middle, and far zones. FIG. 3B depicts a vertical
radiation pattern formed by a LLVLSU. Maximum signal power is
achieved at a down tilt angle of -0.5 degrees in the embodiment
shown. Signal power is gradually reduced by thorough null filling
(-3.125 degrees, -2.125 degrees, and -1.25 degrees), while upper
lobes (>+1.25 degrees) are effectively suppressed by more than
25 dB to avoid excessive levels of RF interference.
[0055] In other embodiments, comparable "Robin Hood" field strength
distribution can be achieved through passive vertical lobe shaping.
In this latter form, a single passive power divider, such as a
rigid power divider, may be followed by individual coaxial feeds to
all panels, or the power division function may be distributed among
a plurality of three-port (or more) power division devices, for
example. In such embodiments, power provided to each panel may be
increased or decreased relative to that to other panels to realize
distribution comparable to that of LLVLSU distribution.
[0056] FIG. 5 illustrates distribution spectra 30 for power 32 and
phase 34 for phased-array antennas in accordance with embodiments
of the present invention. In power spectra 32 and 36, each sector
16 of phased-array antenna 14 includes eight elevations 20 of
individual antenna panels 18, as shown in FIG. 1. The stepwise
power 32 and phase 34 distributions of FIG. 5 may be realized to
any desired level of accuracy by either active or passive vertical
lobe shaping. Other power and phase distribution spectra are also
contemplated by the present invention. For example, FIG. 5
indicates that the maximum power level for power spectra 32 is
provided to the third panel, while the maximum power level for
power spectra 36 is provided to the sixth panel, etc. Still other
embodiments may vary power to each radiator rather than to each
panel, as shown in a third power spectra 38 of FIG. 5, in part
through further variation in the signal strength coupled to each
radiator within each panel 18.
[0057] FIG. 6 presents phased-array antenna signal strength 40 as a
function of distance, in accordance with an embodiment of the
present invention. In this embodiment, a particular power
distribution 32, shown in FIG. 5, in combination with predetermined
values of element spacing and phasing, can provide particular
values of beam tilt and downward lobe suppression. Conventional
antenna designs are generally limited to realizing signal strength
42 that is much higher in the near zone 44, and much lower in the
far zone 46, than a signal strength 48 distribution of an antenna
embodying the present invention. Other embodiments of phased-array
antennas 14, such as, for example, one wherein the exemplary
panel-by-panel power distribution 32 illustrated in FIG. 5 is
replaced by a power distribution 38 that is unique for each
radiator in each panel 18 within a sector 16, can achieve signal
strength/gain 50 that is further improved for many locations over
the service area.
[0058] FIGS. 7A and 8A depict a perspective, semi-transparent view
of a phased-array antenna panel 100, according to an embodiment of
the present invention. In a preferred embodiment, support member
110 advantageously provides a continuous reflector face 112 (or
backplane) for a number of crossed dipole radiators 120, which are
arranged in parallel columns on the support member 110. A number of
striplines are provided within support member 110 to connect the
crossed dipole radiators 120 to signal distribution cables and
couplings disposed behind the support members 110 of phased-array
antenna 14, shown in FIG. 1. In the depicted embodiment, two
columns, each including eight crossed dipole radiators 120, are
provided on each panel 100, and four striplines 132, 134, 136, 138,
arranged in complementary pairs, connect the crossed dipole
radiators 120 to the signal distribution cables. Each crossed
dipole radiator includes two conductors, one for each dipole
radiator.
[0059] In a preferred embodiment, the radiators 120 are transverse,
quadrilateral, crossed-dipole radiators. A perspective view of an
exemplary transverse, quadrilateral, crossed-dipole radiator 120 is
also provided in FIG. 7A, whereof salient characteristics are
described, in more detail, in one or more related copending patent
applications. Transverse quadrilateral crossed dipole radiators 120
can be configured to exhibit low cross coupling, and, when suitably
positioned and oriented, and fed with suitably phased signals, to
exhibit low mutual coupling.
