(12) United States Patent
`Smith et al.
`
`USOO621 1841B1
`(10) Patent No.:
`US 6,211,841 B1
`(45) Date of Patent:
`Apr. 3, 2001
`
`(54) MULTI-BAND CELLULAR BASESTATION
`ANTENNA
`
`(75) Inventors: Martin Smith, Chelmsford; Dean
`Kitchener, Brentwood; Dawn K
`Power, Bishops Stortford, all of (GB)
`(73) Assignee: Nortel Networks Limited, Montreal
`(CA)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/473,722
`(22) Filed:
`Dec. 28, 1999
`e a Vs
`(51) Int. Cl." ..................................................... H01O 21/12
`(52) U.S. Cl. .......................... 343/813; 343/797; 34.3/844;
`343/853
`(58) Field of Search ..................................... 343/813, 844,
`343/797, 700 MS, 853, 810, 811, 812,
`814, 815, 816, 817, 818, 819, 820, 846,
`848
`
`(56)
`
`3,938,161
`
`References Cited
`U.S. PATENT DOCUMENTS
`2/1976 Sanford ..............................., 343/829
`
`7/1999 Sanzgiri et al. .............. 343/700 MS
`5,923.296
`8/1999 Martek ................................. 343/893
`5,940,048
`5,966,102 * 10/1999 Runyon ................................ 343/820
`
`
`
`* cited by examiner
`
`Primary Examiner Tho Phan
`(74) Attorney, Agent, or Firm-Lee, Mann, Smith,
`McWilliams, Sweeney & Ohlson
`(57)
`ABSTRACT
`The present invention relates to a multi-band cellular bas
`estation and in particular relates to antennas for Such bas
`estations. There is a growing need for mult-band basestation
`antennas for mobile communication Systems, to Serve exist
`ing 2nd generation Systems, and emerging third generation
`systems. For example, GSM and DCS1800 systems cur
`rently coexist in Europe, and emerging 3rd generation
`systems (UMTS) will initially have to operate in parallel
`with these systems. The present invention provides a dual/
`triple/multi-band performance cellular basestation antenna
`having a shared aperature, having a first Set of radiating
`elements operable at a first frequency range, a Second Set of
`radiating elements operable at a Second frequency range;
`wherein the first Set and Second Set of radiating elements are
`arranged in an interleaved fashion.
`
`14 Claims, 4 Drawing Sheets
`
`0.085
`
`Low band dipoles
`
`N 0.085
`
`N
`
`loss
`
`x X
`High band
`XX1 dipoles
`>{XX
`S
`O >K X r
`O
`O
`17
`-a-
`-- 0.08
`First embodiment of a dual polarised triband basestation
`antenna using two radiating layers.
`
`Ground Plane
`
`0.04
`
`1
`
`Kathrein USA, Inc., Exhibit 1118
`
`

`

`U.S. Patent
`
`Apr. 3, 2001
`
`Sheet 1 of 4
`
`US 6,211,841 B1
`
`
`
`F.9. I ( - 4x4 3D-FIPA (Top and side views)
`Prior Art
`
`Fl9.O I b - Wideband planar array for a two octave
`Prior Art
`bandwidth
`
`2
`
`

`

`U.S. Patent
`
`Apr. 3, 2001
`
`Sheet 2 of 4
`
`US 6,211,841 B1
`
`0.33, k X
`X
`
`on
`
`X
`X
`X
`X
`X
`FligO 2 - Tricellular array - triangular lattice
`
`0.085
`
`S
`
`X
`X High ba
`XX1 dipoles
`X
`X
`of 0.17
`Fig. 3a
`
`xx Low band dipoles N Na
`
`IT
`
`0.085
`
`0.055
`
`Ground Plane
`
`004
`s b
`
`First embodiment of a dual polarised triband basestation
`antenna using two radiating layers.
`
`3
`
`

