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Mobile Phone Patent Abstract
The mobile phone is equipped for at least two frequency bands and
includes an antenna coupled to a multiplex type filter. The multiplex
type filter contains at least two disparate bandpass filters for
separate reception or transmission frequency bands. A first bandpass
filter of the at least two disparate bandpass filters has as a passband
a first frequency band. A second bandpass filter of the at least
two disparate bandpass filters has as a passband a second frequency
band. An input impedance of the first bandpass filter in the second
frequency band is higher than an input impedance of the second bandpass
filter in the second frequency band, and an input impedance of the
second bandpass filter in the first frequency band is higher that
an input impedance of the first bandpass filter in the first frequency
band, so that coupling of signal power at frequencies in the first
frequency band to the second bandpass filter and coupling of signal
power at frequencies in the second frequency band to the first bandpass
filter is essentially reduced.
Mobile Phone Patent Claims
What is claimed is:
1. A mobile phone (1) for at least two frequency bands (5, 10),
said mobile phone comprising an antenna (20) coupled to a multiplex
type filter (25),
wherein the multiplex type filter (25) comprises at least two disparate
bandpass filters (30, 35) for either separate reception or separate
transmission frequency bands (5, 10), said at least two disparate
bandpass filters (30, 35) including a first bandpass filter (30)
having as a passband a first frequency band (5) and a second bandpass
filter (35) having as a passband a second frequency band (10), an
input impedance of the first bandpass filter (30) in the second
frequency band (10) is higher than an input impedance of the second
bandpass filter (35) in the second frequency band (10) and an input
impedance of the second bandpass filter (35) in the first frequency
band (5) is higher than an input impedance of the first bandpass
filter (30) in the first frequency band (5);
whereby coupling of signal power at frequencies in the first frequency
band (5) to the second bandpass filter (35) and coupling of signal
power at frequencies in the second frequency band (10) to the first
bandpass filter (30) is substantially reduced.
2. The mobile phone (1) as defined in claim 1, wherein said multiplex
type filter (25) contains a third bandpass filter (40) for a third
frequency band (15), separated from the first and second frequency
bands (5, 10), the third bandpass filter (40) having as a passband
the third frequency band (15), an input impedance of the third bandpass
filter (40) in the first and in the second frequency bands (5, 10)
is higher than an input impedance of the first bandpass filter (30)
in the first frequency band (5) and higher than an input impedance
of the second bandpass filter (35) in the second frequency band
(10), an input impedance of the first bandpass filter (30) in the
third frequency band (15) is higher than an input impedance of the
third bandpass filter (40) in the third frequency band (15), an
input impedance of the second bandpass filter (35) in the third
frequency band (15) is higher than an input impedance of the third
bandpass filter (40) in the third frequency band (15);
whereby coupling of signal power at frequencies in the first and
second frequency bands (5, 10) to the third bandpass filter (40)
and coupling of signal power at frequencies in the third frequency
band (15) to the first and second bandpass filters (30, 35) is substantially
reduced.
3. The mobile phone (1) as defined in claim 2, wherein the third
frequency band (15) at approximately 1900 MHz.
4. The mobile phone (1) as defined in claim 3, wherein the third
frequency band (15) is a 1900 MHz GMS band.
5. The mobile phone (1) as defined in claim 1, wherein the first
frequency band (5) is at approximately 900 MHz and the second frequency
band (10) is at approximately 1800 MHz.
6. The mobile phone (1) as defined in claim 5, wherein the first
frequency band (5) is a 900 MHz GMS band.
7. The mobile phone (1) as defined in claim 5, wherein the second
frequency band (10) is a 1800 MHz GMS band.
8. The mobile phone as defined in claim 1, wherein in the multiplex
type filter (25) at least one of the bandpass filters (30, 35, 40)
follows a matching circuit (45, 50, 55), the matching circuit (45,
50, 55) transforming a low input impedance of said at least one
of the bandpass filters (30, 35, 40) to a high input impedance in
at least those of the frequency bands (5, 10, 15) different from
the passband of said at least one of the bandpass filters (30, 35,
40).
9. The mobile phone (1) as defined in claim 8, wherein the matching
circuit (45, 50, 55) is a transmission line (60).
10. The mobile phone (1) as defined in claim 9, wherein the transmission
line (60) has a length approximately equal to a quarter of the wavelength
of a center frequency of the passband of the corresponding bandpass
filter (30, 35, 40).