[0060] In the embodiment in FIG. 7A, eight equally-spaced dipole
radiators 120 are provided in each of two staggered columns. The
effective vertical spacing of successive radiators 120, alternating
between the columns, is preferably offset by half, providing
roughly half-wave spacing between radiator 120 centers in the
embodiment shown. As addressed in a related copending application,
the effective transmit and receive characteristics of the antenna
are affected both by radiator-to-radiator spacing and by feed line
phasing. A line through the centers of proximal radiators 120 in
alternating columns forms a 45 degree angle with respect to a
centerline of support member 110. Other numbers of equally-spaced
dipole radiators 120 in each column, such as two, four, six,
twelve, sixteen, etc., are also contemplated by the present
invention.
[0061] In a preferred 900 MHz band embodiment, the radiators 120
within each column are separated, along the length of the antenna
panel 100, by approximately 12 inches (e.g., 12.033 inches), and
are offset with respect to the radiators within the adjacent
column, along the length of the antenna panel 100, by approximately
6 inches (e.g., 6.017 inches). In this embodiment, the columns are
separated by approximately 71/2 inches (7.680 inches). In a
preferred 1800 MHz band embodiment, the dimensions are all reduced
by a factor of 0.5; other embodiments may be similarly
accommodated. It is noted that the signals actually radiated and
received by the inventive system are greater than, less than or
equal to these center frequencies. For example, one 900 MHz band
embodiment may include a range of frequencies for base station
reception, e.g., 890-915 MHz, and a range of frequencies for base
station transmission, e.g., 935-960 MHz.
[0062] In one embodiment, support member 110 is extruded from a
high-strength material, such as an alloy of aluminum, and several
cavities, extending longitudinally, are formed therein. Other
fabrication methods and materials may be used to form support
member 110, such as, for example, cold rolling, welding, etc. In
the embodiment shown, support member 110 includes four (4) signal
ground cavities 104, in which respective striplines 132, 134, 136,
138 are disposed. Support member 110 may also include one or more
structural cavities 108, in order to provide additional lateral
dimension, strength, etc.
[0063] Another embodiment of antenna panel 100 is depicted in FIGS.
7B and 8B. In this embodiment, raised sections 122 are formed on
support member 110 to provide additional support for dipole
radiators 120. The frequency range supported by this embodiment may
be, for example, the 900 MHz band.
[0064] In this embodiment, array panel 100 has an overall length of
approximately 100 inches (e.g., 98.00 inches), an overall width of
12 inches (e.g., 12.60 inches) and an overall height of 2 inches
(e.g., 1.91 inches). Generally, the array panel 100 has a thickness
of approximately 0.1 inches (e.g., 0.08 inches), including the
perimeter of the panel as well as the center webs 114 and cross
members 106. The raised sections 122 are elevated above the support
member 110 by approximately 0.2 inches (e.g., 0.17 inches) and
offset by approximately 4 inches (e.g., 3.84 inches) from the
centerline of the support member 110. Two outer center webs 114 are
respectively disposed under the centerline of each raised section
122, while two inboard center webs 114 are respectively disposed
between the centerline of the array panel 100 and the centerlines
of the raised sections 122. Four, generally-rectangular signal
ground cavities 104 are thereby formed, each enclosing
approximately the same volume. For example, the two inner signal
ground cavities may be approximately 2 inches in width, and 11/2
inches in height (e.g., 2.06 inches by 1.58 inches), while the two
outer signal ground cavities 104 may be approximately 21/4 inches
in width and 11/2 inches in height (e.g., 2.29 inches by 1.58
inches).
[0065] As shown in FIG. 8B, a circular groove 121 is formed in each
side of support member 110 to receive a mating circular flange from
a radome installed over the panel (shown as a dashed line in FIG.
7B). The radome may be constructed from an RF-transparent material
suitable for a radome, such as, for example, polycarbonate. In this
embodiment, groove 121 may have a radius of approximately 1/4
inches (e.g., 0.22 inches). The radome includes two end caps and a
center portion, the outer surface having a curved shape and a
maximum height above the support member 110 of approximately 8
inches (e.g., 7.75 inches). Countersunk holes (not shown), of
approximately 1/2 inch diameter, are provided in the raised
sections 122 to accommodate the installation of each radiator 120.
The two inner conductors of each radiator 120 pass through the
holes in the raised section 122 and connect to a respective
stripline disposed within the ground signal cavity 104 below.
[0066] Another embodiment of antenna panel 100 is depicted in FIGS.