`

`U.S. Patent
`
`Apr. 3, 2001
`
`Sheet 3 of 4
`
`US 6,211,841 B1
`
`0.08
`X Low band dipoles
`
`
`
`
`
`
`
`High band
`dipoles
`
`X X
`XX
`X
`X x
`
`.
`
`E.
`
`O085
`
`0.055
`
`Ground Plane
`
`O.O
`
`>XXX
`0.04
`?
`Fig. 4b
`Fig. 4a
`Second embodiment of a dual polarised triband basestation
`antenna using two radiating layers-interleaved high band and
`low band arrays using a triangular lattice.
`0.085
`
`k Low band dipoles
`Triband elements X
`YX ised
`X
`
`
`
`
`
`Frequency selective
`ground screen
`
`X ||
`Fig. 5a i?
`
`Ground Plane
`
`a Fis sh
`
`Third embodiment of a dual polarised triband basestation
`antenna.
`
`4
`
`

`

`U.S. Patent
`
`Apr. 3, 2001
`
`Sheet 4 of 4
`
`US 6,211,841 B1
`
`0.252
`
`0.752
`
`
`
`W = Low frequency wavelength
`Wu = High frequency wavelength
`
`Multiband array with increased vertical element spacing, and
`high frequency elements staggered at three different horizontal
`positions.
`
`Fig. 6
`
`5
`
`