11. The mobile phone (1) as defined in claim 1, wherein the multiplex
type filter (25) has one common input (65), the input (65) is shared
by the at least two bandpass filters (30, 35), and the multiplex
type filter (25) has an output (70, 75) for each of the at least
two bandpass filters (30, 35) respectively.
12. The mobile phone (1) as defined in claim 1, wherein the multiplex
type filter (25) has one common output (115), the at least two bandpass
filters (30, 35) of the multiplex type filter (25) share a common
output (115), and the multiplex type filter (25) has an input (85,
90) for each of the at least two bandpass filters (30, 35), respectively.
13. The mobile phone (1) as defined in claim 1, wherein the multiplex
type filter (25) is a surface acoustic wave filter.
14. The mobile phone (1) as defined in claim 1, wherein the multiplex
type filter (25) is a strip line filter, a microstrip filter, a
multilayer filter, a ceramic filter or is based on helical resonators.
Mobile Phone Patent Description
BACKGROUND OF THE INVENTION
Mobile phones for at least two frequency bands are already known.
The Motorola Micro Tac 8900 mobile phone provides automatic shifting
between the GSM 900 MHz band (global system for mobile communications)
and the GSM 1800 MHz band.
From the EP 0 355 973 B1, a digital mobile phone is known. The
digital mobile phone includes an antenna, a receiver input for receiving
signals on a first frequency, and a transmitter output for transmitting
signals on a second frequency, different from the first frequency.
The digital mobile phones comprise a duplex type filter, having
a reverse attenuation from the transmitter output to the receiver
input. The duplex type filter is used to couple the antenna to said
receiver input and transmitter output. The duplex type filter replaces
thereby an antenna switch to couple the antenna to the receiver
and the transmitter respectively, and its control logic.
SUMMARY OF THE INVENTION
In a mobile phone a duplex type filter and more generally a multiplex
type filter may advantageously be used either in a multiband receiver
or a multiband transmitter chain to reduce circuit complexity by
saving switches and the accompanying control logic in the multiband
receiver or transmitter chain and therefore to save space on the
printed circuit board and costs.
Using known filter technologies as e. g. Surface Acoustic Wave
(SAW) filters, it could be difficult to realize duplex type filters
or multiplex type filters having widely separated passbands. Therefore,
it may be a problem to secure high input impedance for the disparate
bandpass filters in frequency bands outside of the corresponding
passband. It is therefore an advantage, to use a matching circuit
transforming a low input impedance of the corresponding bandpass
filter to a high input impedance in the passbands of the other bandpass
filters utilized in the multiplex type filter.
By using a transmission line for the matching circuit, circuit
complexity may be further reduced and costs for unnecessary circuit
components can be saved.
BRIEF DESCRIPTION OF THE DRAWINGS
Exemplary embodiments of the invention are shown in the figures
and explained in greater detail in the description below.
FIG. 1 shows a block diagram of a first embodiment of the invention
in a reception line a of mobile phone.
FIG. 2 is a block diagram of a second embodiment of the invention
in a reception line of a mobile phone.
FIG. 3 is a first circuit for a duplex type filter.
FIG. 4 is a second circuit for a duplex type filter.
FIG. 5 is a transmission line.
FIG. 6 is a first circuit for a triplex type filter.
FIG. 7 is a second circuit for a triplex type filter.
FIG. 8 frequency diagrams for the impedance of the bandpass filters
of a triplex type filter.
FIG. 9 is a block diagram of mobile phone.
FIG. 10 is a block diagram of fourth embodiment of the invention
in a transmitter path of a mobile phone.
DETAILED DESCRIPTION
FIG. 1 shows a block diagram of a first embodiment of the invention.
In FIG. 1, 1 designates a mobile phone comprising a multiplex type
filter 25 having a first bandpass filter 30 and a second bandpass
filter 35. The multiplex type filter 25 in FIG. 1 therefore constitutes
a duplex type filter. A common input 65 of the multiplex type filter
25 is connectable to an antenna 20 by a switch 120. A first transmitter
port 125 is also connectable to the antenna 20 via the switch 120.
