Field of the invention
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The invention relates to a radio unit and an antenna arrangement therefor and in
particular to an antenna arrangement suitable for two or more frequency ranges.
Background of the Invention
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In the last century, radio transmission of modulated signals has become one of the
must widespread means for communication over distance. In recent years, the use of
radio communication has become even more ubiquitous with the advent of e.g.
wireless local networks and mobile telephones.
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A key parameter in radio communication systems is the design of the antennas
which translate between electrical signals in wires and components and
electromagnetic waves which propagate through space. The performance and
efficiency of a radio communication system is heavily dependent on the
performance of the antennas and therefore much research into optimal antenna
structures have been carried out over the years.
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In recent years, the increased use of radio communication for small portable radio
units, such as mobile phones, has led to increased research into antenna structures
suitable for this purpose. For example, in order to obtain a low form factor for
mobile phones, significant research has been undertaking in order to develop small
antenna structures that operate efficiently.
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In addition, the complexity of radio units tends to increase and nowadays radio units
typically serve multiple purposes. For example, mobile phones capable of operating
on different frequency bands have become commonplace. As another example,
many mobile phones are likely to in the near future have built in satellite location
functionality based on the Global Positioning System (GPS).
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Accordingly, it is currently desirable to develop practical and efficient multi band or
frequency antennas which can operate in a plurality of different frequency ranges.
For example, for a combined portable radio communication unit with a built in GPS
receiver, it is desirable to have a multi band antenna capable of efficient reception at
both around e.g. 400MHz and 1575 MHz.
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Conventionally, multi band antennas for such purposes are formed by implementing
two or more decoupled resonators within a single housing and connecting the
antenna connector to both resonators. Typically, a substantially helical coil antenna
element is combined with a straight quarterwave wire antenna element with the
endpoints electrically connected to each other and the antenna connector. Thus, a
transmit signal fed to the antenna will be galvanically fed to both antenna elements
although radiation will predominantly be from the resonator tuned to the frequency
of the transmit signal.
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However, such a structure has a number of associated disadvantages.
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Firstly, the resonators tend to be coupled due to the close proximity and the small
size of the structure. Although the design process seeks to minimise this coupling, it
cannot be avoided and it furthermore limits the design freedom of the antenna
structure. Specifically, in order to maintain low coupling, the antenna structure
typically comprises a substantially helical coil for the lowest frequency combined
with a straight wire resonator for the higher frequency. A second substantially
helical coil for the higher frequency would typically result in too strong a coupling.
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Accordingly, the size of the antenna arrangement is relatively large which is
particularly undesirable for portable applications.
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Furthermore, such antenna structures must be designed very carefully in order to
reduce coupling. Therefore, the addition of a new or different frequency range
requires not only a new antenna element to be designed but also a redesign of the
entire antenna structure with specific consideration to minimising coupling.
Typically, a complete structural redesign is needed. Accordingly this is a very
inflexible approach which requires dedicated antenna structures for radio units
depending on the exact frequency bands that must be covered.
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Also, due to the interdependence between the different antenna elements, a
complicated design process is required. Specifically, any modifications to one
antenna element may affect the performance of other antenna elements and this must
be taken into account in the design.
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Hence, an improved antenna arrangement for a radio unit would be advantageous
and in particular an antenna arrangement allowing for increased flexibility, reduced
size, facilitated redesign, simplified and reduced cost manufacturing, improved
upgradeability and/or improved performance would be advantageous.
Summary of the Invention
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Accordingly, the Invention seeks to preferably mitigate, alleviate or eliminate one or
more of the above mentioned disadvantages singly or in any combination.
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According to a first aspect of the invention there is provided an antenna arrangement
comprising: a first resonator having an associated first resonance frequency; and a
second resonator having an associated second resonance frequency and comprising a
and a coupling section coupled to the first resonator for coupling a signal between
the first and second resonator; and wherein the first and second resonators are
galvanically isolated from each other and are coupled to each other by a transformer
coupling.
The second resonator may include a radiating section additional to the coupling
section.
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Thus, the invention may provide a multi band antenna arrangement wherein the first
resonator is suitable for receiving and/or transmitting radio signals in a frequency
range around the first resonance frequency and the second resonator is suitable for
receiving and/or transmitting radio signals in a frequency range around the second
resonance frequency. The first resonator may thus provide a first antenna element
for a first frequency range and the second resonator provides a second antenna
element for a second frequency range.