`

`US 6,211,841 B1
`
`1
`MULTI-BAND CELLULAR BASESTATION
`ANTENNA
`
`FIELD OF THE INVENTION
`The present invention relates to a multiband cellular
`basestation and in particular relates to antennas for Such
`basestations.
`
`2
`null fill-in. However, arrays are inherently narrowband
`because the electrical Separation distance between elements
`changes with frequency, and this affects the array perfor
`mance. In particular, if the element Separation becomes too
`large (electrically) then grating lobes will appear in the
`pattern, where these are Secondary main lobes. These cause
`a reduction in gain and an increase in the interference in the
`network (if they appear in the azimuth plane).
`Due to the narrowband characteristics of array antennas,
`the use of wideband arrays has been very restricted. In the
`design of a wideband array, the wideband properties of the
`individual elements, and the wideband characteristics of the
`array must be considered Separately.
`In “The Three-Dimensional Frequency-independent
`Phased Array (3D-FIPA), J. K. Breakall, IEE Ninth Inter
`national Conference on Antennas and Propagation, ICAP
`'95, Conference publication No. 407, pp.9-11 a design is
`presented for a three-dimensional frequency-independent
`phased array (3D-FIPA) which at the IEE ICAP 95 confer
`ence. This is achieved by applying a log-periodic principle
`whereby multilayer dipole arrays are formed that maintain
`all electrical Spacings and heights over a user Specified
`range. The design results in an antenna that maintains nearly
`constant pattern characteristics, gain, and VSWR over a
`wide bandwidth. FIG. 1 shows top and side views of the
`form of the array where dual polar elements (crossed
`dipoles) are employed. The uppermost layer of dipoles are
`shown emboldened to illustrate the layer that would be
`excited at the lowest frequency of operation.
`The 3D-FIPA preserves all spacings and heights above
`ground (expressed in wavelengths) for active elements as the
`frequency is varied. However, the ground plane Size does not
`scale with frequency but has a fixed physical size. This will
`introduce a frequency dependent effect on the antenna
`performance. In view of the three dimensional nature of the
`array it may become difficult to manufacture a low cost
`Structure if many dipole layers are required.
`In Wideband Arrays with variable element sizes, D. G.
`Shively, W. L. Stutzman, IEE Proc., Vol.137, Pt. H, No.4,
`August 1990 a wideband array structure is presented that
`operates over a two octave bandwidth. The array consists of
`large and Small cavity-backed Archimedean Spiral elements
`in alternate positions. The general planar case is a filled grid
`version of the array shown in FIG. 1b.
`The diameter of the large spirals is twice that of the small
`Spirals. These elements are circularly polarised and radiate
`when the perimeter of the Spiral is approximately one
`wavelength. Consequently, the maximum spiral perimeter
`(dictated by the diameter) determines the lowest frequency
`of operation. AS the frequency is increased, the location of
`the active region of the Spiral moves towards the centre of
`the Spiral. However, the aperture size does not Scale with
`frequency, and consequently, the gain and beamwidth of the
`array do not remain constant with frequency. In fact, the gain
`increases with frequency as the beamwidth decreases and
`therefore is not Suitable for a multiband basestation antenna.
`
`OBJECT OF THE INVENTION
`The present invention seeks to provide a dual or triple
`frequency band performance cellular basestation antenna
`having a shared aperture. The present invention also seeks to
`provide Such an antenna which is of minimum dimensions.
`STATEMENT OF THE INVENTION
`In accordance with a first aspect of the invention there is
`provided a dual band base Station antenna comprising:
`
`15
`
`BACKGROUND TO THE INVENTION
`There is a growing need for multiband basestation anten
`nas for mobile communication systems, to serve existing 2"
`generation Systems, and emerging third generation Systems.
`For example, GSM and DCS1800 systems currently coexist
`in Europe, and emerging 3" generation systems (UMTS)
`will initially have to operate in parallel with these Systems.
`At a given base site there may be a need to cover all three
`bands, and if Separate antennas are used for each band this
`results in an unacceptably large number of antennas.
`Typically, two antennas are used per Sector at a base site,
`which allows for receive diversity on the uplink.
`Consequently, for a base site covering all three bands this
`would result in 6 antennas for an omnidirectional base site,
`and 18 antennas for a trisector, or tricellular arrangement.
`The problem is similar in North America where AMPS/
`NADC, PCS, and 3' generation systems will have to
`25
`coexist.
`Some of the frequency bands of interest are shown in
`Tables 1-3. Table 1 shows the frequency bands of some first
`and second generation systems. Table 2 shows the IMT-2000
`recommendations regarding frequency allocations for third
`generation Systems, along with the actual spectrum avail
`ability in Europe. Table 3 shows the spectrum availability in
`various parts of the world compared to the IMT-2000
`recommendations.
`There are a number of issues to consider regarding the
`basestation antenna. Firstly, it would be preferred that a
`Single Structure covering all three frequency bands exists to
`minimise the number of antennas at any given base Site. It
`would be preferred that the different bands should therefore
`have a shared aperture. The antenna Structure should be
`designed for ease-of-manufacture and it should also be
`designed Such that the Structure has minimum cost. It is
`possible that antennas of different beamwidths will be
`required for different cell types (eg. Omni-, trisectored,
`tricellular, microcell) and so the design should be flexible
`enough to allow for this. In addition, the number of antennas
`can be minimised if polarisation diversity is employed rather
`than Space diversity, Such that dual polarised antenna con
`figurations need to be considered.
`Some cellular basestation antenna manufacturers have
`dual frequency band dual polar products, but these comprise
`colocated Separate antennas, the Separate antennas being
`used for the two Separate bands and are simply Stacked on
`top of each other, the antennas having been packaged as a
`Single item or placed Side by Side. Vertically polarised
`antennas are known for use in the UMTS 1920–2170 MHz
`range, but commercial versions of DCS1800/UMTS cross
`polar antennas have yet to appear on the market. Large
`Structures, however, are not favoured by town planners and
`the like: base Station Structures should be as Small and as
`inconspicuous as possible.
`BaseStation antennas are generally array antennas, Since
`these allow flexibility in the control of the radiation pattern.
`The pattern characteristics can be varied by altering the
`individual element amplitude and phase weights, which is
`useful for providing electrical downtilt, and for providing
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`6
`
`