7C and 8C. In this embodiment, raised sections 122 are formed on
support member 110 to provide additional support for dipole
radiators 120. The frequency range supported by this embodiment may
be, for example, the 1800 MHz band. In this embodiment, array panel
100 has an overall length of approximately 50 inches, an overall
width of 12 inches and an overall height of 2 inches. Generally,
the array panel 100 has a thickness of approximately 0.1 inches,
including the perimeter of the panel as well as the center webs
114; no cross members are used in this embodiment. As shown in FIG.
8C, a circular groove 121 is formed in each side of support member
110 to receive a mating circular flange from a radome installed
over the panel (shown as a dashed line in FIG. 7C). The radome may
be constructed from an RF-transparent material suitable for a
radome, such as, for example, polycarbonate. In this embodiment,
groove 121 may have a radius of approximately 1/4 inches. The
radome includes two end caps and a center portion, the outer
surface having a curved shape.
[0067] FIG. 9 depicts a perspective front view of a phased-array
antenna panel, in accordance with an embodiment of the present
invention, while FIG. 10 depicts a perspective rear view of a
phased-array antenna panel, in accordance with an embodiment of the
present invention.
[0068] Signal distribution cable connectors 142, 144, 146, 148 are
coupled to signal splitters 310, 312, which divide the respective
signals carried by signal feed lines 320, 322. In the embodiment
depicted in FIG. 10, the signal(s) carried by signal feed line 320
are split by signal splitter 310, and then provided to signal
distribution cable connectors 142, 146, while the signal(s) carried
by signal feed line 322 are split, by signal splitter 312, and then
provided to signal distribution cable connectors 144 and 148. In
this embodiment, each dipole radiator is advantageously coupled to
both signal feed lines 320, 322. In a preferred embodiment, signal
splitters 310, 312 divide the respective signals carried by signal
feed lines 320, 322 into orthogonal components.
[0069] Radome 302 is substantially transparent to the frequencies
of interest, and encloses antenna panel 100 in order to protect
dipole radiators 120 against the adverse effects of weather, etc.
In one embodiment, a single sector 16 may be employed, and
additional backplane surfaces 300 may be attached to each side of
antenna panel 100.
[0070] FIGS. 11A to 11D show a single panel stack 60,
corresponding, in the embodiment shown in FIG. 1, to a sector 16,
as viewed from inside the phased-array antenna 14. The stack 60
includes a plurality of radiator panels 62, a pair of junction
boxes 64, a pair of (transmitting) power amplifiers (PAs) 66, a
pair of receiving amplifiers (RAs) 68, a pair of diplexer/filters
70, a pair of first tee junction/power divider assemblies 72, a
plurality of second tee junction/power divider assemblies 74, a
plurality of third tee junction/power divider assemblies 76, a
plurality of final power dividers 78, and a plurality of
interconnecting cables 80. FIGS. 11A to 11D show an embodiment that
includes auxiliary reflective extension surfaces 82 to either side
of the panels 62; in other embodiments, additional panels 62
forming sectors 16 to either side may obviate the extensions
82.
[0071] The arrangement of tees 72, 74, 76, 78 interconnected by
cables 80 provides transmitter 66 signal output distribution and
receiver 68 signal input collection by way of filter/diplexers 70.
Transmission is addressed expressly in the following discussion;
receive functionality mirrors transmission. Each tee 72 divides the
diplexed transmit signal between two outputs, connected by cables
80 to the inputs of the next two tees 74, which further divide the
signal and pass it via further cables 80 to the final four tees 76
in each string. The tees 72, 74, 76 in at least some embodiments
can exhibit substantially identical propagation timing
characteristics, but may differ in the amount of power delivered
from the input to each output.
[0072] The proportions of signal distribution 30 shown in the chart
of FIG. 5 are achieved in the embodiment shown using two values of
power splitting, specifically approximating 60:40 and 70:30
splitting, over the three tiers of tees 72, 74, 76. The value of
signal strength for transmitting or gain for receiving associated
with each panel is the product of the power splits to a good
approximation. For example, if each of the successive tees feeding
a panel has a 30% branch, and the 30% branches are concatenated to
feed that panel, then the proportion of transmitter energy reaching
that panel is 0.3*0.3*0.3, or 2.7%. Similarly, a 70%, 60%, 60%
concatenation provides 25.2% of the available power to a panel.
