ACTIVE ANTENNA ARRAYS
Field of the Invention
The present invention relates to active antenna arrays for mobile
telecommunications systems.
Background Art
Active Antenna Arrays (AAA), otherwise known as smart antennas, have
recently gained popularity as candidate technology for base stations (BS) of
future cellular/mobile networks. In the context of AAA, each radiator of the BS
antenna array is fed by a dedicated RF transceiver /RF front-end, as shown in
Figure 1. In Figure 1, a base station 2 has an active antenna array comprising
a series of N antenna elements 4 1... 4N, each being coupled to a respective RF
transceiver 67....6 . Typically each RF transceiver comprises a transmit path
which includes a digital to analog converter DAC, a frequency up-conversion
stage and a power amplifier PA, and a receive path which includes a low noise
amplifier, a frequency down-conversion stage and an analog to digital converter
ADC. Appropriate phase shifts are applied, either in the transceivers, or in
baseband signal processing, to the transmit and receive paths of the array in
order to "steer" the antenna beam.
Current and future base stations may be required to support different
mobile telecommunication systems, e.g. 2G (e.g. GSM), 3G (e.g. WCDMA) or
4G (e.g. LTE), operating on different frequencies, which may be in a range from
400 MHz to 2.6 GHz.. This might require separate antenna array configurations
for each system, which is clearly costly and generally inconvenient
Summary of the Invention
The present invention provides an active antenna array, adapted for use
with a plurality of different mobile telecommunications systems, comprising:
a plurality of antenna elements, which are divided into a plurality of
antenna groups;
a plurality of transceivers, which are divided into a plurality of transceiver
groups equal in number to said plurality of different systems, each transceiver
group being adapted to operate on a respective mobile telecommunications
system of said plurality of different systems,
and including a feeding and phase shifting network coupled between said
transceivers and said antenna elements, whereby, for each said antenna group,
a member of each said transceiver group is selectively coupled to antenna
elements thereof.
As preferred, the transceivers are additionally formed into a plurality of
transceiver sets, each set comprising a member from each said transceiver
group, and each antenna group is coupled to a respective transceiver set.
In another aspect, the invention provides an active antenna array,
adapted for use with a plurality of different mobile telecommunications systems,
comprising:
a plurality of antenna elements, which are divided into a plurality of
antenna groups, each group comprising more than one antenna element;
a plurality of transceivers, which are divided into a plurality of transceiver
sets, wherein each transceiver of a transceiver set is adapted to operate on a
respective mobile telecommunications system of said plurality of different
systems;
and a feeding and phase shifting network,
wherein each transceiver set is coupled through the phase shifting
network to a respective antenna group, whereby at least one transceiver of the
transceiver set is selectively coupled to antenna elements of the respective
antenna group.
In at least an embodiment of the invention, the efficient design of multiband
(multi-band is the commonly used term for multiple mobile
telecommunication systems) active antenna arrays (AAA) is based on the fact
that the total number of RF transceivers required for the synthesis of multi-band
AAA can be reduced by employing one transceiver of each band/ system to
feed multiple antenna elements through either a passive or an active feeding
network. Therefore an advantage arises in that the amount of hardware,
weight, cost and complexity required for an AAA to operate with different mobile
telecommunications systems can be reduced where RF transceivers of each
band of the AAA coupled to the antenna elements are not allocated on a one to
one basis, but instead a phase shifting and feeding (multiplexing/
demultiplexing) network is provided so that each transceiver is coupled to more
than one antenna element. Although this may result in some diminution in
quality in some situations, it has been found that in the majority of practical
situations encountered, a diminution in quality is not significant.
In an embodiment, said phase shifting network is arranged such that for
each antenna group, a member of each transceiver set is coupled to each
antenna element of the antenna group via respective phase shifting elements.
In one embodiment, the total number of transceiver elements is equal to
the total number of antenna elements, because of commonly used
configurations of such arrays. However in other embodiments, different
numbers may be employed. It is preferred however that the total number of
antenna elements should be an exact multiple of the number of transceiver sets
so that each transceiver set is multiplexed to the same number of antenna
elements.
In further embodiments one or more transceivers of a transceiver set
may be decoupled from one or more antenna elements of the respective
antenna group.