`

`3
`a first Set of radiating elements operable at a first fre
`quency range having a centre-band wavelength );
`a Second Set of radiating elements operable at a Second
`frequency range having a centre-band wavelength 2,
`and a ground plane;
`wherein the first frequency range is of the order of 4x-%
`of the Second frequency range;
`wherein the first Set of radiating elements is arranged in
`two columns spaced less than 2 apart;
`wherein the Second Set of radiating elements are inter
`leaved about the two columns of the first radiating elements,
`the Second Set of radiating elements being Spaced less than
`22 apart; and
`wherein the elements are spaced apart from the ground
`plane.
`The frequency bands are determined, typically, by
`national and Supra-national regulations. The provision of a
`multi-band antenna reduces the size of an antenna Structure
`Such as are associated with a cellular communications
`basestation.
`Preferably the radiating elements are Spaced from the
`ground plane by a quarter of a wavelength at their mid-band
`frequency.
`The Second Set of radiating elements can be in the same
`plane as the first Set of radiating elements.
`The radiating elements can be crossed dipoles.
`The radiating elements can also be patches, Single dipoles,
`or other Suitable elements.
`The radiating elements can be polarised, for example
`linearly or circularly polarised whereby to provide diversity.
`In accordance with another aspect of the invention there
`is provided a method of operating a dual band base Station
`antenna, Said antenna comprising:
`a first Set of radiating elements operable at a first fre
`quency range having a centre-band wavelength 2,
`a Second Set of radiating elements operable at a Second
`frequency range having a centre-band wavelength 2,
`and a ground plane;
`wherein the first frequency range is of the order of 4–%
`of the Second frequency range;
`wherein the first Set of radiating elements is arranged in
`two columns spaced less than 2 apart;
`wherein the Second Set of radiating elements are inter
`leaved about the two columns of the first radiating elements,
`the Second Set of radiating elements being Spaced less than
`22 apart; and
`wherein the elements are spaced apart from the ground
`plane.
`wherein, in a transmit mode, the method comprises the
`Steps of feeding Signals to the radiating elements of a
`particular frequency band at an appropriate frequency
`whereby mutual coupling effects between the first and
`Second Sets of radiating elements allow Signals to radiate
`effectively; and
`wherein, in a receive mode, the method comprises the
`Steps of receiving incoming Signals using the radiating
`element of a particular frequency band at an appropriate
`frequency whereby mutual coupling effects between the first
`and Second Sets of radiating elements allow Signals to be
`received effectively.
`BRIEF DESCRIPTION OF THE DRAWINGS
`In order that the present invention can be more fully
`understood and to show how the same may be carried into
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`US 6,211,841 B1
`
`4
`effect, reference shall now be made, by way of example only,
`to the figures as shown in the accompanying drawing sheets
`wherein:
`Table 1 shows frequency bands for some North American
`and European mobile communications Systems,
`Table 2 shows IMT frequency allocation recommendation
`for third generation Systems,
`Table 3 shows spectrum availability in various parts of the
`world;
`Table 4 shows the variation with frequency for a wide
`band element array.
`Table 5 shows the array performance for a triangular
`lattice array.
`FIGS. 1a and b show first and second examples of prior
`art antennas,
`FIG. 2 shows a tricellular array with triangular lattice.
`FIGS. 3a and b show a first embodiment of the present
`invention;
`FIGS. 4a and b show a second embodiment of the present
`invention;
`FIGS. 5a and b show a third embodiment of the present
`invention;
`FIG. 6 shows a fourth embodiment of the present inven
`tion;
`Graph 1 shows the azimuth radiation pattern for an 8
`element array of dipoles Spaced 2/1 from a reflector;
`Graph 2 shows the azimuth pattern for 2x8 array of
`dipoles at 1940 MHz
`Graph 3 shows the azimuth pattern for a triangular lattice
`array at 1940 MHz.
`Graph 4 shows the elevation pattern for a triangular lattice
`array at 1940 MHz.
`Graph 5 shows an azimuth pattern for a straight (vertical)
`dipole above an infinite ground plane,
`Graph 6 shows an azimuth pattern for an inclined dipole
`above an infinite ground plane;
`Graphs 10 to 15 show the azimuth pattern at 880, 920,
`960, 1710, 1940, and 2170 MHz for a second configuration
`of the fourth embodiment; and
`Graph 16 shows the azimuth pattern at 920 MHz for a
`third configuration of the fourth embodiment.
`DETAILED DESCRIPTION OF THE
`INVENTION
`There will now be described by way of example the best
`mode contemplated by the inventors for carrying out the
`invention. In the following description, numerous specific
`details are set out in order to provide a complete under
`Standing of the present invention. It will be apparent,
`however, to those skilled in the art that the present invention
`may be put into practice with variations of the Specific.
`Typically, GSM basestation antennas have a gain of the
`order of 16 dBi, although lower gain versions are also used
`where, the gain of these is typically between 13-15 dBi.
`Azimuth 3 dB beamwidths are typically 60-65, although
`Some antennas have wider beamwidths of 85-90. In many
`cases two basestation antennas have been used per Sector to
`provide receive Space diversity, and each base site would be
`used to serve three 120 sectors. In this configuration one of
`the antennas in each Sector would be used as the transmit
`antenna as well as being used as a receive diversity antenna.
`This requires a diplexer at the base of the mast, and results
`in base Sites with Six antennas. Operators today are deploy
`
`7
`
`