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The coupling section of the second resonator provides a relatively strong coupling to
the first resonator but may provide only a relatively weak radiating effect whereas
the radiating section may provide a relatively low coupling but a strong radiating
effect. Specifically, the radiating effect of the second resonator may be substantially
exclusively provided by the radiating section and the coupling may be substantially
exclusively provided by the coupling section.
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The term 'radiating' is used as a common term for both the receiving and
transmitting antenna performance, i.e. the radiating section may be operable to
generate an electromagnetic signal from an electrical current as well as generate an
electrical current from a received electromagnetic signal. The coupling may thus be
from the first resonator to the second resonator or from the second resonator to the
first resonator.
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The antenna arrangement uses a magnetic coupling between the first and second
resonator to transfer signals to and from the second resonator similar to a
transformer coupling. Accordingly, the antenna arrangement preferably has a strong
magnetic coupling between the first resonator and the coupling section of the second
resonator. Therefore, it is not necessary to minimise coupling between the first and
second resonator and the antenna arrangement is much less sensitive to the effect of
one resonator on the other resonator.
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Specifically, the invention may allow increased design freedom and reduced
interdependence between the design of the first and second resonator. Specifically,
the second resonator may simply be located close to the first resonator to achieve the
desired coupling while not significantly affecting the performance of the first
resonator. Thus, the galvanic isolation and reduced interdependence between
resonators allows an antenna arrangement wherein additional frequency bands may
be covered by simply adding an additional resonator without redesigning the first
resonator. Thus, all that is required is the physical proximity between the first and
second resonator.
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Hence, a simple, low cost antenna arrangement may be provided which is flexible
and allows for easy upgradeability and/or facilitated re-design for new frequency
bands.
-
Furthermore, the reduced interdependence between the first and second resonator
provides increased design freedom which for example may be used to reduce the
size of the antenna arrangement.
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According to a feature of the invention, the antenna arrangement comprises a first
antenna housing element comprising the first resonator and a second antenna
housing element comprising the second resonator wherein the second antenna
housing element is detachable from the first antenna housing element.
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This provides for a particularly advantageous implementation. Specifically, this may
provide for easy manufacturing and a high degree of flexibility. For example,
different housing elements may be manufactured individually comprising resonators
for different frequencies. A desired frequency performance of the antenna
arrangement may be achieved simply by combining the appropriate housing
elements. Thus, a desirable antenna arrangement may be implemented by simply
selecting and joining the appropriate building blocks in the form of antenna housing
elements comprising suitable resonators.
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According to a different feature of the invention, the second antenna housing
element is operable to be substantially friction mounted on the first antenna housing
element.
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This provides for a particularly simple and efficient way of implementing the
antenna arrangement which provides a high degree of flexibility.
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According to a different feature of the invention, the second housing element
provides galvanic isolation of the second resonator.
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Preferably the second housing element is made out of an isolating material and the
second resonator is preferably completely contained in this material. For example,
the resonator may be enclosed in a second antenna housing element by injection
moulding. The same approach may be used for the first resonator and antenna
housing element. This provides for an easy to manufacture, robust and/or efficient
implementation providing the desired galvanic isolation.
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According to a different feature of the invention, the first resonator comprises a
substantially helical coil. This is a particularly suitable implementation of the first
resonator which typically tends to reduce the size of the antenna arrangement. The
resonator may for example be substantially formed by a helical coil or only part of
the resonator may be in the form of a substantially helical coil.
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According to a different feature of the invention, the radiating section comprises a
substantially helical coil. This is a particularly suitable implementation of the second
resonator which typically tends to reduce the size of the antenna arrangement. The
radiating section may for example be substantially formed by a helical coil or only
part of the radiating section may be in the form of a substantially helical coil.
Preferably, both the first and second resonators comprise substantially helical coils
resulting in an antenna arrangement of small dimensions which is particularly
suitable for a portable radio unit.
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According to a different feature of the invention, the second resonator is located
inside the first resonator.
-
Specifically, the second antenna housing element may simply be placed inside the
first antenna housing element. For example, if the first resonator is a substantially
helical coil, the second resonator may be located within the substantially helical coil.