[0073] Tees that are all split equally (50:50) provide
substantially uniform power distribution, with relatively basic
beam formation. In the alternative, an extensive variety of
distributions 30 can be realized by allowing each of the seven tees
72, 74, 76 to have a power split optimized for one position within
the panel stack 60, rather than the combination of 70:30 and 60:40
splits in the embodiment shown. Power distribution between multiple
radiators has been noted as a factor in controlling signal strength
40 at each distance from an antenna, as shown in FIG. 6. Selection
of particular internal construction for each tee can provide a
realization for such power distribution. Judicious compromise may
permit product simplification and concomitant reduction in system
cost while approaching specific performance goals to any preferred
degree.
[0074] Phasing between stacked panels 62 can be made independent of
power distribution to a significant extent by normalizing tee 72,
74, 76 phase as noted and using relative cable 80 length to control
propagation delay. In the embodiment shown, phase is made
substantially uniform by equalizing propagation delays throughout
with equal-length cables 80; in other embodiments, phase adjustment
along with power distribution can provide further control of beam
characteristics over the cell, such as by further reducing rear and
side lobes, further adjusting beam tilt and principal beam shape,
and the like.
[0075] The combination of power distribution and phasing may be
further varied from sector 16 to sector 16 within a phased-array
antenna 14, shown in FIG. 1, in order to compensate for factors
such as terrain variation, limits to coverage permitted to a
particular antenna 10 by political boundaries, and the like. Thus,
an antenna 14 on a dedicated tower 16 located in profoundly flat
terrain over consistently conductive soil (a reliable ground plane)
may support a maximally-sized cell with uniform feed to all sectors
16, for example. As an alternative example, a building-topping
radiator antenna 14 may be sited near a lake with a stony bluff
beyond in one direction and gently rising forest opposite thereto,
and may be required to service a cell of nonuniform perimeter,
requiring that power/phase distribution in each stack 60 be
tailored to azimuth-dependent characteristics of the cell.
[0076] The modified quadrilateral construction of the radiator
dipoles 140, 142 and their spacing further provides low voltage
standing wave ratio (VSWR) over at least a bandwidth required for
cellular telephony, namely about 7.6% for the basic 900 MHz GSM
band, or up to 9.1% for the P-, E-, or R-extended versions of that
band. For the 1.8 GHz GSM band, bandwidth is again about 9.1%, with
the gap between transmit and receive frequencies roughly equal to
that of the E-GSM band.
[0077] A preferred embodiment of the inventive super economical
broadcast system has an antenna gain of 30 dBi, a feeder line loss
of 15 dB (0.25'' line, 200 m mast @960<Hz), a gain of 30 dB, due
to the active components described above, feeding down to the
standard BTS that has a noise factor of 3.5 dB. Using a cascaded
Friis formula, the NFsys at the antenna port is <1.0 dB.
Accordingly, Ga-NF sys=30.0-1.0=29.0 dBi (in uplink). Downlink
transmitter power varies between 0.1 and 80 W. With feeder lines,
duplex filter and jumper cables totaling -15.0 dB, the Pa input
power to antenna is 80 W, such that the EIRP is 80 W*1000=80,000
W.
[0078] Compared to the known antenna installation discussed in the
Background section above, the improvement in uplink is
20.9-11.0=18.0 dB, while the improvement in downlink is
30.0-15.5+10 log 80/16=14.5 +7=21.5 dB. The EIRP improves by a
factor of 141.
[0079] While the EIRP calculation assumes nominal antenna gain, the
actual gain provided by the inventive super economical broadcast
system is developed at a distance greater than 5,000 m, and at a
height above ground corresponding to the vertical lobe maximum.
Closer to the base station, the full gain has not developed and the
gain at the height of vertical lobe maximum is lower than a
standard antenna. Additionally, the gain pointing to ground level
is further reduced due to the narrow lobe. In this way, the
inventive Robin Hood principle delivers lower radiated EIRP in the
near zone.
[0080] The many features and advantages of the invention are
apparent from the detailed specification, and thus, it is intended
by the appended claims to cover all such features and advantages of
the invention which fall within the true spirit and scope of the
invention. Further, since numerous modifications and variations
will readily occur to those skilled in the art, it is not desired
to limit the invention to the exact construction and operation
illustrated and described, and accordingly, all suitable
modifications and equivalents may be resorted to that fall within
the scope of the invention.
* * * * *