`

`US 6,211,841 B1
`
`15
`
`25
`
`S
`ing dual-polarised antennas which means that only three
`antennas are required per base site, resulting in a much more
`compact configuration. The dual polarised antenna elements
`are at +45, which has become the industry standard con
`figuration. Downtilt of the main beam of between 0-8 is
`used, and the first null is generally filled in, Such that it is
`16-18 dB down on the peak gain. For DCS1800 antennas
`the Specification is essentially the same except that the gain
`might be 18 dBi rather than 16 dBi.
`The antennas used in a typical TDMA (IS-136), another
`2" generation system, are broadly similarly with the gain
`Similar to DCS1800 at 18 dBi. The tilt of the beam varies
`from 4 uptilt to 12 downtilt. The lower gain antennas that
`are used vary from 10 dBi to 16.5 dBi. The azimuth 3 dB
`beamwidths are typically 60.
`The required operational bandwidth of a threeband
`antenna in accordance with the invention can conveniently
`be considered as two distinct bands, a lower band in the
`range 880-960 MHz (8.7%) for GSM and an upper band in
`the range 1710–2170 MHz (23.7%) for DCS1800 &
`IMT2000. The array aperture is scaled for the two bands to
`preserve the radiation pattern characteristics, and to avoid
`grating lobes. However, whilst the element Spacing must be
`Scaled in the vertical direction to prevent grating lobes, the
`elevation pattern shape does not need to be preserved. The
`full height of the low band array can be employed to realise
`a higher gain in the high band, and a narrower elevation
`beamwidth.
`FIG. 3 shows a first embodiment of the invention. The
`antenna comprises an upper radiating layer that Serves the
`GSM band, where this consists of crossed dipoles (+45) on
`a rectangular grid. The embodiments operate in a ta-5
`crossed dipole fashion, following Standard manufacturing
`practice. For the purposes of illustration the figure shows
`only four elements per column, although eight or more
`elements would be required in order to achieve a gain of
`16-18 dBi. The dipole elements in the Figure have a length
`of 16.3 cm, which corresponds to 2/2 at 920 MHz (centre of
`the GSM band). Consequently, the vertical and horizontal
`extent of the tilted dipole is 11.5 cm (16.3/V2). The vertical
`and horizontal Spacing for the elements is Set to 17 cm,
`where this corresponds to 2/2 at 880 MHz (bottom of the
`GSM band). The spacing from the ground plane is set to 8
`cm, and this is approximately 2/4 at 880 MHz. The two
`radiating layers can be considered where the apertures for
`the different layers are Scaled to Suit the different operating
`frequency bands.
`The radiating layer serving the DCS1800 and the UMTS
`band is situated below the GSM layer, at a distance of 4 cm
`50
`from the ground plane. These elements are also arranged on
`a rectangular lattice. The dipole lengths in this case are 7.7
`cm, which results in a horizontal and vertical extent of the
`tilted dipoles of 5.5 cm. The element spacing in the vertical
`and horizontal planes is 8.5 cm, and this corresponds to 0.48
`at 1710 MHz (bottom of DCS1800 band) and 0.62 at
`2170 MHz (top of UMTS band). If eight elements were used
`in the vertical direction for each radiating layer then the
`array length would be slightly more than 1.3 m (determined
`by the GSM layer). Note that the Figures are not scale
`drawings and the dimensions given are representative of the
`actual dimensions for an array with this type of Structure.
`The high band array under certain conditions will expe
`rience Some blocking from the low band array. A Second
`embodiment of the invention is shown in FIGS. 4a and b. In
`this case a triangular lattice as shown in FIG. 2 is used for
`the high band array, and the Spacing is Such that the array
`
`6
`aperture for the high band is more Sparsely populated. The