This is a particularly practical implementation for many applications.
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According to a different feature of the invention the second resonator is located
outside the first resonator. Specifically, the second antenna housing element may
simply be placed around the first antenna housing element. For example, if the
second resonator is a substantially helical coil, the first resonator may be located
within the substantially helical coil. This is a particularly practical implementation
for many applications.
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According to a different feature of the invention, the first resonance frequency is
associated with a cellular communication system frequency and the second
resonance frequency is associated with a Global Positioning System (GPS)
frequency. The invention may provide a suitable antenna arrangement e.g. for a
combined cellular communication unit and GPS unit.
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According to a different feature of the invention, the antenna arrangement further
comprises a third resonator having an associated third resonance frequency; wherein
the first, second and third resonator are magnetically coupled and galvanically
isolated from each other.
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The antenna arrangement is suitable for multi band radio units and may easily be
modified to provide efficient antenna performance on three or more different
frequency bands.
-
According to a different feature of the invention, the antenna arrangement further
comprises a magnetic element operable to increase the magnetic coupling between
the first and second resonator.
-
This may allow increased coupling which improves performance and reduces losses
associated with the coupling of the first and second resonator. The magnetic element
may be particularly suitable for lower frequencies where losses in magnetic elements
tend to be lower.
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According to a different feature of the invention, the antenna arrangement comprises
a single galvanic antenna connector connected only to the first resonator. Preferably
only one galvanic connection exists for coupling the antenna to a receiver and/or
transmitter.
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According to a different feature of the invention, the coupling section is located
towards an end of the first resonator connected to the antenna connector. This
provides a particularly suitable implementation and improves the coupling of the
signal between the first and second resonator.
-
According to a different feature of the invention, the coupling section and the
radiating section is formed by a single conductive wire. This provides for a
particularly simple, easy to manufacture and/or low cost implementation.
-
The antenna arrangement may preferably be comprised in a radio unit.
-
According to a different feature of the invention, the first resonator is galvanically
coupled to a transmitter for feeding a signal to the antenna arrangement, and the
antenna arrangement is operable predominantly radiate frequencies of the signal in a
first frequency range around the first resonance frequency from the first resonator
and to predominantly radiate frequencies of the signal in a second frequency range
around the second resonance frequency from the second resonator.
-
The antenna arrangement is suitable for operating as a transmit antenna. The
magnetic coupling provides the signal energy of the second frequency range to the
second resonator from where it is effectively radiated.
-
The signal fed to the antenna arrangement does not necessarily contain energy in
both the first and second frequency ranges simultaneously although it may do so.
Specifically, the transmit signal may be a dual band signal having simultaneous dual
band transmissions or non-simultaneous dual band transmissions.
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According to a different feature of the invention, the first resonator is galvanically
coupled to a receiver and the radio signals in a first frequency range around the first
resonance frequency is predominantly received by the first resonator and radio
signals in a second frequency range around the second resonance frequency is
predominantly received by the second resonator.
-
The antenna arrangement is suitable for operating as a receive antenna. The
magnetic coupling provides the signal energy of the second frequency range from
the second resonator to the receiver.
-
According to a different feature of the invention, the radio unit comprises a radio
unit housing and the first resonator is internal to the radio unit housing and the
second resonator is comprised in an antenna housing element external to the radio
unit housing.
-
This may provide for a simple way of upgrading a single band receiver being
designed with an internal antenna. Specifically, the antenna functionality required
for supporting a second frequency band may simply be achieved by adding an
antenna housing element comprising the second resonator to the existing radio unit.
Thus, no redesign of the radio unit is required.
-
Preferably the radio unit is a portable radio unit.
-
These and other aspects, features and advantages of the invention will be apparent
from and elucidated with reference to the embodiment(s) described hereinafter.
Brief Description of the Drawings
-
An embodiment of the invention will be described, by way of example only, with
reference to the drawings, in which
- FIG. 1 illustrates an implementation of an antenna arrangement for a two band radio
unit in accordance with prior art;
- FIG. 2 illustrates an example of an antenna arrangement in accordance with an
embodiment of the invention;
- FIG. 3 illustrates an antenna arrangement comprising antenna housing elements in
accordance with an embodiment of the invention; and
- FIG. 4 illustrates a radio unit in accordance with an embodiment of the invention.