Transmitter stages are connected to the first transmitter port 125
and are not shown in FIG. 1. The multiplex type filter 25 has a
first output 70 and a second output 75 whereby the first output
70 is the output of the first bandpass filter 30 and the second
output 75 is the output of the second bandpass filter 35. The common
input 65 of the multiplex type filter 25 is shared by both bandpass
filters 30, 35. Via the first output 70, the first bandpass filter
30 is connected to a first amplifier stage 135 and to further reception
states not shown in FIG. 1. Via the second output 75, the second
bandpass filter 3S is connected to a second amplifier stage 140
and further reception stages not shown in FIG. 1.
The first bandpass filter 30 permits reception in a first frequency
band 5 which is shown in FIG. 8a). The first frequency band 5 is
the GSM 900 MHz frequency band. More precisely, the mobile phone
1 would receive signals in the first frequency band 5 at frequencies
of approximately 947 MHz and transmit signals at frequencies of
approximately 890 MHz via the antenna 20. The second bandpass filter
35 permits reception of signals via the antenna 20 in a second frequency
bald 10 at approximately 1800 MHZ as shown in FIG. 8b), so in the
GSM 1800 MHz band. The reception and transmission frequencies in
the second frequency band 10 are separated in a similar manner as
explained for the first frequency band 5. The first and the second
frequency bands 5, 10 do not overlap and are widely separated in
frequency. The first frequency band 5 is the passband of the first
bandpass filter 30, and the second frequency band 10 is the passband
of the second bandpass filter 35.
The switch 120 is controlled by a control logic not shown in FIG.
1 to connect the antenna 20 to the receiving or the transmitting
paths according to the requirements during a telephone call.
According to FIG. 8a) the first bandpass filter 30 presents an
input impedance Z of 50.OMEGA. to the antenna 20 in the first frequency
band 5. This impedance is adapted to the impedance of the antenna
20. The dotted line in FIGS. 8a), b), and c) shows the filter input
impedance Z as a function of the frequency f. So the first bandpass
filter 30 has a high input impedance Z of some hundred Ohms in the
second frequency band 10. The second bandpass filter 35 presents
an input impedance Z of 50.OMEGA. to the antenna 20 in the second
frequency band 10 and a high input impedance Z of some hundred Ohms
in the first frequency band 5.
In FIG. 2, a block diagram of a second embodiment of the invention
is shown. In this embodiment, the antenna 20 of the mobile phone
1 is connectable via an antenna switch circuit 100 to the first
transmitter port 125, a second transmitter port 130, a first receiver
port 105, and a second receiver port 110. The transmitter ports
125, 130 are input ports of the antenna switch circuit 100 and the
receiver ports 105, 110 are output ports of the antenna switch circuit
100. The antenna switch circuit 100 is controlled by a control logic
not shown in FIG. 2 and connects the several ports 125, 130, 105,
110 to the antenna 20 according to the requirements during a telephone
call. A transmitter line connected to the first transmitter port
125 and the second transmitter port 130 is not shown in FIG. 2.
The first reception port 105 of the antenna switch circuit 100 is
connected to a first input 85 of the multiplex type filter 25. The
second reception port 110 of the antenna switch circuit 100 is connected
to a second input 90 of the multiplex type filter 25. Thereby, the
first input 85 of the multiplex type filter 25 is the input of the
first bandpass filter 30 and the second input 90 of the multiplex
type filter 25 is the input of the second bandpass filter 35. The
first bandpass filter 30 and the second bandpass filter 35 share
a common output 115 of the multiplex type filter 25, which is connected
to the first amplifier stage 135 and further reception stages not
shown in FIG. 2.
The effect of the multiplex type filters 25 in FIG. 1 and FIG.
2 is the same, only the input and output connection arrangements
are different.
FIG. 3 shows the multiplex type filter 25 of FIG. 1 in more detail.
In FIG. 3, the common input 65 of the multiplex type filter 25 is
connected to the first bandpass filter 30 via a first matching circuit
45 and to the second bandpass filter 35 via a second matching circuit
50. Thereby the first matching circuit 45 comprises a first inductor
165. At its first end the first inductor 165 is connected to the
common input 65 and via a first capacitor 145 to ground. At its
second end, the first inductor 165 is connected to the first bandpass
filter 30 and via a second capacitor 150 also to ground. The second
matching circuit 50 comprises a second inductor 170. At its first
end, the second inductor 170 is connected to the common input 65
and via a third capacitor 155 to ground. At its second end, the
second inductor 170 is connected to the second bandpass filter 35
and via a second capacitor 160 also to ground.