In common situations, the number of different of mobile systems to be
serviced may be 2 (dual-band) or 3 (tri-band). The systems serviced may be of
any type in use or envisaged, e.g. GSM (2G), UMTS (WCDMA, 3G) and LTE
(4G). These systems may have operating frequencies in a wide frequency
range, for example for as low as 400 MHz to approaching 3 GHz. Since it is
difficult to devise a single antenna device that can operate satisfactorily over
such a large frequency range, it may be possible in accordance with the
invention to have each antenna element comprising more than one antenna
sub-element, each sub-element operating on a different part of the anticipated
frequency range. However in accordance with an embodiment, it is preferred to
have each antenna element formed as a single device which is sufficiently
wideband to cover a significant part of the total possible frequency range. As
preferred, it is proposed to have a first embodiment having antenna elements
which are responsive to frequencies between about 400 MHz and 1500 MHz. .
In another embodiment, higher frequencies between about 1,6 GHz and 2.7
GHz are covered by a single antenna element, which range includes 1.8, 1.9
GHz (GSM), 2.1 GHz (WCDMA), and 2.7 GHz for 4G systems such as LTE.
Said phase shifting network(s) may be divided into downlink paths
coupled to transceiver transmit paths, and uplink paths, coupled to the
transceiver receive paths. The downlink path may comprise power dividers in a
transmit path, coupled to each transceiver, for splitting the power from each
transceiver. These are normally passive devices such as Wilkinson power
dividers. Multiplexing units, which are also passive devices, may be connected
to the inputs of the antenna elements and arranged for receiving inputs from
various transceivers. The uplink path may include corresponding
demultiplexing devices coupled to the antenna elements and power combiners
coupled to the transceivers. The phase shifting devices, positioned between
power dividers/ combiners and multiplexing/demultiplexing units, may be
passive devices or active devices. For high power applications, e.g. powers of
the order of watts, passive devices are preferred since they have smaller
losses. For example transmission lines of a certain length may be employed,
which may be tunable, e.g. by having an adjustable dielectric filling. For low
power application such as e.g. 250 mW, active devices such as integrated
circuit phase shifting devices may be employed, which are tunable by means of
an applied voltage. These devices have insertion losses, for example about
3dB, which makes them unsuitable for high power applications.
The multiplexing/demultiplexing units may be different technologies such
as ceramic-based, cavity-based or microstrip-based, selected in accordance
with power requirements and the number of inputs required.
Brief Description of the Drawings
Embodiments of the invention will now be described, by way of example
only, with reference to the accompanying drawings, wherein:
Figure 1 is a diagram illustrating a known configuration of an active
antenna array employed in a base station of a mobile telecommunications
system;
Figure 2 is a diagram illustrating a configuration of an active antenna
array employed in a base station, for the purpose of explaining the present
invention, having a multi-band architecture;
Figure 3 is a schematic block diagram of a first embodiment of the
invention, showing an architecture for multi-band AAA in which a Passive
Feeding Network is employed;
Figure 4 is a schematic block diagram of a second embodiment of the
invention, showing an architecture for multi-band AAA in which an Active
Feeding Network is;
Figure 5 is block diagram of the feeding network incorporated in the
architectures of Fig. 3 and Fig. 4 . Phase shifters can be either passive
(passive feeding network of Fig. 3) or active (passive feeding network of Fig. 4)
Figure 6 is a schematic block diagram of a third embodiment, forming a
specific example of a dual-band AAA of the present invention;
Figure 7 is a block diagram of a module employed in the AAA of Fig. 6,
for the case of downlink transmission (Tx), for coupling two transceiver
elements operating on different bands to two antenna elements;
Figure 8 is a block diagram similar to Figure 7, for the case of uplink
reception (Rx), for coupling two transceiver elements to two antenna elements;
and
Figure 9 comprises graphs showing simulated performance of the
feeding network of Fig. 7 and 8 for a receiving antenna port and a transmitting
antenna port.
Description of an Embodiment
A design of a multi-band (m-band) AAA BS is shown in Fig 2, for
explanation of this invention (in this specification the term "band" is used to
denote a mobile telecommunications system, in accordance with common
parlance). N antenna elements 201. .2 0 V are provided, the same number as in
Figure 1. Each antenna element is fed from a set 221. ..22N, each set
comprising m dedicated RF front-ends (transceivers) 241... 24m, each front-end
designed to operate on a different band/system. Thus it may be seen that the
total number of transceivers is also divided into m groups, each group operating
on a respective system. Each feed set 221...22N is fed through a respective
multiplexing network 261...26N to a respective antenna element 201 ...20N.