-
Detailed Description of an Embodiment of the Invention
-
The following description focuses on an embodiment of the invention applicable to a
portable radio unit comprising a cellular communication system radio unit operating
in the 400 MHz frequency band and a Global Positioning System (GPS) receiver
operating in the 1575 MHz frequency band.
However, it will be appreciated that the invention is not limited to this application
but may be applied to many other radio communication applications.
-
Antennas for multiple frequency radios are required to have more than one
resonance in order to efficiently accommodate several frequency ranges. This is
conventionally achieved by adding a second decoupled resonator within the antenna
to provide coverage for the second frequency band.
-
FIG. 1 illustrates an implementation of an antenna arrangement for a two band radio
unit in accordance with the prior art. The antenna arrangement uses two decoupled
and connected resonators to provide frequency coverage of the two distinct
frequency bands around 400MHz and 1575 MHz respectively.
-
The antenna arrangement 100 comprises a first resonator 101 for covering the 400
MHz frequency band. The first resonator is galvanically coupled to a transceiver 103
though a suitable connector 105 and transmission line. The first resonator is a helical
coil in order to reduce the size of the antenna arrangement.
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In order to cover the 1575MHz band, a second resonator 107 has been added. The
second resonator 107 is also connected to the transceiver 103 through the connector
105. Thus, the first and second resonators 101, 107 are electrically connected at one
end. In order to reduce the coupling between the antenna elements, the second
resonator is typically designed as a straight quarter wave wire antenna since for
example a helical coil would result in a strong coupling to the first resonator 101.
Specifically, the second resonator should be orthogonal to the first resonator and
therefore the design freedom for designing the second resonator is very limited.
-
Accordingly, a conventional multi band antenna arrangement is typically of an
undesirable large size. For example, to cover the frequency bands of 400MHz and
1575 MHz an antenna arrangement having a length of 5 cm is typically required.
-
Also, the addition of the second resonator 107 affects the performance of the first
resonator 101 and requires this to be retuned since both resonators are coupled
directly to the same feed. Additional resonance with a third resonator would further
require redesign and retuning of all three resonators and typically a complete
structural redesign would be required.
-
FIG. 2 illustrates an example of an antenna arrangement 200 in accordance with an
embodiment of the invention.
-
Similarly to the antenna arrangement 100 of FIG. 1, the antenna arrangement 200 of
FIG. 2 comprises a first resonator 201 which is connected to a transceiver 203
through a connector 205. The first resonator 203 is in the specific embodiment a
helical coil having a resonance frequency of around 400 MHz.
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In addition, the antenna arrangement 200 comprises a second resonator 207 which is
tuned to a second resonance frequency of 1575 MHz. However, in contrast to the
antenna arrangement 100 of FIG. 1, the second resonator 207 of FIG. 2 is not
electrically connected to the connector or to the transceiver 203. Rather the first and
second resonators 201, 207 are galvanically isolated from each other.
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Furthermore, in contrast to the arrangement of FIG. 1, the first and second resonators
201, 207 are not orthogonal but are rather magnetically coupled to each other.
Specifically, the first and second resonators 201, 207 are magnetically coupled
through a coupling section 209 of the second resonator. Accordingly, a current
variant in one resonator will cause a magnetic field fluctuation that will result in a
varying current being induced in the other resonator. Hence, the coupling between
the first and second resonators 201, 207 provides a transformer effect allowing for
signals to be coupled from one resonator to the other.
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The second resonator 207 further comprises a radiating section 211. The radiating
section 211 and coupling section is preferable made from a single wire. For
example, the coupling section 209 may be formed by a tightly wound wire and the
radiating section 211 may be formed by a straight section or a very loosely wound
section of the same wire.
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When a signal is coupled to the coupling section 209 of the second resonator 207, a
current will be induced. As this current flows in the radiating section 211, a strong
electromagnetic signal will be transmitted. Likewise, when receiving a signal, an
electromagnetic current will flow in the radiating section 211 and thus in the
coupling section 209 thereby resulting in the received signal being coupled to the
first resonator.
-
The first and second resonators 201, 207 are in the embodiment of FIG. 2 comprised
in the same housing and may for example be formed by injection moulding
techniques as is well known in the art.