Without using the first matching circuit 45, the input impedance
Z of the first bandpass filter 30 depends on the frequency f according
to the continuous line in FIG. 8a) This means, that for frequencies
outside the first frequency band 5 the input impedance Z of the
first bandpass filter 30 is approximately zero. Therefore, signals
with frequencies of the second frequency band 10 would easily be
coupled to the first bandpass filter 30 and therefore generate loss
in the signal strength of the signal passed through the second bandpass
filter 35, adapted to the antenna impedance of 50.OMEGA. in the
second frequency band 10. The first matching circuit 45 transforms
the low input impedance Z of the first bandpass filter 30 outside
the first frequency band 5, at least in the second frequency band
10, to a high input impedance Z of some 100 Ohms. This transformation
is indicated in FIG. 8a) by arrows. Therefore, coupling of signals
at frequencies outside the first frequency band 5, especially in
the second frequency band 10, into the first bandpass filter 30
is strongly reduced. In the first frequency band 5, the first matching
circuit 45 leaves the impedance Z of the first bandpass filter 30
at the antenna impedance of 50.OMEGA..
In FIG. 8b), the input impedance Z of the second bandpass filter
35 is shown as a function of the frequency f. The continuous line
in FIG. 8b) shows the input impedance Z of the second bandpass filter
35 as a function of the frequency f without using the second matching
circuit 50. Thereby, the input impedance Z of the second bandpass
filter 35 equals 50.OMEGA. in the second frequency band 10 and equals
approximately zero outside the second frequency band 10. The second
matching circuit 50 transforms the input impedance Z of the second
bandpass filter 35 at frequencies outside the second frequency band
10, especially in the first frequency band 5, to high values as
indicated by arrows in FIG. 8b) and leaves the input impedance Z
of the second bandpass filter 35 at approximately 50.OMEGA. in the
second frequency band 10. Therefore, coupling of signals at frequencies
of the first frequency band 5 into the second bandpass filter 35
is strongly reduced. The input impedance Z of the second bandpass
filter 35 after the transformation is shown as a dotted line in
FIG. 8b).
An alternative matching circuit may be constituted by a transmission
line 60 as shown in FIG. 5 for the first matching circuit 45 as
an example. A transmission line can also be used for the other matching
circuits in the multiplex type filter 25. The length of the transmission
line 60 is thereby chosen e.g. as a quarter of the wavelength of
the center frequency of the frequency band of the corresponding
bandpass filter. For the example of FIG. 5, the center frequency
of the first frequency band 5 which is the passband of the first
bandpass filter 30 is at approximately 900 MHz. Such a transmission
line also leaves the input impedance Z in the passband of the corresponding
bandpass filter at the antenna impedance of 50.OMEGA. and increases
the input impedance Z outside the passband of the corresponding
bandpass filter to some hundred Ohms, especially in the passbands
of the other bandpass filters utilized in the multiplex type filter
25.
The transmission line 60 may be a coaxial cable. The central conductor
of the coaxial cable is connected at one end with the common input
65 and at the other end with the corresponding bandpass filter.
The outer conductor of the transmission line 60 is connected to
ground.
FIG. 6 shows an example of a multiplex type filter 25 with three
disparate bandpass filters 30, 35, 40 following a matching circuit
45, 50, 55, respectively. In comparison with the above described
embodiments, the third bandpass filter 40 is added for a third frequency
band 15, the center frequency of which is approximately at 1900
MHz. The third frequency band 15 may be the GSM 1900 MHz band and
is the passband of the third bandpass filter 40, separated in frequency
from the passbands of the first and second bandpass filters 30,
35, so that the passbands of the first, the second, and the third
bandpass filter 30, 35, 40 do not overlap. According to FIG. 1,
the embodiment shown in FIG. 6 is an example for a multiplex type
filter 25 with a common input 65 and separate outputs. Thereby,
in comparison with the embodiment of FIG. 1, the common input 65
additionally is connected to the third bandpass filter 40 via a
third matching circuit 55. The output of the third bandpass filter
40 would be a third output 80 of the multiplex type filter 25. The
third matching circuit 55 may have a structure as shown in FIG.
3 or FIG. 5. By choosing a transmission line for the third matching
circuit 55 the length of the transmission line should be a quarter
of the wavelength of the center frequency of 1900 MHz of the third
frequency band 15.