`Same number of elements is used as for the low band array,
`but these are distributed in the vertical direction over the
`Same extent as the low band elements. Consequently, the
`high band array aperture is only reduced (Scaled) in the
`azimuth plane. Thus the azimuth pattern is preserved, but the
`elevation pattern will clearly change, although this does not
`necessarily represent a problem.
`A computation has been made of the performance of the
`high band array at 1940 MHz with two columns of eight
`elements, and with a separation between the columns of
`27/2. The elements are distributed on a triangular lattice
`where the vertical Separation between elements within a
`column is 2.7 (17.5 cm). The offset between the columns
`in the vertical direction is then 27/2 (8.8 cm). The
`computation assumed vertical dipoles Spaced 7/4 from a
`ground plane, and for this case the directivity of the array
`was computed to be 20.4 dBi, and the elevation beamwidth
`was approximately 60. However, the azimuth 2 dB beam
`width is only 44.7 and the 10 dB beamwidth is only 88.4°.
`This is too narrow for a tricellular arrangement. Other results
`are shown below, for the case where the horizontal Separa
`tion between columns is only 0.33
`7 (0.058 m). In this
`case the performance achieved is well Suited for a tricellular
`arrangement.
`The structure shown in FIGS. 4a and b could be modified
`Such that both radiating layers are in the same plane. The
`radiating layer would be placed asso/4 above a Solid ground
`plane, and a frequency Selective ground plane is then intro
`duced at a distance of 27/4 behind the radiating layer, and
`Such that it sits between the radiating layer and the Solid
`ground plane. The frequency Selective ground plane can
`comprise an array of shorted crossed dipoles, slightly longer
`than those present in the radiating layer, and positioned
`directly behind each of the high band elements. These then
`act as reflectors in a similar fashion to a Yagi-Uda array, and
`are only effective in the high band and not the low band. For
`the low band the Solid ground plane Still acts as the reflector.
`Note that Some empirical adjustments may be required to
`optimise the frequency Selective ground plane, where the
`parameters to be adjusted are the shorted dipole lengths, and
`the Spacing from the radiating layer. Also note that this
`structure has the same number of layers as those of FIGS.3a
`and b and FIGS. 4a and b and therefore there is no additional
`cost associated with having coincident radiating layers.
`FIGS. 5a and b shows a third embodiment. In this case
`there are three columns of elements. The left hand column
`consists of Some triband elements that serve both the low
`band (GSM) and the high band (DCS1800/UMTS). For
`operation in the high band this column is combined with the
`centre column, which consists of elements that are resonant
`in the high band but not the low band. Thus an array of
`elements with a triangular lattice is formed. For low band
`operation the left hand column of elements is combined with
`the right hand column, which consists of elements that are
`only resonant in the low band. This structure minimises the
`number of radiating elements required, but it means that
`three different element types are being employed. Also, all
`radiating elements will be located on the same layer, and So
`a frequency Selective ground Screen would have to be
`employed (if dipole-type elements are used).
`A feed network for either of the above embodiments
`would have several layers and could be located behind the
`ground Screen. For example, the first and Second embodi
`ment would require four Separate feed layers, two for each
`radiating layer to accommodate the two polarisations. The
`number of ports on the antenna could be either two or four.
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`8
`
`