-
The antenna arrangement 200 of FIG. 2 provides for an efficient antenna
arrangement that may conveniently be designed or modified for operation on
different frequencies. Specifically, as the first and second resonator 201, 207 are
strongly coupled, the resonators 201, 207 are not designed to be orthogonal and
accordingly may be designed without this restriction.
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Furthermore, as the first and second resonators 201, 207 are not galvanically
connected to each other and the transceiver, the interdependence between the
resonators is greatly reduced. Accordingly, the first and second resonator may be
individually designed without consideration of the other resonator. Specifically, the
embodiment provides for separate control over the resonance frequencies of the first
and second resonators 201, 207. The separation of the second resonator into a
coupling section and radiating section and the therewith associated separation of
functionality provides an increased design freedom and reduced interdependence
between the first and second resonator.
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The first and second resonators 201, 207 may for example both be designed fully or
partially as substantially helical coils thereby resulting in the length of the antenna
arrangement 200 being substantially reduced. The antenna arrangement is therefore
particularly suitable for portable radio units. Furthermore, the reduced
interdependence results in modifications to one resonator not requiring
modifications to the other resonator. Thus, the design and dimensioning is
significantly facilitated and the flexibility is increased allowing for modifications to
be introduced which only affect the resonator being modified.
-
Accordingly, in the antenna arrangement of FIG. 2, transformer coupling of the
different resonators is utilised in order to achieve separate control over resonance
frequencies (and thus the length) of the resonators thereby making shorter antenna
possible. Furthermore, by utilising the transformer principle, no galvanic connection
is required between resonators and an additional resonance may easily be added.
-
As a specific example, the first resonator 201 may be a substantially helical coil and
the second resonator 207 may be comprise a half wave wire having approximately
1/3 wavelength of the wire formed as a substantially helical coil situated within the
substantially helical coil of the first resonator 201. In this case, the substantially
helical coil will form the coupling section and the remaining straight wire will form
the radiating section.
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The first and second resonators may be comprised in different antenna housing
elements which preferably are detachable with respect to each other. FIG. 3
illustrates a cross section of an antenna arrangement 300 comprising antenna
housing elements 301, 303 in accordance with an embodiment of the invention. The
antenna arrangement 300 comprises a first antenna housing element 301 comprising
the first resonator and a second antenna housing element 303 comprising the second
resonator. FIG. 3 illustrates a helical coil of the first resonator and specifically shows
the wire in cross section when going into the figure 305 and coming out of the figure
307.
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FIG. 3 furthermore illustrates a second resonator wire 309 having a length
substantially equal to half a wavelength of the resonance frequency of the second
resonator. Part of the second resonator wire 309 is formed as a helical coil to reduce
the length of the antenna arrangement 300 and to provide the coupling section. In the
example of FIG. 3, the first resonator is completely enclosed in the first antenna
housing element 301 and the second resonator is completely enclosed in the second
antenna housing element 303. The antenna housing elements 301, 303 are in the
example made of an electrically isolating material and thereby provide galvanic
isolation of the resonators. However, the first resonator is electrically connected to
an antenna connector (not shown) for connection to a suitable radio unit.
-
In the antenna arrangement of FIG. 3, the first and second antenna housing element
301, 303 are separate elements that may be detached from each other. Specifically,
the first housing element 301 comprises an inner bore 311 into which the second
housing element 303 may be inserted. In some embodiments, the first and second
antenna housing elements 301, 303 may be made from resilient materials allowing
for a friction fit between the antenna housing elements 301, 303. However, in the
illustrated embodiment, the bore 311 of the first housing element 301 comprises a
thread and the external circumference of the second antenna housing element 303
comprises a complementary thread thereby allowing the second antenna housing
element 303 to be screwed into the first antenna housing element 301.
-
The structure of FIG. 3 provides for a very flexible approach wherein an antenna
arrangement may be easily customised or modified. For example, manufacturing of
a range of different antennas may be simplified by manufacturing a number of
antenna housing elements shaped as the first antenna housing element 301 and a
number of antenna housing elements shaped as the second antenna housing element
303. A given two band antenna arrangement may then be implemented simply be
selecting two antenna housing elements having the appropriate resonance
frequencies and combining these. Furthermore, new frequency bands may easily be
added to the range simply be manufacturing an antenna housing element comprising
a resonator suitable for the new frequency band. This new antenna housing element
may be used with all the existing antenna housing elements without requiring any
redesign.
