Telecommunications – Transmitter and receiver at same station – With transmitter-receiver switching or interaction prevention
Reexamination Certificate
1999-08-16
2003-02-25
Trost, William (Department: 2746)
Telecommunications
Transmitter and receiver at same station
With transmitter-receiver switching or interaction prevention
C455S083000, C455S107000, C455S121000, C455S193100, C343S702000
Reexamination Certificate
active
06526263
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an antenna impedance adjuster suitable for a portable radio-signal transceiver which transmits and receives radio signals in time division multiple access (TDMA) system.
2. Descriptuion of the Related Art
A portable radio-signal transceiver is presently designed to have a radio signal transmitting band and a radio signal receiving band for making communication through radio signals. In general, a radio signal transmitting band is designed to have a frequency band remote from the same of a radio signal receiving band.
A whip antenna usually has a relatively high impedance. The impedance is different from a characteristic impedance of radio-signal receiving and transmitting circuits, and hence, it is necessary to match impedance between the whip antenna and the radio-signal receiving and transmitting circuits in order to minimize transmission loss therebetween.
FIG. 1
illustrates a conventional portable radio-signal transceiver. As illustrated in
FIG. 1
, the portable radio-signal transceiver
1
is comprised of a whip antenna
2
, a matching circuit
4
electrically connected to the whip antenna
2
, a radio signal transmitting circuit
8
, a radio signal receiving circuit
9
, a switch
7
for electrically connecting the matching circuit
4
to one of the radio signal transmitting and receiving circuits
8
and
9
, and a control circuit for controlling operation of the switch
7
, the radio signal transmitting circuit
8
, and the radio signal receiving circuit
9
.
The portable radio-signal transceiver
1
operates as follows.
When a radio signal is to be transmitted, the control circuit
10
transmits a control signal S
2
to the radio signal transmitting circuit
8
to thereby operate the radio signal transmitting circuit
8
, and at the same time, transmits a control signal S
1
to the switch
7
to thereby cause the switch
7
to electrically connect the matching circuit
4
to the radio signal transmitting circuit
8
therethrough. Thus, the radio signal transmitting circuit
8
transmits a radio signal through the matching circuit
4
and the whip antenna
2
.
When a radio signal is to be received, the control circuit
10
transmits a control signal S
3
to the radio signal receiving circuit
9
to thereby operate the radio signal receiving circuit
9
, and at the same time, transmits a control signal S
1
to the switch
7
to thereby cause the switch
7
to electrically connect the matching circuit
4
to the radio signal receiving circuit
9
therethrough. Thus, the radio signal receiving circuit
9
receives a radio signal through the matching circuit
4
and the whip antenna
2
.
In the conventional portable radio-signal transceiver illustrated in
FIG. 1
, since the switch
7
is switched between the radio signal transmitting and receiving circuits
8
and
9
in accordance with the control signal S
1
transmitted from the control circuit
10
for making radio signal communication through the matching circuit
4
, the matching circuit
4
has to match impedance both in a radio signal transmitting band and a radio signal receiving band.
However, when the matching circuit
4
matches the antenna
2
to the radio signal transmitting and receiving circuits
8
and
9
, it becomes more difficult to match all transmitting and receiving bands to characteristic impedance of the radio signal transmitting and receiving circuits
8
and
9
due to fluctuation in frequency characteristics of the antenna
2
and the matching circuit
4
, as the radio signal transmitting and receiving bands become wider. As a result, the portable radio signal transceiver has to operate with transmission loss being generated to some degree.
In addition, the conventional portable radio signal transceiver is accompanied further with problems that an output transmitted from the radio signal transmitting circuit
8
varies due to an input impedance in a radio signal transmitting band of the antenna
2
, and that a noise figure (NF) is deteriorated due to mismatching with an input impedance of the radio signal receiving circuit
9
, resulting in degradation in sensitivity for receiving radio signals.
Japanese Unexamined Patent Publication No. 6-244756 has suggested an apparatus for matching antenna impedance. The suggested apparatus a first impedance matching circuit used when radio signals are to be transmitted, a second impedance matching circuit used when radio signals are to be received, a switch which electrically connects an antenna to one of the first and second impedance matching circuits, and a controller which receives timing signals of TDMA type to thereby control the switch.
Japanese Unexamined Patent Publication No. 8-274679 has suggested a portable telephone comprising an antenna, a matching circuit which is designed to switch matching characteristics, and a control circuit which transmits a control signal for switching matching characteristics of the matching circuit between radio signal transmission and radio signal receipt.
Japanese Unexamined Patent Publication No. 9-331206 has suggested an antenna matching circuit suitable for TDMA type portable telephone. In operation, a radio signal receiver receives radio signals from an antenna, and a radio signal transmitter transmits radio signals through the antenna. Radio signals to be transmitted have a frequency different from a frequency of radio signals to be received. A first antenna matching circuit matches impedance in the antenna at a frequency of received signals, and a second antenna matching circuit does the same at a frequency of transmitted signals. A controller electrically connects the first antenna matching circuit and the radio signal receiver to the antenna while a radio signal is being received, and electrically connects the second antenna matching circuit and the radio signal transmitter to the antenna while a radio signal is being transmitted.
Japanese Unexamined Patent Publication No. 6-244756 has suggested an antenna-impedance matching circuit comprising first means for matching impedance, which is electrically connected to an antenna, and has a switch for switching impedance between radio signal transmission and radio signal receiving to thereby match impedance to an antenna, and a controller which receives timing signals each indicating a timing at which radio signals are to be transmitted and received, to thereby control an operation of the switch so that impedance of the first means is matched to the antenna.
Japanese Unexamined Patent Publication No. 8-274679 has suggested a portable cellular phone making communication in time division multiple access (TDMA), comprising an antenna through which a radio signal is to be transmitted and received, a variable matching circuit which varies matching characteristics, and a control circuit which transmits a control signal by which matching characteristics of the matching circuit is switched between radio signal transmission and radio signal receipt.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems in the conventional portable radio-signal transceiver, it is an object of the present invention to provide an antenna impedance adjuster which is capable of reducing transmission loss between an antenna and internal circuits to thereby enhance output-load characteristic of a radio signal transmitting circuit, and preventing degradation in sensitivity of a radio signal receiving circuit.
There is provided an antenna impedance adjuster including (a) an antenna through which radio signals are received and transmitted, (b) a radio signal receiver which receives radio signals having been received through the antenna, (c) a radio signal transmitter which transmits radio signals through the antenna, (d) an adjuster which matches an impedance between the antenna and the radio signal receiver in radio signal receiving band and an impedance between the antenna and the radio signal transmitter in radio signal transmitting band, (e) a first switch which electrically connects the adjuster to one
NEC Corporation
Nguyen Simon
Scully Scott Murphy & Presser
Trost William
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