The rest of the base station is indicated at 28.
Each transceiver 24 1...24m is commonly provided with a transmit path
which includes a digital to analog converter DAC, a frequency up-conversion
stage and a power amplifier PA, and a receive path which includes a low noise
amplifier, a frequency down-conversion stage and an analog to digital converter
ADC. Appropriate phase shifts are applied to the transmit and receive paths of
the array in order to "steer" the antenna beam. However for the purposes of
this specification, a "transceiver" will be understood to mean an RF unit which
includes a receive path and/or a transmit path, with appropriate reception and/or
transmission components.
In Figure 2, each antenna element of the BS antenna array (usually in
the form of a panel), is fed from m dedicated RF front-ends, each of them
designed to operate at a different frequency band. In that case, the RF signals
of each of the m RF front-ends 241 ...24m that feed the same antenna element
20/ have to be multiplexed on an RF multiplexer 26/, and also the antenna
element 20/ has to be wideband enough so that all the m-bands are included in
the antenna operating bandwidth.
The approach of Fig. 2 for the design of multi-band AAA has the main
disadvantage that for the synthesis of an m-band, N-antenna element AAA,
(mxN) RF front-ends are required. This increases significantly the cost of the
BS, the complexity of it, and also its weight and volume. For all these reasons,
more efficient architectures for multi-band AAA are preferred.
In the following Figures, similar parts to those of Figure 2 are denoted by
the same reference numerals.
Figure 3 is a schematic block diagram of a first embodiment of the
invention, showing an architecture for multi-band AAA in which a respective
Passive Feeding Network is employed, to distribute and multiplex/demultiplex
the transmit/receive RF signals of m RF transceivers (each of them operating at
a different band) to/from M wideband antenna elements. Figure 4 is a
schematic block diagram of a second embodiment of the invention, showing an
architecture for multi-band AAA in which a respective Active Feeding Network is
employed to distribute and multiplex/demultiplex the transmit/receive RF signals
of RF transceivers (each of them operating at a different band) to/from M
wideband antenna elements.
In Figures 3 and 4 , an AAA supports m bands, while an antenna panel is
composed of N radiating or antenna elements 201... 20N. According to the AAA
architecture, the N antenna elements are grouped in (N/M) sets or groups 30 of
M elements 201. ..20M, 20M+1 ...202M, etc. (for this reason the modulus of N/M
should be zero). Then, each of these groups 30 is fed by either a passive
(Figure 3) network 321..32(N/M) or active feeding network (Figure 4)
341...34(N/M). (Passive and active feeding networks are characterized by
phase shifting devices in the networks being active or passive in construction).
The inputs of each feeding network 32 or 34 are respectively coupled to a set
221...22N/M of RF transceivers 24 ...24m, each transceiver of a set
designed to operate at one of the m different systems (bands) that are
supported by the AAA. In the general case, the number of mobile
telecommunication systems m supported by the AAA (and hence the number of
independent transceivers that feed each feeding network) and the number of
antenna elements M fed by the same feeding network are completely
independent from each other, and it could be either smaller (mM).
The functionality of the feeding networks 32, 34 is depicted in the block
diagram of Fig. 5, which is a block diagram of a single feeding phase shifting
network for both transmit signals and receive signals. For the case of downlink
transmission (Tx-mode) from the base station, in the first stage of the feeding
network the RF transmit signals of each of the m transceivers are divided in M
copies by 1:M power dividers 50. Then, each copy is phase-shifted by an
appropriate amount by a corresponding phase-shifter i ,j 52. Finally, M
multiplexers 54 are provided coupled to respective antenna elements
207....20M, and which receive a phase shifted signal from each power divider
50. Thus all the RF phase shifted signals (different bands) which are to be
transmitted into the same antenna element are multiplexed before being fed in
the wideband antenna element. In the case of uplink operation (Rx-mode) of
the base station, the reciprocal functionality is implemented, in that multiplexers
54 function as demultiplexers for received signals, and power dividers 50
function as power combiners. It is important to note that all the components
before the multiplexers are single-band components, the multiplexers are multiband,
and the antenna elements are the only components that have to be
wideband.