-
In the example of FIG. 3, the second resonator is located inside the first resonator,
i.e. the second antenna housing element 303 is inserted into the first antenna housing
element 301. However, in other embodiments, it may be advantageous to locate the
second resonator outside the first resonator.
-
FIG. 4 illustrates a radio unit 400 in accordance with an embodiment of the
invention. In the example of FIG. 4, the second resonator is located outside the first
resonator.
-
The radio unit 400 comprises a housing 401 forming the outer shell of the
functionality of the radio unit 400. A first antenna housing element 403 is attached
to the housing 401 or may be formed as an integral part of the housing 401. The first
antenna housing element 403 comprises a first resonator 405 tuned to a first
resonance frequency. The first resonator 405 is connected to a transceiver 407
though a connector 409. A radio unit 400 comprising these parts may be arranged to
operate on a first frequency band associated with the first resonance frequency.
-
However, in some cases it may be advantageous to modify a radio unit as described
about to operate on an additional second frequency band. The radio unit 400 may
accordingly be modified by placing a second antenna housing element 411 around
the first antenna housing element 403 as illustrated in FIG. 4. The second antenna
housing element 411 comprises a second resonator 413 in the example in the form of
a partly substantially helical coil. The second resonator 413 is tuned to the second
frequency band and is magnetically coupled to and galvanically isolated from the
first resonator as described above. Preferably, the second antenna housing element
411 may be made from a resilient material, such as a rubber material, and have
dimensions allowing it to tightly fit the first antenna housing element 403 thereby
providing a friction fit of the second antenna housing element 411 on the first
antenna housing element 403.
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When transmitting in the first frequency band, the transmit signal will predominantly
be radiated by the first resonator 405. However, when transmitting in the second
frequency band, the transmit signal will be predominantly transmitted from the
second resonator 413 due to the magnetic coupling and tuning of the first and second
resonator. Likewise, when receiving in the first frequency band, the received signal
will predominantly be from the first resonator 405. However, when receiving in the
second frequency band, the received signal will be predominantly be from the
second resonator 413 due to the magnetic coupling and tuning of the first and second
resonator.
-
Thus, in this embodiment, a radio unit may easily and simply be modified to operate
on different frequency bands. This may provide for a simplified and reduced cost
manufacturing process where the same radio unit housing 401 may be reused for
both single band and multiple band radio units.
-
In some applications antenna resonators are located internal to a radio unit housing
in order to reduce the form factor of the radio unit. The described antenna
arrangement is very suitable for providing an additional frequency band to such a
resonator as galvanic connection is not required. Thus, a second resonator having a
second resonance frequency may be included in an antenna housing element which
can be attached to the external of the radio unit housing thereby providing for
efficient antenna performance at the second frequency.
-
In some applications, the magnetic coupling between the first and second resonator
may be increased by including magnetic material that increases the magnetic
coupling between the resonators. For example, if two helical coils are located coaxially,
a magnetic element may be placed inside the inner helical coil. However, as
losses in magnetic materials typically rise with increasing frequency, this approach
is more advantageous at lower frequencies. The magnetic material may comprise a
ferromagnetic material such as iron.
-
It will be appreciated that although the above description has focused on antenna
arrangements comprising two resonators at different frequencies, the disclosed
principles also apply to larger number of resonators. For example, a three band
antenna arrangement may be implemented by implementing three galvanically
isolated and magnetically coupled resonators having different resonance frequencies.
-
Although the present invention has been described in connection with the preferred
embodiment, it is not intended to be limited to the specific form set forth herein.
Rather, the scope of the present invention is limited only by the accompanying
claims. In the claims, the term comprising does not exclude the presence of other
elements or steps. Furthermore, although individually listed, a plurality of means,
elements or method steps may be implemented by e.g. a single unit or processor.
Additionally, although individual features may be included in different claims, these
may possibly be advantageously combined, and the inclusion in different claims
does not imply that a combination of features is not feasible and/or advantageous. In
addition, singular references do not exclude a plurality. Thus references to "a", "an",
"first", "second" etc do not preclude a plurality.