FIG. 8c) shows the input impedance Z of the third bandpass filter
40 as a function of the frequency f. The continuous line shows the
input impedance Z of the third bandpass filter 40 as a function
of the frequency f without the use of the third matching circuit
55. Thereby, in the third frequency band 15, the input impedance
Z of the third bandpass filter 40 equals the antenna impedance of
50.OMEGA.. outside the third frequency band 15, the input impedance
Z of the third bandpass filter 40 equals approximately zero. The
third matching circuit 55 transforms the input impedance Z of the
third bandpass filter 40 outside the third frequency band 15 to
a high impedance, especially in the first and second frequency band
5, 10, as indicated by arrows in FIG. 8c), and leaves the input
impedance Z of the third bandpass filter 40 in the third frequency
band 15 at approximately 50.OMEGA.. Therefore, coupling of signals
at frequencies of the first and second frequency bands 5, 10 into
the third bandpass filter 40 is strongly reduced. The first and
the second matching circuits 45, 50 should transform the input impedance
Z of the corresponding first and second bandpass filter 30, 35 to
a high value also in the third frequency band 15 to reduce coupling
of signals at frequencies of the third frequency band 15 into the
first and second bandpass filters 30, 35.
FIG. 4 shows the multiplex type filter 25 of the second embodiment
described according to FIG. 2 in more detail. The embodiment shown
in FIG. 4 corresponds to the embodiment shown in FIG. 3 with two
exceptions: First, in FIG. 4 the first matching circuit 45 and the
second matching circuit 50 share the common output 115.
Second, in FIG. 4 the first bandpass filter 30 and the second bandpass
filter 35 have different inputs whereas the input of the first bandpass
filter 30 corresponds to the first input 85 of the multiplex type
filter 25 and the input of the second bandpass filter 35 corresponds
to the second input 90 of the multiplex type filter 25. The first
input 85 and the second input 90 are not connected to each other.
The function of the multiplex type filter 25 according to FIG. 4
is the same as the function of the multiplex type filter 25 shown
in FIG. 3. The first and/or the second matching circuit 45, 50 may
also be constituted by a transmission line, respectively, the length
of which corresponding to a quarter of the wavelength of the center
frequency of the passband of the preceding bandpass filter. Therefore,
the outputs of the first and the second bandpass filter 30, 35 are
matched to the common output 115 by the first and the second matching
circuit 45, 50.
According to the second embodiment shown in FIG. 2, FIG. 7 shows
an embodiment with a multiplex type filter 25 comprising three bandpass
filters 30, 35, 40 with a following matching circuit 45, 50, 55
which may be a transmission line as described above, respectively.
Therefore, the embodiment shown in FIG. 7 corresponds to the embodiment
shown in FIG. 6 with two exceptions: First, in FIG. 7, the first,
the second, and the third matching circuit 45, 50, 55 share tile
common output 115. Second, in FIG. 7 the first, the second, and
the third bandpass filter 30, 35, 40 have different inputs which
are separated from each other and therefore not connected electrically.
The input of the first bandpass filter 30 corresponds to the first
input 85 of the multiplex type filter 25, the input of the second
bandpass filter 35 corresponds to the second input 90 of the multiplex
type filter 25 and the input of the third bandpass filter 40 corresponds
to a third input 95 of the multiplex type filter 25. Therefore,
the outputs of the first, the second and the third bandpass filter
30, 35, 40 are matched to the common output 115 by the first, the
second and the third matching circuit 45, 50, 55.
The function of the multiplex type filter 25 shown in FIG. 7 corresponds
to the function of the multiplex type filter 25 shown in FIG. 6.
A multiplex type filter 25 with three bandpass filters 30, 35,
40 may be called a triplex type filter.
The embodiments, shown in FIG. 3 and FIG. 4 comprise two bandpass
filters, where the first bandpass filter 30 has its passband in
the first frequency band 5 and the second bandpass filter 35 has
its passband in the second frequency band 10. The multiplex type
filter 25 with two bandpass filters could also comprise the first
bandpass filter 30 for the first frequency band 5 and the third
bandpass filter 40 for the third frequency band 15. Such a multiplex
type filter 25 with two bandpass filters could also comprise the
second bandpass filter 35 for the second frequency band 10 and the
third bandpass filter 40 for the third frequency band 15.