The first RF components of the proposed passive o r active feeding
networks 32, 34 are the 1:M power divider/combiners. These are passive twoway
components and could be either perfectly balanced or unbalanced,
preferably implementing amplitude tapering for the antenna elements of the
same group 30.
The phase-shifters i ,j 52 of the feeding network are used to maintain a
certain phase progression per band across the antenna elements fed through
the same feeding network ( beam steering applications). In the general case of
an AAA similar with that of Fig. 1 or Fig. 2 , the phase-shift required (per band)
between consecutive antenna elements to achieve a certain beam scanning
angle would be set actively by N independent transceivers of the same band,
This can be achieved e.g. by shifting the phase either in the digital domain of
the transmitter or in the RF-section of the transmitter, The same is valid for the
receive path. In the case of the architecture of Figures 3 and 4 , there are only
N/M independent transceivers per band that can maintain (in the digital domain
or in the RF-section of the transceiver) the phase progression required to
achieve a certain beam scanning angle. Given that each of these transceivers
will feed M consecutive antenna elements, the phase-shifts that can be set by
the independent transceivers should equal to M times the phase progression
required between adjacent antenna elements to maintain a certain beam
scanning angle. Then the phase-shifters i 52 of the feeding network should
be used to maintain the phase progression required between the consecutive
antenna elements of the same group 30. In the case of a high-power AAA,
employed in macro-cell deployments, in which the beam scanning requirements
are limited (i.e. 0 0 -10° off-broadside) it can be shown that passive components
such as passive microwave transmission lines, designed to provide a
progressive phase-shift in the middle of the phase-shifts range required to
achieve all the beam scanning angles needed, can provide an adequately good
solution. In this case, the feeding network can be exclusively passive (Fig. 3),
since power dividers and multiplexers are usually passive devices.
Furthermore, in this case, the passive feeding network is a two-way microwave
circuit and, therefore, a single network could be used both for the downlink (Tx)
and the uplink (RX).
Nevertheless, in applications that require large beam scanning angles,
such as AAA for small-cell deployments, multi-sector deployments etc, a
passive solution for the phase-shifters is not adequate. Instead, the phaseshifters
should be active (voltage controlled chips) and should be controlled by
the transceivers of the bands that are feeding RF signals into the feeding
network. In that case, the feeding network will be an active one (Fig. 4). It is
noted that such active RF phase-shifters are usually lossy (e.g. <50 %
efficiency). Nevertheless, in the context of low-power AAA (of the order of 250
mW) such lossy components are not necessarily completely out of context.
Finally, given that active RF phase-shifters are usually one-way devices, two
feeding networks are required per group of antenna elements; one for downlink
(Tx) and one for uplink (Rx).
As regards the RF multiplexers/demultiplexers of Figure 5, the required
operation of these devices is much dependent on the specific AAA architecture
and the exact system configuration. In the most generic case that can be
envisaged (all the bands under consideration feeding in the same antenna),
these multiplexers/demultiplexers have to multiplex/demultiplex all the Tx and
Rx RF signals of all the bands under consideration. For the case of an FDD
(Frequency multiplex) system, in which the Tx and Rx signals are assigned on
different frequency bands , this device should multiplex/demultiplex 2m different
bands. Another approach could be that this device only multiplex/demultiplex
the entire m bands of the multi-band AAA ('entire bands' meaning that both the
Tx and Rx spectrum are included in the total spectrum of each multiplexed
band). In that case, conventional duplexing devices would be required at the
RF front-end (RF chains) of each of the bands for duplexing Tx and Rx signals
(for the case of an FDD system). Nevertheless, other cases for the exact
operation of the multiplexing devices can be also considered, depending on the
exact AAA architecture. One such case will be discussed in the following
example.
Referring to Figure 6, an embodiment of dual band (m=2) AAA is
presented. The two bands of interests are 2.1 GHz for UMTS deployment (DL:
2.1 1 - 2.17 GHz, UL: 1.92-1 .98 GHz ) and 2.6 GHz for LTE deployment (DL:
2.62 - 2.19 GHz, UL: 2.50-2.57 GHz). The AAA is composed of N=8 radiating
elements (in the general case N should be any even number), while the
antenna elements are grouped in pairs (M=2). For this specific case m=M. The
employed radiating elements are wideband, dual-polarized, while one
polarization (+45°) is employed for downlink transmission (Tx port / +45°) and
the orthogonal (-45°) for uplink reception (Rx port) (this assumption has an
impact on the operation of the multiplexing devices of the passive/active feeding
network).