`

`US 6,211,841 B1
`
`7
`If two ports are required to limit the number of coaxial
`cables running down the mast, then a splitter/combiner
`arrangement would have to be integrated into the antenna.
`A further array configuration is shown in FIG. 6 in which
`the interleaved arrays of the lower and upper frequencies use
`two and three columns, respectively with 0.25 wavelength
`azimuth spacing, and 0.75 wavelength elevation spacing.
`This spacing can be varied from half of a wavelength to one
`wavelength.
`The feature of Several interleaved or criss crossed col
`umns of low and high band elements, allows the combina
`tion of the two upper bands into one, while maintaining a
`reasonably constant azimuth beamwidth. The closer spacing
`of the columns in this array has been found to counteract the
`narrowing of the pattern due to the use of Slant dipoles. This
`allows an increase in the elevation spacing from 0.5 to 0.75
`wavelengths, which creates more room for the interleaved
`elements. The closer azimuth spacing however does not
`allow two column interleaving for the two bands, hence the
`three columns for the upper band. The azimuth weighting of
`the columns, controlled by the number of occupied positions
`in each column, has changed from 1:1 to 1:2:1. The tapered
`three column aperture has a similar beamwidth to the
`untapered two column case.
`The dipoles are half wavelength in length at the centre of
`each band, approximately 0.16 m and 0.08 m. The elements
`are each Spaced 0.25 wavelengths from the ground plane, i.e.
`at 0.08 m and 0.04 m respectively. The low band elements
`effectively ignore the Smaller high band elements which are
`closer to the ground plane than them. However the high band
`elements are affected by parasitic coupling to the larger low
`band dipoles which are forward of them. These parasitic
`excitations perturb the high band azimuth patterns, particu
`larly at the lowest part of the upper frequency band. The
`azimuth beamwidth in this part of the band can be narrow.
`This problem can be overcome by lengthening the low band
`dipole, which is counterintuitive, to shift the problem out of
`band. The low band dipole is now greater than one wave
`length long across the upper band, which Stops the parasitic
`effect from narrowing the azimuth beam. The low band
`dipole is electrically too long, and a matching circuit is
`required to compensate for any inductive reactance in the
`low band. The length of the low frequency dipoles can be
`increased from 0.16 to 0.18 m to push parasitic interaction
`out of the band of interest, as shown in graph 13.
`For a tricellular arrangement an azimuth 2 dB beamwidth
`of 60 is required, and ideally a 10 dB beamwidth of
`approximately 120 (assuming a path loss exponent of 3.5),
`Since for a tricellular arrangement, the range to the cell
`boundary varies with angle. At the +60 points relative to
`boresight the range is half that on boresight. ASSuming a
`(1/r") path loss law the difference in path loss is:
`10nlog(2r)-10nlog(r)=1 Onlog(2)
`For n=3.5, which is a typical value for urban environments,
`10nlog(2)=10.5 dB.
`Consequently, in this case the antenna 10 dB beamwidth
`needs to be 120 to provide reasonably uniform coverage
`throughout the cell.
`What is claimed is:
`1. A dual band base Station antenna comprising:
`a first Set of radiating elements operable at a first fre
`quency range having a centre-band wavelength 2 and
`a centre-band frequency f;
`a Second Set of radiating elements operable at a Second
`frequency range having a centre-band wavelength ).
`and a centre-band frequency f;
`
`1O
`
`15
`
`25
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`8
`
`and a ground plane;
`wherein the centre-band frequency f of the first fre
`quency range is of the order of 4–% of the centre-band
`frequency f. of the Second frequency range;
`wherein the first Set of radiating elements is arranged in
`two columns spaced less than 2 apart;
`wherein the Second Set of radiating elements are inter