An example of dimensioning corresponding matching filters is given
below. Therefore, it is supposed, that the multiplex type filter
25 comprises the second bandpass filter 35 and the third bandpass
filter 40. The second bandpass filter 35 in this example would be
preceded by the first matching circuit 45 and the third bandpass
filter 40 in this example would be preceded by the second matching
circuit 50. For the first inductor 165, a value of 3,3 nH is chosen.
For the second indicator 170, a value of 2,7 nH is chosen. For the
first, the second, the third, and the fourth conductor 145, 150,
155, 160, a value of 3,3 pF is chosen respectively. As a result,
the input impedance Z of the second bandpass filter 35, according
to FIG. 8b), would be higher than or equal to 400.OMEGA. at least
in the first frequency band 5 and in the third frequency band 15.
According to FIG. 8c), the input impedance Z of the third bandpass
filter 40 would be higher than or equal to 400.OMEGA. at least in
the first frequency band 5 and in the second frequency band 10.
The input impedance Z of the second bandpass filter 35 and the third
bandpass filter 40 in the corresponding passbands would be approximately
equal to the antenna impedance of 50.OMEGA..
To prevent essential signal coupling at frequencies of the passband
of one bandpass filter of the multiplex type filter 25 to another
bandpass filter of the multiplex type filter 25, the input impedance
Z of the other bandpass filter of the multiplex type filter 25 in
the passband of the one bandpass filter of the multiplex type filter
25 should be high enough in comparison with the input impedance
Z of the one bandpass filter of the multiplex type filter 25 in
this passband.
According to FIGS. 9 and 10, the multiplex type filter 25 can also
be used in the transmitter path of the mobile phone 1. Thereby,
FIG. 9 shows the multiplex type filter 25 comprising the first bandpass
filter 30 and the second bandpass filter 35 sharing the common input
65 The first bandpass filter 30 is connected to the antenna switch
circuit 100 via the first amplifier 133 and the second bandpass
filter 35 is connected to the antenna switch circuit 100 via the
second amplifier 140. Via the antenna switch circuit 100, the first
amplifier 135 or the second amplifier 140 may be connected to the
antenna 20. Via the antenna switch circuit 100, the antenna 20 may
also be connected to receiver ports not shown in FIG. 9.
FIG. 10 shows the multiplex type filter 25 with the first bandpass
filter 30 and the second bandpass filter 35 having separate, electrically
not connected inputs and sharing the common output 115. The common
output 115 is connected to the antenna 20 via the first amplifier
135.
Concerning the input impedance Z of the corresponding bandpass
filters utilized in the multiplex type filter 25 and transformed
by a matching circuit, respectively, if necessary, it is also important,
to prevent essential signal coupling at frequencies of the passband
of one bandpass filter of the multiplex type filter 25 to another
bandpass filter of the multiplex type filter 25. Therefore, the
input impedance Z of the other bandpass filter of the multiplex
type filter 25 in the passband of the one bandpass filter of the
multiplex type filter 25 should be high enough in comparison with
the input impedance Z of the one bandpass filter of the multiplex
type filter 25 in this passband, as described above, even if the
input impedance Z of the bandpass filters of the multiplex type
filter 25 in their passbands do not have to be adapted to the antenna
impedance but to the output impedance of elements preceding the
multiplex type filter 25. Matching circuits in the multiplex type
filter 25 may also be constituted by transmission lines as described
above.
If in the transmitter or receiver path the multiplex type filter
25 is used with bandpass filters sharing a common output, the following
amplifier has to be a wideband amplifier, including in its passband
the passbands of the bandpass filters of the multiplex type filter
25 used.
Regardless of the use of the multiplex type filter 25 in a transmitter
or receiver chain, the desired frequency bands are separated by
the bandpass filters included in the multiplex type filter 25. Therefore,
switches can be saved to switch the desired frequency band into
the transmitter or receiver path of the mobile phone. Such switches
produce insertion loss and need a control logic. As narrow bandpass
filters for the different frequency bands are needed in any case,
they may, according to the invention, be combined to a multiplex
type filter and therefore save the switches and there control logic.
The multiplex type filter 25 may be a SAW filter (Surface Acoustic
Wave), a stripline filter, a microstrip filter, a multilayer filter,
a ceramic filter or may be based on helical resonators.
In all drawings of the described embodiments of the invention,
same elements are designated with the same numerals, respectively.
It is also in the scope of the invention to use more than three
bandpass filters optionally with a matching circuit, respectively,
in the multiplex type filter 25, if more than three frequency bands
are required for reception or transmission
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