In Fig. 6, 4 modules 60 are each composed of a transceiver set 227224
comprising a pair of RF front-ends 247, 242 (one for 2.1 GHz and one for 2.6
GHz), a feeding and phase shifting network 327. .324 and a pair of antenna
elements 207,202 of each antenna group 30. For this implementation, block
diagrams of each of these modules 60 are shown in Fig. 7 and Fig. 8,
comprising downlink (Tx) and the uplink (Rx) circuits, respectively.
Referring to Figure 7, transceiver 247 comprises a section 70 for UMTS
IF and BB signals, followed by a transmitter section 72. Transceiver 242
comprises a section 74 for LTE IF and BB signals, followed by a transmitter
section 72. Each transmitter section 72 comprises I and Q paths 76, 78,
including DAC 80, multipliers 82, where the base band signal is multiplied by a
phase shifted IF signal from LO 84, which is phase shifted at 86, 88. The IQ
signals are combined at 90 and fed to a power amplifier 92.
In Figure 7, the output of the two power amplifiers 92 (at 2.1 GHz
(UMTS) and 2.6 GHz (LTE), respectively), without being filtered, are provided to
a phase shifting transmit network 321 T, where the outputs are divided at power
dividers 96 and outputs thereof are appropriately phase-shifted in phase shifters
98, 99. Duplexers 100 receive signals from each power divider, and a
combined signal from the two transceivers is fed from each duplexer to the
appropriate antenna element 207,202. In this case each antenna element is a
dual polarized antenna, and the output signal is applied to one of the two
orthogonal polarizations of the antenna elements 201, 202, in this case the +45°
input of antenna element 201, and the +45° input of antenna element 202.
For the case of uplink reception shown in Figure 8, similar parts to those
of Figure 7 are denoted by the same reference numerals. Transmit sections 72
are replaced by receive sections 120, and the phase shifting network 32 1 is
changed from a dividing and multiplexing function 32 1T to a demultiplexing and
combining function 321R. The received signals at the polarization ports -45° of
the two antenna elements 201,202 are demultiplexed at 102 by a reverse
reciprocal process to that of Figure 7, to the received signal at the 1.9 GHz
(UMTS) band and that at the 2.5 GHz (LTE) band, then the signals are phaseshifted
at 104, 106, and finally the signals of the same band are combined in
power combiners 108 before being amplified at 110 in LNAs (low noise
amplifiers) of each receiver 120 (depending on the exact system configuration
the LNAs could be placed immediately after the demultiplexers). . The output of
each LNA is split into two IQ paths 76, 78, where the signals are converted to
base band at 82, 84,86,88, and applied to ADCs 112.
Given that the Tx and Rx operations are considered on different antenna
polarizations (and hence different antenna ports), the Tx feeding network is
completely independent from the Rx feeding network. Nevertheless, the
employed multiplexing/demultiplexing devices should also provide the required
isolation between the Tx and the Rx signals of the same band. For example,
the duplexing devices in Fig. 7 (downlink), apart from the isolation between the
two Tx signals, should also provide the required isolation between the TX
signals of both bands to the corresponding Rx signals. It is significant to note
that such multiplexing units will receive downlink signals from different mobile
telecommunication systems, that such demultiplexing units will receive uplink
signals from different mobile telecommunication systems, and therefore these
signals will be widely spaced in frequency. This therefore simplifies the
construction of such units, since filtering requirements are reduced as
compared with the common multiplexing situation, where all multiplexed signals
are on the same frequency band.
ln order to manifest the aforementioned requirements, the results of the
simulation of the passive feeding networks of Fig. 7 and Fig. 8 are presented in
Fig. 9. For this simulation, all the power combiner/dividers, the phase-shifters
and the duplexers are all designed as passive components. Specifically,
regarding the duplexers, they are ceramic diplexers. Specifically, in Fig. 9, the
performance (S-parameters) of the passive feeding networks of Fig. 8 (receiving
antenna port) and Fig. 7 (transmitting antenna port), respectively, are
presented. These results shown that, for example, at the downlink transmission
case (Fig. 7) not only the Tx signals of the two bands are adequately isolated,
but also good isolation between the UMTS Tx and Rx signals and the LTE Tx
and Rx signals is achieved. Similar performance is achieved for the Rx cases.