`leaved around the two columns of the first set of
`radiating elements, the Second Set of radiating elements
`being Spaced less than 2 apart, and
`wherein the elements are spaced apart from the ground
`plane.
`2. An antenna in accordance with claim 1 wherein the first
`Set of radiating elements are spaced from the ground plane
`by approximately a quarter of a wavelength at centre-band
`frequency f. and wherein the Second Set of radiating ele
`ments are Spaced from the around plane by approximately a
`quarter of a wavelength at centre-band frequency f.
`3. An antenna in accordance with claim 1 wherein the
`Second Set of radiating elements are in the same plane as the
`first Set of radiating elements.
`4. An antenna in accordance with claim 1 wherein the first
`and Second Sets of radiating elements are dipoles.
`5. An antenna in accordance with claim 1 wherein the first
`and Second Sets of radiating elements are dual polarized.
`6. An antenna in accordance with claim 1 wherein the first
`and Second Sets of radiating elements are crossed dipoles.
`7. An antenna as claimed in claim 6 wherein the dipoles
`of the first Set of radiating elements are arranged to be
`greater than one wavelength long, in the frequency range of
`the Second set of radiating elements, and wherein a matching
`circuit is provided which is arranged to compensate for any
`inductive reactance in the frequency range of the first Set of
`radiating elements.
`8. An antenna in accordance with claim 1 wherein the
`frequency bands are determined by national regulations.
`9. An antenna according to claim 1 wherein the frequency
`bands comprise three operating bands, two of which are
`amalgamated.
`10. An antenna in accordance with claim 1 wherein either
`one or both of the frequency bands comprise two distinct
`operating bands, wherein the centre-band frequency is the
`average of the lowest frequency in the lower frequency
`operating band and the highest frequency in the upper
`frequency operating band.
`11. A base Station equipped with a dual band antenna
`comprising a first Set of radiating elements operable at a first
`frequency range having a centre-band wavelength ), and a
`centre-band frequency f;
`a Second Set of radiating elements operable at a Second
`frequency range having a centre-band wavelength ).
`and a centre-band frequency f.;
`and a ground plane;
`wherein the centre-band frequency f of the first fre
`quency range is of the order of 4–% of the centre-band
`frequency f. of the Second frequency range;
`wherein the first Set of radiating elements is arranged in
`two columns spaced less than 2 apart;
`wherein the Second Set of radiating elements are inter
`leaved around the two columns of the first set of
`radiating elements, the Second Set of radiating elements
`being spaced less than 2 apart; and
`wherein the elements are spaced apart from the around
`plane.
`
`9
`
`

`

`US 6,211,841 B1
`
`9
`12. A method of operating a dual band antenna, Said
`antenna comprising:
`a first Set of radiating elements operable at a first fre
`quency range having a centre-band wavelength ), and
`centre-band frequency f;
`a Second Set of radiating elements operable at a Second
`frequency range having a centre-band wavelength ).
`and a centre-band frequency f;
`and a ground plane;
`wherein the centre-band frequency f, of the first fre
`quency range is of the order of 4–% of the centre-band
`frequency f. of the Second frequency range;
`wherein the first Set of radiating elements is arranged in
`two columns spaced less than 2 apart;
`wherein the Second Set of radiating elements are inter
`leaved around the two columns of the first radiating
`
`10
`elements, the Second Set of radiating elements being
`Spaced less than 2 apart; and
`wherein the first and Second Sets of elements are spaced
`apart from the ground plane;
`wherein, in a transmit mode, the method comprises the
`Steps of feeding Signals to either of the first and Second
`Sets of ra