Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
1998-11-17
2001-04-03
Kuntz, Curtis (Department: 2643)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S090300, C455S550100, C343S895000
Reexamination Certificate
active
06212413
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to mobile communication devices having multi-filar helix antennae.
BACKGROUND OF THE INVENTION
In recent years there has been a rapid growth in the ownership and use of mobile cellular telephones. However, a limitation of cellular telephones remains the restricted geographical coverage provided by cellular networks. For example, remote, sparsely populated areas may either suffer from very poor quality coverage or no coverage at all. This has led to the implementation of satellite telephone networks such as INMARSAT™ where a mobile telephone communicates directly with an overhead satellite, the satellite relaying signals to and from some fixed position earth station. It is likely that demand for satellite telephone services will increase providing that mobile terminals can be made small enough to be attractive to users.
The demands placed upon the radio transmitting and receiving components of a mobile telephone are extremely high in the case of satellite telephone systems. This applies especially to the antenna. It is envisaged that the antenna of choice for satellite telephones will be the quadrifilar helix (QFH) antenna (K. Fujimoto and J. K. James, “Mobile Antenna Systems Handbook”, Norwood, 1994, Artech House, pp. 455, 457). A QFH antenna
1
is illustrated in FIG.
1
and comprises four inter-wound resonant helical antenna elements
2
a
to
2
d
. The elements are arranged around a common axis A with starting points
3
a
to
3
d
respectively, offset from one another by 90 degrees and short circuited together (by short circuit connector
4
) at the top of the antenna
1
. In a receiving mode, signals received by the helical elements
2
b
to
2
d
are phase shifted, relative to the signal applied to the first helical element
2
a
, by 90, 180, and 270 degrees prior to combining the signals. Phase shifting may be achieved, for example, using baluns as described in U.S. Pat. No. 5,450,093. When the antenna is used in a transmitting mode, this process is reversed, with a signal to be transmitted being split into four identical components, which components are then phase shifted prior to application to respective helical elements
2
a
to
2
d.
FIG. 2
shows in axial cross-section the spatial gain pattern of a typical QFH antenna, where the axis A coincides with the longitudinal axis of the QFH antenna
1
of FIG.
1
. This pattern can be thought of either as the radiating strength of the antenna in the transmitting mode or the sensitivity of the antenna in the receiving mode. The gain pattern of
FIG. 2
corresponds to right circularly polarised signals, given that the helical elements
2
a
to
2
d
are left handed helices. If the helical elements are right handed helices, then the gain pattern of
FIG. 2
would apply to left circularly polarised signals.
It is apparent that the gain of the QFH antenna is concentrated in the upper axial direction (as viewed in
FIG. 1
) as a main frontal lobe
5
which is generally hemispherical in shape. Only a small backward lobe
6
is present. The spatial gain characteristic of the QFH antenna is ideal for satellite telephones which must communicate with satellites in or passing across a hemispherical (or dome-shaped) region above the earth.
One drawback of the QFH antenna is its relatively large size. A typical QFH antenna may be ten centimetres long and has a diameter of two centimetres, the same order as the dimensions of a typical satellite telephone. In practice, where the antenna projects from the top of the telephone, the antenna can double the total length of the phone. In order to improve the portability of satellite telephones having QFH antenna, it is therefore desirable to be able to fold away the antenna when the phone is not in use. A folding antenna of this type is disclosed in EP0694985 where the antenna is coupled to the phone by a rotatable joint.
A satellite telephone
7
having a foldable antenna
1
is illustrated in
FIG. 3
, where
FIG. 3A
shows the antenna
1
in its extended position and
FIG. 3B
shows the antenna
1
in its folded position. When extended, and as has been described above, the spatial gain pattern of the antenna is optimised for communicating with an overhead satellite. However, this is not the case when the antenna is folded away and where the frontal lobe
5
of the gain pattern is directed towards the ground (at least when the phone is in the upright position). Whilst it may not be necessary to transmit signals from the satellite telephone to a satellite with the antenna
1
in this position, it will generally be necessary for the telephone to receive paging signals from a satellite so that the telephone can be alerted to incoming calls. However, the gain afforded by the backward lobe of the QFH antenna is unlikely to be sufficient to allow for this purpose when the antenna is folded away, even if, as may be the case, paging signals are transmitted at a higher power level than other satellite originating signals.
It has been proposed to overcome this problem by providing a second paging antenna in addition to the main QFH antenna. This additional antenna would be smaller than the QFH antenna but would be arranged such that its gain is always optimised for satellite communication. Whilst the gain of the antenna would not necessarily be sufficient to allow transmissions from the telephone to a satellite, it would be sufficient to allow the telephone to receive paging signals. This solution is undesirable however because it both increases the cost and the size of the telephone.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome or at least mitigate the disadvantages of known satellite telephones. In particular, it is an object of the present invention to provide a satellite telephone having an antenna which can be moved from an extended to a folded position but which provides for satisfactory reception of incoming signals in either position.
This and other objects are achieved by taking advantage of the ability to control the spatial gain pattern of a multi-filar helix antenna using the relative phasing of signals applied to or received from the individual helical elements.
According to a first aspect of the present invention there is provided a mobile communication device comprising:
a multi-filar helix antenna having a plurality of inter-wound helical antenna elements, the antenna being rotatable between a first extended position and a second folded position; and
a phase shifting arrangement coupled to said helical elements for producing a first set of relative phase shifts between signals applied to or received from the antenna elements when the antenna is in said first position, the phase shifting arrangement being responsive to movement of the antenna from said first to said second position to change said first set of phase shifts to a different, second set of phase shifts.
The present invention makes it possible to optimise the spatial gain characteristics of a multi-filar helix antenna in both the extended and folded positions of the antenna.
In one embodiment of the present invention, the communication device comprises detection means coupled to the antenna for detecting when the antenna is rotated between said first and second positions and for providing an electrical signal indicative of said movement to the phase shifting arrangement. The phase shifting arrangement applies either said first or said second set of phase shifts in dependence upon said signal.
In an alternative embodiment of the present invention, the phase shifting arrangement comprises a mechanical switching arrangement which is arranged to be moved between first and second switching positions by rotation of the antenna between its first and second positions. In said first switching position, said first set of phase shifts are applied and in said second switching position said second set of phase shifts are applied.
The device may comprise a rotatable joint coupling the antenna to a main housing of the communication device so that the an
Kuntz Curtis
Nokia Mobile Phones Ltd.
Perman & Green LLP
Taylor Barry W.
LandOfFree
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