An advantage of the above described embodiments is the design and
implementation of multi-band or multi-system AAA with a reduced number of
transceivers in order to reduce the weight, cost and complexity of the overall
AAA.
The description and drawings merely illustrate the principles of the
invention. It will thus be appreciated that those skilled in the art will be able to
devise various arrangements that, although not explicitly described or shown
herein, embody the principles of the invention and are included within its spirit
and scope. Furthermore, all examples recited herein are principally intended
expressly to be only for pedagogical purposes to aid the reader in
understanding the principles of the invention and the concepts contributed by
the inventors to furthering the art, and are to be construed as being without
limitation to such specifically recited examples and conditions. Moreover, all
statements herein reciting principles, aspects, and embodiments of the
invention, as well as specific examples thereof, are intended to encompass
equivalents thereof.
CLAIMS:
. An antenna array, adapted for use with a plurality of different
mobile telecommunications systems, comprising:
a plurality of antenna elements (201 ...20N), which are divided into a plurality of
antenna groups (30), each group comprising more than one antenna element
(201 ..20M);
a plurality of feeding and phase shifting networks (321 ,341 ..32,34(N/M));
characterized in that
the antenna array is an active antenna array, and includes a plurality of
transceivers, which are divided into a plurality of transceiver sets (221 ..22N/M),
each set comprising more than one transceiver (241 ..24m), and wherein each
transceiver of a transceiver set is adapted to operate on a respective mobile
telecommunications system of said plurality of different systems (m);
wherein each transceiver set is coupled through a respective feeding and phase
shifting network to a respective antenna group, so that each transceiver of a
transceiver set is coupled to each antenna element of the respective antenna
group in order to provide an active antenna array, generating a predetermined
phase progression of antenna signal across adjacent elements of said plurality
of antenna elements.
2. An active antenna array as claimed in claim 1, wherein selected
members of the respective said transceiver set are coupled to each antenna
element of the antenna group via a respective phase shifting device (52, 98, 99,
104, 106) in order to generate said predetermined phase progression.
3. An active antenna array according to any preceding claim,
wherein each transceiver set comprises two transceivers which serve a
respective system of two systems, preferably a UMTS system and an LTE
system, and each said antenna group comprises two antenna elements.
4. An active antenna array according to any preceding claim,
wherein each phase shifting network includes an uplink path (321 ) and a
downlink path (321 T), and for the downlink path, one or more multiplexing
devices (100), each of which is coupled to an antenna element to receive a
plurality of downlink signals of different mobile phone systems from different
transceivers of a said set.
5. An active antenna array according to any preceding claim,
wherein each phase shifting network includes an uplink path (321 R) and a
downlink path (321T), and for the uplink path, one or more multiplexing devices
(102), each of which is coupled to an antenna element to feed a plurality of
uplink signals of different mobile phone systems to different transceivers of a
said set.
6. An active antenna array according to claim 4, wherein each phase
shifting network includes a downlink path (321 T), which includes power dividers
(96) coupled to said transceivers, multiplexers (100) coupled to said antenna
elements, and phase shifting devices (98, 99) selectively coupled between said
power dividers and multiplexers.
7. An active antenna array according to claim 5, wherein each phase
shifting network includes an uplink path (321 R), which includes power
combiners (108) coupled to said transceivers, demultiplexers (102) coupled to
said antenna elements, and phase shifting devices (104, 06) selectively
coupled between said power dividers and demultiplexers.
8. An active antenna array according to any preceding claim,
wherein the phase shifting network includes active phase shifting devices (52),
preferably integrated circuit elements.
9. An active antenna array according to any of claims 1 to 7, wherein
the phase shifting network includes passive phase shifting devices (52),
preferably transmission line lengths.
10. An active antenna array according to any preceding claim,
wherein each said antenna element is a dual polarised antenna (201 , 202),
wherein one polarisation is coupled to a transmit path of the respective
transceivers, and the other polarisation is coupled to the receive path of the
respective transceivers.
11. An active antenna array according to any preceding claim,
wherein each said antenna element is sufficiently wideband to cover at least
part of operating frequencies of said plurality of different systems.